Other works by same author
in collaboration with
PROF. SAMUEL SHELDON
DYNAMO ELECTRIC MACHINERY; its
Construction, Design and Operation
VOL. I. DIRECT CURRENT MACHINES
Eighth Edition completely re -written ,
5^x7|< Cloth 338 Pages, Illustrated Net $2.50
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ELECTRIC TRACTION AND TRANSMIS-
SION ENGINEERING
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Telegraph Engineering
A MANUAL FOR PRACTICING TELEGRAPH
ENGINEERS AND ENGINEERING
STUDENTS
BY
ERICH HAUSMANN, E. E., Sc. D.
% •
Assistant Professor of Physics and Electrical Engineering
at the Polytechnic Institute of Brooklyn, and
Member of the American Institute
of Electrical Engineers.
WITH 192 ILLUSTRATIONS
NEW YORK
D. VAN NOSTRAND COMPANY
25 PARK PLACE
1915
COPYRIGHT, 1915,
BY
D. VAN NOSTRAND COMPANY
Stanbopc ipress
F. H. GILSON COMPANY
BOSTON, U.S.A.
DEDICATED To
Sorter 8>amu?
IN APPRECIATION OF HIS INSPIRING INFLUENCE
PREFACE
THIS book is intended for electrical engineering students
and as a reference book for practicing telegraph and tele-
phone engineers and for others engaged in the arts of elec-
trical communication. It presents in a logical manner the
subject of modern overland and submarine telegraphy
from an engineering viewpoint, its theoretical and practical
aspects being correlated. No attempt is made to describe
all telegraphic devices and to explain their operation, but
rather to consider one or more representative types for the
accomplishment of the various desired objects, thus per-
mitting a presentation of the subject matter in proper per-
spective. The book is the outgrowth of the course in
Telegraph Engineering given by the author for a number
of years at the Polytechnic Institute of Brooklyn.
A knowledge of elementary electricity and magnetism
is presupposed. For understanding the mathematical
demonstrations a knowledge of algebra will in many cases
suffice, but in other cases, appearing toward the latter part
of the book, the calculus is a necessary adjunct, the study
of which frequently precedes or accompanies the vocational
studies of students and progressive telegraph workers.
That the use of higher mathematics is important in the
thorough pursuit of telegraph and telephone transmission
studies is evident from an inspection of the writings of
Lord Kelvin, Heaviside, Kennelly, Pupin, Campbell, Mal-
colm and others. Those not versed in mathematical
vii
Viii PREFACE
processes, however, may yet share in the value of the
demonstrations by an analysis of their conclusions and an
examination of the numerical illustrations based upon them.
The solution of practical problems appended to each chap-
ter will assist in a complete understanding of the principles
presented.
The author expresses his appreciation and thanks to Mr.
Herbert W. Drake, Apparatus Engineer of the Western
Union Telegraph Company, for making helpful suggestions
and for reading the page proofs of the first six chapters.
He also gratefully acknowledges the inspiration and en-
couragement in the preparation of this work derived from
his intimate association with Dr. Samuel Sheldon, Professor
of Physics and Electrical Engineering at the Polytechnic
Institute of Brooklyn.
E. H.
BROOKLYN, N. Y.
January, 1915.
CONTENTS
CHAPTER I.
SIMPLEX TELEGRAPHY.
ART. PAGE
1. Simplex Signalling i
2. The Use of Relays 3
3. Closed- and Open-circuit Morse Systems 5
4. Telegraph Instruments 8
5. Best Winding for Receiving Instruments 16
6. Sources of Current 20
7. Telegraph Codes 25
8. Telegraph Lines 28
9. Speed of Signalling 33
10. Simplex Repeaters 35
Problems 43
CHAPTER II.
DUPLEX TELEGRAPHY.
r. Duplex Telegraph Systems 45
2. The Differential Duplex 46
3. Artificial Lines 51
4. Polarized Relays 53
5. The Polar Duplex 56
6. Improved Polar Duplex 63
7. Short-line Duplex 66
8. The Bridge Duplex 67
9. Advantage of Double-current Duplex Systems 74
10. Duplex Repeaters 76
11. Half-set Repeaters 80
Problems , 83
CHAPTER III.
QUADRUPLEX TELEGRAPHY.
1. Quadruplex Systems 85
2. Operation of Quadruplex Systems 87
3. Avoidance of Sounder-armature Release during Current Rever-
sals in Neutral Relay 94
ix
X CONTENTS
ART. PAGE
4. The Postal Quadruplex 96
5. The Western Union Quadruplex 98
6. Quadruplex Repeaters 100
7. Duplex-diplex Signalling 102
, 8. Phantoplex System 103
Problems 106
CHAPTER IV.
AUTOMATIC AND PRINTING TELEGRAPHY.
1. Wheatstone Automatic Telegraphy 108
2. Ticker Telegraphs. 115
3. The Barclay Page-printing Telegraph System 121
4. Other Printing Telegraph Systems 133
Problems 134
CHAPTER V.
TELEGRAPH OFFICE EQUIPMENT AND TELEGRAPH TRAFFIC.
1. Protective Devices 135
2. Peg Switch Panels 136
3. Main and Loop Switchboards 138
4. Distributing Frames 143
5. Instrument Tables 145
6. Power Switchboards 146
Traffic.
7. Types of Messages 150
8. Classes of Service and Tariffs 152
9. Handling of Traffic 154
10. The Telegraph in Railway Operation 157
n. Telegraph Statistics 159
Problems 161
CHAPTER VI.
MISCELLANEOUS TELEGRAPHS.
1. Multiplex Telegraph Systems 162
2. The Murray Multiplex Page-printing Telegraph 163
3. The Pollak-Virag Writing Telegraph 167
4. The Telautograph 170
5. Telephotography 175
CONTENTS xi
ART- PAGE
6. Television j82
7. Military Induction Telegraphs 184
Problems !88
CHAPTER VII.
MUNICIPAL TELEGRAPHS.
1. Fire-alarm Telegraphy X8g
2. Fire-alarm Signal Boxes 192
3. Public Alarms 200
4. Fire-alarm Central Stations 202
5. Signalling Devices at Apparatus Houses 210
6. Operation and Routine of a Fire-alarm Telegraph System 212
7. Police Patrol Telegraphs 217
8. Statistics of Police and Fire Signalling Systems 221
Problems 223
CHAPTER VIII.
RAILWAY SIGNAL SYSTEMS.
1. Classes of Railway Signalling 224
2. Types of Signals 225
3. Manual Block Signal Systems 231
4. Location of Automatic Block Signals 232
5. Automatic Block Signalling 237
6. Automatic Block Signals on Electric Railways 242
7. Interlocking Plant Signals 247
Problems 251
CHAPTER IX.
TELEGRAPH LINES AND CABLES.
1. Aerial Open Lines 253
2. Wire Spans 261
3. Economical Span Length - 266
4. Telegraph Cables 269
5. Underground Cable Installation 273
6. The Earth as a Return Path 279
7. Electrical Constants of Telegraph Conductors 282
8. Elimination of Inductive Interferences on Telegraph and Tele-
phone Lines 288
9. Simultaneous Use of Lines for Telegraphy and Telephony 293
Problems 300
Xli CONTENTS
CHAPTER X.
«
THEORY OF CURRENT PROPAGATION IN LINE CONDUCTORS.
ART. PAGE
1. The Transmission of Current Impulses along Telegraph Lines. . . 303
2. Propagation of Alternating Currents along Uniform Conductors
of Infinite Length 306
3. Velocity of Wave Propagation over an Ideal Line 313
4. Wave Propagation along Conductors of Finite Length 314
5. Simplified Equations of Wave Propagation 321
6. Current and Voltage Distribution on Lines for any Terminal Con-
dition 324
7. Effect of Impedance at Sending End 328
8. Illustration of Sine-wave Telegraphic Transmission 330
9. Current in Leaky Line Conductors 334
10. Illustration of Direct-current Signalling on a Leaky Telegraph
Line 338
11. Simplex Signalling with Generators at Both Line Terminals 341
12. Duplex and Quadruplex Signalling 344
Problems 346
CHAPTER XL
SUBMARINE TELEGRAPHY.
1. Theory of Cable Telegraphy 347
2. Illustration of Current Growth at the Receiving End of a Cable. 354
3. Transmission of Telegraphic Signals 355
4. Speed of Signalling 363
5. Picard Method of Signalling 367
6. Gott Method of Signalling 369
7. Duplex Cable Telegraphy 372
8. Sine-wave Signalling 374
9. Design of Submarine Cables 375
10. Types of Cable Service and Tariffs 381
Problems. 385
APPENDIX.
TABLES.
I. Trigonometric Functions 388
II. Exponential Functions 39°
III. Logarithms 392
IV. Hyperbolic Functions 394
TELEGRAPH ENGINEERING
CHAPTER I
SIMPLEX TELEGRAPHY
i. Simplex Signalling. — The transmission of intelligence
between two points by means of electricity was accom-
plished in 1837 by Professor Samuel F. B. Morse of New
York University.* Seven years later he constructed the
first telegraph line in this country (Baltimore to Washing-
ton). The modernized system comprises a conveniently-
operated switch called a key, for opening and closing the
circuit at one place, a source of electric current, an electro-
magnetic receiving device capable of producing an audible
effect, called a sounder, at another place, and a line wire con-
necting the two places or stations. Signals are transmitted
over such a circuit by opening and closing the circuit by
means of the key for long and short intervals in ac-
cordance with a prearranged code, and are interpreted
at the other station by the sounds produced by the move-
ments of a pivoted spring-controlled lever actuated by an
electromagnet which is traversed by the current pulses
established by the key. In order to transmit messages in
either direction, the apparatus mentioned is duplicated
and connected with the single line wire as shown in Fig. i.
The earth is generally utilized as the return path for the
* Earlier electric telegraphs are described in J. J. Fahie's " A History of
Electric Telegraphy to 1837."
2
TELEGRAPH ENGINEERING
current, thereby saving the expense of another line wire
and also avoiding the additional resistance introduced
thereby. The resistance of the ground-return path GG is
negligible in comparison with the resistance of the line wire,
for in nearly all cases it is less than one ohm. This low
resistance is due to the enormous cross-sectional area of the
earth path, although the conductivity of the earth's crust is
poor. Recent experiments, made by Lowy, indicate that
the specific resistance of a variety of rocks is greater than
io5 ohms per centimeter cube, depending upon the amount
of moisture in them. To attain low earth resistances it is
=rB
— G
Fig. i.
essential that good connections be made between the line
wire and earth, by iron pipes driven in damp ground or
more usually by attachment to municipal water pipes.
When the line is idle the circuit of Fig. i is kept closed
by means of the circuit-closing switches s, 5 in parallel with
the keys K, K, causing a current to flow continually from
ground G at station A through switch s, battery (or
generator) B, sounder S, line L, sounder 5, battery (or
generator) By and switch 5 to ground G at station B. When
the operator at station A wishes to send messages, he
interrupts the current by opening his circuit-closer s (as
SIMPLEX TELEGRAPHY 3
shown in Fig. i) and then establishes current pulses by
depressing his key for long or short intervals producing
respectively so-called dashes and dots, various combi-
nations of which constitute the letters and numbers of a
code. These current pulses flow through the windings of
both sounders, causing the armatures on the levers to be
attracted and released repeatedly and causing the other
ends of these levers to strike against lower and upper
stops, / and u. The long and short intervals between the
two different sounds produced by striking the lower and
upper stops are translated by ear as dashes and dots by
both operators. The sending operator therefore hears his
own message and is enabled to detect possible errors; it
also serves as an indication that the line is not open-cir-
cuited. When the operator is through sending signals, he
again completes the circuit by means of the circuit-closer,
thereby enabling the other operator to answer.
The system described permits of signalling in only one
direction at a time, and is therefore called a single Morse,
or conveniently, a simplex telegraph system. It is still in
use at present for short distances, and with more sensitive
receiving instruments may be used for longer distances.
2. The Use of Relays. — The lever of a sounder must
have a certain mass so as to produce loud and distinct
sounds when striking the stops. A definite magnetizing
force is required to move the lever with positiveness in
opposition to its adjustable retractile spring. This mag-
netizing force is measured by the product of the number of
turns of wire on the sounder winding and the current
traversing it. Sounders of the usual construction require
from 150 to 500 ampere- turns for proper operation.
4 TELEGRAPH ENGINEERING
On long lines having high resistance the current is
necessarily small for practicable voltages, and it would not
be feasible to use ordinary sounders wound with a great
many turns of fine wire to secure a proper magnetizing force
because of the additional resistance introduced. Instead,
more sensitive instruments, called relays, are used, which
have light armatures with contact points that open and
close local circuits containing sounders and local batteries.
Such relays for simplex signalling require a magnetizing
force of from 70 to 300 ampere-turns.
For a given impressed voltage E on a perfectly insulated
ground-return line of length / miles, having a resistance of
R ohms per mile, with two receiving instruments each of
Rr ohms resistance, the steady current in the circuit is
If 7min be the minimum current which will actuate the
receiver, the limit of transmission for a given voltage E is
(i)
If the electromotive force E be developed by Nb series-
connected primary batteries, each of voltage e and internal
resistance Rb, then replace E in the foregoing equations by
Thus, if two 2o-ohm sounders requiring a current of
•5- ampere be the receiving instruments on a i2.4-ohm-per-
mile ground-return line, the maximum length of line
operated on 140 volts would be
I2.4\0.20
_ 2 x 20
) = 52 miles;
/
SIMPLEX TELEGRAPHY
whereas if i5o-ohm relays requiring a current of 0.04
ampere be the receiving instruments, the distance of trans-
mission over this line would be
12.4
- 2 X 150
J= 258 miles,
a distance five times as great as before. By the use of
lines of lower resistance per unit length, the distance of
transmission can be increased in both cases.
The voltage necessary for telegraphic transmission over
a given distance can also be found from equation (i).
Voltages over 200 are rarely employed in simplex signalling.
The windings of relays and sounders are generally des-
ignated by their resistance although the number of turns
is the important consideration; this is done because of the
ease in measuring the resistance of a finished instrument.
3. Closed- and Open-circuit Morse Systems. — The
simple Morse circuit of Fig. i is normally closed, that is,
it carries a current when no messages are transmitted, and
is therefore called a closed-circuit system. The connections
®
Fig. 2.
of a closed-circuit system employing relays and local cir-
cuits at the stations are shown in Fig. 2, which also includes
an intermediate station. When the operator at station A
6 TELEGRAPH ENGINEERING
depresses his key the three relays R will be actuated and
their armatures will be drawn from the rear stops r and
strike the front contact screws /, thereby completing the
three local circuits and permitting the local batteries b to
operate the sounders. As many as thirty or forty inter-
mediate stations may be connected in series on a single
line, but only one operator can send at one time; all oper-
ators, however, may receive the message whether intended
for them or not. If another operator wishes to send he
must wait until the line is idle, or else, if the urgency of
his message warrants, he may interrupt traffic by opening
the circuit at his station with the switch s, and then trans-
mit. Such interruption also takes place when one oper-
ator wishes to verify a portion of a message transmitted by
another.
The closed-circuit telegraph system is used throughout
the United States. It is important that the relays on a
circuit be of the same type, or, more specifically, that they
have the same number of turns on their windings for the
same core construction, so that the common current in the
circuit will occasion the same magnetizing force in each
relay and insure proper functioning of the armature.
If primary or secondary cells are used as the source of
current, they may be grouped together forming one bat-
tery at one station, may be divided into two batteries
located at the terminal stations, or may be apportioned
among the various stations forming a number of separate
batteries, care being exercised not to have some batteries
connected in opposition to others. A single battery in a
circuit conduces to uniform care of all cells and to economy
of maintenance. On the other hand, should a circuit with
a single battery at a terminal station become grounded, all
SIMPLEX TELEGRAPHY
stations beyond the ground would be rendered inoperative
and unable to communicate with each other. A ground
on a circuit with two terminal batteries prevents through
operation, but the stations on each side of the ground can
temporarily maintain local communication.
Another simplex telegraph system is used extensively in
Europe, namely the so-called open-circuit system, in which
the main-line circuit is really normally closed but does not
include a source of current when no messages are being
transmitted. The system derives its name from the fact
that all batteries are normally open-circuited. The con-
nections of two terminal stations and one intermediate
station using the open-circuit system are shown in Fig. 3,
Fig. 3-
the letters having the same significance as before. The de-
pression of a key at a station introduces the source of
current at that station into the circuit and causes the
operation of the relays at all the other stations. These in
turn operate the sounders through the local batteries, as
before.
In the open-circuit system the voltage of the batteries
or generators at the various stations should be the same
and sufficient individually to operate the entire circuit,
whereas in the closed-circuit system the current sources
may be subdivided arbitrarily so long as the aggregate
voltage is sufficient to operate the entire circuit. Since
8 TELEGRAPH ENGINEERING
current flows when no messages are sent in the closed-
circuit system, a greater amount of electrical energy is
required for the operation of this system than the open-
circuit system. When the connections of Fig. 3 are em-
ployed, the sending operator does not hear the signals
that he sends out on the line, but this disadvantage can be
avoided by shifting the relays from their present position
to the points on the line marked x and connecting the
back key contacts directly with the points a.
In the foregoing figures relays and sounders were rep-
resented as having a single core, while in reality they have
two cores connected at the rear with a soft iron yoke.
The windings on the two cores are usually connected in
series. This method of graphic representation will be re-
tained for the sake of clearness.
4. Telegraph Instruments. — Keys. A key extensively
used on closed-circuit systems is the Bunnell key illustrated
in Fig. 4. It consists of a steel lever carrying a flat hard-
Fig. 4.
rubber knob at one end, and pivoted near the other end in
trunnion screws that are mounted in uprights extending
from the elliptically-shaped brass base. The movement
of the lever is adjustable by the knurled screw at its rear
end. The other end of the lever is kept up normally by
means of the spring shown, the tension thereof being regu-
SIMPLEX TELEGRAPHY
lated by the knurled screw through the middle of the
lever. When the knob is depressed a platinum point on
the under side of the lever makes contact with a similar
point fixed in a cone-shaped cap fastened to, but insulated
from, the base. This latter contact point is connected
by a brass strip to the front binding post, which is also
insulated from the base; the other terminal is fastened
directly to the base and therefore is in metallic connection
with the contact point carried on the lever. An auxiliary
lever, called a circuit-closer, carrying a taller knob, is
pivoted on the base to move horizontally, so as to engage,
when pressed toward the key lever, an extended clip on
the fixed contact point, thereby short-circuiting the key.
In holding the key for sending,
the index finger should rest on the
knob, with the thumb and second
finger on its edge for steadying
the motion of the key. Depres-
sing the key closes or makes the
circuit and releasing the key opens
or breaks the circuit.
Occasionally horizontally-oper-
ated keys with double contacts
are employed, requiring but half
the motions in the formation of
telegraphic characters that are
necessary with the usual vertically-
operated keys. Fig. 5 shows the
BunneU " double-speed " key. The
lever is attached to a post at the rear end of the key by
means of a flat spring. It stands normally midway be-
tween the two platinum contacts that are supported in a
Fig. 5.
10 TELEGRAPH ENGINEERING
U-shaped piece, mounted on, but insulated from, the base.
This connects with the binding post, the other terminal
being the post which supports the lever. In operating the
key, the knob should be allowed free play between thumb
and finger, and the hand given a sidewise rocking motion.
Moving the lever to the right or left closes the circuit.
Many semi-automatic key transmitters, called vibroplex
or mecograph transmitters, are used, and permit experi-
enced operators to signal faster than with the keys already
described. The horizontally-operated lever has a pendulum
extension having an adjustable vibration rate. To form a
dash the operator holds the key knob to the left for a suit-
able length of time; to form dots the key is moved to the
right and held there while the pendulum transmits auto-
matically any desired number of dots.
Fig. 6.
Sounders. Fig. 6 shows a typical sounder. It consists
of a horseshoe electromagnet with two series-connected
coils protected by hard-rubber shells, and a pivoted brass
or aluminum lever carrying a soft-iron armature properly
placed with respect to the magnet poles. The lever is
SIMPLEX TELEGRAPHY II
pivoted near one end in trunnion screws mounted on an
inverted U-shaped standard, this end being held down nor-
mally by a spring whose compression is regulated by a
knurled screw at the top of the standard. The motion of
the lever is limited at the other upright by the two screws
at the left, their adjustment being fixable by the locknuts.
The parts mentioned are mounted on a brass surbase which
is in turn mounted on the wooden base carrying the bind-
ing posts that connect with the coil terminals. Perfect
sounders produce a clear loud tone and act quickly.
Sounders for main line use, that is for short lines without
relays, are generally wound to have a resistance of 20
Fig. 7.
ohms, but many have resistances up to 150 ohms; for
local circuit use they are usually wound to a 'resistance of
4 ohms.
For enhancing and concentrating the signals emitted by
sounders, these instruments are encased in resonators, such
as shown in Fig. 7. They are especially adapted for oper-
12 TELEGRAPH ENGINEERING
ators located in large offices or in noisy railway stations,
and for operators using typewriters in recording received
messages. The type illustrated is capable of being turned
through three-fourths of a revolution, and is provided with
a message clip.
Relays. — A relay widely used is shown in Fig. 8. It
consists of a horizontally mounted electromagnet, the two
cores of which are joined at the back by a soft-iron yoke.
This electromagnet is movable longitudinally through the
bobbin guide by means of the screw at the right, so as
to vary the length of the gap between the magnet poles
Fig. 8.
and the armature, which is mounted in front of them.
This armature is pivoted at the lower end, while the upper
end or tongue plays between two adjustable screws, with
locknuts, supported on the bobbin guide. An adjustable
retractile spring suitably mounted keeps the armature
normally away from the magnet poles and against the
back stop screw which contains a small piece of insulating
material. When the relay is energized the platinum con-
tact on the tongue touches a similar contact in the front
stop screw and thereby completes the local circuit which
is joined to the left-hand binding posts. The right-hand
SIMPLEX TELEGRAPHY
binding posts are the terminals of the magnet winding, and
connect with the lines.
In practice, relays have resistances ranging from 20 to
300 ohms, but i5o-ohm relays are the most extensively
used. A i5o-ohm relay in considerable use consists of
6500 turns of No. 30 B. & S. single-silk-covered copper
wire and operates commercially on 0.05 ampere, although
it can be adjusted to work reliably on a current as small as
o.oio ampere. The average distance between the armature
and pole faces of the magnets is about 0.03 inch. When
traversed by a 25 cycle alternating current of 0.08 ampere
the impedance of the relay is about 550 ohms.
The number of turns of copper wire which can be accom-
modated on any magnet bobbin may be quickly found by
multiplying the length of the winding space in inches by the
permissible depth of the winding in inches and dividing this
result by a winding constant for the selected wire size, values
of which constant are given in the following wire table:
B.&S.
gage
Diameter
of bare
wire in
mils
Winding constants
B.&S.
gage
Diameter
of bare
wire in
mils
Winding constants
Single-silk-
covered
copper wire
Enameled
copper wire
Single-silk-
covered
copper wire
Enameled
copper wire
16
I?
18
19
2O
21
22
23
24
25
26
27
28
50.82
45-26
40.30
35-89
31.96
28.46
25-35
22.57
2O. IO
17.90
15.94
14.20
12.64
0.00267
O.OO2I4
0.00173
0.00138
O.OOIIO
o . 000884
0.000708
0.000568
0.000458
0.000370
0.000299
0.000244
0.000202
29
30
31
32
33
34
35
36
37
38
39
40
11.26
10.03
8.928
7-950
7.080
6.305
5-6I5
5-ooo
4-453
3-965
3-531
3-145
O.OOOl68
0.000142
O.OOOI2I
O.OOOIO5
o . 0000889
0.0000766
0.0000658
0.0000570
0.0000497
0.0000437
o . 0000388
0.0000348
0.000137
O.OOOII3
0.0000928
0.0000767
0 . 0000645
o . 0000484
o . 0000398
0.0000334
0.0000268
0.0000227
o . 000845
0.000673
0.000534
0.000413
0.000327
0.000267
O.OOO2IO
O.OOOI7O
14 TELEGRAPH ENGINEERING
When a constant electromotive force is impressed on the
terminals of a relay or sounder the current does not in-
stantly assume its ultimate value because of the inductance
of the electromagnet. As the inductance of a winding
surrounding iron depends on the current traversing the
winding and the position of the armature, it is difficult to
calculate the growth of current as a function of time for
these telegraph instruments. The lower curve of Fig. 9
Fig. 9.
shows the growth of current strength in a typical relay as
obtained experimentally by means of an oscillograph. Ab-
scissas represent time — one inch corresponds to 0.037
second; ordinates represent current strength — one inch
corresponds to 0.030 ampere. The upper curve shows the
current in the circuit controlled by the relay contacts. It
will be observed that one-thirtieth of a second elapses after
impressing voltage on the relay coils before armature chat-
SIMPLEX TELEGRAPHY 15
tering ceases and the local circuit is closed. This time,
with different instruments, varies in some way with the
ratio of the inductance to the resistance of the relay.
When the impressed voltage is withdrawn the relay
armature is not immediately drawn back by the spring be-
cause of the residual magnetism in the cores. To attain
quick release the armature when drawn toward the magnet
poles should not quite touch them. This condition is ob-
tained by the stop screws or else by the insertion of small
non-magnetic pins in the pole faces so as to project about
6*2 of an inch.
Registers. — Where it is desired to record automatically
the received signals, as in small telegraph offices, or with
Fig. 10.
the District Telegraph Messenger Service, an ink-recording
sounder or register may be used. A register consists of an
electromagnet and a pivoted armature lever which presses
a paper tape against an inked wheel when actuated. Spring-
i6
TELEGRAPH ENGINEERING
driven clockwork moves the tape past the inked printing
wheel, the motion beginning at the first current impulse
and ending some seconds
after the last impulse. Fig.
10 shows a register and
Fig. ii shows an automatic
paper winder used with it
for winding up the paper as
it is delivered from the reg-
ister.
5. Best Winding for Re-
ceiving Instruments. — On a
telegraph line the windings
on the receiving instruments
might have many turns of
small wire or fewer turns of larger wire for the same wind-
ing space. The former windings require a smaller current
than the latter for a given magnetizing force, but at the
same time have a greater resistance. On reflection it will
be observed that a best, winding exists for each set of
conditions, which winding results in the greatest transmis-
sion distance for lines of given cross-section. The method
of determining this ideal winding is given below.
If A be the winding space on an electromagnet in square
inches and d be the diameter of the wire over insulation in
inches, the number of turns will be
A
n = -, (2)
which takes no account of bedding of wires in preceding
layers or of interleaving insulation. If D be the wire
diameter in mils, and z be the mean length of a turn in
SIMPLEX TELEGRAPHY 17
inches, the resistance of the copper wire forming the wind-
ing will be
0.87 nz . , v
Rr = —jy- ohms (3)
at 20° cent., where the constant 0.87 is the resistance of a
copper wire i inch long and o.ooi inch in diameter.
The steady current traversing the circuit of length /
miles with N identical relays in series for an impressed
unidirectional voltage E is
where R is the line resistance per mile. The line is assumed
perfectly insulated from ground. Therefore the ampere-
turns are
EA
nl =
from which
l=Rd2(nJ~
Taking g as the thickness of insulation in inches,
d = - - + 2 g inches,
In order to find the maximum distance of transmission as a
function of wire diameter, this equation is differentiated
with respect to D and equated to zero. Whence
^3 _ i.742JV(tt/) D_ irfiozgN (nl) =
E E
i8
TELEGRAPH ENGINEERING
which is of the form Z)3 - PD - Q = o. The solution of
this form is
— cos
-cos
-1
\*
mils.
(6)
This result gives the size of wire to be used in winding the
coils of the receiving instrument, and substituting this
value in equation (3) gives the instrument resistance.
As a numerical illustration consider relays having the
following constants:
Sectional area of winding on both coils = A = i.o sq. in.,
Mean length of turn = z = 2.4 inches,
Number of relays in circuit = N = 10,
Impressed voltage = £ = 120 volts,
Ampere-turns necessary for actuation = nl = 200,
Thickness of silk insulation = g = o.ooi inch.
For these values
I.74ZJV (nl)
E
1.74 X 2.4 X 10 X 200 , ,
- = 69.6,
1 20
Q = 1000 gP = 1000 X o.ooi X 69.6 = 69.6,
and consequently the wire diameter for the relay is
69.6
D
cos
-cos
-1
_
= 2 V23.2cos(| cos"1 0.312) =9.632 cos 23°57' = 8. 80 mils.
* If the bracketed expression is greater than unity, hyperbolic cosines
are taken. For cosine tables see the Appendix.
SIMPLEX TELEGRAPHY 19
The nearest standard wire size hereto is No. 31 B. & S.
gage, for which D = 8.93 mils. Using No. 31 wire, the
number of turns on both relay bobbins is
_ i .00 _ _ o A
(0.00893 + 0-002)2 -
and the resistance of the instrument is
0.87 nz 0.87 X 8360 X 2.4
-- = 2I9 ohms-
Thus the ideal relay winding for the given conditions
would consist of 8360 turns of No. 31 copper wire having
a resistance of 219 ohms. With 10 of these instruments
the maximum distance of telegraphic transmission is such
that the resistance of the whole line exclusive of relays is
(from equation 4)
En A7r> 120 X 8360
-- NRr = - — * -- 10 X 219 = 2826 ohms.
200 200
Using a i2.4-ohm-per-mile line, this means a transmission
distance of -- = 228 miles.
12.4
• The dependance of the ideal winding upon the impressed
voltage and number of relays used in the circuit, for
otherwise identical conditions assumed in the foregoing
illustration, is shown in the table on the following page.
The same method may be used in determining the most
suitable windings for main-line sounders.
In practice there are various standard relay and sounder
'resistances, and for a given set of conditions, that type of
instrument winding is selected which will approach closely
to the ideal winding. Usual resistances of receiving instru-
ments are 20, 50, 75, 100, 150, 250 and 300 ohms. Main-
2O
TELEGRAPH ENGINEERING
line relays of 37.5 ohms resistance are also used on many
commercial and railway telegraph lines.
40 Volts
80 Volts
Number
of
relays
Calcu-
lated
wire di-
ameter,
in mils
Nearest
B. &S.
gage
num-
ber
Relay
resist-
ance in
ohms
Maximum
line resist-
ance exclu-
sive of
relays
Calcu-
lated
wire di-
ameter
in mils
Nearest
B. &S.
gage
num-
ber
Relay
resist-
ance in
ohms
Maximum
line resist-
ance exclu-
sive of
relays
2
6.QI
33
506
1416
S-oi
36
1700
4760
6
11.67
29
94
576
8-37
32
334
2036
IO
14.94
27
39-5
367
10.70
29
94
1340
is
18.2
25
16.4
258
12.90
28
61
949
20
2^.9
24
10.6
198
14.94
27
39-5
734
30
25-5
22
4-36
137
18.20
25
16.4
5i6
120 VoltS
160 Volts
6
6.91
33
5o6 '
4248
6.04
34
762
7028
IO
8.80
3i
219
2826
7.68
32
334
4740
13
9-99
30
144
2274
8.70
3i
219
384i
16
11.02
29
94
1916
9.60
30
144
3224
20
12.28
28
61
1576
10.70
29
94
2680
30
14-94
27
39-5
IIOI
12.90
28
61
1898
6. Sources of Current. — In telegraphy the current for
main and local circuits is furnished occasionally by primary
batteries (such as Gravity, Fuller, Edison-Lalande, Dry,
and Leclanche cells), more frequently by storage or second-
ary batteries, but is furnished chiefly by dynamo electric
machines.
Primary Batteries. — Primary cells consist of two dissim-
ilar metals (or one may be carbon) immersed in an electro-
lyte; and when these are connected externally by means of
an electric circuit, the chemical energy of the cell is gradually
converted into electrical energy, and a current is main-
tained in the circuit. By this action one of the metal
electrodes, the anode, is slowly consumed. To prevent
SIMPLEX TELEGRAPHY 21
the adhesion of liberated gas at the other electrode, or
cathode, during current delivery, a depolarizer is em-
ployed which combines readily with the gas evolved. In
some cells, as in the Fuller and Leclanche types, the cathode
and depolarizer are contained in porous cups. When com-
mercial metals containing impurities are used, the anode is
also consumed by local action without contributing to the
production of current in the circuit. This deleterious proc-
ess, which goes on whether the cell delivers current or not,
is minimized by amalgamation of the anode.
Cells such as the Gravity, Fuller and Edison-Lalande
types are suitable for closed-circuit work, while the Dry
and Leclanche cells are suitable for intermittent service.
Of primary batteries the Gravity cell is the most exten-
sively used in telegraphy. Fig. 12 shows the Crow-foot
gravity cell, the copper being placed in
the bottom of the jar and the zinc sus-
pended from the upper edge. Zinc
sulphate (ZnS04) is the electrolyte and
copper sulphate (CuS04) is the depo-
larizer of this cell, which yields a volt-
age of about i.o, and has an internal
resistance of approximately 2 to 3 ohms.
When a battery furnishes current to
several circuits, its internal resistance
causes the current in each circuit to become less as the
number of circuits connected in parallel to the same bat-
tery increases.
Storage Batteries. — Storage or secondary batteries are
reversible cells which can be charged from some source of
direct current and later discharged. Charging increases
the chemical energy of the cell, and this energy reverts to
22
TELEGRAPH ENGINEERING
electrical energy during discharge. The usual form of
storage battery consists of a lead peroxide (PbC^) positive
grid and a spongy lead (Pb) negative grid in an electrolyte
.of dilute sulphuric acid of specific gravity 1.2. During
discharge these electrodes are gradually changed to lead
sulphate (PbSC^), a poor conductor of electricity. Re-
charge converts the electrodes to their initial states. The
voltage of the cells when fully charged is 2.5, and the voltage
beyond which it is inadvisable to discharge them, because
of otherwise excessive sulphating, is 1.8.
The rating of these storage bat-
teries in ampere-hours is based on
a uniform 8-hour discharge. A more
rapid discharge results in a lowered
ampere-hour capacity. The capacity
of a cell depends primarily on the
size and number of plates and their
character, and is generally from 40
to 60 ampere-hours for each square
foot exposed surface of positive plate.
Fig. 13 shows a 56o-ampere-hour
storage cell made by the Electric
Storage Battery Company.
Fig* I3* The Edison storage battery is also
suitable for telegraphic purposes. Its positive electrodes
consist of grids of nickel-plated steel supporting nickel
oxide intermixed with flakes of pure nickel, and the nega-
tive electrodes consist of similar grids containing iron
oxide. The electrolyte is a 21 per cent solution of caustic
potash in distilled water and is contained in a nickel-plated
sheet-steel case.
The ampere-hour capacity of these batteries is based on
SIMPLEX TELEGRAPHY
a 5-hour discharge rate. The voltage of a cell is 1.2 at
normal discharge; for charging 1.85 volts are required per
cell. Fig. 14 shows the appearance of an 8o-ampere-hour
Fig. 14.
Edison storage battery, and also the positive (at the right)
and negative plates.
Storage cells may be charged directly from direct-current
service mains or through boosters and motor-generators.
If only alternating current is available, it may be changed
into direct current for the charging of storage batteries by
means of electrolytic or mercury-vapor rectifiers, or by
means of converters or motor-generators.
Generators. — Electric generators are extensively used in
large telegraph offices for the operation of long lines and
local instruments. They may be driven by steam or gas
engines, but more generally by electric motors which re-
ceive either direct or alternating current from service
mains. For the operation of telegraph circuits of all types
different voltages are required from about 25 to 400 volts.
The voltages now considered standard for main-line
TELEGRAPH ENGINEERING
operation are 80, 160, 240 and 320 by the Western Union
Telegraph Company, and 85, 125, 200 and 385 by the
Postal Telegraph-Cable Company, while for local circuit
operation they are 26 and 52 with the former and 40 volts
Fig. 15-
with the latter company. The generators for the two higher
voltages are generally duplicated so as to permit of re-
versal of potential, as necessary in duplex and quadruplex
service (see Chapters II and III). With printing tele-
graph systems no volts are generally used.
Fig. 16.
The arrangement of generators at a telegraph office is
shown in Fig. 15, the voltages indicated being those of the
Postal Telegraph-Cable Company. Protective resistances,
r, in series with the generators, are used to prevent injury
to the machines in case of line short-circuits, etc. Fig. 16
SIMPLEX TELEGRAPHY 25
shows the appearance of General Electric Company motor-
generator sets each composed of a direct-current motor
and generator. The 22O-volt 3 -wire direct-current system
with neutral wire grounded is sometimes used, where avail-
able, for telegraphic purposes. Dynamotors and mercury-
vapor rectifiers are also frequently employed.
It is common practice to have a source of electromotive
force at both ends of simplex lines instead of a single
source of equal total voltage at one end, because of better
line operating characteristics during wet weather.
7. Telegraph Codes. — Telegraph codes consist of vari-
ous combinations of dots, dashes and spaces for the rep-
resentation of letters, numerals and punctuation marks.
Two codes are in extensive use, the American Morse, or
simply Morse, and the Continental Morse, or simply Con-
tinental. The Morse code is used throughout the United
States and Canada for overland signalling except in print-
ing telegraphy. In punctuation, however, the Phillips
Punctuation code has generally superseded it because of
its greater completeness. The Continental, or so-called
universal code, is in use throughout the world for sub-
marine telegraphy and also in almost every country except
those mentioned for overland signalling. The codes are
given on the two pages following.
In the code characters the length of a dot is taken as
the unit of measurement of dashes and spaces. The ordi-
nary dashes are three times as long as dots, the long
dashes for letter / and cipher in the Morse code are re-
spectively five and seven times as long as a dot, the spaces
between the elements of letters are equal to dots, the
longer spaces in the letters C, 0, R, Y, Z and & of the
26
TELEGRAPH ENGINEERING
ALPHABET
LETTERS
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
• x
Y
Z
&
FIGURES
1
2
3
4
5
6
7
8
9
0
MORSE
CONTINENTAL
MORSE
NUMERALS
CONTINENTAL
- — or
or
or -
- - or —
or •
or
SIMPLEX TELEGRAPHY
fore words
tter
, repeat
i. 1:
r i
ll h
2, 2?
II
i
i
i
i
jS*'
1
PHILLIPS
i
• 1
i i
II
j
i i
j 1
i f i
; ; i :
!!;i
i
;i
1 1
i 1
j!
i
1
i
1 1
1' 1
I1 '
ll 1
II 1
„ '
ii !:
ii M
1
1
i i
::i:
• 1 1
:• !
! i
|
II 1
II 1
ii n
i
1 1
i
i i
I i i i
i 1 i i i
• i i
i i i
1 ! 1
1 1
!
111
ii 1 1
il ii
0
i
i
i
i
1
/
1VJLN3N
i i
1 1
i
I
i
: i
i i
jj
i
I
SCTTJATIO
1;
i !
i i
1
i
1
i
1 i
1 1
: i
I :'
1 i!
i
i
I
j
i
i
1
i
i
£
i
i
i
i i
I
1
1 i
1
ll
I
O 1
1 i
i
i I
i
1
1
i !
1
i
i 1
1 1
1
i
, I
1
s-^>~~-
^£
c
co a
T3
.2
&
*J
0 C <->
-2 -2'i
Comma
Interrogation
Exclamation
ijfj
fa QE <Q
#*
~C d
£ S
CO
« bO
™ c S
C 3 =5
v o *2
Pence
Capitalized lette
Colon followed
quotation
Decimal point
Paragraph
1
5
0
M
0
1
Parenthesis
Brackets
Quotation mark
Quotation withi
quotation
»..»»<•
28 TELEGRAPH ENGINEERING
Morse code are twice as long as dots, and the spaces be-
tween letters and between words are respectively three and
six times as long as dots.
The Continental code, having more dashes than the
Morse code, requires a little longer time in the transmission
of any given message expressed in that code than when
expressed in Morse code.
A partial list of abbreviations used in commercial teleg-
raphy follows:
Scotus — Supreme Court of the United States
Bk— Break
Ck — Check
Fm — From
Ga — Go ahead
Min — Wait a minute
Nm — No more
No — Number
x (placed after check) — Get reply to message
x x x ... — Omission
4 — Where shall I go ahead?
8 — Wait, I am busy
Thus, in case of doubt as to the accuracy of a transmitted
message, the receiving operator breaks and sends the let-
ters bk, ga and the last word correctly received; whereupon
the sending operator continues from that word. Abbre-
viations used in differentiating the various classes of tele-
graphic service are given in § 8 of Chap. V, and of cable
service are given in § 10 of Chap. XI.
'•x
8. Telegraph Lines. — Galvanized iron, hard-drawn
copper and occasionally steel wire are used for telegraph
lines. The sizes generally employed on overhead lines are
SIMPLEX TELEGRAPHY
29
from No. 9 to 14 B. & S. (Brown & Sharpe) gage copper
wire and from No. 4 to 12 B. W. G. (Birmingham Wire
Gage) iron wire. The increasing use of hard-drawn copper
wire for telegraph lines is due to its having a lower resist-
ance than iron for the same tensile strength, and to the
fact that it is practically non-corrosive. Telegraph con-
ductors in cables for transmission over relatively short
distances are of from No. 14 to 19 B. & S. soft copper.
The weights, diameters and resistances of telegraph line
wires are given in the following table:
Hard-drawn copper wire
Galvanized iron wire (E. B. B. quality)
B.&S.
Gage
No.
Diameter
in mils
Weight in
pounds per
mile
Resistance
at 60° fahr.
per mile in
ohms
B.W.G.
No.
Diam-
eter in
mils
Weight in
pounds per
mile.
Resistance
at 60° fahr.
per mile in
ohms.
9
10
II
12
13
14
114.4
IOI.Q
90.74
80. 81
71.96
64.08
208
166
132
105
83
65
4.22
5-28
6.6s
8.36
10.55
13.29
4
6
8
9
10
ii
12
238
2 2O
203
180
165
148
134
1 20
109
787
673
573
450
378
305
250
200
165
5-97
6.98
8.20
10.44
12.43
I5-4I
18.80
23-50
28.48
Soft copper wire
14
11
17
18
19
64.08
57-07
50.82
45-26
40.30
35 89
65
52
42
32
25.6
20.7
13.12
16.54
20.67
26.55
33-6o
41.47
Temperature rise increases the resistance of copper
0.24 per cent per degree fahr. and increases that of iron
0.35 per cent per degree fahr. reckoned from o° fahr.
Copper-clad or bimetallic wire is also used to some extent
for telegraph lines. It consists of a steel core to which is
welded a coating of copper, forming a wire of high tensile
30 TELEGRAPH ENGINEERING
strength and fairly low resistance. Several grades are
available that differ in conductivity, depending upon the
relative amounts of copper and steel used.
Bare overhead conductors are supported by glass insu-
lators mounted on wooden, or sometimes concrete and steel
telegraph poles. These points of support offer leakage cur-
rent paths from the conductor to ground. Even in dry
weather the insulation resistance between the conductor
and ground is not infinite, but of the order of 10 to 100
megohms per mile of line, while in wet and foggy weather
the insulation resistance may fall to a fraction of i megohm
per mile.
In the foregoing pages only perfectly insulated lines were
considered. On actual lines, because of the distributed
nature of the leakage paths, it is more difficult to determine
the exact relation between the various factors involved.
A rough- approximation on lines of short or medium length
to the actual conditions is obtained by considering all the
leakage paths to be grouped into one equivalent path at
the middle point of the line, as shown in Fig. 17.
Fig. 17.
It is evident from the figure that even though the circuit
is open at one station, current flows from the battery at the
other station through the relay, part of the line, and the
equivalent leakage path to ground. It follows, therefore,
that at no time is the current flow in the receiving in-
SIMPLEX TELEGRAPHY 31
struments wholly interrupted; and consequently their re-
tractile springs must be adjusted to release the armatures
on a certain minimum current strength. In damp weather
when the insulation resistance of the line is lowered the
relays must be more delicately adjusted, because the
currents flowing in the circuit when one switch and when
both switches are closed are more nearly equal.
Thus, on a 6oo-mile No. 9 B. & S. aerial copper line
having a 25o-ohm relay and an 80- volt battery at each
end, and having an insulation resistance of 10 megohms
per mile, the steady current traversing the relay when one
key is open is
/ = = 0.0044 ampere,
. 10,000,000
250 + 300 X 4-22 + -
ooo
and when both keys are closed the current is
7 = — - = 0.0528 ampere.
2 X 250 + 600 X 4.22
On the other hand, if the insulation resistance be taken as
one-half megohm per mile, the current when one key is
open would be
80
7 = =0.034 ampere,
250 + 300 X 4-22 + S00?000
ooo
showing that under these conditions the relay must be
adjusted to operate on 0.0528 ampere and release the
armature on 0.034 ampere. If so adjusted and if the in-
sulation resistance falls still lower, the line would be ren-
dered inoperative.
With assigned insulation resistance, terminal resistance
32 TELEGRAPH ENGINEERING
and relay adjustment, it is possible, on the basis of the
foregoing paragraphs, to determine the maximum permis-
sible length of line for line conductors of any size. Let
/ = maximum length of ground-return line in miles,
R = line resistance per mile in ohms,
Rr = resistance of each relay in ohms,
N — number of relays in circuit (assumed uniformly
distributed between terminal stations),
R{ = insulation resistance per mile in ohms,
E = voltage impressed at each end of line,
/! = current in amperes necessary to actuate relay, and
72 = current in amperes which will just cause release
of armature,
r 4. -*
I " [ 7
2 2 /
and
Eliminating E from equations (7) and (8), and solving for I,
there results,
n,r 2..
IT' -R(h-ij-
from which the maximum transmission distance is
an expression not involving the impressed voltage.
As a numerical illustration, consider a No. 9 B. & S.
copper conductor having a 25o-ohm relay at each end
which is adjusted to operate on 0.06 ampere and .release
SIMPLEX TELEGRAPHY 33
on 0.04 ampere. For an insulation resistance of | megohm
per mile, the maximum permissible length of line is
// 250 \2. 2 X 0.04 X 500,000
V V 4.22 / 4.22 (0.06-0.04)
2 X 4-22
= - 59-3 + 691.0 = 631.7 miles.
The voltage of the battery at each end should be
E = ^ (NRr + Rl) = — (2 X 250 + 4-22 X 631.7)
2 2
= 95 volts,
as obtained by using equation (8).
This approximate solution of the telegraph circuit will
be referred to again because it is less involved than the
exact solution which is considered in Chap. X. Experi-
ence has proven that the maximum distance of trans-
mission on long aerial lines is limited principally by line
leakage.
9. Speed of Signalling. — The speed with which signals
may be transmitted over a telegraph line depends upon
three factors, namely the speed of the sending operator,
the nature of the line, and the responsiveness of the receiv-
ing instrument.
An experienced operator can send from 30 to 40 five-
letter words per minute by hand transmission. Semi-
automatic devices may be availed of to raise this sending
speed. Much higher speeds are attainable by automatic
transmitters, as described later (§ i, Chap. IV).
It was pointed out in the last section that the current
through the receiving device connected to a leaky line
does not cease altogether upon opening one key. It is
34 TELEGRAPH ENGINEERING
evident that the greater the line insulation resistance the
more rapid will be the current change in the relay coils
with movements of the key, and consequently the quicker
the actuation and release of the relay armature. On a
long line with considerable leakage, rapid signalling may
cause the duration of contact for dots to be so short as to
prevent the current in the relay from attaining a value
sufficient to attract its armature. More deliberate or
"heavy " sending must then be resorted to, implying
slower signalling speed. Thus, the shorter the line the
higher may be the speed of signalling.
Further, the line itself, especially if a cable, limits the
speed of transmission. As most large telegraph offices are
in the business centers of cities, short sections of nearly all
long aerial lines are placed in cables under ground and there-
fore the speed of signalling on these lines is limited by the
cable sections. In cables a conductor is very near its
return conductor or the grounded sheath, and conse-
quently its electrostatic capacity is high. It will be
shown in § 4 of Chap. XI, that the signalling speed over
cables (having negligible inductance and leakance) is in-
versely proportional to the product of total line capacity
and total line resistance. That is, if C be the capacity in
farads per mile of conductor, and R be the resistance in
ohms per mile, then
V Signalling speed » JL_ ^L., (IO)
where / is the length of the cable in miles. This propor-
tionality shows that for a given size of cable the signalling
speed varies inversely with the square of its length.
It is safe to say that the speed possibilities on long
SIMPLEX TELEGRAPHY 35
fairly well insulated aerial lines even with short cable sec-
tions is greater than the operating speed of the receiving
instruments. In § 4 it was stated that the time of current
growth in a relay depends upon the ratio of its inductance
to its resistance. Rather than increase the relay resistance
to obtain rapid response, it is more advisable to reduce its
inductance. This may be done by decreasing the number
of turns, by connecting the two coils in parallel instead
of in series, by increasing the reluctance of the magnetic
circuit either by removing the iron yoke or by lengthening
the air gap between armature and magnet cores, and by
using a shunting condenser. Some of these suggestions,
however, conflict with the conditions for maximum mag-
netization with a given current.
The necessary mass of the relay armature should be
apportioned in such a way as to possess the least moment
of inertia about the pivots so as to acquire a high velocity
under the action of a given force. The greater part of
its mass should therefore be near the axis. The contact
points, however, are preferably placed far from the pivots
in order to reduce the angular motion of the armature and
permit signals to follow each other in rapid succession.
By embodying the features mentioned relays have been
constructed which respond to signals sent at speeds as
high as 400 words per minute.
10. Simplex Repeaters. — It was shown in § 8 that
leakage is the important factor in limiting the distance of
telegraphic signalling. Using a No. 9 B. & S. copper con-
ductor with two 25o-ohm relays with given adjustment
(which implies a given signalling speed) it was found that
the maximum permissible length of line is 631.7 miles
36 TELEGRAPH ENGINEERING
when the insulation resistance is assumed as J megohm
per mile. If a No. 6 wire, which has double the cross-
section (R = 2.09), were used instead, the maximum length
of line under otherwise identical conditions would be 865.9
miles. Thus, using a conductor of twice the size and
costing twice as much would only increase the distance of
transmission 37 per cent. It is apparent from this illus-
tration that the cost of transcontinental telegraphy over a
single continuous circuit would be prohibitive.
If such long lines are subdivided into several shorter
sections, say from 300 to 600 miles in length, each section
terminating in a relay, signals may be automatically trans-
Fig. 18.
mitted thereby into the next section, and so on to the
terminus of the line, without requiring unduly large lino
conductors. The speed of signalling will then be that of
the section which allows the slowest transmission less the
speed loss in the relays. Two-line sections of such an
arrangement are shown in Fig. 18, from which is seen the
possibility of transmitting toward the right, but also the
futility of endeavoring to transmit in the opposite direc-
tion. In order to permit of signalling in either direction,
the intermediate relays R^ R3 . . . are replaced by re-
peater sets.
A repeater set consists of two relays and two transmit-
SIMPLEX TELEGRAPHY
37
ters which are electrically and mechanically arranged to
allow signalling in either direction and in such a way as
to automatically prevent one transmitter breaking at the
repeater station the line circuit which it controls when
that circuit is repeating into the other. Two standard
closed-circuit repeaters which accomplish these results will
now be described.
Weiny-Phillips Repeater. — The connections of a Weiny-
Phillips repeater set are shown in Fig. 19, in which T and Tf
are the transmitters, and R and R' are the relays. Each
relay has an extra magnet, H or H' ', called a holding-coil,
mounted above the ordinary magnets so as to act on the
same moving element, as illustrated in Fig. 20. Its wind-
ing has a tap at its middle point, so that if current enters
at this point, it will traverse the two parts of the winding,
a and b, in opposite directions, and consequently produce
no magnetization in the core. The transmitter T has a
small auxiliary lever m, insulated from and controlled by
the main lever, each lever making contact with a platinum
TELEGRAPH ENGINEERING
contact point when the magnets of the transmitter are
energized. The switches 5 and s' on the transmitters
Fig. 20.
enable an operator to sever the two circuits, leaving each
complete in itself for simplex operation. Fig. 21 shows the
Weiny-Phillips transmitter.
Fig. 21.
Normally, when both the eastern and western circuits
are closed at the distant stations, current flows through all
magnet windings of the repeater set. Thus, normally,
SIMPLEX TELEGRAPHY 39
current flows from the western station through the main-
line coils of relay R, circuit-closing switch of the key K,
and contact y' (which is closed) of the transmitter T", to
ground at G '. Similarly, current flows from the eastern
station through R', K' ', and y to G. Both relay armatures
are therefore attracted and keep the. transmitter coils
energized through the batteries B and B' '. The contacts
x, y and x', y' are thus normally closed and currents from
the batteries BI and J52 flow through both windings of the
holding coils. Generators are very frequently used instead
of batteries.
When the western operator opens the circuit preparatory
to signalling, the main-line coils of relay R are deprived of
current and the armature is released, inasmuch as the hold-
ing coil // exerts no attraction due to the neutralization of
magnetizing forces developed in the two windings. This
results in opening the circuit of the magnet of transmitter
T and the release of its armature. The positions of the
moving elements of the instruments at this instant are as
shown in Fig. 19. The circuit of the winding bf of the
holding coil Hf is broken at x and consequently the un-
interrupted current flowing through its associate winding
a! holds the tongue of relay Rr against its contact stud
irrespective of current condition in the main-line coils.
This in turn maintains current flow through the winding of
transmitter T' and prevents the opening of the western
circuit at yr , and the opening at x' of coil b of the holding
coil H, which is therefore not magnetized. In this way
the continuity of the western circuit is preserved at the
repeater while repeating eastward. A moment after
breaking the circuit at x, the eastern circuit is broken at
y and the distant relay releases its armature.
40 TELEGRAPH ENGINEERING
When the western operator depresses his key, relay R
will be actuated, and then the transmitter T closes the
eastern circuit at y, which is followed by the closing of
coil bf at x. The distant eastern relay is thus energized.
Signalling in the reverse direction is accomplished in the
same manner.
Atkinson Repeater. The Atkinson repeater set con-
sists of two ordinary relays R and R', two transmitters T
and Tf similar in design to the Weiny-Phillips transmitters,
and two repeating sounders S and S' which combine the
functions of relay and sounder, the connections of the set
being shown in Fig. 22. The contacts of the repeating
sounders are shunted across the corresponding relay
contacts.
Normally, when no messages are being transmitted,
the windings of all the repeater instruments carry current.
Thus, the western line current traverses the contact x
(which is closed) of the transmitter T and the winding of
relay R' to ground. Similarly, the eastern line current
traverses x' and R to ground. Both relay armatures are
therefore in contact with their front connecting studs and
keep the transmitter magnets energized by means of
the batteries B and B' '. The contacts y and y' are
thus normally closed and currents from the batteries b
and V actuate the repeating sounders S and S' respec-
tively.
When the western operator opens the key prior to signal-
ling, relay R' loses its magnetism and its armature falls
back, thereby opening the circuit of the magnet of trans-
mitter Tfj inasmuch as sounder S' remains energized and
does not short-circuit the relay contacts. The lever of
this transmitter first opens a circuit at y' and immediately
SIMPLEX TELEGRAPHY 41
afterward opens a circuit at x'. The conditions are then
as shown in Fig. 22. The opening of the circuit at yf
causes the demagnetization of sounder 6* and the release
of its armature. The magnet of transmitter T will thereby
be kept energized regardless of the armature position of
relay R. In this way the continuity of the western cir-
cuit is preserved at x. The circuit opened at x' is the
eastern line circuit. Thus, the relay at the eastern station
Fig. 22.
releases its armature as the distant western operator opens
the circuit.
As this operator then depresses his key, relay R' is
energized and its armature closes the transmitter circuit
at T', the result of which being the closing of the eastern
circuit at #', followed by the closing of the circuit of re-
peating sounder S. The actuation of the sounder, how-
ever, does not open the circuit of the transmitter magnet
T, because the relay R, energized by the eastern line
battery (not shown) at the closing of contacts x', keeps its
circuit closed.
42 TELEGRAPH ENGINEERING
Signalling in the reverse direction can be traced through
the repeater in the same manner.
Other Repeaters. — Many other closed-circuit simplex
repeaters are in use, among which may be mentioned the
Milliken, Ghegan, Horton, Neilson and Toye repeaters.* f
They all differ in the methods employed to prevent one
transmitter breaking the circuit, that is repeating into the
other circuit. Repeaters may also be arranged for re-
peating into two or more circuits; the Maver multiple
repeater* is one of this type.
For the satisfactory operation of repeaters, attendants,
each in charge of a certain number of sets, are required to
supervise the working of the repeaters and make such ad-
justments as are necessary to maintain uninterrupted
service despite changes in weather conditions and irregu-
larities in sending. With several types of self-adjusting
repeaters, such as the Catlin and D'Humy repeaters,f this
supervision may be dispensed with.
There are various types of open-circuit repeaters, the
simplest of which, employing only two double-contact re-
Fig. 23.
lays, is represented in Fig. 23. When no messages are
being transmitted, no current flows through the line wires
and repeater relays, and consequently both relay arma-
* For description see Maver's "American Telegraphy."
t Described in McNicoPs " American Telegraph Practice."
SIMPLEX TELEGRAPHY 43
tures rest against their upper contact studs. When the
western operator depresses his key, relay Rf attracts its
armature, and current, supplied by battery B', flows over.
the eastern line. At the same time the magnet circuit of
relay R is broken at the upper contact point so that the
continuity of the western circuit remains uninterrupted.
PROBLEMS.
1. How far would it be possible to telegraph over a perfectly
insulated ground-return line having 8.36 ohms resistance per mile of
length with an impressed voltage of 1 20, if the current necessary to
actuate the two 75-ohm relays is 0.07 ampere?
2. How many gravity cells, each having a voltage of i.o and an
internal resistance of 2.5 ohms, would be required to transmit signals
over an 8o-mile telegraph line which has a resistance of 5.28 ohms per
mile and is equipped with two i5o-ohm relays requiring a current of
0.04 ampere ?
3. Three relays are adjusted to operate on 250 ampere- turns,
and have the following constants:
Relay No. i 20 ohms resistance 2400 turns,
Relay No. 2 75 ohms resistance 4500 turns,
Relay No. 3 150 ohms resistance 7500 turns.
If these relays were connected in series across 2o-volt mains, which
relays would operate ? What voltage would cause all three to oper-
ate?
4. What is the best winding for four main-line sounders operating
on 400 ampere-turns when used on a telegraph line which requires
40 volts? The sounders are of identical construction and have a
winding cross-section of 0.9 square inch and a mean length of turn
of 2.2 inches; double-cotton-insulated wire to be used, the insulating
covering being four mils thick.
5. Over how long a line, having 13.3 ohms resistance per mile,
could the four sounders of the preceding problem operate when the
impressed voltage is 40 volts ?
6. Four separate telegraph lines, each having a total resistance of
1000 ohms including receiving instruments, are supplied with cur-
rent by one battery of 100 gravity cells, which has an internal re-
44 TELEGRAPH ENGINEERING
sistance of 220 ohms. Determine the current strength in a circuit
when only one circuit is closed and also when all four circuits are
closed.
7. Decipher the following message:
8. What would be the costs per mile of two telegraph lines of
standard sizes having approximately 10.5 ohms resistance per mile,
one constructed of galvanized iron and the other of hard-drawn
copper wire? The costs of iron and copper may be taken as 4^ and
1 6 cents per pound respectively.
9. A 4oo-mile No. 6 B. W. G. aerial iron line, having a 25o-ohm
relay and a 120- volt generator at each end, shows an insulation re-
sistance of i megohm per mile in wet weather. What currents flow
through one relay when the key at the other station is open and
when closed?
10. Calculate the maximum permissible length of a No. 10 B. & S.
copper telegraph line having six 25o-ohm relays which are adjusted
to operate on 0.05 ampere and release on 0.025 ampere, if the in-
sulation resistance of the line be taken as \ megohm per mile. 'Com-
pute the proper voltage to be impressed at each end.
11. If the speed of telegraphic' signalling over a loo-mile cable
of No. 1 6 B. & S. copper, having a capacity of 0.12 microfarad per
mile, is 200 five-letter code words per minute, what would be the
possible signalling speed over a 6o-mile cable of No. 19 B. & S. wire
having a capacity of o.n microfarad per mile?
CHAPTER II
DUPLEX TELEGRAPHY
i . Duplex Telegraph Systems. — By duplex signalling
is meant the simultaneous transmission of signals in oppo-
site directions without interference over a single line.
Four operators are required for each duplex circuit, one
sending and one receiving operator at each station. The
message capacity of a duplexed line is therefore twice that
of the same line when operated simplex. When telegraphic
traffic over a given line exceeds that which can be handled
satisfactorily by simplex signalling, it is advisable to install
the necessary apparatus at the terminal stations for duplex
signalling, thereby avoiding the expense of erecting another
line. Duplex telegraphy was first performed in 1853 by
Dr. Wm. Gintl; its practical operation began about 1868.
Duplex circuits do not permit of the intromission of inter-
mediate stations, but. repeating stations may be inserted
on long duplex lines. In telegraph systems intended for
duplex signalling, the receiving instruments at both sta-
tions must be in circuit at all times ready to respond to
signals sent from the distant station, and yet so designed
that the receiving instrument at each station will not
respond to signals sent by that station. These condi-
tions are met in various ways in the different duplex
systems.
There are three systems of duplex telegraphy: the dif-
ferential duplex, the polar duplex and the bridge duplex
45
46
TELEGRAPH ENGINEERING
systems.* The first system, although now infrequently used
for duplex signalling, is an essential part of the quadruplex
telegraph system to be described in the next chapter, and
consequently will be here discussed. Where it is advis-
able to employ a battery at one end of the line only, a
combination of the differential and polar duplex systems
may be used for duplex operation over short distances.
2. The Differential Duplex. — The differential duplex,
also known as the single-current duplex and as the Stearns
duplex, utilizes a differential relay as the receiving instru-
ment. This is a relay with two windings, identical as to
number of turns and resistance, through which currents
G'
Fig. x.
may flow in the same or in opposite directions around its
iron cores. The corresponding turns of the windings are
preferably wound side by side so as to avoid the formation
of consequent magnetic poles. For clearness in diagrams,
however, these windings will be shown as being adjacent.
The scheme of connections of the differential duplex is
represented in Fig. i, which shows a line L extending be-
tween the two stations A and B, having a ground return
* Early duplex schemes are described in Prescott's " Electricity and the
Electric Telegraph."
DUPLEX TELEGRAPHY 47
path. The relays R and Rr have two windings each (a, b
and a' , b'), the common terminal being joined to the levers
of keys K and Kr respectively. The similar batteries
B and Bf are connected with like poles to the front con-
tacts of the keys, while resistance coils d and d> ', having a
resistance equal to the internal battery resistance, are con-
nected to the rear key contacts. In this way the resistance
of the circuit is unaltered whether the keys are on the front
or the rear contacts. The resistance coil r is adjusted to
have a resistance equal to that of the line xy plus the
resistance from the point y to ground at G' and the ground
resistance G' to G, and similarly the coil r' to have a re-
sistance equal to that of the line plus that from the point
x to ground at G and back to G' (the ground resistance
being usually neglected). With this adjustment, if a cur-
rent enter either relay at the junction of its two coils, it
would divide equally between the two paths to ground
presented to it, each path including one of the relay coils.
The equal components of this current in the two coils
circulate around the core in opposite directions and
consequently the magnetomotive force developed by one
is neutralized by that developed by the other, thereby
exerting no attractive force on the relay armature.
The resistances of the coils r and r' are experimentally
adjusted in practice so that the home relay is not affected
by movements of the keys. The resistances may, however,
be determined as follows: The resistances of the two bat-
teries will be assumed equal and of value Rb ohms each,"
the resistances of the two relays likewise of Rr ohms each;
then from the symmetry of the circuit the two coils r
and r' will also have equal resistance, say r ohms. The
line will be assumed perfectly insulated from ground and
48 TELEGRAPH ENGINEERING
of resistance Rl ohms. For exact neutralization of mag-
netizing forces in the two relays, the resistance of the
one path,
f + r + * (i)
must equal that of the other path, which is
2 _!_ I
* &
2
+ ^ + r) = R, (^ + r )
Whence
(r> 2 1? i;>7\
#r#6 + RbRl + ^ + £42] = o.
4 2 /
Therefore the resistance of each coil is
r = — + - V(Rl+Rr)(Rl+Rr + 4R*). (3)
2 2
Thus, if 2oo-ohm relays are connected to the ends of a
20oo-ohm line and if a 2oo-volt gravity battery having 250
ohms internal resistance be employed at each end, then
the resistance coils r and r' would each have a resistance of
_ 2 OOP
+ - V(20oo + 200) (2000 + 200 + 4 X 250)
2 2
= 2327 ohms.
These values are indicated in Fig. 2, and it may be verified
that the resistances of the four paths: m, n, p, m — (2, pt
m, q, Gf — G', /, q, m, G — g, s, t, q, are all equal and have a
resistance of 2677 ohms.
DUPLEX TELEGRAPHY 49
An inspection of Fig. i will reveal the principle of opera-
tion of this system. If neither key be depressed, no cir-
cuit containing an E.M.F. is closed and therefore no relay
is actuated. The depression of only one key at either
station will fail to actuate the relay at that station because
of equal and oppositely directed currents in the halves of
100 -J- 100
Rj = 260
Fig. 2.
its relay coils, but will actuate the relay at the remote sta-
tion because of the additive action of these currents. The
depression of both keys connects both batteries in opposi-
tion and, since no current then flows in the line wire nor in
the line coils b, af, of the relays, both relays are actuated
by the currents flowing in their other coils. Although a
key has no control over the home relay, it will be ob-
served that when both keys are depressed each relay is
operated by current from the home battery.
Thus in this system a relay is properly actuated when-
ever the key at the other station is depressed regardless of
the position of the other key.
In the numerical illustration, the steady currents in
milliamperes traversing the relay coils under the various
conditions, are readily seen to be those given in the follow-
ing table. The figures following the braces give the
equivalent currents through one coil and the stars indicate
the operation of the relays.
TELEGRAPH ENGINEERING
CURRENTS IN RELAY COILS
Relay
Coil
Neither
key de-
pressed
Key K only
depressed
Both keys
depressed
Key K' only
depressed
R
a
b
j|
si?
7*}75*
JJ*
R'
a'
b'
o|°
11 *•
IS*
21*
In the manipulation of the two keys as shown, there are
constantly recurring intervals during which the key levers
are in an intermediate position, touching neither contact
stud. This condition is apt to cause confusion of signals,
especially on leaky lines. In differential duplex circuits
where primary cells are used, this confusion of signals may
be avoided by the employment of transmitters so designed
that contact is made with one stud an instant before con-
tact is broken with the other. The appearance of such
continuity- preserving transmitters, operated magnetically by
means of a local circuit, is shown in Fig. 3.
Fig. 3.
The connections of one station of a duplex circuit using
this transmitter, are shown in Fig. 4, wherein T is the
transmitter, and j and k are the contact studs, the other
DUPLEX TELEGRAPHY
letters having the same significance as before. The trans-
mitter has an auxiliary spring lever, insulated from the
main lever, which may make contact either with the fixed
study or with the stud k attached to the main lever. When
the key is depressed the contact aty is made before that at
k is broken, and when the key is released, the contact at k
is made before that aty is broken. In this way the circuit
from m to ground is always complete. The momentary
short-circuits of the line battery during the excursions of
the transmitter lever do not prove injurious to the battery.
3. Artificial Lines. — The resistances r and r' of Fig. i,
each possessing a resistance equal to that of the line plus
that of the terminal apparatus at the remote station, are
aptly termed artificial lines. But, since actual telegraph
lines have electrostatic capacity with respect to ground,
for more exact imitation the artificial lines should also
have capacity. When the artificial line has the same
capacity as the line wire, then the currents through them
and through the relay coils will rise and fall at the same
rate. That this result is essential is evident from the fact
TELEGRAPH ENGINEERING
that if the current should rise more quickly to its ultimate
value or decay more rapidly to zero in one relay coil than
in its companion coil, the armature would give a momen-
tary kick and produce a false signal upon each depression
or release of the home key. When the resistance and
capacity of the artificial line in a duplex circuit are so
adjusted that the depression of a key produces no effect
upon the home relay, the circuit is said to be balanced.
The arrangement of an artificial line which is used by
the Postal Telegraph-Cable Company for duplex telegraphic
Fig- 5-
signalling is given in Fig. 5. The resistance between the
terminals A and B can be varied from 10 to 11,100 ohms,
and each of the two condenser sets can be adjusted from o.i
to 3.0 microfarads. This wide adjustment permits of its
use on lines of different lengths, resistances and capacities.
Parts of the 400- and i6oo-ohm resistances are connected in
series with the two condenser sets in order to vary the time
of their charge and discharge to approximate the cor-
responding times for the line.
The design of the Western Union artificial line is shown
DUPLEX TELEGRAPHY
53
in Fig. 6. The resistance between the terminals " Ground"
and " Relay" can be varied from 25 up to 11,000 ohms,
and each of the two condenser sets can be adjusted from
i to 3! microfarads. One of the resistances connected in
series with the condensers can be varied from 100 to 500
10 W| lyi i i l MI i i«i i
* X
1 2 | 2 I J$ X Ji
Fig. 6.
ohms while the other adds from 200 to 1000 ohms. When
a line becomes leaky in wet weather, the resistance of its
artificial lines must be lowered for balance.
4. Polarized Relays. — The polar duplex telegraph
system depends for its operation upon reversals in the
direction of current flow. In this system, the function of
the key is not to make and break the circuit as in the
54
TELEGRAPH ENGINEERING
Stearns duplex, but instead to present alternately the
positive and negative poles of the battery to the line.
Obviously the receiving instrument employed must oper-
ate upon current reversals, and such an instrument is
called a polarized relay.
The principle of the simple polarized relay may be ex-
plained with the aid of Fig. 7. A U-shaped permanent
magnet magnetized to have two equal South poles as indi-
cated at (a) has pivoted at its mid-point a soft iron arma-
ture which projects upward and plays between two pole
pieces that are attached to the ends of the magnet, as
shown at (b). The North magnetic pole is then shifted
to the position shown, and it is evident that the armature
SL
(a)
(6)
s",LUn
W)
Fig. 7.
will remain against whichever pole piece it is placed, for no
retractile spring is used. A winding surrounds each pole
piece and the two windings are connected in series. Re-
membering that a current traversing a winding around an
iron core will cause the formation of magnetic poles as
shown at (d), it will be evident that if a current traverses
the windings as indicated by the arrows at (c) the mag-
netization due to the permanent magnet in the left-hand
pole piece will be partially neutralized while that in the
other pole piece will be strengthened. Consequently the
armature will be drawn over toward the stronger right-
hand pole piece, and make contact with the right contact
DUPLEX TELEGRAPHY
55
screw. If the direction of current flow be reversed, the
left-hand pole piece will be the stronger and therefore the
armature will make contact with the left-hand contact
stud. Thus, every time the direction of current changes,
the armature will move from one contact screw to the
other.
The windings of the polarized relay may also be wound
differentially in the same way as with the ordinary or neu-
tral differential relays, already described.
Each coil contains an equal number of
turns belonging to the two windings. To
avoid complicated diagrams, differentially-
wound relays will be represented as in
Fig. 8, with a tap m at the middle point
of the winding. When current is sent through the coils
differentially in either direction the armature will not move
from the position previously assumed.
Fig. 8.
Fig. 9.
Fig. 9 shows one form of differentially-wound polarized
relay. The armature is pivoted in a brass casing just
TELEGRAPH ENGINEERING
below the upper end of the semicircular-shaped permanent
magnet and extends between the adjustable pole pieces of
the electromagnet coils that are mounted on the other end
of the permanent magnet. The post supporting the con-
tact points is shown at the left.
In practice polarized relays usually have resistances of
from 50 to 500 ohms, and will operate satisfactorily on
currents of from 5 to 200 milliamperes. When traversed
by currents of from 10 to 15 milliamperes, the inductances
of such relays are from 1.5 to 6 henrys when the air gap
between armature and pole faces is about 0.02 inch.
5. The Polar Duplex. — The connections of the ap-
paratus used on a polar duplex line for primary battery
operation are shown in Fig. 10. The pole-changing trans-
Fig. 10.
mitters, represented by C and C', consist of double arma-
ture relays, each armature playing between two contact
studs. When the key K is not depressed, retractile springs
hold the armatures x and y respectively in contact with
the positive and negative terminals of the battery B, but
when the key is depressed the armatures are attracted
DUPLEX TELEGRAPHY 57
and x and y are respectively in contact with the negative
and positive poles of the battery. In other words, depres-
sion of the key reverses the polarity of the home battery
with respect to the circuit.
The differentially-wound polarized relays are shown at
P and Pf and control the operation of the local sounders
S and Sr respectively. The letters 5 and n on the relay
poles represent the South and North poles due to the
permanent magnets alone. The properly-balanced arti-
ficial lines are shown at AL. The proper resistance of
the artificial line may be calculated similarly to the method
given in § 2.
When both keys are open, it is seen that the negative
terminals of both main batteries are connected to the
mid-points of the relay windings, and that therefore no
current traverses the line coils a, ai and e, ei of the relays.
Currents, however, will flow in the artificial line coils 6, 61
and /, /i, and these are in such direction as to strengthen
the left-hand poles of the polarized relays and weaken their
right-hand poles, and consequently both armatures will
be drawn to the left and away from the sounder contacts.
Hence both sounders are idle when both keys are open.
If only key K be depressed, the positive pole of battery
B is connected to the line and the conditions are exactly
as represented in the figure. About twice as much cur-
rent flows through the line coils of the relays as through
the artificial line coils, so that the operation of the relays
depends upon the direction of current in the line coils.
The current in the coils a and a\ strengthens the left-hand
pole and weakens the right-hand pole of relay P} and con-
sequently the armature stays away from its sounder con-
tact. At the other station the current in the line coils
58 TELEGRAPH ENGINEERING
e and e\ strengthens the right-hand pole and weakens the
left-hand pole of relay P', and therefore the armature
closes the local circuit and the sounder S' responds. In
like manner the depression of key K' only will operate
the sounder S. Thus, the manipulation of one key
controls the operation of the distant sounder, but does not
control the home sounder.
When both keys are simultaneously closed, no current
again flows over the line, because the positive poles of
both batteries are in contact with the line. The currents
in the artificial line coils are now in such a direction as to
weaken the left-hand poles and strengthen the right-hand
poles of both relays. Both armatures are then held against
the local circuit contacts and both sounders operate. In
this way signalling can be carried on in opposite directions
over a single wire. If relays are used that have their
armatures magnetized South, reversal of the batteries will
cause the system to operate in the same way.
Continuity-preserving pole-changers may be used with
polar duplex systems if current is supplied by primary
batteries, but their use is not so important as the use of
continuity-preserving transmitters with differential duplex
systems. For, assume key K to be depressed while key K'
is open, and consider the instant when the armatures of
the pole-changer C are midway between their contacts.
The battery B is then completely cut off from the circuit
and the line circuit is completed to ground at G only
through all coils of the relay P and the artificial line. The
line current from battery B' flowing through these coils of
the home relay strengthens the left-hand pole and weakens
the right so that sounder S does not operate. At the other
station more current traverses the coils /, /i than the coils
DUPLEX TELEGRAPHY 59
e, e\ and consequently the left-hand pole of relay Pf is
strengthened and the other is weakened, so that sounder Sf
is not operated until the armatures of the distant pole-
changer touch their front contacts. Conversely, sounder
S' will release its armature at the instant when armatures
x and y leave their front contacts. Again, assume that key
K is held down, as in Fig. 10, which means that the relay
armatures of P and P' are respectively on their left and
right contact studs, and that sounder 5" is actuated. If
now key Kf is also depressed the pole-changer C' operates,
and its armatures will be drawn toward their front stops.
Consider the instant when these armatures are in their
intermediate positions, touching neither contacts. The
battery Bf is then completely isolated, and the only path
for the line current at station B is through all four coils
of relay P' and through the artificial line to ground at G '.
The current supplied by battery B enters the relay P at
junction y and divides between the line and artificial line
coils. The current through the coils of relay P' keeps the
right-hand pole magnetized stronger than the left so that
sounder Sf will remain actuated. At the other station
more current flows through the coils b and b\ than through
the others, and is in such direction as to magnetize the
right-hand pole stronger than the left and consequently
the sounder S will operate as soon as the armatures x' and
y' leave their rear contacts. Conversely, sounder 5 will
remain actuated until these armatures again touch their
rear contacts. Thus false signals can hardly ensue with
the polar duplex if properly balanced.
A polar duplex circuit is balanced in practice by first
adjusting the polarized relays, with all current cut off, so
that the armatures will move with equal force from their
60 TELEGRAPH ENGINEERING
intermediate positions to either stop and remain there.
Then connect the relays in circuit. At one station alter-
nately depress and release the key while varying the re-
sistance of the artificial line until such manipulation of the
key does not alter the behavior of the home relay. The
capacity of the artificial line is adjusted by first moving
back that magnet pole piece which is on the side away
from the local circuit contact, and then, starting with all
the condensers in circuit, gradually diminish the capacity
and alter the resistances in series with the condensers,
while depressing and releasing the key at intervals, until
the relay armature will not kick with every movement of
the key. This adjustment signifies that the current grows
and decays simultaneously in both relay windings. Then
restore the pole piece to its proper position, and the balance
is complete. The other station is adjusted similarly.
A single-armature pole-changer, such as illustrated in
Fig. n, is extensively used with duplex telegraph circuits
Fig. ii.
when operated by generators. The armature moves be-
tween two contacts, one being connected to the positive
terminal of one generator and the other contact to the
negative terminal of another similar generator, the two
DUPLEX TELEGRAPHY
6l
other generator terminals being grounded as shown in
Fig. 12. Another generator supplies current to the local
pole-changer circuit. The same generators may furnish
Fig. 12.
current to other duplex circuits, by connecting these cir-
cuits, each with protective fuses, /, /, /, to the positive and
negative bus-bars.
This figure shows the transmitting arrangement used by
the Postal Telegraph-Cable Company. At the instant of
transferring contact from one stud to the other a spark is
produced and drawn across the air gap, thereby bridging
the two 2oo-volt generators through the 3oo-ohm protec-
tive resistances. These resistances (usually in lamp form)
protect the machines in cases of accidental short-circuit.
This spark is effectively quenched by the provision of a
discharge path to ground through a ^-microfarad con-
denser, for each machine, as shown. Three-hundred ohm
or 6oo-ohm protective resistances are usually connected in
series with the generators.
In order to find the current strength in the various por-
tions of a polar duplex circuit let Rp, Rb, Rl and r be re-
spectively the resistances of the polarized relays, battery or
protective resistance in series with generator, perfectly in-
62 TELEGRAPH ENGINEERING
sulated line, and artificial line, let 7, 7i and 72 be respectively
the current supplied by each battery or generator, current
in artificial line and current in line wire, and let E be the
voltage of each battery or generator. Then, when both
keys are open or both closed
•p
I = I\ = = - and 72 = o; (4)
2
when one key is closed
E-RJ 2 (E - RJ)
,.
2, (5)
2
E (2 Rp + Rl + 2 r)
whence 7 = - — —
4-
In order to have 72 twice as great as I\, the artificial lines
•p
should have a resistance of r = — 2 + -K/.
2
Where only generators of higher voltage are in service,
as necessary for the operation of long quadruplex telegraph
circuits (see next chapter), the potential may be reduced
to values sufficient for duplex operation by the intro-
duction of a leakage path to ground. The connections of
one station of such a leak duplex circuit, as used by the
Postal Telegraph-Cable Company, are shown in Fig. 13.
Fourteen-hundred-ohm resistances are in series with the
generators, and 22oo-ohm shunt or leak paths are provided
to ground. The difference of potential between the point
y and ground does not exceed - - X 380 or 233
1400 + 2200
volts and this occurs when the armature is midway between
DUPLEX TELEGRAPHY
the pole-changer contacts. Assuming that each winding of
the polarized relay has a resistance of 150 ohms and that
the artificial line has a resistance of 1700 ohms, this poten-
tial difference would fall to
380 — 1400
380
or 159 volts,
1400
(1700 + 15°) 22QQ
22OO + I7OO + 150
when the armature makes contact so that no current flows
over the line. In this way the voltages available at the
pole-changer contacts are rendered materially less than the
terminal voltages of the generators.
6. Improved Polar Duplex. — The arrangement of the
improved polar duplex circuit due to Davis and Eaves and
now employed by the Postal Telegraph Company is shown
in Fig. 14. The principle of operation is identical with
that already described in connection with Fig. 10, and it
will be observed that the transmitting arrangement used
is that of Fig. 12. The additional features of this duplex
circuit are the resistances g, h, j, k, I and m and the con-
densers c, cf, Ci and c^ the functions of which will be ex-
plained presently.
It was pointed out in the last section in describing the
polar duplex circuit, that with the home key open, (i) the
TELEGRAPH ENGINEERING
home sounder is not operated until the distant pole-changer
armature touches its front contact and (2) that it will
cease to operate at the instant this armature leaves this
front contact. Also, that with the home key closed,
(3) the home sounder will operate as soon as the distant
pole-changer armature leaves its rear contact and (4) will
remain actuated until this armature again touches its rear
contact. Thus, conditions 2 and 3 permit of faster trans-
mission of signals than the others. The introduction of
the non-inductive resistances g, h, j and k, each of 500-
ohms resistance and the 12 -microfarad condensers c and cf
Fig. 14.
is for the purpose of quickening transmission for the slow
conditions (i) and (4).
When both keys are open the negative generator termi-
nals touch armatures y and yf of the pole-changers and no
current traverses the line, line coils of both relays, or re-
sistances g and j. Currents, however, flow from the gen-
erators tov ground, through the artificial lines, lower relay
windings and resistances h and k back to their respective
generators. As a consequence the condensers c and c' will
be charged respectively to the potential differences exist-
ing across the resistances h and &, the plates w and z being
charged positively. If, now, key K is depressed, the
armature y of pole-changer C travels from the rear to the
front contact. In its intermediate position, the armature
DUPLEX TELEGRAPHY 65
isolates the generators D. A current 'now flows from the
generator Df to ground, through the left-hand artificial line,
relay P, resistances h and g, line, upper coils of relay P' and
resistance j back to the generator; and this current is
about one-half that which flows from the same generator
through the right-hand artificial line, lower coils of relay
Pr and resistance k back to the generator. The charge on
condenser c remains practically unchanged because its
potential difference, that across coils g and h, is due to a
current of approximately half the initial strength though
double the initial resistance. This condenser will produce
no appreciable discharge.
At the other station, however, the potential difference of
condenser c' is now that across coil k minus that across
coil 7, and is therefore approximately half that possessed
before and in the same sense. This condenser will then
discharge partially and a current pulse flows from q through
the lower coils of relay P', both artificial lines, relay P,
resistances g and h, line, upper coils of relay Pf to the other
condenser terminal at p. This current does not affect the
relay P, but it does tend to operate the relay P' momen-
tarily. This discharge current through all coils of P' is in
the same direction as that which will flow through its
upper coils when the pole-changer armature y reaches the
front contact. Thus the condenser discharge begins the
operation of the home relay at the instant the distant
pole-changer armature leaves the rear contact, and this
operation is completed by the generators as this armature
reaches its front contact. The improvement for the fourth
condition can be traced similarly.
The function of the four 6oo-ohm non-inductive resist-
ances /, /', m and m' ', with the four i-microfarad condensers
66
TELEGRAPH ENGINEERING
Ci> Ci, £2 and £2', shunted around the relays is to provide an
auxiliary path to ground, for inductive 'disturbances from
neighboring telegraph, telephone or high-tension transmis-
sion lines, which does not include the relay windings, thereby
eliminating such interference with the operation of the
duplex circuit. The shunt circuits offer a further advantage
in that the first portion of the current pulse for each
signal over this home shunt path reaches the other end of
the line a little in advance of the current which passes
through the home relay windings. This action assists in
attaining a high signalling speed.
7. Short-line Duplex. — The circuit of the Morris
duplex, which system is successfully employed by the
Western Union Telegraph Company on many short lines,
is shown in Fig. 15. It utilizes a neutral relay at one sta-
Fig. 15.
tion and a polarized relay at the other, and employs main-
line generators at one station only. The artificial line has
a resistance equal to the resistance from the point x to
ground at G '. The resistance of the compensating rheo-
stat r\ is adjusted so that three times as much current flows
through the line when the key K' is depressed as when Kf
is open. These conditions are:
r = SI + Rr + rlt (7)
DUPLEX TELEGRAPHY 67
where Rp and .Rr are the resistances of the polarized and
differential neutral relays respectively, R^ is the resistance
in series with the generator, RL is the resistance of the
assumedly perfectly-insulated line and r is the resistance
of the artificial line. Thus, if Rl = 1000 ohms, Rb = 300
ohms, Rr = 200 ohms and Rp = 400 ohms, then
r = ri + 1400,
600 (200 -f 2 r)
ri= 800+ ,r
whence r = 4966 ohms and r\ = 3566 ohms.
The function of the repeating sounder RS is to eliminate
false signals when key K is depressed while the other key
is held down. The reversal in magnetization of relay R
takes place quickly and before its armature has an oppor-
tunity to fall back to its rear contact and open the circuit
of sounder S. In view of the foregoing descriptions, the
operation of this duplex system may be readily understood
without further comment, by tracing the conditions when
no keys, either of the two keys, and both keys are depressed.
8. The Bridge Duplex. — The form of the bridge duplex
circuit resembles that of the Wheats tone bridge, in having
four arms with the home receiving instrument connected
across opposite arm junctions, as shown in Fig. 16. For
the station A the bridge arms are: winding a of the re-
tardation coil /, line xy plus the paths from y to ground at
the right-hand station, artificial line A LI, and the winding b
of the same retardation coil. The arrangement for station
B is identically the same. The simple polarized relays are
68
TELEGRAPH ENGINEERING
connected across the junctions x, w and y, z. The artificial
line at each station is adjusted to equal the resistance of
the line and the apparatus at the distant station, and the
resistances of the two coils of each retardation coil are equal.
When both keys are idle, the armatures of the pole-
changers C and C' rest against their rear stops which are
joined to the positive generator terminals, and therefore
no current traverses the line wire. At station A a current
divides at the point m, one part traversing winding a and
relay P, and the other part traversing winding bj both
Fig. 16.
currents then combining at the point w to flow through the
artificial line A LI to ground and back to the other generator
terminal; while at station B, a current divides at the
point n, one part traversing winding c and relay P' ', and
the other part traversing winding d, both currents then
combining at the point z to flow through the artificial line
ALz to ground and back to the other generator terminal.
It will be observed that the direction of the currents through
the two relays is such that the relay armatures touch their
idle contacts and therefore do not close tjie local sounder
circuits, as indicated in the figure.
When the key K is depressed, the armature of pole-
changer C touches the negative generator terminal, and
consequently more current flows over the line than through
either artificial line, and this current flows from y to x.
DUPLEX TELEGRAPHY 69
The line current entering at the point y is made up of the
current coming through the coil c and that coming from z
through the relay Pf . The direction of this current is
such that the right-hand pole of the relay will be more
strongly magnetized than the left and consequently its
armature closes the sounder circuit. At station A the
arriving current divides at the point x, and that part
which traverses the relay P is in such direction as to mag-
netize the left-hand pole more strongly than the right, so
that this relay will not close the sounder circuit. Thus,
the depression of one key controls the operation of the
distant relay and sounder.
If both keys are closed, both pole-changer armatures
will be in contact with the negative generator terminals,
and again no current will flow over the line. Currents will
now flow through relay P' from z to y, and through relay
P from w to x, and their direction is such as to magnetize
the right-hand poles stronger than the others and con-
sequently the relay armatures will close both sounder cir-
cuits. Although each relay is caused to operate by its
home battery, yet its action is controlled entirely by the
distant key.
It will be noted that each receiving instrument is always
shunted, so that only a part of the generator current can
flow through the relay. The magnitudes of the currents
in the various paths can best be compared by means of a
numerical illustration.
Using 8oo-ohm polarized relays, 3oo-ohm resistances in
series with each generator, and retardation coils with 500
ohms resistance per winding, at the ends of a i poo-ohm
perfectly-insulated line, requires that the artificial lines be
adjusted to have a resistance of 2500 ohms. The joint re-
70 TELEGRAPH ENGINEERING
sistance of the paths from the points x or y to ground at
the corresponding station is then 600 ohms (calculated
according to equation (9) following); thus the resistances
of the artificial lines are correct, viz. 1900 + 600 = 2500
ohms. The steady currents, in milliamperes, flowing
through these paths for various sending conditions with
1 50- volt generators, are given in the following table, and
their directions are indicated by + and — in connection
a = 600 Rl = 1900 C = 500
ffcov.
Fig. 17-
with the scheme of Fig. 17, the + sign signifying a cur-
rent flowing upwards or toward the right, while — denotes
a current flowing downwards or toward the left. The stars
represent the operation of relays.
CURRENTS IN BRIDGE DUPLEX CIRCUIT
3
ft,
fc
a?
Condition
'a)
s
g
I
^
O
c
^
1
a
§
§
1
ft
$
Neither key depressed
+48
+13
+35
-13
-48
0
-48
-13
-13
-35
+48
Key K depressed
— 120
—71
— 49
—13
_j_ ^
-81
-tf
+n*
—71
— 49
+120
Key K' depressed
+120
+71
+ 10
+13*
—36
+81
—13
+7T
+ 10
— I2O
Both keys depressed . ...
-48
-13
-35
+13*
+48
0
+48
+13*
+13
+35
-48
fBy equation (80) of Chap. X.
DUPLEX TELEGRAPHY 71
The resistance of the terminal apparatus when a = b is
calculated from the equation
R _ aP (2 Rb + g) + RbAL (2 a + P) + all (a + P) , ,
which is obtained by an application of Kirchhoff's laws.
Since, for a perfectly insulated line
AL = Ro + Rl,
by combining with equation (9) there results that the
proper resistance of the artificial line should be
where p _*(« + 2*»)
The bridge-duplex arrangement used by the Western
Union Telegraph Company embodies various improve-
ments on the system described, and will now be considered.
The retardation coil comprises two 5oo-ohm coils wound
upon a circular core of rectangular cross-section, made up
of soft iron wires. The core has an inside diameter of 3!
inches, an outside diameter of 5! inches, and is if inches
wide; it is composed of about 6000 turns of No. 26 B. & S.
annealed iron wire. Each winding has 7900 turns of No. 29
B. & S. double-cotton-covered copper wire and has a re-
sistance of about 400 ohms. Its resistance is brought up
to 500 ohms by adding approximately no turns of No. 28
german silver wire wound back on themselves, to render
this compensating winding non-inductive.
Each 5oo-ohm coil possesses considerable inductance,
and consequently a current coming over the line wire meets
at first with great opposition in traversing the retardation
72 TELEGRAPH ENGINEERING
coil, because of the counter electromotive force of self-in-
duction which is developed in it. This electromotive force
is in such direction as to assist in the rapid growth of cur-
rent in the polar relay to a value momentarily greater
than the steady value. This initial pulse of current
through the relay causes its armature to be moved from
stop to stop with great rapidity. The retardation coils do
not hinder outgoing currents very much because differing
currents pass through the two windings of the coils differ-
entially, and the magnetism developed in the core by one
winding is neutralized to some extent by that developed
by the other, and hence the coils for this condition are less
inductive than before.
In order that the speed of pole-changer armatures shall
be. high, two series-connected electromagnets are provided
on each instrument, one on either side of the armature.
The iron cores of the front magnet are laminated while
those of the rear magnet are solid and surrounded by
copper sleeves, thereby causing the magnetism to be es-
tablished much more rapidly in the front than in the rear
magnets. Light retractile springs hold the armatures
against their back contacts when the keys are elevated.
When the key is depressed, current flows through both
pole-changer electromagnets, but the armature is drawn
toward the front contact because sufficient attraction is
first exerted by the front magnet. As the armature is
now further from the rear magnet, subsequent full magneti-
zation of this magnet cannot cause its return. However,
when the key is released, the rear magnet retains its mag-
netism much longer than the other, and consequently the
armature is brought over to its rear contact far more
rapidly than if the spring alone were acting. For 26-volt
DUPLEX TELEGRAPHY 73
local-circuit operation each electromagnet has a resistance
of 4 ohms, while for 52-volt operation each has 13 ohms
resistance.
A milliammeter, reading to 50 milliamperes in either
direction, is placed in series with the polarized relays to
measure the current flowing and to facilitate line balancing.
When the artificial line resistance and capacity are so ad-
justed that the milliammeter needle is practically unaffected
by the manipulation of the home key, a good working
balance is established.
For increasing the resistance of short lines for operation
at the voltages usually employed in duplex signalling, a
line-resistance box is used at each station. It contains
two separate and identical sets of resistances (five 25o-ohm
resistances in each set) simultaneously adjustable by means
of a double lever. These resistances are interposed in the
real and artificial lines at the points w, x, y and z, Fig. 16.
The variation of each line resistance, requires an adjust-
ment of the distant artificial line. The insertion of this re-
sistance, which is almost perfectly insulated from ground,
in the line circuit during wet weather, raises the apparent
insulation of the whole line, that is the insulation resist-
ance per ohm of line is greater than before.
The method of quenching the sparks produced at the
pole-changer contacts is similar to that shown in Fig. 12,
but the ground connection at the point x is replaced by a
2o-ohm resistance lamp connected in series with the con-
densers; or a single \ mf. condenser may be used instead
of the two J mf. series-connected condensers. In practice
non -ad jus table i mf. condensers are also connected to the
points m and n of Fig. 16, their other terminals being
grounded.
74
TELEGRAPH ENGINEERING
9. Advantage of Double-current Duplex Systems. — It
has been stated that the differential or single-current
duplex is infrequently used because of the superiority in
practice of the polar- and bridge-duplex systems, these
latter being called double-current duplexes. Considerable
difficulty is experienced in maintaining operation over
single-current duplex lines when the weather is unfavor-
able, because the line insulation is poor. That this is the
case can be seen from the following illustration.
In § 2 a 474-mile, 2ooo-ohm differential duplex line with
two 2oo-ohm relays was considered. A 2oo-volt gravity
battery having an internal resistance of 250 ohms and a
23 2 7 -ohm artificial line was employed at each end. The
2827
Fig. 18.
table in that section shows the current strengths in the
relay coils when the line is perfectly insulated. If the in-
sulation resistance should fall to i megohm per mile, and
considering the distributed leakage to be concentrated at
the middle of the line, the conditions are representable by
Fig. 18.
It can readily be verified that the currents then travers-
ing the relay coils, under otherwise identical conditions,
will be as shown in the following table. The figures fol-
lowing the braces give the equivalent currents through one
relay coil.
DUPLEX TELEGRAPHY
75
CURRENTS IN NEUTRAL RELAY COILS, EXPRESSED IN
MILLIAMPERES
Relay
R
Coil
Neither
key de-
pressed
Key K only
depressed
Both keys
depressed
Key K' only
depressed
a
b
:l°
SH
III-
Jfsr
Rf
a'
b'
:}°
5sl"
Z\*°
SH
To assure satisfactory operation under these conditions the
relays must be adjusted so that they will not operate on
18 milliamperes through one coil, but will operate on 40
milliamperes. For longer lines or for poorer insulation this
margin of 22 milliamperes will be reduced and operation
rendered unsatisfactory.
Consider a polar duplex line to have the same constants.
When this line is perfectly insulated, the currents travers-
ing the relay coils are as tabulated below, the values being
computed in accordance with equations (4), (5) and (6).
CURRENTS IN POLARIZED RELAY COILS, EXPRESSED IN
MILLIAMPERES
Relay
Coil
Both keys
raised or de-
pressed
One key only
depressed
R
a
b
7Sh
ih«
R'
a'
b'
nfr
•£}«
When the line is poorly insulated, and the multitude of
leakage paths be considered grouped at the middle point q
of the line, and one key be depressed, this point q, being
midway between + 200 and — 200 volts, will be at zero
potential with respect to ground, and consequently leak-
76
TELEGRAPH ENGINEERING
age will cause no alteration in current distribution, and the
current values in the last column still apply. The follow-
ing table shows the currents then traversing the relay
windings for all key positions. A margin of at least 40
CURRENTS IN POLARIZED RELAY COILS, EXPRESSED IN
MILLIAMPERES
Relay
Coil
Both keys
raised or de-
pressed
One key only
depressed
R
a
b
Sir
wf«
R'
a'
b'
f>
"El"
milliamperes is effective for operating the relays. Of course,
if these leakage paths were considered uniformly distrib-
uted along the line, the tabulated values would be altered
somewhat, but it is clear that the double-current duplex
systems are not as sensitive to weather variations as is the
single-current system and consequently excel it in operation.
10. Duplex Repeaters. — Duplex repeaters are not as
complicated in theory as simplex repeaters, for it is only
necessary to connect the magnet of the pole-changer that
controls one circuit with the contact points of the receiving
relay of another line. A still simpler arrangement, dis-
pensing with pole-changers, and called a direct-point re-
peater, is widely used.
Polar Direct-point Repeater. — The schematic diagram
of the polar direct-point repeater is given in Fig. 19. The
repeating station is equipped with four generators, D\ and
A, two differentially-wound polarized relays, P\ and P2,
and two artificial lines. The elements of the originating
and receiving stations A and B are also shown. When
both keys K and K' are elevated they rest on the rear con-
DUPLEX TELEGRAPHY
77
tacts which are connected to the negative generator termi-
nals. For this condition all four relay armatures will rest
against their left contacts, as indicated in the figure. The
armatures of repeater relays PI and P2 will be against the
negative contacts of generators D\ and Z>2, no current will
flow over either line wire, and sounders S and S' will not
be actuated.
The depression of key K causes a greater current to flow
over the western line and line coils of relays P and PI
than through their artificial line coils, and its direction
will be such as to move only the armature of relay PI to
the right, thereby touching the positive generator termi-
Fig. 19.
nal .of DI. A greater current will then flow over the
eastern line and line coils of relays P2 and P' than through
their artificial line coils, and its direction is such as to
move only the armature of relay P' ', which then closes the
local sounder circuit. Thus key K controls the operation
of repeater relay PI, of relay P' and of sounder 5" at the
remote station. In the same way key K' controls the
operation of repeater relay P2, relay P and sounder S.
When both keys are depressed it will be seen that all
relay armatures press against their right-hand contacts, no
current flows over either line, and both sounders are oper-
ated. Thus messages being transmitted in opposite direc-
78 TELEGRAPH ENGINEERING
tions over a single wire are simultaneously repeated without
interference.
Fig. 20 shows the connections of the direct-point duplex
repeater used by the Postal Telegraph-Cable Company.
The principle of operation is identical with that just de-
scribed, but there are several additional features. For the
operation of reading sounders Sz and S^ at the repeating
station, the leak relays LI and LZ in series with 2o,ooo-ohm
Fig. 20.
resistances r, r (shunted by i-mf. condensers) are bridged
from ground to the armatures of the repeater relays PI
and PZ- The transmission of signals from one station to
the other through the repeater for the various positions of
the keys can readily be traced, the pole-changers C and Cr
remaining in the positions shown.
This repeater arrangement permits of separation, by
the upward movement of the switches a and a', into two
polar-duplex sets. Thus duplex signalling may be effected
between the left-hand station and the repeater station by
manipulating the key K\ and the distant key, and also
distinct duplex signalling may be carried on between the
DUPLEX TELEGRAPHY
79
repeater station and the right-hand station by manipulat-
ing the key K2 and the distant key. These sets differ from
those described in connection with Figs. 10 and 12 only in
the introduction of the leak relays. The unmarked coils
are 3Ooohm protective resistances.
Bridge Direct- point Repeater. — The arrangement of the
repeater used with the bridge duplex by the Western
Union Telegraph Company is shown in Fig. 21. The in-
strument positions represented are for the normal con-
dition, that is, no signals being sent in either direction,
the positive generator terminals being connected to the
Fig. 21.
line at both stations. Reference to the explanation of the
bridge duplex and Fig. 16 will indicate that the armatures
of the two repeater relays PI and P% and Consequently
those of the leak relays LI and L% rest against their left-
hand contacts. Further, no current traverses the two
line wires, and the two reading sounders 63 and S4 at the
repeating station are not actuated.
When the key at the western station is depressed,
thereby bringing the line in contact with the negative
terminal of the home generator, current will flow through
the repeater relay PI from the point x to y, and conse-
quently its armature will be drawn over to the right.
80 TELEGRAPH ENGINEERING
This will cause the operation of sounder 53 through the
leak relay LI, and the negative generator terminal will be
in contact with the junction n of the right-hand retardation
coil. Current will then flow over the eastern line and
through the relay P% from the point y' to x' so that the
armatures of relays P% and Z^ will remain as shown. The
eastern line current is in such direction as to operate the
polarized relay and sounder at the eastern station (see § 8).
The depression of both keys will cause all armatures to
rest against their right-hand contacts, thereby actuating
the sounders Sz and ,£4 and also the sounders at the termi-
nal stations.
When the double-throw triple-pole switches a and b are
moved to the left, the repeater is separated into two dis-
tinct bridge-duplex sets that differ from that already de-
scribed only in the addition of the leak relays. It can be
seen, then, that the western and repeating stations and
that the repeating and eastern stations can engage in
separate duplex signalling, both the repeater and leak re-
lays being in use in this divided service. The resistances
r are adjustable to have the following values: 8,000, 12,000,
16,000 and 20,000 ohms.
ii. Half-set Repeaters. — Where it is found desirable to
join a duplex line with a simplex line for through simplex
operation in either direction, a half-set repeater is used.
One-half of the apparatus necessary for a simplex repeater
of any type will serve as a half-set repeater.
The connections oi a Weiny-Phillips half-set repeater
joined between a simplex line and a polar-duplex circuit
are shown in Fig. 22. The repeater apparatus is shown
between the two broken lines, while the simplex and
DUPLEX TELEGRAPHY
8l
duplex receiving apparatus are shown respectively on the
left and right sides as A and B. This apparatus is usually
interconnected at a switchboard by means of flexible
double-conductor cords equipped with plugs or wedges
which fit into appropriate jacks, these cords being repre-
sented, for the sake of simplicity, by dotted lines.
The operation of the repeater transmitter T is con-
trolled by the armature of the polarized relay P, and the
operation of the pole-changer C is controlled by the arma-
ture of the repeater relay Ri. The function of the differ-
(S)
Fig. 22.
ential holding coil H of the Weiny-Phillips relay has been
explained in § 10 of Chap. I.
In the normal condition, when the distant keys on both
lines are depressed (or circuit-closers closed) current flows
over the simplex line, distant relay and relays R and RI,
and the duplex line will be in contact with the negative
generator terminal. The armature of relay P will rest
against the right-hand contact regardless of the position of
the armature of the pole-changer C (because the distant
pole-changer makes contact with the negative generator
terminal), and consequently the armatures of sounder $3
and of transmitter T will be attracted. Equal and oppos-
82 TELEGRAPH ENGINEERING
ing currents traverse the windings of the holding coil H
so that its core is not magnetized; nevertheless the arma-
ture of the repeater relay will be attracted owing to the
current in the main coil RI. The attraction of this arma-
ture closes the magnet circuit of pole-changer C and its
armature places the negative generator terminal in con-
tact with the junction m of the relay windings. This
action does not affect relay P, but the distant polarized
relay on the duplex line responds and operates its local
sounder.
When the key at the distant office on the simplex line
is raised, no current flows through this line and relays R and
RI, and, therefore, their armatures will be released. The
armature of the repeater relay opens the circuit of the
pole-changer magnet which causes the positive battery
terminal to be placed on the junction m. The relay P
will not be affected, but the distant relay on the duplex
line will open the home sounder circuit. In this way
signals formed by the key on the simplex line are repeated
to a distant station on a duplex line.
If, instead, the distant key on the duplex line be raised,
the armature of relay P will be drawn over to the left-
hand side, causing the magnet of transmitter T to be de-
energized. This action opens the simplex line at x, and
consequently the distant sounder on the simplex line re-
leases its armature. Although no current flows through
the relay RI the magnetism developed in the core of the
holding coil H by current in one of its coils is sufficient to
hold over the armature, which action keeps the distant
sounder on the duplex line energized. When the key at
the remote end of the duplex line is again depressed, the
armature of relay P is drawn to the sounder contact and
DUPLEX TELEGRAPHY 83
the armature of the transmitter is again attracted, thereby
closing the simplex line at the repeating station. Thus
the composite circuit operates as a closed-circuit simplex
line.
Some important duplex circuits are operated simplex
through half-set repeaters by current reversals instead of
ordinary Morse simplex operation, because of higher speed
possibilities and lesser dependence upon weather con-
ditions. The Associated Press leased wire is operated in
this way, the signalling being carried out by mecograph
transmitters.
PROBLEMS.
1. A perfectly-insulated differential duplex line has a resistance of
1500 ohms and is equipped with a i4o-ohm differential relay at
each end. If the battery resistance is 200 ohms, calculate the proper
resistance of the artificial lines.
2. When one key of the circuit of Prob. i is closed, thereby in-
troducing a 1 60- volt battery, how much current flows through the
line and through each artificial line ?
3. A 2000-ohm polar-duplex line has a 3oo-ohm polarized relay,
and a 2644-ohm artificial line at each end. Using 6oo-ohm re-
sistances in series with the 2oo-volt generators, determine the current
strength in each relay coil for the various positions of the signalling
keys.
4. If the line of the preceding problem be operated on 380 volts
as a leak duplex with 22oo-ohm leak paths, compute the current
strengths in the relay coils when one key is depressed and when both
keys are either raised or depressed.
5. A Morris duplex line, having 800 ohms resistance, employs a
3oo-ohm polarized relay at one end and a i4o-ohm differential neutral
relay at the other end. Using 6oo-ohm protective resistances in
series with the generators, determine the proper resistance values of
the artificial line and compensating rheostat.
6. Derive equation (9) for the terminal resistance of a bridge-
duplex circuit.
84 TELEGRAPH ENGINEERING
7. What should be the resistance of the artificial lines used with
a perfectly-insulated bridge-duplex circuit having a looo-ohm line,
when using 6oo-ohm polarized relays, 2oo-ohm protective resistances
and 5oo-ohm (each winding) retardation coils?
8. If in unfavorable weather conditions the line of Probs. i and 2
has a total leakage resistance to ground of 1500 ohms, considered
concentrated at the mid-point of the line, determine the relay ad-
justment that will cause satisfactory operation.
CHAPTER III
QUADRUPLEX TELEGRAPHY
i. Quadruplex Systems. — A quadruplex telegraph sys-
tem provides for the simultaneous transmission of two
groups of signals in one direction and also two groups of
signals in the opposite direction without interference over
a single telegraph line. When in full use, eight operators
are required for each quadruplex circuit, two receiving
and two sending operators being located at each terminal
station. Quadruplex signalling was devised by Thomas
A. Edison, and was first placed in operation in 1874 by the
Western Union Telegraph Company. It is now employed
on many lines over distances up to 500 miles.
Quadruplex systems are generally based on a combi-
nation at each station of the single-current and double-
current duplex systems, which have been described in the
foregoing chapter. The single-current, or Stearns duplex,
permits of the simultaneous transmission of one message
in each direction through changes in current intensity, and
the double-current system, either the polar or bridge
duplex, permits of the simultaneous transmission of one
message in each direction through changes in current
direction. When these duplex systems are combined to
form a quadruplex circuit, the latter is called the polar
side, or first side, of the system, and the former is called the
neutral side, or second side, of the system.
The manner in which these systems are combined is
85
86 TELEGRAPH ENGINEERING
illustrated in Fig. i, which shows one station A equipped
with apparatus only for sending and the other station B
equipped with apparatus only for receiving messages.
This circuit permits of the simultaneous transmission of
two independent messages over one wire in the same
direction, which transmission is called diplex signalling.
Key K is a form of continuity-preserving pole-changer,
which, when depressed, causes its lever contact a to raise
the upper spring u away from the fixed contact b, and per-
mits the lower spring / to follow until it strikes against this
fixed contact. The key Kf is a transmitter which changes
the number of cells of the battery B which is included in
Fig. i.
the circuit. Both keys are normally held in their upper
positions by retractile springs. Relay R is a neutral relay
which has its spring so adjusted that the armature will not
be attracted when the small current, supplied by the left-
hand part, or short end, of the battery traverses the relay
winding, but will be attracted when supplied with current
from the entire, or long end, of the battery. Instantaneous
reversal of current direction has no effect upon this relay
(see § 3). The polarized relay P responds only to cur-
rent reversals and is not influenced by changes in current
intensity, so long as this intensity exceeds 3 to 5 milli-
amperes.
When neither key is depressed the short end of the
QUADRUPLEX TELEGRAPHY 87
battery is in circuit and key contacts a and b are re-
spectively connected to the negative and positive battery
terminals. It will be seen that the current then flowing is
not strong enough to operate the neutral relay R and is
in the wrong direction to operate the polarized relay P.
When key K is depressed (as shown in the figure) the cur-
rent flowing is not altered in intensity, but is reversed in
direction, and consequently relay P responds and causes
the actuation of its sounder 6*2 through the local battery
Bf. When key K' is also depressed the direction of current
flow remains unaltered but its intensity is now sufficient to
operate neutral relay R, which in turn operates sounder Si.
Thus, pole-changing key K controls the polarized relay,
and the transmitting key K' independently controls the
neutral relay, thereby enabling the simultaneous trans-
mission of two messages from one station to another over
a single wire.
2. Operation of Quadruplex Systems. — By duplicating
the apparatus necessary for the diplex circuit just de-
scribed and employing differentially-wound relays and an
artificial line at each end of the line wire, as in the duplex
systems, it is possible to send two messages in each direc-
tion at the same time, thereby affording quadruplex tele-
graphic signalling. Such a quadruplex circuit extending
between two stations A and B, and operated by batteries,
is shown in Fig. 2. It will be observed that the pole-
changers C and C' are electromagnetically controlled by the
keys K and K'j and that the transmitters T and T are
similarly controlled by the keys K\ and Kz. The short
ends of the main batteries B and Bf are connected in circuit
when the keys KI and K2 are open, and the entire batteries
88
TELEGRAPH ENGINEERING
are in circuit when these keys are depressed. The figure
shows the long-end battery to have three times as many cells
as the short-end battery. The positive and negative ter-
minals of these batteries are connected to the line junctions
x, y, when the keys K and K' are raised and depressed
respectively.
The figure represents the condition when the circuit is idle,
all four keys being in the raised position. In this condition
the positive terminals of the short ends of both main-line
batteries are joined to the junctions x and y, consequently no
current flows through the line coils of all relays nor through
the line wire. A current will flow, however, from each
Fig. 2.
main battery through the artificial line coils of both re-
lays, through the artificial line, and back to the other
battery terminal. These currents are too weak to oper-
ate the neutral relays R and R', and they are in the wrong
direction to operate the polarized relays P and P'. Con-
sequently the armatures of all sounders, S, S', Si and 62,
will remain drawn up by their retractile springs.
When key K is depressed the armatures of pole-changer
C will be attracted and the negative terminal of the home
QUADRUPLEX TELEGRAPHY 89
battery will be connected to the junction x, and the posi-
tive terminal will be grounded. The main-line batteries
are now cumulatively connected, and more current traverses
the line and line coils of all relays than flows through the
artificial lines and artificial line coils of these relays. For
ease in presentation, let the current traversing the artificial
lines be considered of unit intensity, and let the adjust-
ment of these lines be such that the current in the line
wire when either key K or K' only is depressed be 2
units. Currents, then, of i unit intensity flow through
the artificial line coils of all relays, and opposing currents
of 2 units intensity flow through their line coils. The
surplus of i unit current through all the line coils of the
relays is insufficient to actuate the neutral relays R and
R'\ it is in the proper direction to operate polarized relay
P', but is in the wrong direction to operate polarized re-
lay P. In the same way, the depression of key Kf only
causes the operation of relay P. Thus the depression of
a pole-changing key causes the operation of the distant
polarized relay and the actuation of the sounder con-
trolled by it.
The depression of both pole-changing keys places the nega-
tive battery terminals to the junctions x and y, and, since
the two identical main-line batteries are opposed to each
other, no current flows over the line wire. Currents of
unit intensity flow through the artificial line coils of all
relays, and, as before, are too weak to operate the neutral
relays R and R' . The direction of these currents is such
as to operate both polarized relays.
The closing of key KI, all other keys being open, intro-
duces the long end of battery B into the circuit. Its
voltage being assumed three times that of the short-end
90 TELEGRAPH ENGINEERING
battery B', the opposing line currents will not neutralize,
but a current of 2 units will flow from station A to sta-
tion B and through the line coils of all relays. At station
A a current of 3 units intensity flows through the arti-
ficial line coils of the relays and artificial line, while at
the other station a current of i unit intensity flows through
the corresponding circuit. The currents through the two
coils of relay R are in opposite directions around the core
and, consequently, partially neutralize each other, the
surplus of i unit current being insufficient to operate this
instrument. This surplus current in the artificial line coils
of the relay P is in such direction as to hold its armature
away from the sounder contact. The currents through
the two coils of relay Rf are in the same direction around
the core and are equivalent to a current of 3 units travers-
ing a single coil. This current is strong enough to operate
relay R'} for this instrument is so adjusted. The currents
flowing through the coils of polarized relay P' are both
in the wrong direction to operate this instrument. Thus,
the depression of key K\ causes the operation of neutral
relay R'\ similarly the closing of key KZ causes the opera-
tion of neutral relay R.
The depression of both keys KI and K2 connects the long
ends of both batteries to the circuit. No current flows
over the line wire, but currents of 3 units intensity traverse
the artificial line coils of all relays. These currents are
sufficiently strong to operate the neutral relays R and R' ',
but are in the wrong direction to operate the polarized re-
lays P and P' . Sounders S and 5", therefore, respond to
the depression of both transmitting keys KI and Kz.
When keys K and KI are closed, the negative terminal of
the long-end battery B is joined to the point x, while the
QUADRUPLEX TELEGRAPHY 91
positive terminal of the short-end battery Bf is joined to
the point y. A current of 4 units intensity will flow over
the line from the right toward the left, a current of
3 units will flow through the artificial line circuit at the
left and a current of i unit will flow through the artificial
line circuit at the right. It will be seen that the relays
P' and Rf respond, thereby operating sounders S2 and S'.
In the same manner, the currents in the various portions
of the circuit and the relays affected, for the remainder of the
16 possible combinations of key positions, may be traced.
Having given the constants of any circuit, the currents
r3<0oo
Fig. 3.
traversing the various relay coils can be determined in the
usual manner.
The main-circuit connections of one station of a quad-
ruplex circuit, using the Field key system with a single
generator instead of the battery, are shown in Fig. 3. The
function of the pole-changer C is the reversal of the gen-
erator Dj while that of the transmitter T is the variation
of available potential difference by means of the resist-
ances r-i and r3. When the armature of the transmitter is
92 TELEGRAPH ENGINEERING
attracted, the added resistance r2 is short-circuited and the
resistance from the point x to ground at G is 2 X 300 or
600 ohms, and when this armature is released the resist-
. ooo (1200 + 600) , ,
ance is — — ^ or 600 ohms, as before. The
900 + 1 200 + 600
terminal resistance therefore remains unaltered regardless
of the position of the transmitter armature.
To consider the variation in current produced by the
movements of the transmitter armatures, let, as in the
preceding chapter:
Rp = resistance of polarized relays,
Rr = resistance of neutral relays,
Rb = resistance of protective coils in series with
generators,
r = resistance of artificial lines,
and E = voltage of generator.
Then, if the apparatus at the distant station is also as
shown in Fig. 3 (that is, all keys open), the line current is
zero and the current supplied by each generator is
7 = _ E _ , .
'
„
of which, the part that traverses the artificial line circuit is
E-I(Rb + ra) .
the remainder traversing the leak resistance r3. When the
armatures of both transmitters are attracted, the current
flowing through the artificial line circuit is
QUADRUPLEX TELEGRAPHY 93
Thus, if the resistances of the various paths are as indi-
cated in the figure, the currents traversing the artificial
line circuit when the transmitter armatures are both re-
leased and when both attracted are respectively 35.3 and
106 milliamperes. The attraction of the armatures thus
triples the current flowing and this larger current is sufficient
to operate the neutral relays. The currents for other key
positions might be similarly determined.
At times it is feasible to raise the current ratio from 3 to
i up to 4 to i, which may be done by changing the added
resistance to 1800 ohms and altering the leak resistance to
800 ohms, if the resistance in series with the generator
remains the same. For any other current ratio r, or
other series generator resistance Rb, the added and leak
resistances should be respectively
rz = Rb(r- i) (4)
and
. ,-. (5)
^
In practice two generators at each station are more fre-
quently employed in quadruplex service than one gener-
ator. The connections of one station, according to the
Field key system with two generators, are shown in Fig. 4.
Its similarity to the preceding figure will be noticed, and
consequently the foregoing equations apply to this ar-
rangement also. The relay contacts marked S are those
against which the armatures must rest in order to operate
the sounders.
To balance a quadruplex circuit the distant generators
may be disconnected from the circuit while the resistance
of the home artificial line is adjusted to equal the resist-
ance of the line plus the terminal apparatus at the other
94
TELEGRAPH ENGINEERING
end. In order that the removal of the distant generators
will not alter the terminal resistance, a switch, Si, is ar-
Fig.4-
ranged to introduce a resistance rg from the junction x to
ground which equals the resistance connected in series
with the generators.
3. Avoidance of Sounder-armature Release During
Current Reversals in Neutral Relay. — When a neutral re-
lay of a quadruplex circuit is actuated, and the position of
the pole-changing key at the other station is altered mean-
while, the magnetism in the core of this relay is reversed.
This means that the magnetism falls to zero and then
rises to the same intensity in the opposite direction. As a
consequence the attracting force also passes through zero,
and a moment exists when the relay armature is not held
against its front contact point. During this brief interval
the local sounder circuit is opened and the sounder armature
is momentarily released. In the operation of a quadruplex
system such periods of zero magnetism in the neutral
relay cores are constantly recurring, and result in false
signals.
QUADRUPLEX TELEGRAPHY
95
Fig. 5.
Various methods have been adopted for avoiding the
release of the sounder armature during these short non-
magnetization periods of the neutral relay. One method
has already been mentioned in connection with the Morris
duplex system, described in § 7 of the fore-
going chapter; namely, the insertion of a
repeating sounder. The connections of the
local-sounder and repeating-sounder cir-
cuits are illustrated in Fig. 5. The repeat-
ing sounder RS has a heavy armature lever
so as to render its action slow. It is evi-
dent that when the magnetism of the neu-
tral relay R passes through its zero value,
the relay armature would have to be drawn against its
rear contact before the sounder S would release its arma-
ture. Since, in practice, the relay armature falls back but
a small distance before magnetism of sufficient intensity
in the opposite direction is again established to attract the
armature, it follows that no false signals will arise.
Another device, for accomplishing
this result, now extensively used on
the quadruplex circuits of the Postal
^ Telegraph- Cable Company, is the Diehl
relay arrangement, which is shown in
Fig. 6. It will be observed that the
sounder 5* is actuated as long as the
armature of relay R is away from its
rear stop. When this armature touches
its rear contact, the local battery, which supplies current
to the relay R', is short-circuited through a protective re-
sistance, and consequently neither this relay nor the
sounder is energized.
Fig. 6.
96
TELEGRAPH ENGINEERING
Neutral relays equipped with an extra coil, which re-
ceives current during the period of current reversal in the
other coils from a condenser or from a reactor, are also
used in order to avoid false signals. The arrangement
used by the Western Union Telegraph Company with its
quadruplex circuits is shown in Fig. 7. Each winding of
the main relay has a resistance
of 350 ohms while the extra or
holding coil H has a resistance
of 225 ohms. The condenser
C has a capacity of about 3
microfarads. As the condenser
is charged to the difference of
potential across the points a
and b, the instant the dis-
tant pole-changer armature leaves either contact in the
act of reversing the polarity of the distant generator,
the condenser immediately discharges through the hold-
ing coil, thus keeping the armature attracted during
the interval that the current reverses in the main relay
coils. The Freir self -polarizing neutral relay also gives
satisfaction with quadruplex systems.
In order that the period of current reversal be as short
as possible the movements of the pole-changer armatures
between their contacts should be reduced as much as prac-
ticable. Quick reversals of magnetism in the relay cores
are made possible by the use of relays possessing little
inductance and having laminated cores.
4. The Postal Quadruplex. — The Davis-Eaves quad-
ruplex is now largely used by the Postal Telegraph-Cable
Company, and is illustrated in Fig. 8, which shows the ap-
QUADRUPLEX TELEGRAPHY
97
paratus at one station. This arrangement is modelled
after the improved polar duplex described in § 6 of the fore-
going chapter. The functions of the bridge coils g and h
with the bridged condenser c, and the shunt paths con-
taining the resistances / and /' and the condensers Ci and
cij have there been explained. The operation of the
transmitter T in varying the available potential by means
of the leak resistance r3 and the added resistance rz has
been considered in connection with Figs. 3 and 4. The
condenser c3 curbs the sparking at the transmitter contacts.
The pole-changer C and the transmitter T are equipped
with permanent magnets, />/>, so arranged as to hasten the
return of their armatures to the rear contact points.
Neutral relay R controls the operation of sounder Si
through the Diehl relay R' ', as explained by means of
Fig. 6. A high-resistance leak path to ground is provided
by closing a switch introducing resistance r' . Four local
generators are shown in order to avoid complication of
the diagram, but in practice only one generator is em-
ployed. The constants of the main circuit are: resistances
of g = h = 500 ohms, of / = /' = r^ = 600 ohms, of r$ = 450
ohms, of R — 60 ohms, of P = 200 ohms, and of r' — 25,000
ohms; capacities of c\ = c\ = c$ = i microfarad, and of
98
TELEGRAPH ENGINEERING
c = 1 2 microfarads. The generator voltage should be from
250 to 385 volts.
5. The Western Union Quadruplex. — The quadruplex
circuits, now the standard of the Western Union Telegraph
Company, embody the principles of the bridge duplex,
already considered in § 8 of Chap. II. The connections of
the apparatus at one station of the Western Union quad-
ruplex are shown in Fig. 9. The retardation coil 7,
the milliammeter A, the pole-changer C, the line resist-
ance box, and the method of quenching the sparking at
the pole-changer contacts have already been described
in connection with the bridge duplex. The variation in
Fig. 9.
available potential is again effected by the Field system, T
being the transmitter and rz and r$ being respectively the
added and leak resistances. Both the repeating sounder
and neutral-relay holding-coil methods (see § 3) are utilized
in tiding over the period of zero magnetization in the
neutral relay core. Each artificial line is adjusted to
equal, in resistance and capacity, the main-line wire plus
the apparatus at the distant station. The ground resist-
ance rg facilitates line balancing. This resistance is also
contained in the artificial line box, as shown in Fig. 6 of
the preceding chapter, and connects with the terminal
marked "Ground Balance."
QUADRUPLEX TELEGRAPHY 99
When the distant pole-changer places the negative gen-
erator terminal to the line, the armature of the polarized
relay at the home station will close its local sounder circuit,
but when it places the positive terminal to the line the
polarized relay will not operate its sounder. An alteration
in current intensity from a minimum to a maximum value,
or vice versa, does not affect the polarized relay whether
it be against one contact or the other. Each polarized re-
lay is unaffected by the movements of the home pole-
changer.
The neutral relay is connected in the circuit exactly as
in Fig. 2, that is, one winding is connected in series with
the line wire while the other is connected in series with the
artificial line. Each neutral relay operates only on the
attraction of the armature of the distant transmitter, for
the current then traversing this receiving instrument is
three times as great as when the transmitter armature is
not attracted, and because the retractile spring on the re-
lay is adjusted so that its armature will not be attracted
when the relay is traversed by the weaker current.
The charge residing in the condenser c, bridged across
the line and artificial line through the holding coil of the
neutral relay, will be relieved whenever the distant pole-
changer armature leaves either contact. This discharge
causes a pulse of current to traverse the holding coil,
which pulse is sufficient to hold the armature of the neutral
relay (if attracted prior to current reversal), against the
front contact while the reversal of magnetism takes place
in the main cores of the relay. As a further safeguard
against the development of false incoming signals on the
second side of the quadruplex the repeating sounder RS
is used.
100
TELEGRAPH ENGINEERING
The constants of the main circuit are: resistances of
coils a = b = 500 ohms, of resistance lamps in each main
potential lead = 600 ohms, of r? = 1200 ohms, of r$ =
900 ohms, P = 600 or 800 ohms, R = 700 ohms and
rg = 600 ohms; capacities of c' = i microfarad, and of
c = i to 3 microfarads. The generator voltage should be
sufficient to develop a current of from 0.09 to 0.15 am-
pere in the line wire when both transmitters and one pole-
changer are closed.
When extremely bad weather renders the second side of
the quadruplex inoperative, the quadruplex circuit may
be used as a duplex circuit by keeping the two trans-
mitters closed.
6. Quadruplex Repeaters. — In general, any two quad-
ruplex sets can be connected together to form a quadruplex
repeater. The scheme of connections of a quadruplex
•WEST
LINE
Fig. 10.
repeater is shown in Fig. 10. The polarized relays PI and
Pz control the operation of pole-changers C\ and Cz re-
spectively, and the neutral relays RI and R2 control the
operation of transmitters T"2 and T\ respectively. It is
possible also to have the pole-changers controlled by the
QUADRUPLEX TELEGRAPHY ibl
neutral relays and the transmitters by the polarized re-
lays. For more satisfactory operation repeating sounders
may be interposed between each neutral relay and its
corresponding transmitter, as already explained.
The armature positions indicated in the figure are for
the normal condition, that is, when all keys at both eastern
and western stations are open. This means that the
positive terminal of the short-end battery or generator is
joined to the line at each station as well as at the repeat-
ing station. The generators at the repeating station are
not shown, but the pole-changer contacts are marked to
show their respective polarities (the other generator termi-
nals are grounded).
When the pole-changing key at the western station
is depressed, twice as much current flows (toward the
western station) through the line coils of relays Ri and PI
as through their other coils. This causes the operation of
relay PI but not of relay Rlm The armature of pole-changer
Ci is attracted, thereby placing the negative generator
terminal to the eastern line. This action does not affect
the repeater relays R2 and P2 nor the distant neutral re-
lay, but only the eastern polarized relay.
If, instead, the transmitter key at the western station
be depressed, the long end of the home battery or gener-
ator will be joined to the line. Twice as much current
flows (toward the repeating station) through the line coils
of relays RI and PI as through their artificial line coils.
This causes the operation of relay RI but not of relay PI.
The attraction of the relay armature energizes the trans-
mitter T2, which impresses the greater generator voltage at
the repeating station on the eastern line. This causes
more current to flow through the artificial line coils of
102 TELEGRAPH ENGINEERING
relays R2 and P2 than through their other coils. The
surplus current is insufficient to operate relay R% and in
the wrong direction to operate relay P2- The distant neu-
tral relay only responds to the depression of the western
transmitter key.
In the same way the conditions may be traced, for
other key positions at the two terminal stations, through
the repeating station.
It is practicable to secure quadruplex operation over a
portion of a line that at other portions is operated duplex.
Thus, a number of lines between New York and Chicago
are operated polar duplex between these terminal sta-
tions, and are also simultaneously operated differential
duplex between New York and Buffalo. Such a circuit
requires repeating apparatus at Buffalo that is formed by
combining a direct-point duplex repeater with a quadru-
plex set.
7. Duplex-diplex Signalling. — A system of telegraphy
that permits of duplex or diplex transmission, but not
both simultaneously as in quadruplex signalling, is called
ll|c
Fig. ii.
a duplex-diplex system. One such system, devised by
Crehore, utilizes both an alternating current and a direct
current, these currents being separated by means of in-
ductances and condensers. Fig. n shows the schematic
QUADRUPLEX TELEGRAPHY 103
arrangement of apparatus at one station for an open-
circuit duplex-diplex system.
Continuity-preserving keys KI and K2 respectively con-
trol the currents supplied by the battery B and alternator
A. The neutral relay R and the polarized relay P are in
parallel with each other, and in series with the line. The
inductance of the polarized relay is neutralized by the
properly-adjusted condenser C. The key K2 is shunted by
a reactor / which has large inductance but little resistance.
If key KI is depressed, a direct current flows through
relay R and no current flows through relay P because of
the presence of condenser C. Thus relay R as well as the
distant neutral relay will operate on the depression of the
direct-current key KI.
Depression of key K% introduces the alternator into the
circuit, as shown. Because of the high inductance of re-
lay R, only a small current will flow through it, and its
retractile spring is adjusted so that the armature will not
be attracted on this weak current. Polarized relay P as well
as the distant polarized relay will, however, be actuated.
In this way either duplex or diplex transmission may be
effected, the corresponding home instruments being also
responsive to the outgoing signals. In duplex signalling
one direct-current key and one alternating-current key
must be used. Alternating currents of fifty to one hun-
dred and fifty cycles may advantageously be employed.
A quadruplex system may also be built up on the fore-
going principles by applying alternating current to the
ordinary duplex systems.
8. Phantoplex System. — To increase the message-
carrying capacity of simplex, duplex or quadruplex lines by
104
TELEGRAPH ENGINEERING
additional superimposed channels, the so-called phanto-
plex system is employed by the Postal Telegraph-Cable
Company. The arrangement of this system adapted to a
quadruplex circuit and thereby affording sextuplex signal-
ling, that is, the transmission of three messages in each
direction simultaneously without interference, is shown in
Fig. 12 for one station. The quadruplex connections will
be recognized as those of the Field key system and ex-
plained with the aid of Fig. 4, the local circuits being
omitted for simplicity.
Fig. 12.
The secondary winding of a sending transformer, /, is
introduced between the armature of 'the transmitter and
the junction of. the neutral relay windings. The primary
winding of this transformer receives current from the
alternator A (frequency from 60 to 125 cycles) when
the armature of the transmitter T' rests against its rear
stop, the transmitter being actuated by the current from
battery b through the key K. The two primary windings
of the receiving transformer t' are connected in the line
and artificial line circuits, their secondary windings being
properly connected in series to the phantoplex relay X,
and through the condenser c. This phantoplex relay oper-
QUADRUPLEX TELEGRAPHY 105
ates a sounder (not shown) when its armature rests against
its rear stop.
When the key K is raised, as shown, an alternating
electromotive force is induced in the secondary winding of
the sending transformer, thereby superimposing an alter-
nating current upon whatever steady currents traverse this
winding. When no alternating current is superimposed on
the main circuit at the other station by its sending trans-
former (that is, the distant key corresponding to K is
closed), then the alternating current developed at / divides
equally between the line and artificial line circuits. The
voltages induced in the secondary windings of the home-
receiving transformer oppose each other, and do not cause
the attraction of the armature of phantoplex relay X. Its
local circuit will be closed and the sounder actuated — the
proper condition, for the distant key is closed. The alter-
nating current that traverses the line wire also flows
through one primary winding of the distant receiving
transformer, no current flowing through its other primary
winding. As a result the distant phantoplex relay will be
energized, thereby opening its local circuit. Thus the dis-
tant phantoplex sounder will not be energized when key K
is raised. Repeating sounders are used so that the flutter-
ing of the armatures of the phantoplex relays, due to the
alternating currents traversing their windings, will not
affect their local sounders.
Condensers ci, c% and c$ provide a direct path past the re-
sistances and relay windings for the alternating currents.
The alternating currents are of an intensity insufficient to
energize the quadruplex relays.
io6
TELEGRAPH ENGINEERING
PROBLEMS.
1. In the battery quadruplex circuit of Fig. 2, the long-end
battery has 300 volts and the short-end has 100 volts, the internal
resistance being 2 ohms per volt. Taking the resistance of the
assumedly perfectly-insulated line as 2000 ohms, and the resistances
of the polar and neutral relays as 400 and 200 ohms respectively,
calculate according to the method of § 2, Chapter II (using Rr = 600),
the proper resistance of the artificial line when both short ends of
the battery and when both long ends of the battery are in circuit.
2. With the artificial lines adjusted to 2800 ohms calculate the
currents, in milliamperes, traversing the relay coils of the quadruplex
circuit of Prob. i for all key positions, and record the results in
tabular form as indicated below. In the last column for each relay
should be placed the equivalent current in one coil, and if this cur-
rent is of sufficient intensity or of the proper direction to operate the
particular relay, this figure should be starred. The neutral relays
are adjusted so that a current greater than 0.050 ampere is necessary
for their operation.
Keys closed
(Fig. 2.)
none
K
K'
KK'
KK*
KK'K2
Relay P
Relay R
ll
2£
Relay P'
Relay R'
QUADRUPLEX TELEGRAPHY 107
3. If the two 3Oo-ohm protective resistances of the single-gen-
erator quadruplex circuit shown in Fig. 3 are replaced by 2oo-ohm
resistances, determine the proper values of the added and leak re-
sistances necessary for a 3 to i current ratio.
4. Calculate the strengths of the currents in the artificial line
circuit of Prob. 3, when both transmitter armatures are released and
also when both are attracted.
5. Compute the terminal resistance of the Postal Quadruplex,
the constants of which are given in § 4, if the artificial line has a
resistance of 2000 ohms.
6. Develop the diagram of connections of a telegraph line circuit
that extends from city A, through city B, to city C, which simulta-
neously affords two channels of communication (differential duplex)
between cities A and B and two channels (polar duplex) between
cities A and C.
CHAPTER IV
AUTOMATIC AND PRINTING TELEGRAPHY
i. Wheatstone Automatic Telegraphy. — When rapid
or accurate telegraphic signalling is to be accomplished,
automatic transmitting and receiving devices are availed of,
and consequently such rapid telegraphs are usually called
automatic telegraph systems. The Wheatstone automatic
system has been most extensively used and permits of
satisfactory telegraphic transmission at speeds up to 400
words per minute. The messages to be transmitted are
perforated in specially prepared oiled or parchmentized
paper tapes in accordance with the Morse code, and these
tapes are then automatically propelled through a transmit-
ter, which is really a high-speed pole-changer, driven by
springs or weights, or, more modernly, by electric motors.
The Wheatstone transmitter is connected in the line circuit
in the same way as is the pole-changer of a duplex circuit.
The messages are received at the distant station by an
inking polarized relay, called a Wheatstone recorder, which
records the message in the Morse code on a tape, as is done
by a register.
The transmitting tapes are prepared by means of three-
key mallet perforators or keyboard perforators, and appear
as in Fig. i, which shows the punching for the word " relay. "
The Morse characters are also shown, the letter / in auto-
matic telegraphy being written: dot, dash, dash, dash
(Postal), or dot, dot, dash, dash (Western Union), instead of
108
AUTOMATIC AND PRINTING TELEGRAPHY
109
a long dash. The size of standard perforator tape is 0.47
inch wide and from 4 to 5 mils thick. The center line of
holes, or guide holes, are o.i inch apart when the perforator
O 00 O 00 O C OO OO OO
ooooooooooooooooooooooooooo
O OO O O O O O O O OO OO
Fig. i.
is properly adjusted. A dot appears as three holes in a
vertical line, a space appears as one guide hole, and a dash
appears as four holes: two guide holes and two others, one
above the first guide hole and the other below the second
guide hole. Longer spaces are allowed between words,
sentences and messages.
A mallet perforator with interchangeable punch-blocks
Fig. 2.
and removable punch-ends is shown in Fig. 2. The de-
pression of the left plunger punches a dot, the center plunger
punches a space, and the right plunger punches a dash.
no
TELEGRAPH ENGINEERING
The punching operator uses a rubber-tipped mallet in
each hand for depressing the plungers. The plungers are
restored by springs to their normal position after each de-
pression, which action advances the tape one space after
the depression of the dot or space plungers, and two spaces
after depression of the dash plunger, the tape feeding being
accomplished by a small spur-wheel which engages in the
guide holes.
The principle of operation of the Wheatstone high-speed
transmitter can be explained with the aid of Fig. 3, which
illustrates simplex transmission from the left-hand to the
right-hand station. Only those mechanical features of the
transmitter are shown which serve directly in the capacity
of pole-changer. The transmitting tape / is moved along
over a slotted platform, in the direction indicated by the
arrow, by means of the spur-wheel w which engages in the
guide holes. Another wheel, not shown, is mounted above
the spur-wheel and serves to press the tape against the
platform. Rods / and b pass freely through a guide plate
g so that they remain respectively in ;line with the front
and back rows of holes, and are spaced longitudinally so
that their distance apart equals the distance between two
adjacent guide holes. The rocking beam r carries out-
AUTOMATIC AND PRINTING TELEGRAPHY III
wardly-projecting pins p, p, which limit the upward
motion of the rods against the tendency of the spring s.
The eccentric gear-wheel k, driven at any desired speed
by clockwork, or by an electric motor, causes the rocking
beam to oscillate through a small arc around its central
pivot. With each downward movement of the rod b the
tape moves forward one space or the distance between two
successive guide holes. The motions of the rods / and b
are transmitted to the pole-changer C by means of the
cranks, rods and the ivory collets c, c. The function of the
jockey-roller / is to hasten the movements of the pole-
changer and to insure steady contacts.
If the transmitter is set in operation without carrying a
tape, the rise and fall of the rods will be unhindered, and
every time the front rod / is in its upper position, the posi-
tive terminal of the battery B is connected to the line
while its negative terminal is grounded, and every time
the back rod b is in its upper position (as in Fig. 3) the
negative battery (or generator) terminal is joined to the
line. Thus the battery is reversed with every half oscil-
lation of the rocker arm when the transmitter is operating
idly.
These current reversals cause the armature of the polar-
ized relay P to oscillate simultaneously, which motion is
translated to the printing wheel shaft a that is kept re-
volving by means of the gear-wheel d. Whenever the
positive battery terminal is joined to the line at the trans-
mitter, the direction of the current through the polarized
relay is such as to hold the printing wheel i against the
inking wheel h which dips in the ink reservoir e. And
when the negative battery terminal is connected to the
line, the current direction is such as to press the inking
112 TELEGRAPH ENGINEERING
wheel almost against the moving receiving tape tr . These
currents are called spacing and marking currents respec-
tively. Thus, when the transmitter operates without tape,
a succession of dots appears on the receiving tape.
At the instant represented in the figure rod b has passed
through the tape, thereby sending a marking current and
causing the printing wheel to press almost against the
receiving tape and leave an ink mark thereon. The rock-
ing beam then draws down rod b and allows rod/ to rise;
meanwhile the tape has moved forward one space. In
this case the signal is a dot, and consequently rod / in its
upward motion meets the front or lower hole and so passes
through it. The complete transit of this rod causes the
shifting of the pole changer C and the sending of a spacing
current; consequently the printing wheel i is withdrawn
from the receiving tape to the inking wheel. A dot is
printed on the receiving tape.
If, instead, the signal were a dash, the upward movement
of rod / would be arrested by the tape, because in a dash
perforation there is no lower hole in line with the upper
hole. As a consequence, the pole-changer would not be
operated. Tracing the operation further, the upward
movement of rod b would also be restricted, but the next
upward movement of the other rod / would cause it to pass
through the lower hole, which movement reverses the pole-
changer. The time elapsing since the last reversal is
sufficient to form a dash signal on the receiver tape. It
will be observed that the current pulse for a dash signal
is of the same direction as for a dot signal, but three times
as long. For relatively low transmission speeds the signals
may be read from a sounder connected to the local-circuit
contacts of the receiving relay.
AUTOMATIC AND PRINTING TELEGRAPHY 113
Fig. 4 shows an automatic transmitter made by Muir-
head & Co., Ltd., for cable signalling. It is provided with
a local pole-changer, speed regulator, speed indicator, and
a switch for shifting connections from transmitter to hand-
key sending, which at the same time lifts the paper wheel
off the spur-wheel. The mechanical devices of the trans-
Fig. 4-
mitter are somewhat different from those shown in Fig. 3,
but have the same function.
The connections of the Wheatstone automatic system for
duplex operation are indicated in Fig. 5, which shows only
the electrical features at one station. The connections are
those of the polar duplex, already described, with a choice
TELEGRAPH ENGINEERING
of pole-changers. When the switch S is to the left as
shown, the automatic transmitter C is in circuit, and when
this switch is shifted to the right, the pole-changer Ci con-
trolled by the key K is in circuit. The Wheatstone recorder
P is immune from the movements of the home transmitting
devices C or Ci and will only respond to the operation of
either the distant automatic transmitter or the distant
manually-operated pole-changer. The Wheatstone system
is almost invariably operated duplex.
Repeaters for use with the Wheatstone automatic system
resemble polar direct-point duplex repeaters (§ 10, Chap. II)
thereby dispensing with automatic transmitters at the
repeating station for through operation. A Wheatstone
recorder may be introduced at the repeater as a leak relay
to enable the attendant to discern the character of the
signals passing through the repeater.
The system described has been used by the Western
Union Telegraph Company for many years. The auto-
matic system used by the Postal Telegraph- Cable Company
differs herefrom in the reception of the signals. It em-
ploys instead of the inking Wheatstone recorder, an elec-
tromagnetic punch, or reperforator, invented by d'Humy.
The reperforator punches characters in a moving tape
somewhat similar to those of the transmitting tape. If the
AUTOMATIC AND PRINTING TELEGRAPHY 115
completed receiving tape be passed slowly through a repro-
ducer, whose speed is in control of the receiving operator,
the messages can be read by ear and simultaneously copied
by hand or on a typewriter. The punches of the reper-
forator are adjusted to travel over a very short distance,
and their motion is rendered rapid by strong retractile
springs and by a series condenser in the punch magnet cir-
cuits. Such small and rapid motion of the punches com-
bined with a tape take-up device are the essential features
of the reperforator, for they shorten the time of tape
stoppages during punching and compensate for these stop-
pages respectively, thereby preventing tearing of the tapes.
2. Ticker Telegraphs. — A ticker telegraph system com-
prises a transmitter and a number of receiving instruments,
called tickers, which print the messages in ordinary type
on paper tape as they are received. The various ticker
systems for the dissemination of news and stock quotations
differ widely in the mechanical construction of instruments,
but the fundamental operating principles are not very
different.
A schematic diagram of a transmitter with one ticker
of such a tape-printing system is given in Fig. 6. The
transmitter consists of a shaft 5 driven by a constant-
speed motor M through a friction clutch k. Mounted on
this shaft is a current-reversing commutator c, formed by
a pair of metal crown-shaped wheels which are fitted
into but insulated from each other. The wheels connect
through brushes with the negative and positive terminals
respectively of generators D and Z>', the other generator
terminals being grounded. The shaft also carries an
escapement wheel e, and a contact arm a which passes
n6
TELEGRAPH ENGINEERING
over the contact points located on the contact disk C.
The escapement is controlled by an electromagnet m
through the keyboard K. Upon the depression of any
key no current from the battery B will flow through the
electromagnet until the contact arm a reaches the contact
stud corresponding to the key depressed. At that instant
the armature of magnet m will be attracted, thereby
arresting the rotation of the shaft and commutator. Thus
the shaft is stopped at a particular place for each depressed
key.
At the receiver the type-wheel T is rotated by clock-
Fig. 6.
work through the gear-wheel g, but this rotation is con-
strained by means of the escapement wheel w. The arma-
ture of polarized relay P controls this escapement wheel.
The rear end of the armature of printing relay R, when
this instrument is operated, presses the tape, which moves
over the armature, against the type-wheel; consequently
that letter will be printed on the tape which, at the mo-
ment of operation of the relay R, is in the lowest position.
If n characters are to be employed in transmission, there
must be n keys on the keyboard, n notches on the escape-
AUTOMATIC AND PRINTING TELEGRAPHY 117
ment wheel e, n contact studs on C and n segments on the
commutator c\ the commutator brushes and the contact
arm a being properly aligned with respect to the notches
on the escapement wheel. Thus, depressing any given key
will always stop the shaft at the same place. At the
receiver there are also n characters on the type-wheel and
n teeth on the escapement wheel.
In operation, when no keys are depressed, the trans-
mitter shaft revolves uniformly and the current supplied
to the line is periodically altered in direction by the com-
mutator. This reversal of polarity occurs so rapidly that
the current in relay R never reaches a value sufficient to
cause the attraction of its armature before the next re-
versal takes place, consequently the rear end of this
armature does not press the tape against the type-wheel.
However, the alternating current traversing the sensitive
polarized relay P causes its armature to shift its position
with each reversal in polarity, thereby operating the escape-
ment. One revolution of the transmitter shaft produces
n current reversals and the escapement wheel at the re-
ceiver moves through n notches, or one revolution. It is
evident, then, that if the type-wheel is started with its
characters in a certain position, it will always remain
during proper operation in the same relative position with
respect to the transmitter shaft. The proper position of.
the type-wheel is such that the letter a will be in the
printing position when the a-key of the transmitting key-
board is depressed.
Upon the depression of any key the motion of the shaft
and commutator will be momentarily arrested. This
stopping is permitted by the friction clutch without affect-
ing the rotation of the motor. During this instant the
Il8 TELEGRAPH ENGINEERING
current ceases to alternate in direction, and relay R is
enabled to attract its armature. This action presses the
tape against the type-wheel, thus printing the character
corresponding to the key that is depressed at the trans-
mitter keyboard. As the armature resumes its former
position through the intervention of spring s, the tape is
moved forward one space by clockwork and is ready for
the printing of the next character.
The system just described is known as a single- wire and
single type-wheel ticker system. To avoid spelling figures,
which occur very frequently in stock quotations, figures
and fractions should also be provided on the keyboard
and type-wheel. Adding to the 26 letters of the alphabet
10 figures and say 7 fractions would increase the size of
the wheel and would materially decrease the speed of oper-
ation. Instead, it is customary to use two type- wheels
on the same ticker-shaft and adjacent to each other, one
containing letters and a couple of dots, and the other con-
taining figures and fractions. As the numbers of charac-
ters on both type-wheels should be identical, the fractions
may be repeated and the still-existing deficiency may be
made up by dots. A ticker so equipped is called a two-
wheel ticker.
In two-wheel tickers provision must be made for shifting
either the type-wheels or the tape in order to print from
either wheel. This shifting is accomplished electromag-
netically in a variety of ways in the various ticker systems.
For fast working an additional wire is generally used for
the current which actuates the shifting magnet, thus neces-
sitating two line wires to each ticker.
Should, for any reason, the type-wheel of a ticker be
thrown out of step with the transmitter, as may occur
AUTOMATIC AND PRINTING TELEGRAPHY 119
upon sticking of the escapement wheel or momentary inter-
ruptions of the line wire, a jumble of letters on the tape will
Fig. 7.
result. Automatic devices, termed unison devices, are availed
of to bring the tickers back into step whenever desired.
Fig. 8.
Generators are now more frequently employed in the
operation of ticker systems than batteries, the generator
I2O
TELEGRAPH ENGINEERING
leads being provided with fuses and protective resistances.
Condensers are also used in these systems for the elimina-
tion of sparking at the transmitter contacts.
The appearance of the ticker used by the Stock Quota-
tion Telegraph Company in New York is shown in Fig. 7.
Fig. 9.
It has 8 ohms resistance and requires about 0.65 ampere
for operation. Figs. 8 and 9 show respectively the key-
board and motor-driven transmitter used at the central
station of a ticker system. The cost of ticker service is
about $20 per month. Fac-simile reproductions to full
.SUPREME. COURT. OF. THE. U.S.
.80
SP
U
.9! |
.700.833
.147
Fig. 10.
scale of the received tapes of a news ticker and a stock
quotation system are given in Fig. 10; the significance of
AUTOMATIC AND PRINTING TELEGRAPHY 121
the stock abbreviations on the lower tape being BO = Balti-
more & Ohio, SP = Southern Pacific, and U = Union
Pacific.
3. The Barclay Page-printing Telegraph System. -
The Barclay printing telegraph system is now extensively
used by the Western Union Telegraph Company, and com-
prises a keyboard perforator, an automatic transmitter,
and a receiving polarized relay which repeats the arriving
BARCLAY PRINTING TELEGRAPH CODE
A — ^_. „ O 9 _ - _
B @ - — _ P O _ __ _
C : _ - _ Q I _ _ _
D$ _ __ R 4 p. _ _
E 3 ___ S # __ -
T X __ - T 5 ...
G& __ _ u T _-_
H * -__ V J — «_ .
I 8 ___ W 3 _ .__
J ' . -- - XI _ . -
Kf --- Y6 _._
L) . __ Z " __ _
ce
Type Shift __ - ^^ Carriasre Return ^ ^^ mm^
--- ,
Space -. . « Paper Feed.
signals into a set of local relays which control the opera-
tions of the printing magnets, the received message being
directly printed in page form on message blanks. This
system may be operated successfully through several re-
peaters. Its capacity is about 100 words per minute over
lines 1000 miles long.
Transmitting Apparatus. Messages to be transmitted
are first perforated in prepared paper tapes, exactly as
122 TELEGRAPH ENGINEERING
in the Wheatstone automatic telegraph system described in
§ i, only a different code is employed. The code used in
the Barclay system has three elements for each character
and these are separated from each other by short or long
spaces, as shown on the preceding page. The spaces be-
tween the various words, figure groups, etc., are formed
by three closely-spaced dots. Thus, the perforations in
the transmitting tape for the word " relay" would appear
>oo oo o oo o o oo o oo o o o ooo
lOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
>OO O O O O OO OOO OOO OOO OOO
RELAY
Fig. II.
as in Fig. n (compare with Fig. i showing perforations
according to Morse code).
The Kleinschmidt perforator, now largely used with the
Barclay page-printer, is shown in Fig. 12, and is a purely
mechanical device for punching the tape, but derives its
motive power from an electric motor. All the perforations
representing a letter, figure or other character on the tape,
as well as their proper spacing, are produced by a single
depression of the key. After this depression, the tape is
advanced a distance commensurate with the space occupied
by the letter or figure. After about 60 letters are punched
an indicator lamp illuminates giving a warning that the
end of a line (on the receiving page) is approaching. The
pointer, which indicates the number of letters perforated,
is returned to zero by the depression of the indicator key
before the limiting number of 75 characters have been
prepared.
The automatic transmitter used with the Barclay print-
AUTOMATIC AND PRINTING TELEGRAPHY 123
Fig. 12.
ing system is a Wheatstone transmitter, or high-speed pole-
changer, as described in § i. A front elevation of the upper
portion of this transmitter is shown in Fig. 13, wherein
most of the letters refer to the same parts as in Fig. 3.
Fig. 13.
124 TELEGRAPH ENGINEERING
The pole-changer contacts are shown at k and fe, and con-
nect respectively with the negative and positive terminals
of the generators. In operation the adjustment of the
rods / and b must be very precise, and is effected by the
screws e and e' '. When the switch 5 is thrown to the left
the paper wheel P, which is shown bearing upon the tape,
is raised out of engagement with the spur-wheel w, thereby
halting the progression of the tape. A local pole-changer
for hand signalling is located in the base of the automatic
transmitter. In practice, when the transmitter operates
without tape, from 40 to 70 current reversals take place per
second.
When the front rod / is at the upper end of its travel the
positive generator terminal is joined to the line, and when
the other rod is in a similar position the negative generator
terminal connects to the line. Thus, for each letter there
are six current pulses, three positive and three negative,
and the code is so arranged that there is at least one long
current pulse among the first five, either positive or nega-
tive, per character. In the letter R (• — "), for example,
these current pulses have the following sequence: short
negative, short positive, long negative, long positive, short
negative, long positive, the last pulse corresponding to the
space between this and the next following letter. The
significance of the code elements are therefore:
dot = short negative current;
dash = long negative current;
short space = short positive current;
long space = long positive current.
Receiving Apparatus. — The current impulses sent out
by the transmitter are received by a differentially-wound
AUTOMATIC AND PRINTING TELEGRAPHY
125
polarized relay of special construction to render it quick
acting. To attain this end, its magnetic circuit has several
air gaps, the moving element has a small moment of
inertia, and the two coils of each winding are connected in
parallel. The series resistance of each winding is 150 ohms.
A top view of this relay is shown in Fig. 14, in which a is
Fig. I4.
the armature tongue, e is the separately-excited energizing
coil which takes the place of the usual permanent magnet,
m, m are the main winding bobbins with the pole-pieces p,
p] c, c are the platinum contacts, and k is the knurled
screw which moves the bridge b carrying these contacts.
The connections of the main line and artificial line cir-
cuits of automatic duplex apparatus as arranged in the
126
TELEGRAPH ENGINEERING
Fig. 15.
Barclay printing telegraph system are shown in Fig. 15
for one terminal station. In the figure, C is the pole-
changer, D, D are the generators, P is the polarized relay
with its coils connected in
parallel, AL is the artificial
line, and g is a differential
galvanometer which aids in
line balancing. Repeaters
for use with this system re-
semble polar duplex direct-
point repeaters.
The main-line' relay con-
trols through the intervention of a " printer relay," a " sepa-
rator relay," an " escapement magnet" and a " sunflower"
distributing switch, the operation of five " distributing
relays" with multiple contact points, which in turn control
the operation of 32 "printer" magnets. The actuation of
the distributing relays, as dependent upon the nature of
the received current impulses, may be studied with the
aid of diagram Fig. 16, in which the various intermediate
devices mentioned are indicated.
The separator relay is a neutral relay which is adjusted
to be responsive only to long current impulses in either
direction. The escapement magnet is a polarized relay
which controls the movement of the escape wheel. This
wheel has 45 teeth and is mounted on the same shaft as
the unison wheel with 15 teeth, the shaft tending to rotate
under the influence of an electric motor. The six current
pulses of each letter or character, alternately negative
and positive, that traverse the escapement magnet cause
the escape wheel to turn through a distance corresponding
to 3 teeth and the unison wheel through a distance of one
AUTOMATIC AND PRINTING TELEGRAPHY 127
tooth. As the unison wheel turns, its teeth successively
butt against the toes of the six pivoted levers marked
i, 2, 3, 4, 5 and 6; thereby establishing connections with
the five distributing relays and the sixth pulse or " final"
relay. However, the circuits of the five distributing relays
are only completed when the armature of the separator relay
is on its front contact, which occurs only when a long cur-
rent pulse traverses its winding.
Suppose the letter R is being received; the impressed
pulses are: short — , short +, long — , long -f, short,—
and long +. Fig. 16 shows the armature positions during
the first pulse. The armatures of the line and printer
relays are respectively on their right and left contacts, the
armature of the separator relay is not attracted, and the
armature of the escapement magnet is toward the right.
The unison wheel has turned through one-sixth the distance
between two teeth, thereby causing a tooth to engage the
toe of pivoted lever i. But inasmuch as the circuit of
distributor relay i is interrupted at the separator relay
armature, the closing of its circuit at the sunflower does
not cause the operation of relay i, which remains inop-
erative until the end of the cycle of current pulses for the
selected letter. During the second pulse the armatures of
the line and printer relays and of the escapement magnet
will be in their opposite positions, and the armature of the
separator relay will still remain unattracted. Therefore the
completion of the circuit of relay 2 at the sunflower does
not cause the operation of relay 2. The third pulse is of
dash duration, so the separator relay is capable of attract-
ing its armature by current supplied by generator D. The
escape wheel has moved another half notch, bringing a
tooth of the unison wheel in engagement with the toe of
128
TELEGRAPH ENGINEERING
SEPARATOR
RELAY
IT T
ESCAPEMENT
MAGNET
5 32 PRINTERS MAGNETS
Fig. 16.
AUTOMATIC AND PRINTING TELEGRAPHY 129
pivoted lever 3. Relay 3 will therefore be operated and
remain so until the expiration of* the remaining three-
current pulses. The fourth pulse likewise causes the oper-
ation of distributor relay 4. As the fifth pulse is of short
duration, relay 5 will not be actuated. Thus for the letter
R, relays 3 and 4 are operated and close local circuits (not
shown in this figure) which hold all printer magnets open
except that which prints the letter R, as will be described
subsequently. The closing of sunflower contact 6 causes a
current pulse always of long duration, since it represents
the interval between letters, to flow from the generator Dr
through the rear spring contact of the final relay, through
the particular printer magnet corresponding to the letter
R, which places this letter in the printing position, and
through the trip magnet which causes the type-wheel to
come in contact with the message blank. Since the estab-
lishment of this sixth pulse the armature of the final mag-
net has been moving forward due to the current through
its winding. This movement soon opens the circuit of
the printer and trip magnets, but is adjusted not to do so
until the proper printing of the desired letter is accomplished.
Immediately after opening this circuit, the armature comes
in contact with its front stop, thereby establishing a current
through the left-hand or " reset" coils of the five distribut-
ing relays, which is in a direction to cause the armatures
of the relays previously energized to resume their normal
position on the left, in readiness for the next letter.
The distributing system, whereby a particular printer
magnet out of thirty-two is selected by means of the five
distributing relays, is shown in Fig. 1 7 . Relay i is equipped
with two contacts, relay 2 with four contacts, relay 3 with
eight contacts, relay 4 with sixteen contacts, and relay 5
130
TELEGRAPH ENGINEERING
with thirty-two contacts. The small contact levers shown
in the figure are insulated from each other.
The sequence of the long-current pulses in any letter or
Fig. 17.
character determines the relay or group of relays that will
be operated in the selection of the particular printer mag-
net. In the transmission of letter R the third and fourth
relays are operated, causing their armatures to move to-
AUTOMATIC AND PRINTING TELEGRAPHY 131
ward the right. This condition is represented in Fig. 17,
and it is evident that the only printer magnet circuit that
is closed is that which places the letter R in the printing
position, the direction of current flow being indicated by
the arrows. Current simultaneously traverses the trip
magnet which urges the type-wheel, now rotated to its
proper position, against the paper, causing the printing
of the letter R thereon. In a similar manner the selection
of the printer magnet for any other letter or character is
accomplished.
The printing of the " upper-case" characters, given in
the second column of the Barclay printing code, is accom-
plished by raising the type- wheel, which carries 56 char-
acters grouped in two rows, so that the upper-case letters
are brought into the printing line. Raising the type-
wheel is done by the type-shift magnet T and its assisting
magnet A, and the type- wheel remains raised until a
" space" is transmitted, which lowers the type-wheel (if
raised) through the operation of the type-release magnet
R, as shown also in Fig. 17. As the sixth current pulse is
of insufficient duration to cause the proper actuation of
the type-shift magnet T, the assisting magnet A keeps the
circuit of the other closed until the type-wheel is raised.
Since magnets T and A are connected in parallel, both
will be magnetized when the sixth current pulse of the
type-shift group passes through their coils. Magnet A
attracts its armature and causes current to flow from gener-
ator D through the coils of the type-shift magnet until
the armature of this magnet is at the end of its travel.
When this occurs the windings of both magnets are short-
circuited, the assisting magnet releasing its armature,
thereby opening the circuit of generator D. The armature
132 TELEGRAPH ENGINEERING
of the type-shift magnet is held down by the catch c engag-
ing the pin p; consequently the type-wheel is maintained
in its upper position for the printing of upper-case letters
until released by the attraction of catch c by the type-
release magnet R, which operates on the reception of the
" space" character.
Shifting of the paper for line spacing is accomplished by
the paper-feed magnet which is actuated by the sixth pulse
following 5 dash current pulses. Its operation is identical
with that of the type-shift magnet, being assisted also by
an auxiliary magnet, not shown in the diagram.
The carriage, holding the paper upon which the message
is printed, is returned to the starting position by means
of the carriage-return magnet, the mechanism, as before,
not being shown in the figure. When the armature of this
magnet is attracted, causing the return of the carriage,
the circuit of the final relay is opened at the normally-
closed contacts m. As a result, the current through the
final relay is interrupted before its armature spring breaks
contact with its rear stop, through which current continues
to flow from generator Df to energize the carriage-return
magnet. The instant the carriage arrives at its starting
position, the circuit-breaker B opens the circuit of the
carriage-return magnet, which in releasing its armature,
completes at m the circuit of the final relay, thereby per-
mitting this relay to reset the distributing relays.
Reverting to Fig. 16, the lever of the synchronizing mag-
net is seen to act upon the unison wheel. The function of
this magnet is to restore f the unison wheel to the zero
position, if, for any reason, it gets out of step with the in-
coming current pulses. The winding of this instrument,
which is of the polarized type, is such that its permanent
AUTOMATIC AND PRINTING TELEGRAPHY 133
magnetization is opposed by negative current pulses and
assisted by positive current pulses. Since the armature
of this magnet is adjusted not to operate on short-current
pulses, only long positive current pulses bring the synchro-
nizer into action. Such pulses occur in some letters, and
occur invariably at the end of each letter or character.
In proper operation, the hook on the synchronizer lever
rests in spaces between the teeth of the unison wheel, and
would interfere with its motion at the end of each letter
were not the synchronizer magnet energized at that instant
by a long positive pulse. Should any pulses of a letter be
lost, this magnet would restore synchronism upon the
reception of the next following long positive current pulse.
4. Other Printing Telegraph Systems. — The Mor-
krum page-printing telegraph system is also used at
present both by the Western Union Telegraph and Postal
Telegraph-Cable Companies. The Baudot tape-printing
system is extensively used abroad, the system being
operated simplex, duplex or multiplex. The Hughes tape-
printing system is largely employed in Europe, about 3000
instruments being now in use. The Rowland multiplex
and the Wright page-printing systems were for a time used
on some circuits of the Postal Company. The Burry page-
printing telegraph is used by the Stock Quotation Tele-
graph Company for disseminating general and financial
news in New York City and vicinity.
Many other systems have been invented and are now
used more or less here and abroad for the direct printing
of the received messages, among which may be mentioned
the systems of Munier, Murray, Essick, Dean, Creed,
Siemens, Kinsley and Buckingham, the last being the fore-
134 TELEGRAPH ENGINEERING
runner of the Barclay printing system, herein described.
Multiplex page-printing telegraph systems will be consid-
ered in Chap. VI.
PROBLEMS
1. Show the appearance of a transmitting tape for automatic
telegraphic transmission with perforations representing the word
"Wheatstone."
2. How many words may be telegraphically transmitted in one
direction over a wire by the Wheatstone automatic system in 6 hours
if the perforated tape is passed through the transmitter at the rate
of 4 words per second? Allow two per cent for idleness in changing
tapes.
3. Fill out the letter designations of the blank printer magnet
circles of the Barclay printer shown in Fig. 17.
4. When the speed of the Barclay transmitter is such that forty
current reversals take place per second when running without tape,
and considering the length of the average letter to be the average
of the characters of the Barclay code, how many five-letter words
could be transmitted per minute in each direction with this printing
system?
CHAPTER V
TELEGRAPH OFFICE EQUIPMENT AND TELEGRAPH TRAFFIC
i. Protective Devices. — Fuses are used in telegraph
circuits to protect these circuits from damage which might
result from an excessive flow of current through them.
They are made of fusible material, generally of lead or of
an alloy of tin and lead, and assume the form of wire or
strips provided at each end with a copper terminal which
engages the contacts of the fuse receptacles. With en-
closed fuses the fusible material is surrounded by a finely-
divided non-combustible powder that is contained in an
insulating casing. All fuses are placed at accessible places,
generally in telegraph offices, so as to facilitate replacement
in case of their melting.
Fuses are rated at 80 per cent of the greatest current
they can carry indefinitely without melting. Thus, a
fuse would carry a current 25 per cent greater than the
normal rated current strength. For telegraph service
fuses of ^-ampere capacity and upward are used. Line
fuses also offer protection to terminal apparatus when the
lines are crossed with electric distributing and other high-
voltage lines.
Lightning arresters are employed at telegraph offices
and also on lines, as a protection against injury to terminal
apparatus and attendant operators, that would otherwise
result from lightning strokes or relieved abnormal induced
charges. These arresters provide a short path to ground
135
136
TELEGRAPH ENGINEERING
through a small insulating gap, generally of air, that is
readily broken down and rendered conductive by such
discharges. The length of these gaps is such that the oper-
ating voltages in telegraph service cannot initiate arcs
across the spark gaps.
In practice, satisfactory fuses and lightning arresters for
telegraph circuits assume a variety of forms, concededly
more or less familiar. The type of protector now used by
the Western Union Telegraph Company is shown in Fig. 8.
2. Peg Switch Panels. — A switching arrangement
adapted for use at intermediate stations on simplex lines
Fig. i.
is shown in Fig. i, and is called a peg switch panel or a strap
and disc switch panel. The wall panel shown is used where
two-line wires pass through an intermediate office, and pro-
vides means for introducing either set of receiving instru-
ments into either line, for cross connecting, for looping
these lines with or without introducing home instruments,
and for cutting off one side of a line.
This panel consists of four brass straps and two rows of
discs, five in each row. The line terminals are on the
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 137
upper ends of the straps, and the instrument terminals
are along the left edge of the panel. The latter terminals
are in line horizontally with the discs, and each terminal is
in electrical connection with the discs located in the same
horizontal row. The plate g is placed transversely over
the straps and over the two upper discs, but is insulated
from the vertical straps by a small air gap, thereby
serving as the ground plate of a lightning arrester. Any
disc may be connected to either of the straps between
which it is located by means of a brass plug or peg, which
fits in the holes formed between the discs and straps. These
holes are in five horizontal rows numbered i, 2, 3, 4 and 5,
and in four vertical rows lettered a, b, c and d, so that any
one of the 20 holes may readily be referred to. Two re-
ceiving sets, each consisting of relay and key, are also
shown connected to the panel terminals. The insertion
of a plug in any of the four upper holes grounds the corre-
sponding strap.
When it is desired to insert receiving set i into line A,
plugs are inserted in holes 02 and d $ (or £3 and d 2).
If, at the same time, it be desired to complete line B with-
out a receiving set, plugs are inserted in holes a 4 and b 4
(or a 5 and £5). To cross connect the two lines with
receiving instruments in each circuit, plugs are placed in
holes a 2 and d 3, and b 4 and c 5. Instead, to cut off the
western section of line A, leaving receiving set i in its
other section, insert plugs in holes c i, c 2 and d 3. In
order to loop the two eastern wires together with or with-
out intermediate set i, insert plugs respectively in holes
b 2 and d 3 or in holes b 2 and d 2.
For the accommodation of additional lines at inter-
mediate or terminal offices, peg panels having a corre-
TELEGRAPH ENGINEERING
spondingly greater number of straps and discs may be
used. A combination of the peg-switch panel and the
spring-jack device, the latter shown in Fig. 2, forms a
Fig. 2.
widely used panel. The insertion of a wedge, as shown,
raises the shank away from the fixed shoe and introduces
into the line whatever apparatus is connected with the
wedge cord. Single- and double-conductor wedges are used
for various purposes, and more than one wedge may be in-
serted in a spring jack, thus meeting a variety of telegraph-
circuit requirements.
3. Main and Loop Switchboards. — In large telegraph
offices the switching arrangements for the interconnection
of all classes of circuits are located at switchboards. Usu-
ally these switchboards are divided into two parts: the
main switchboard, at which terminate the incoming line
wires, each wire being equipped with a group of pin-jacks;
and the loop switchboard, at which the local office circuits
or loops may be connected from one circuit to another. The
pin- jacks on both switchboards are so connected that each
line or local circuit is complete for normal operation.
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 139
Changes in these normal conditions are effected by single
or double flexible conductors or patching cords having plug
terminals which fit into the jacks. Fig. 3 shows the type
of pin- jacks and plugs
now extensively used on
telegraph and telephone
switchboards.
Main Switchboards. —
All line wires terminate
at the main switchboard
which is equipped with Fi«- 3.
properly connected jacks for the establishment of any
desired connections with these wires.
A main switchboard comprises a variety of circuits. A
. BUSY TEST KNOBS
TO LOOPP
VIA DI8TRIB
40 - 3 LOOP SIMPLEX MORSE WIRE
Fig. 4-
typical panel of the Western Union main switchboard
for terminal offices contains nine types of circuits, five of
which are shown in Fig. 4, the number of circuits of each
140
TELEGRAPH ENGINEERING
type being indicated. The remaining four types are
shown as circuits A, D, E and F in Fig. 6 in connection
RESISTANCE
LAMP3
CABLE FROM LAMPS
TO LOCAL BATTERY FUSES
a
REAR VIEW OF
CABLING FOR
FLOOR DUCTS
SECTION
Fig. 5-
FRONT VIEW
with the loop switchboard, twenty A, four D, ten E and
twenty F circuits being employed. Circuits for combined
telegraphy and telephony are also provided where necessary.
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 141
RESISTANCE LAMP (3 - 12 OHMS PER VOLT)
~
20 • TWO-WIRE TRUNKS (FROM ONE
' END OF BOARD TO OTHER )
fr-^"-
*-^~l SOUNDE
10 - DUPLEX OR QUAD. SETS AND REGULARLY
ASSIGNED LOOPS
RESISTANCE
LAMPS
80- DUPLEX LOOPS WITHOUT REGULAR ASSIGNMENT
POLE CHANGE
TO MAIN SWITCH- )
BOARD JACKS OR >-
REPEATERS VIA I
DISTRIBUTING FRAME )~
(D
'II
64 - TWO WIRE TRUNKS TO MAIN SWITCH B'D.
20 - HALF-REPEATER LOOPS <2 FOR EACH )
20 - FULL-REPEATER LOOPS ( 2 FOR EACH )
24- DOUBLE LOOP REPEATERS (3 FOR EACH)
16 -DUPLEX OR HALF-QUAD. REPEATER LOOPS.
8-TE8TING8ET8
Fig. 6.
142 TELEGRAPH ENGINEERING
Referring to Fig. 4; circuit B is used for simplex service
which may require three loops or sets each, the loops being
included by inserting the plugs of patching cords in jacks
7-8, 9-10 and 11-12; circuit C is used on multi-section
switchboards for extending loops and other circuits from
one section to another; circuit G is used in cases of loop
failures and circuit H is used for testing purposes where
it is required to ground a line. For duplex or quadruplex
circuits it is only necessary to connect the line through
three jacks to the corresponding set via the loop switch-
board and distributing frame, as indicated by circuit /.
The design of this switchboard is shown in Fig. 5, the
jacks bearing numbers corresponding to those in Fig. 4.
Loop Switchboards. — A loop switchboard is generally
installed at large telegraph offices to provide facilities for
conveniently changing local circuit connections of duplex
and quadruplex sets from one operating table to another
at the main office or for distributing these connections to
subscribers or branch offices, so as to take care of varying
traffic requirements. The terminals of such local circuits
extend to pin jacks on the loop switchboard, the board cir-
cuits being so arranged that the local apparatus regularly
assigned to the same circuit is normally conriected thereto,
changes in these connections being made with flexible
patching cords.
A loop switchboard includes a variety of circuits. A
typical panel of the Western Union one-section loop switch-
board comprises the eleven types of circuits shown in
Fig. 6, the number of circuits of each type being indicated.
Circuit A is used in the testing of simplex circuits; cir-
cuit B is used in testing, or in case of failure of the resist-
ances or contacts of an office loop, it replaces the lower
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 143
jack of circuit G; circuits C and D enable simplex apparatus,
loops, repeaters, etc., to be readily joined in series, the
former including a current source; circuit E permits of the
interconnection of apparatus terminating at remote por-
tions of the board by means of two short patching cords
instead of one long one; the jacks of circuit F connect
with receiving sets, repeaters, half -repeaters, etc., or extend
to jacks on the main switchboard; circuits G and H con-
nect the apparatus of a duplex or quadruplex set for
normal operation, the latter circuit being used where an
outside loop is regularly assigned to the set; circuit / is
used for branch office loops that are not regularly assigned
to any particular duplex set, and may replace those nor-
mally assigned in circuits G and H; circuit / normally
joins the two duplex or half -quadruplex sets that constitute
the duplex repeater; circuit K serves as a testing set for
making any desired tests on duplex or quadruplex sets.
4. Distributing Frames. — Before telegraph aerial or
underground lines reach the main switchboard at an office
they pass through a distributing frame generally placed
in back of the switchboard. Office cables extend from this
frame to the main and loop switchboards and to the instru-
ment tables on- which repeater, duplex and quadruplex
apparatus are located. Fig. 7 shows three units of a
Western Union distributing frame. The right or " hori-
zontal" side has 8 horizontal strips which carry terminal
blocks for connection, say, to office apparatus, while the
left or " vertical" side has 3 vertical strips which may
carry similar terminal blocks or office protectors and con-
nect with the incoming line cables. Each horizontal seg-
ment accommodates 20 terminal clips for an equal number
144
TELEGRAPH ENGINEERING
Fig. 7.
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 145
of wires and each vertical strip accommodates 100 pro-
tectors. These connections to terminal clips and pro-
tectors are permanent. Any desired connection may be
made between the different pieces of apparatus in the
office, or between such apparatus and entering lines, by
cross-connecting or " bridle" wires at the distributing
frame. Switchboard rearrangements or changes in traffic
requirements are, therefore, readily met by shifting the
bridle wires without altering the apparatus and line wiring
to the distributing frame.
The type of protector used comprises a one-half ampere
^AMPERE FUSE
RELAXED SPRING INDICATES
BLOWN FU6E
| | LIGHTNING ARRESTER
GROUND PLATE
Fig. 8.
indicating fuse and a lightning arrester formed by two
carbon blocks separated by a thin strip of mica, and is
shown in Fig. 8.
5. Instrument Tables. — Telegraph apparatus at large
telegraph offices is arranged in a very compact form on
instrument tables. One general form of instrument table
construction is shown in Fig. 9, which shows that portion
of one side of a long table occupied by the apparatus of
one quadruplex set. A duplex set requires about 13 inches
and a duplex repeater set about 33 inches of table length.
The location of the apparatus of a Western Union
quadruplex set on this table is generally as indicated in
146
TELEGRAPH ENGINEERING
the figure, the upper shelf being reserved for signalling
purposes. The unit-section instrument tables used by the
Postal Telegraph Cable Company are constructed of angle
and sheet iron with apparatus located on four narrow tiers,
each unit accommodating two quadruplex sets, or four
duplex sets, or four repeater sets.
/
< , - SIGNAL ,. SIGNAL
' SIGNAL * »-~MAMP '' SIGNAL ' /--IrAMP
^'____RELAY_^X »__)LAMP ^. RELA_Y_^' (-LA.MP,
_ _ S.WITCHE8
PLATE '
''''-lwNtt^/^&''' -~ '}^PP~?' ^l'j^^~*-'?.EJ--,/'s'
±— tsxH**£±-af4
NEUTRAL s'
RELAY S '
X^O
Attendants constantly oversee the operation of such
duplex, quadruplex and repeating apparatus, each attend-
ant having supervision of a certain number of sets.
6. Power Switchboards. — A switchboard for a tele-
graph power plant should comprise the necessary switching
facilities, measuring and regulating devices for the placing
of the desired potentials of correct polarity on the terminals
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 147
of the distributing panel from which conductors lead to the
main switchboard. As most telegraph power plants con-
sist of motor-generator units, which alter the voltage of
the available commercial current supply to values suitable
for telegraphic purposes, switchboards for such plants
should also include motor-starting switches and rheostats.
To maintain continuity of service in case of shut-down of
the commercial current supply, arrangements are made if
possible, for break-down connection with another source,
or, if the available current sources are not dependable,
a storage battery or, where practicable, a steam, gas or
oil engine and generator, is installed.
The appearance of a typical power switchboard now used
by the Western Union Telegraph Company for a motor-
generator plant is shown in Fig. 10, scale gV- The board is
mounted directly over the machines, each panel controlling
the motor-generators below it. The left-hand panel con-
trols three machines, one generator having its positive ter-
minal permanently grounded, another its negative terminal
grounded, and the middle generator serves as a spare unit
which may replace either of the others by shifting the re-
versing switch. The smaller switchboard panel is intended
for two machines, one delivering current to the local cir-
cuits and the other a spare unit. All generator and motor-
starting switches and the voltmeters are provided with
enclosed fuses on the face of the board.
The connections of this power board for motor-generators
with direct-current motors are shown in Fig. n. Three
1 60- volt and two 2 6- volt motor-driven . generators are
shown, the outer i6o-volt machines and the left-hand
26-volt machine being in service. When the middle
i6o-volt generator is to replace its left neighbor, it is
148
TELEGRAPH ENGINEERING
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 149
150 TELEGRAPH ENGINEERING
started and brought up to proper voltage by means of its
field-regulating rheostat RR and placed in parallel with
its neighbor by throwing switch E to the left and closing
switch B. Thereafter switches A and then F are opened.
In the figure V and A indicate voltmeters and ammeters
respectively, / indicates fuses and SR represents motor-
starting rheostats with no-voltage release, the terminals
marked M, A and F connecting with the service main,
motor armature and motor field respectively. The gener-
ator leads go to a distributing panel which provides con-
venient means for distributing the proper current to the
various classes of circuits. This panel also includes the
main service switch and instruments.
Switchboards for motor-generators, having alternating-
current single-phase, two-phase or three-phase motors,
differ slightly from the board described in that different
starting devices and motor switches are employed.
TRAFFIC
7. Types of Messages. — Messages for telegraphic
transmission may be written in plain language, be expressed
in code words, or be couched in cipher. Code words are
actual or artificial pronounceable words having not more
than 10 letters. The object of employing code words is
the saving of telegraph tolls, inasmuch as a single word is
given a meaning expressible in plain language only by
several words or even a sentence. A few code words with
their interpretation according to the Western Union
Travelers' code are given below:
ALLAH Arrived all right, address letters to care of
BALMY Are very busy. Please return soon as possible.
BRING There is no occasion for alarm.
COVER Can you send me letter of introduction to ?
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 151
ENTER Arrangements are progressing satisfactorily.
LUNAR I (or ) do not wish to take responsibility for deciding.
You (or ) know all the circumstances and must
decide what shall be done.
PEGGY Market very strong. Prices have advanced since last
advice.
PUNCH Please accept my heartiest congratulations.
SPIKE Have sent telegraphic money order as requested.
SCORN We wish you all a Happy New Year.
Cipher messages are used solely for secrecy. Such
messages consist of unpronounceable groups of letters or
of groups of figures, or both. They can be read only by
the sender and recipient, in accordance with some pre-
arranged scheme. Considerable time is necessary for
couching and deciphering such cipher messages. As an
illustration, the Confederate cipher used during the Civil
War will be cited, the keywords employed by the Confed-
erates being "Complete Victory," ^Manchester Bluff"
and later " Interest. " The cipher is made up by giving
numbers to the letters of the alphabet as below:
abcdef ghi j k 1 mnopqrstuvwxyz
I 2 3 4 5 6 7 8 9 10 n 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
27 28 29 3° 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
To write a cipher message add the respective numbers
corresponding to the letters of the keyword and of the
message (letter for letter, repeating the keyword if neces-
sary), subtract the index number i, and the corresponding
letters will yield the cipher message. Thus to write
" Reach Richmond to-day," using the keyword " Interest,"
proceed as below:
R I CHMOND
18 9 3 8 13 15 14 4
E S T I N T E R
5 19 20 9 14 20 5 18
REACH
185 i 3 8
INTER
9 14 20 5 18
Sum minus one 26 18 20 7 25
Z R T G Y
22 2? 22 l6 26 34 18 21
VAVPZHRU
TODAY (message)
20 15 4 i 25
E S T I N (keyword)
5 19 20 9 14
24 33 23 9 38
X G W I L (cipher)
The last line is the appropriate cipher message.
152 TELEGRAPH ENGINEERING
To decipher a message according to this cipher, subtract
numbers corresponding to keyword from number corre-
sponding to cipher (letter for letter), add the index num-
ber i, and the corresponding letters will yield the message.
By varying this scheme and using different keywords, an
infinite variety of cipher codes may be developed. The
characters of cipher words are transmitted with double
spacing as a safeguard for avoiding errors.
8. Classes of Service and Tariffs. — Several classes of
telegraph service are rendered by the large telegraph com-
panies. The overland services offered by the Postal and
Western Union Companies are: telegrams and night letters;
the latter company also offers day letters.
Present rates (1914) for commercial telegrams from New
York City to the capitals of the states and territories in
the United States and of some of the provinces in the
Dominion of Canada, are given in the table on the follow-
ing page, which includes also the rates to Mexico City and
Dawson City, Yukon. Day rates apply to messages in-
tended for immediate delivery whereas night rates apply to
telegrams for delivery the following morning. The number
before the dash is the rate in cents for telegrams of 10 words
or less (address and one signature free), and the number
following the dash is the charge for each additional word.
Night letters containing 50 words (or less) may be sent
at the lo-word day message rate, one-fifth of this rate being
charged for each additional group of 10 words; and day
letters of 50 words (or less) may be sent at ij times the
night letter rate. Day letters are forwarded as promptly
as the facilities of the company permit only in subordination
to the full-paid telegrams, and night letters are trans-
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 153
RE
ites
Citv
Ra
tes
Day
Night
Day
Night
60-4
5O-3
Carson City, Nev.
100-7
100-7
Juneau, Alaska
Phoenix Ariz.
260-23
100-7
260-23
100-7
Fredericton, N. B
Concord, N. H.
50-3
35-2
40-3
25-1
Little Rock Ark
60-4
50-3
Trenton, N. J.
25-2
25-1
Victoria, Brit. Col
100-7
100-7
100-7
100-7
Santa Fe*. N. Mex
Albany, N. Y.
75-5
25-2
60-4
25-1
Denver, Col
Hartford Conn.
75-5
25-2
60-4
25-1
Raleigh, N. C
Bismarck, N. Dak.
50-3
75-5
40-3
60-4
Dover, Del
Washington, D. C.
30-2
30-2
25-1
25-1
Halifax, N. S
Columbus, Ohio
50-3
40-3
40-3 .
•50-2
(National capitol)
Tallahassee, Fla.
60-4
50-3
Oklahoma City, Okla. . .
Ottawa, Ont. .
75-5
50-3
60-4
4O-3
Atlanta, Ga
Boise, Id
Springfield 111.
60-4
100-7
50-3
50-3
100-7
40-3
(Capitol of Dominion)
Toronto, Ont
Salem, Ore.
50-3
100-7
40-3
100-7
Indianapolis, Ind
Des Moines, la.
50-3
60-4
40-3
50-3
Harrisburg, Pa
Charlottetown, P. E. I..
30-2
75-5
25-1
65-5
Topeka, Kan
Frankfort, Ky.
60-4
50-3
50-3
40-3
?uebec, Quebec
rovidence, R. I.
50-3
30-2
40-3
25-1
Baton Rouge, La
Augusta, Me.
60-4
40-3
50-3
30-2
Columbia, S. C
Pierre, S. Dak..
60-4
75-5
50-3
60-4
Winnipeg Manitoba
75-5
60-4
Nashville Tenn.
50-3
40-3
Annapolis, Md
Boston, Mass.
30-2
30-2
25-1
25-1
Austin, Tex
Salt Lake City, Utah.
75-5
75-5
60-4
60-4
Mexico City, Mexico
Lansing, Mich.
175-12
50-3
175-12
40-3
Montpelier, Vt
Richmond, Va.
35-2
40-3
25-1
30-2
St. Paul Minn
60-4
50-3
Olympia Wash
100-7
100-7
Jackson, Miss
Jefferson City, Mo.
60-4
60-4
50-3
50-3
Charlestown, W. Va
Madison, Wis.
40-3
60-4
30-2
50-3
Helena, Mont
Lincoln, Neb -. . . .
75-5
60-4
60-4
50-3
Cheyenne, Wyo
Dawson City, Yukon. . .
75-5
425-29
60-4
425-29
mitted sometime during the night at the convenience of
the company and are delivered the following morning.
Such deferred service is offered at attractive rates in order
to keep the equipment effectively busy at all hours, or in
other words, to keep up the load factor of the equipment.
Day and. night letters must be written in plain English
and must not contain code words. The letters BLUE,
NL or NITE are prefixed to a message and transmitted
to inform the receiving operator as to the class of service
desired, whether day letters, night letters or night-rate
telegrams respectively. The indication DH (representing
dead head) is used on unpaid messages for company matters,
etc. When a group of messages of one class is transmitted,
154
TELEGRAPH ENGINEERING
a single indication on the first message of a group suffices
for successive messages until a different indication is re-
ceived.
A message blank bearing a message for transmission
should contain the following information:
ITEM No. ITEM
1 Originating city
2 Date
3 Addressee (name and address)
4 Message
5 Signature
6 Indication as to class of service
(Different blanks are used for the
various classes.)
7 Telegraph clerk's number
8 Time of filing
9 Check of number of words
10 Wire number
11 Office call letter at destination
12 Sending operator's sign
13 Time of transmission
14 Receiving operator's sign
BY WHOM WRITTEN
Sender or telegraph
clerk.
Telegraph clerk.
Sending operator.
The first six, the ninth, tenth, thirteenth and fourteenth
items as well as the call-letter of the originating office are
transmitted and appear upon the received message blank
that is delivered to the addressee. If a reply is to be pre-
paid the letters RP followed by the number of words pre-
paid are transmitted and also appear upon sending and
receiving message blanks.
9. Handling of Traffic. — The methods employed in
handling commercial telegraphic traffic depends largely
upon the volume of incoming and outgoing traffic. In a
large center the handling of this traffic at the main office
must be fully systematized in order to facilitate prompt
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 155
transmission and delivery of messages. Somewhat differ-
ent methods of handling traffic are naturally employed at
different places; that used in a large city will here be out-
lined.
The telegraphic stations of a city for the reception and
transmission of messages comprise a main office and many
branch offices distributed throughout the city. The Wes-
tern Union Telegraph Company has about 200 branch
offices in New York City. Messages for transmission may
reach these branch offices either by submission in person
or by representative, or may be collected by messenger
upon call, no charge being made for this service. Messages
may also be telephoned from telephone subscribers' stations
to the main office by requesting the telephone operator
for "Western Union" or for "Postal," and upon connec-
tion, dictating the message to the answering telegraph
clerk. The tolls for a message so sent will either be col-
lected upon delivery or will be charged to the sender on
his telephone bill. Messages received at branch offices
are sent to the main office in two ways : the blanks may be
carried by pneumatic tube carriers from those offices that
are connected with the main office by such tubes, or else
the message is telegraphed to the main office.
The messages arriving at the main office for telegraphic
transmission are sorted at a central distributing place or
routing room and are distributed by mechanical carriers
to division stations, each division being a portion of the
operating floor seating operators who transmit on lines
terminating in some geographical division of the country.
Check boys or girls carry the message blanks from the
division stations to the proper operators. After the oper-
ators have transmitted a message, they indorse the blank
156 TELEGRAPH ENGINEERING
(by inscribing items 10-14 of the scheme given in foregoing
section) and place it in a message clip. Check boys pass
up and down the aisles and remove the blanks from the
clips and take them to the division stations from whence
they are carried mechanically to a searching room. Here
the blanks are examined as to the indorsement and are
filed away and preserved for a reasonable length of time.
Incoming messages are typewritten upon suitable blanks
by the receiving operators or are automatically printed by
the printing telegraphs. These incoming messages are
carried by check boys and mechanical carriers to the
routing room, where they are sorted. Such messages re-
quiring retransmission are carried to the proper sending
operator in the same way as originating messages. The
remaining messages are for local distribution within the
city confines. These city messages are sorted and may
be telephoned directly to the addressee if he be a telephone
subscriber, or else sent to his nearest branch office either
by pneumatic tube or by wire, and from there delivered
by messenger to the addressee.
The traffic manager at a large telegraph office is kept
constantly informed regarding the amount of traffic over
the various interurban and important lines, so that if
necessary he may alter the customary routing of messages
in order that telegraphic business at all centers may be
adequately disposed of with the available existing facilities.
Thus, if an unusual amount of traffic has accumulated at
Philadelphia for transmission to Chicago via New York,
and if the traffic from Philadelphia to Boston, and from
Boston to Chicago is light, the traffic manager would
direct the operators at Philadelphia to send some of the
messages to Chicago via Boston. In the event of severe
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 157
storms felling pole-lines between important centers, the
traffic manager endeavors to re-establish service between
these points over another route even if very circuitous.
Records of the amounts of traffic accommodated on the
various line circuits are kept for the information of tele-
graph engineers who determine the necessity for additional
lines and equipment or suggest rearrangements of existing
facilities for improving the service.
10. The Telegraph in Railway Operation. — The hand-
ling of steam trains in accordance with telegraphic orders
began in 1851, and since that time has been rapidly ex-
tended to all railroad systems. Since 1907 the telephone
' is also used in train dispatching and in the directing of train
movements; at present, about 70,000 miles of railroad in
this country are telephonically handled.
A large majority of all telegraph offices in the United
States are located in railway stations, and large amounts
of commercial and especially railway telegraph traffic are
handled through them. Railway telegraph traffic may
deal with inter-departmental business or with train move-
ments, the latter traffic being usually urgent and requiring
immediate attention. Such traffic on a railroad division
includes the progress of passenger and freight trains,
attendance to emeVgencies as they arise, information on
the location of rolling stock, messages concerning ship-
ments, and so on.
The use of the telegraph for issuing and receiving such
information generally requires two local single-wire circuits
linking the principal office of the division with its various
local offices. One of these circuits, termed the train wire,
is used by the train dispatcher, and the other, termed the
158
TELEGRAPH ENGINEERING
message wire, is used for transmission of commercial and
railway telegrams. On unimportant branch roads both ser-
vices are sometimes handled over a single circuit, whereas
on long or busy railway divisions the more important
offices may be connected to a special circuit to relieve con-
gestion of traffic on the other circuits. Between the
principal division offices of a system and the general offices
or administrative center of the railroad are a series of
circuits, which may be operated simplex, duplex or quad-
ruplex, with or without repeaters, as the traffic or length
of the circuit may warrant. Thus, an idea of the extent
of the telegraph circuits of the Northern Pacific system
(which operates over 6000 miles of main-line track) may be
gained from the following list of principal circuits now
operated out of the St. Paul, Minn., general office. This
list, given by M. H. Clapp, does not include some local
circuits operating out of St. Paul to points in the direct
vicinity of the Twin Cities. There are four repeating
stations on the St. Paul-Tacoma line, at which traffic is
also relayed to different offices to which direct wires are
not provided.
Circuit from St. Paul to
Circuit
operated
Distance
in miles
Tacorna Wash . ...
Quadruplex
1900
1250
1650
Helena, Mont
1130
Billings and Livingston, Mont.
1008
Dickinson N. D. and Glendive, Mont ....
667
Fargo N D and Dilworth Minn.
252
Duluth Minn
Duplex
152
Winnipeg, Man. — Local 32 offices
Simplex
483
Fargo, N. D. — Local 41 offices
252
Duluth Minn. — Local 40 offices .
«•
152
St Paul Division. — Local 30 offices
•«
170
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC 159
ii. Telegraph Statistics. — The United States censuses
of electrical industries show the following statistics of the
domestic telegraph industry in the years 1880, 1902, 1907
and 1912:
COMMERCIAL LAND AND OCEAN TELEGRAPH SYSTEMS
1880
1902
1907
1912
Number of companies or sys-
tems
77
25
25
27
Nautical miles of ocean cable. .
Miles of single wire owned and
leased
Number of messages
Number of telegraph offices
Dollars total income
(a)
291,213
31,703,181 (d)
12,510
16,696,623
16,677
1,318,350 (b)
91,655.287
27,377
40,930,038
46,301
1,577,961
103,794.076
29,056
51 583 868
67,676
1,814,196 (c)
109,377,698
30.864
64 762 843
Average number of employees(e)
Employees salaries and wages
(dollars) (g)
14,928
4,886,128
27,627
15,039,673
28,034 (/)
17,808,249
37,295
24,964,994
(a) Not separately reported.
(b) Includes miles of wire operated by W. U. Tel. Co. outside of the United States.
(c) Exclusive of 314,329 miles of wire wholly owned and operated by railway companies
for their own business.
(d) For 54 companies out of 77.
(e) Does not include railway operators also doing work for telegraph companies.
(/) For 23 companies out of 25.
(g) Two companies in 1907 and one in 1902 did not separate salaries and wages from oper-
ation expense. The wages of persons enumerated above spending a part of their time
in telegraph service are those received for telegraphic service only.
The large decrease in the number of separate companies
from 1880 to 1902 was due to numerous consolidations of
formerly competing companies. Far more than one-half
of the number of telegraph offices tabulated are located
in railway stations, and these offices are not used exclu-
sively for the transmission of messages for the general public.
The extent to which the telegraph industry is controlled
by a few companies is indicated by the fact that the six
largest companies reported 99 and 97.7 per cent of the total
tabulated income in the years 1902 and 1907, respectively.
i6o
TELEGRAPH ENGINEERING
The 1907 census also shows that 625 railway companies
in the United States, operating 225,059 miles of single track,
owned 383,833 and leased 423,991 miles of telegraph wire,
and sent 258,589,333 telegraph messages for railroad busi-
ness during the year.
Comparative telegraphic statistics of various countries
selected from Senate Document No. 399, dated 1914, for
the year 1910 (except where otherwise stated) are tabu-
lated below:
TELEGRAPH STATISTICS OF DIFFERENT NATIONS
Country
Population
Annual
telegrams
per capita
Average
receipt per
domestic
telegram
in cents
Telegraph
offices
Miles of
telegraph
wire
Per 10,000 of population
Austria
Belgium
28,571,934
7,074,91°
2,585,660
38,961,945
63,886,000
41,976,827
20,886,487
32,475,253
49.732,952
246,455
5,591.701
1,062,792
2,240,032
152,009,300
5,294,885
3,315,443
95.410,503
0.73
1.25
1. 31
1.65
0.92
2.18
0.59
0.55
0.60
0.84
1.19
8.09
1.48
0.24
0.80
1.75
1.09
22.4
14.2
14.0
12. 1
18.0
17.2
25.1
19-3 (a)
12.3
9-0
15-0
15-7
I3.4(a)
42.0
15 3
17.2
45.0
1.58
2.31
2.17
5-21
7.06
3-33
2.20
2.36
0.86
13.16
2.49
18.51
7.08
0.55
5-39
7.13
3-42
50
36
34
108
175
135
42
38
20
29
40
357
142
•28
37
48
190
Denmark
France
Germany
Great Britain
Hungary
Italy
Japan
Luxemburg (1905) . . .
Netherlands .
New Zealand
Norway
Russia
Sweden
Switzerland
United States (1912)
(b)
(a) Minimum message rate.
(b) Statistics computed from preliminary report on Land Telegraph Stations: 1912,
issued Feb., 1914.
It will be observed that of the countries tabulated, the
average cost per telegram is least in Luxemburg and most
in the United States, and that the yearly telegrams per
individual is most in New Zealand and least in Russia.
TELEGRAPH OFFICE EQUIPMENT — TRAFFIC l6l
PROBLEMS
1. How are the two lines passing through a four-strap peg switch
panel (see Fig. i) interconnected at this panel without introducing
intermediate receiving instruments into either line?
2. How may a simplex line having three loops at the main switch-
board give service to three additional subscribers or brokers' offices?
3. Show the connections at one end of a duplex line through the
main and loop switchboards and through the distributing frame,
when the operators are stationed at an office some distance away
from the main telegraph office. (Refer to circuit I of Fig. 4, circuit G
of Fig. 6 and Fig. 16 of Chap. II.)
4. How may the duplex line of the preceding problem be tempor-
arily assigned to some' other branch telegraph office?
5. Using the Confederate cipher, the key word "Manchester
Bluff," and the index number i, decipher: YCPNLPDTRTPXCSL.
CHAPTER VI
MISCELLANEOUS TELEGRAPHS
i. Multiplex Telegraph Systems. — Multiplex teleg-
raphy means the simultaneous transmission, without
interference, of a plurality of messages in either or both
directions, over a single line. The duplex, quadruplex,
duplex-diplex and phantoplex systems already described
and also the alternating-current systems of Picard and
Mercadier may be considered multiplex systems, but in
practice this name is applied to those systems utilizing
synchronous rotation of contact distributors located at the
two terminal stations. Inasmuch as the maximum speed
of hand transmission is only about 40 words per minute,
it is evident that the speed possibilities of telegraph lines
even with short cable sections are not being utilized. With
the automatic telegraph the lines are more effectively
used, for speeds of 250 to 400 words per minute in each
direction are maintained. Multiplex telegraphs also con-
duce to better utilization of the lines and permit of signalling
at rates up to about 200 words per minute in each direction.
In the Delany multiplex system the line is successively
assigned for short intervals to several pairs of operators
by means of synchronously revolving distributors, the
intervals being so short that during the hand transmission
of a dot signal by one operator, he has exclusive momen-
tary use of the line several times. Thus, if one pair of
operators receive the line 36 times per second and assum-
162
MISCELLANEOUS TELEGRAPHS 163
ing the average word to have the equivalent of 18 dots,
signalling at the rate of 40 words per minute indicates
3 contacts per dot. Between these contacts the line is
periodically assigned to about five other pairs of operators.
Thus, each telegraphic character is made up of short im-
pulses rather widely separated as compared with their
duration. Such signals are rendered intelligible when
transmitted by pole-changing keys and received by polar-
ized relays, as in the polar or bridge-duplex systems.
The Delany system, adapted for hand signalling, was
used for a number of years but has gradually given way
to the more accurate printing multiplex systems. The
Rowland multiplex page-printing telegraph, which affords
octuplex signalling as a quadruple duplex, was for a time
used on some circuits of the Postal Telegraph-Cable Com-
pany and is now being further improved. The Baudot
tape-printing and the Murray page-printing multiplex
systems are at present considerably used abroad, being
operated as double or quadruple duplex systems. The
Murray multiplex (§ 2) has also begun its operation in this
country, affording a speed of 40 words per minute in each
of eight channels over a single wire between two cities
250 miles apart. A quicker telegraph service is possible
with multiplex printing telegraphs than with ordinary
automatic transmission because of the direct printing of
the received messages.
2. The Murray Multiplex Page-printing Telegraph. -
The principal instruments used in the Murray multiplex
telegraph are keyboard tape perforators, automatic trans-
mitters, distributors and electromagnetically-operated
printers.
164 TELEGRAPH ENGINEERING
The tapes are perforated according to a special 5-unit
code, the units for each letter, figure or other character
being arranged transversely to the tape. The alphabet
perforations are shown in Fig. i to correct size, the letters
being separated by the space character which consists
of one perforation immediately below the guide hole. The
tape passes directly through a constant-speed automatic
transmitter, patterned after the Wheatstone transmitter,
and is then wound in rolls by an automatic tape-winder.
The transmitter is provided with a starting and stopping
abcdefahi'jklm
o o o o o o o
o o o o o o o
ooooooooooooooo oooooooooooooooo
O OOO O OOO OOOOO 000 OO
OOO OO OO O
O O O O O
O O O 0000
OOO OOO
ooo oooooooooooooooooooooooooooo
OO OOOOO OOO OOOOO OOOOO
o o o oo
OOO O OOOOO
n o p q r s t u v w x y z
Fig. i.
lever for use in case the transmitter overtakes the perfor-
ating operator.
The function of the distributors is evident from Fig. 2,
wherein a single line provides four channels of communi-
cation in either direction by means of the distributor arms
D and D', sweeping over the contacts a, b, c and d at
stations A and B respectively. By joining duplex term-
inal apparatus to the contact points at both ends of the line
quadruple duplex or octuplex signalling is rendered possible.
Only one artificial line is used at each station. The con-
tacts are preferably multipled so that a distributor arm con-
MISCELLANEOUS TELEGRAPHS
nects with one duplex set several times in one revolution,
thereby reducing the rotational speed of these arms.
It is absolutely essential that both contact arms occupy
the same relative positions at all times, that is, they must
rotate synchronously. Such rotation is secured by the
a
b
c—0
• i •$
D'
Fig. 2.
use of manually-started motors having tooth-wheel iron
armatures and periodically excited field magnets, the con-
tact arms being mounted directly on the motor shaft.
Periodic field excitation is obtained by the use of reeds
which are kept vibrating at their natural frequency. To
maintain synchronism the distributor at one station sends
DISTRIBUTING
Fig. 3-
to that at the other station one or more governing impulses
during each revolution of the arm, which impulses control
the speed of the distant motor.
The circuit arrangements for securing synchronous rota-
tion of the distributors and for signalling over one of the
communicating channels are schematically shown in Fig. 3,
l66 TELEGRAPH ENGINEERING
the groups of contacts for the other channels (that is, the
return over a and duplex over b, c and d of Fig. 2), as
well as the vibrating reed and distributor motor at station
A, being omitted for the sake of clearness. The toothed
wheel w of the distributor motor, when once set in rotation,
will advance one tooth every time the vibrating reed r
makes one complete vibration due to the impulsive currents
reaching the magnet M every time the reed touches its
front contact. The reed is kept in vibration electromag-
netically in the usual manner, that at station B being
adjusted to operate one or two per cent faster than that
at A. Thus if distributor arm D' reaches the contact
marked — while the other arm D is still on the contact
marked +, a current pulse from battery B will flow over
the line and through the polarized relay P in such direc-
tion as to close the contact of this relay. This momentary
contact enables battery Bf to actuate the governing relay
R and open the vibrator circuit for an instant, thereby
retarding slightly the vibration of the reed and the rota-
tion of the distributor arm D'. If both arms were to pass
over the — contacts simultaneously, the contact of the
polarized relay would be open and no governing impulse
would reach relay R.
Thereafter, the two distributor arms pass together succes-
sively over the main contacts i, 2, 3, 4 and 5, and then over
similar sets of contacts for the other transmitting chan-
nels (not shown). The polarity of the five current pulses
sent out jipon the line at station A depends upon the
positions 'of the rocking pins which, in turn, depend upon
the tape perforations, as in the Wheatstone transmitter,
the various permutations of positive and negative pulses
corresponding to the various letters and other characters to
MISCELLANEOUS TELEGRAPHS 167
be transmitted. At station B the five main contacts are
connected to an equal number of distributing relays which
select the particular printer magnets in a manner very
similar to that explained with the aid of Fig. 16 of Chap. IV.
As the contact arm passes over the contact x, the print-
ing magnet is energized, causing the printing on the receiver
message blank of that letter whose printer magnet was se-
lected by the distributing relays.
From the foregoing it will be understood how this method
of signalling can be extended to give quadruple-duplex or
possibly even sextuple-duplex transmission over a single-
line wire, the received characters over each communicating
channel being directly printed. Messages requiring retrans-
mission to remote places may be directly perforated in
tapes at the intermediate station, the five magnets that
set the punches of the receiving perforator being connected
in series with the corresponding distributing relays of the
printer.
3. The Pollak-Virag Writing Telegraph. — The Pollak-
Virag rapid telegraph system has been installed on a num-
ber of European telegraph lines and affords signalling at
rates up to 700 words per minute over two-wire lines.
Tape transmission is utilized in the Pollak-Virag writing
telegraph, the perforations for the various characters being
of various sizes and located in one or more of six rows.
The paper tape is prepared on a keyboard perforator, all
the perforations for a letter or other character being made
by a single depression of a key. The tape is passed over
a motor-driven drum D, Fig. 4, which is formed of six
electrically-distinct rings. Two brushes, b and &', each
spanning three rings, press the tape against the drum and
i68
TELEGRAPH ENGINEERING
make contact with its rings through the perforations,
the duration of contact depending upon the size of the
perforation. Rings i, 2 and 3 connect to battery B so
that brush b and the upper line wire may have a potential
with respect to the other line wire of say + 50, + 30 or
— 30 volts respectively. Similarly, rings 4, 5 and 6 con-
nect to battery Bf so that brush bf and junction x may have
a potential with respect to ground of say -f 30, — 30 and
— 50 volts respectively. Combinations of contacts of
different durations and in correct sequence with these six
rings occasion current pulses in the line which actuate a
RECEIVER
Fig. 4.
specially-designed receiver to produce in script the various
letters and figures.
The receiving instrument resembles two telephone re-
ceivers (R and Rf, Fig. 4) whose diaphragms are placed
in one plane. In front of the diaphragms is mounted a
permanent magnet, from the center and ends of which
project soft iron strips with forwardly-extending pointed
tips. A small soft iron sheet carrying the mirror m (shown
in the lower right corner) is magnetically held against the
three tips. The motions of the two diaphragms of re-
MISCELLANEOUS TELEGRAPHS 169
ceivers R and Rf are transmitted by means of links to the
tips t and /' respectively, which are located i mm. above
and to the left of the center tip c respectively. Therefore,
if the diaphragm of receiver R vibrates the mirror will
rotate about a horizontal axis, and if the other diaphragm
vibrates the mirror will rotate about a vertical axis. If
both vibrate, the mirror will describe the motion of the
resultant vibration.
A small pencil of light issuing fr6m an electric light /
impinges upon the mirror and is reflected as a spot of light
upon a band of photographic paper p. A revolving
opaque hood H having a helical slit encloses the lamp so
that the spot of light will advance from one side of the
paper to the other, and then jump to the next line, and so
on. If the mirror vibrates in accordance with transmitted
impulses, its motions will be properly recorded. After
exposure, the sensitive paper travels down through solu-
tions which develop and fix the paper in about 15 seconds,
revealing legible script.
The two-line wires join with the terminals of the winding
of receiver R, which is actuated by portions of the battery
B, this receiver forming all vertical components of the
transmitted characters. Both line wires are used as a
single conductor for the other receiver circuit by means
of the neutral points xt formed by a high-resistance shunt
at the transmitter, and y, the mid-point of the winding of
receiver R. In this way battery B' actuates receiver R'
(ground being the return path), this receiver forming all
horizontal components of the characters. In order to
abolish the disturbing influences of. resistance, inductance
and capacity when signalling over long lines, various con-
densers and reactors may be introduced at particular places
iyo
TELEGRAPH ENGINEERING
in the circuit. Condensers connected in parallel with
the receivers R and Rf are introduced to soften the action
of the currents. Synchronous rotation of the hood at
the receiver and the drum at the transmitter is not neces-
sary in this system.
The nature of the perforations and the corresponding
received script is indicated in Fig. 5 for the word " message. "
The direction and relative magnitudes of the impressed
voltages are indicated at the left, and the received graph
for only the vertical components is shown immediately
o o 0
— 1" -" -t "- ~ ~ • " ™
__/lA/l/^j/l^^
i i i
Fig. 5.
below the tape. The actual received trace, which corre-
sponds to both vertical and horizontal movements, is
shown at the bottom.
4. The Telautograph. — The telautograph is an instru-
ment for the electrical reproduction of handwriting at a
distance, invented by Prof. Elisha Gray and perfected by
Geo. S. Tiffany, and consists of a transmitter and a receiver.
The appearance of the instrument made by the Gray
National Telautograph Company is shown in Fig. 6. These
MISCELLANEOUS TELEGRAPHS
171
devices may be operated singly over a private line or con-
nected through a switchboard so as to enable any two
instruments to be used together. Also, a single transmitter
may be arranged to operate a number of receivers simul-
taneously.
At the transmitter the pencil is attached by a system
of levers to two contact rollers which bear against the inner
Fig. 6.
surfaces of two curved rheostats, which are connected across
direct-current supply mains, usually of 115 volts. The
potential difference between either end of each rheostat
and the accompanying roller varies with the position of
this roller, which position changes in writing. These vary-
ing voltages are impressed on circuits which extend to the
172
TELEGRAPH ENGINEERING
receiver, where they terminate in coils wound on copper
bobbins and arranged to move horizontally within intense
magnetic fields against the action of springs. In operation
the two coils are displaced in proportion to the forces acting
on them, which forces are proportional to the currents
traversing the coils, which currents vary with the im-
pressed voltages, and which, in turn, depend upon the dis-
placements of the transmitting rollers from their zero
positions, thereby rendering the displacement of each coil
proportional to that of the corresponding roller. The coils
at the receiver are connected by a system of levers which
actuates the recording pen, the lever system being similar
to that at the transmitter. Thus, the motion of the pen
is the resultant of the motions of the two coils, which mo-
tions are proportional to those of the transmitting contact
rollers, and they are the component motions of the trans-
mitting pencil; therefore, the receiving pen duplicates
the motions of the transmitting pencil.
The simplified scheme of connections of the improved
transmitter and receiver is shown in Fig. 7, which also
PAPER SHIFTER
So
PAPERM8rdFNTETR RECEIVER
TRANSMITTER
Fig. 7.
indicates the various auxiliary devices utilized in realizing
commercial practicability. The apparatus used for the
transmission of the writing motions is apparent, the left
MISCELLANEOUS TELEGRAPHS 173
and right rollers on the transmitter rheostats connecting
directly with the two corresponding receiver coils that are
located in separate annular air gaps of one magnetic cir-
cuit. The two pairs of power terminals connect to com-
mercial electrical supply mains.
The functions of the auxiliary devices are as follows: -
The master switch controls the paper shifter magnet which
operates a clamp that pulls the paper through one line
space over the transmitter platen. Shifting of the receiver
paper is similarly accomplished, the shifting magnet being
locally energized through the contacts of the relay which
is included in one of the two line wires and which is like-
wise under the control of the master switch.
This relay also serves to complete the circuit of the elec-
tromagnet which develops the magnetic field for the
receiver coils. It will be observed that the winding on
the lower bobbin may be periodically short-circuited by the
spring armature of a vibrator. This action causes the
intensity of the magnetic field to flicker rapidly and pro-
duces a minute vibration in the receiver coils. Friction of
the pen on the paper and in the moving parts of the re-
ceiver is greatly reduced by this vibration, and conse-
quently the pen is very sensitive to small changes in the
line currents. Although small alternating currents are in-
duced in the coils by this vibratory motion, the pen-lifting
relay bridged across the line wires will not operate, because
of the equality of these opposing currents.
Pen lifting is accomplished at the receiver by means of
a locally-operated magnet- placed back of the receiver
writing platen, the armature carrying a rod adapted to
move the pen arms and lift the pen away from the paper
when the magnet is energized. This pen-lifter magnet is
174 TELEGRAPH ENGINEERING
controlled by a pen-lifting relay that has a peculiarly
constructed armature which is set into violent vibration
and makes imperfect contact with its contacts points
when alternating current passes through the relay winding,
but which armature is quiescent and makes good contact
with its contact points when no current traverses the
winding. At the transmitter the secondary winding of
a small induction coil is bridged across the line wires through
two condensers, and the primary winding derives its
energy from the power mains through a vibrating armature.
A contact beneath the writing platen is arranged to short-
circuit the vibrator when the platen is not depressed.
Thus, during intervals when no characters are written
no electromotive force is induced in the secondary winding
of the coil, no current traverses the pen-lifting relay and
consequently the circuit of the pen-lifter magnet is closed,
thereby lifting the pen away from the paper. Depression
of the platen by the transmitter pencil in writing, per-
mits operation of the vibrator and occasions an alternating
electromotive force in the secondary winding of the coil.
This induced voltage develops a current that traverses the
two-line wires simultaneously with the "writing" currents
and also traverses the pen-lifting relay. The armature of
this relay is thereby agitated so that the pen-lifter magnet
is effectively open-circuited, and the release of its armature
permits the receiving pen to touch the paper.
Ink for the receiving pen is contained in a small stoppered
bottle with an orifice near the bottom, the ink being re-
tained by atmospheric pressure. When the telautograph
is idle, retractile springs hold the pen in the ink at this
orifice. In order to close the master switch it is necessary
to bring the transmitting pencil to a position corresponding
MISCELLANEOUS TELEGRAPHS
175
to that of the pen and to press the pencil on a button there
located, thereby releasing a catch that holds the master
switch. This process is repeated for each paper-shifting
operation so that sudden large movements of the receiving
pen are avoided.
5. Telephotography. — The electrical transmission of
photographs from one place to another, called telephotog-
raphy, may be accomplished
by utilizing the property of
the element selenium by vir-
tue of which it varies its
electrical resistance under
the influence of light. The
lowering of selenium resist-
ance with increasing inten-
sity of white light is shown
in Fig. 8 for three different
160
120
80
40
80
160
240
320
Fig. 8.
"cells," which are metallic
grids properly coated with selenium. Intensity of illumi-
nation is expressed in luces (sing, lux), the lux being the
intensity of light at one meter's distance from a standard
candle. The resistance R of a cell under illumination /
can be conveniently expressed as
where c is a constant depending upon the selenium cell,
and n is an exponent whose value depends upon the dura-
tion of exposure and wave-length of light, and lies between
0.25 and i.o. The resistance change in selenium with light
variation is not instantaneous, but most of this change
i76
TELEGRAPH ENGINEERING
occurs during the first few instants, as indicated in Fig. 9,
which represents a three minutes exposure of cell B to
light of ico luces intensity, with subsequent recovery.
Dr. Korn has perfected telephotographic apparatus
which is in successful practical operation over several long
distance lines.
The complete apparatus for a station consists of a trans-
mitter and a receiver mounted together, each having a
long tube through which light from the lamps at one end,
passes to the rotating cylinders at the other. The princi-
pal details of the improved Korn transmitter and receiver
are shown in Figs. 10 and 1 1 respectively.
In the transmitter the Nernst lamp L sends out, through
lens A, a beam of light which is received upon the dia-
phragm g, after passing through lens G. The diaphragm
serves to concentrate the light to a point upon the glass
cylinder, around which is placed the photograph in the
shape of a positive film, the cylinder being mounted upon
the rotating shaft V. The beam of light passes through
the photographic film and is reflected upward within the
MISCELLANEOUS TELEGRAPHS
177
cylinder by the prism P and impinges upon the selenium
cell Si. The cylinder T, in addition to its rotary motion,
has an axial movement, so that all parts of the photo-
TRAN8MITTER
Fig. 10.
graph successively pass the point of light. As the cylinder
revolves, the illumination on the selenium cell will change,
thus sending a current of variable intensity to the receiver.
Fig. xz.
The receiver, Fig. n, is provided with a Nernst lamp Lf
which sends out a beam of light through the galvanometer
shutter b. This galvanometer, called a light-relay, con-
sists of an electromagnet d, provided with long perforated
178 TELEGRAPH ENGINEERING
pole-pieces pp, between which is placed the moving ele-
ment M. This consists of a double fine platinum wire
under tension, carrying a small sheet of aluminium foil b.
When a current flows through the wire, the electromagnet
being separately excited, the aluminium sheet is deflected
to one side and the amount of the deflection is propor-
tional to the current flowing. Thus, the intensity of the
beam of light which passes through the light-relay to the
cylinder R depends upon the current in the line. The
cylinder is mounted on a revolving shaft W, which has
also an axial movement, so that all parts of the cylinder
surface are brought successively under the point of light
emerging from the diaphragm. Thus, the variable current
coming from the transmitter causes a corresponding varia-
tion in the amount of light incident upon the receiving
cylinder, and an exact reproduction of the original photo-
graph may be obtained upon developing the received
image.
It is necessary for the proper operation of this apparatus
that the resistance change of the selenium cell be rapid
so that it will respond almost immediately to the variations
of light incident upon it. Such quick action is secured by
the use of a second selenium cell connected with the cell of
the transmitter, so that the resultant conductivity-time
curve of both rises quickly at the start and falls quickly
upon darkening the cell. As the receiver of a station is
not in use when sending, the light-relay of the receiver can
be employed in this connection, as shown in Fig. n. In
the bottom of the vertical mirror-lined chamber is the cell
Sz, which receives illumination from the lamp L' by means
of the reflecting prism P' . To secure a diffused light upon
this selenium cell, a series of glass cylindrical rods is inter-
MISCELLANEOUS TELEGRAPHS
179
posed at r. When the transmitter cell 6*1, Fig. 10, is illu-
minated, a current flows through the home light-relay
deflecting its shield, and thus gives the compensating cell
62 a corresponding illumination. The two cells are con-
nected in opposition, and the resulting current variation
s,
s,
LINE TO
LIGHT RELAY
OF DISTANT
RECEIVER
Fig. 12.
corresponds very closely with the variations of light,
owing to the fact that the two cells are selected to give dif-
ferent resistance changes under the same illumination.
The method of connecting the selenium cells is shown in
Fig. 12. The shape of the differential current which flows
between x and y is shown in Fig. 13, in which the con-
ductivity-time curve of each cell is indicated, one above
and the other below the datum line. As cell 52 is not
illuminated as soon as cell Si, its curve will begin shortly
l8o TELEGRAPH ENGINEERING
after that of the latter. As will be observed, the time of rise
and decay of current are practically identical, and the rate
of change is exceedingly rapid. The use of the compensat-
ing cell results in a considerable gain in photographic detail.
As the normal swing of the light-relay is from o.oi to
0.02 second, a rapid variation of current is permissible,
and the cylinder at the transmitting end can, therefore,
be rotated very rapidly. At present a photograph 9 inches
by 6 inches can be reproduced in less than 12 minutes, the
size of the received image being 4 inches by 2^ inches.
It is obvious that the cylinder at the transmitting station
and that at the receiving station must revolve at the same
speed, otherwise, no image reproduction could be obtained.
The speed of the receiving cylinder is adjusted to be
about one per cent faster than that of the transmitter.
The former is brought to a stop at the end of each revolu-
tion, and when the transmitter cylinder has finished its
revolution, a current impulse of the reverse direction is
sent to the receiving station actuating a relay there and
releasing the cylinder. Both cylinders then start up
together upon the next revolution.
A modification of the light-relay has lately been intro-
duced by Korn, called a step-relay, for controlling weak
high-frequency currents which serve to initiate high-tension
arcs. The currents so started are either sent directly over
the line to affect the receiver, or are used to furnish a per-
forated tape corresponding to the picture for affecting its
transmission at suitable speed. He has also devised an-
other transmitting method which dispenses with selenium
cells and thereby permits of larger line currents. This
method employs a photographically-prepared copper sheet
upon which are formed parallel striations of gelatin in
MISCELLANEOUS TELEGRAPHS
181
greater or less widths depending upon the darkness or
brightness of the various parts of the image to be trans-
mitted. This sheet is placed around a metal cylinder, and
as it revolves and also advances axially, a metal stylus trav-
erses the striations and causes contact to be broken for long
or short intervals in accordance with the width of the stria-
tions. The resulting intermittent currents pass through the
light-relay at the receiver and reproduce the image as before.
Marino has developed a system of color telephotography
which utilizes the sustained high-frequency electrical
oscillations derived from three direct-current arcs that are
shunted by condensers and inductances. These Thomson
arcs are arranged to produce oscillations of different fre-
quencies whose amplitudes are controlled by seven sele-
nium cells, every cell being most sensitive to one of the
seven primary colors. At the receiver these oscillations
control other arcs connected in circuits that are tuned to
the respective frequencies. The manner in which color
variations are transmitted in this system is indicated in
Fig. 14.
A long opaque diaphragm d, with properly placed aper-
tures of about i mm. diameter, passes uniformly in front
of an illuminated plate P bearing the picture to be trans-
mitted. These apertures are spaced transversely about
182 TELEGRAPH ENGINEERING
i mm. apart and longitudinally a distance equal to the
width of the plate, therefore light from every point of the
picture, after passing through a lens, falls successively
on the prism p. Each ray is dispersed by the prism, and
impinges upon the set of selenium cells S located so that
each cell receives light of one color, thereby actuating one
or more of the cells according to its constituent colors.
These cells are in three groups, each group with a battery
being bridged across the inductance (L, U or Z/') connected
in the supply circuit of the arc (a, a' or a"\ Variations
in the resistances of the selenium cells modulate the voltages
across the arcs and consequently affect the amplitudes of
the oscillations that are developed in the three condensive
circuits. These oscillations induce corresponding currents
in the line coils /, and are superimposed upon each other
to form the line current.
At the receiver the three component oscillations of the
line current are sorted out by means of the tuned oscillatory
circuits c, c' and c", and are rectified by audion or crystal
detectors D, D' and D" . The detectors vary the potential
difference of the three receiving arcs A, A' and A", and
consequently vary their brilliancy. In front of the arcs
are colored screens — s, a mixture of red and orange; s', a
mixture of yellow, green and blue; and s", a mixture of
indigo and violet — the emitted rays from all three arcs
being recombined and focussed upon a particular point of
the receiving plate R. Each resulting beam is therefore
rendered identical in color variations and intensity with
the original.
6. Television. — The property of selenium of varying
its resistance under the influence of light is also utilized
MISCELLANEOUS TELEGRAPHS 183
in experiments to attain a practical method of seeing at
a great distance by means of a connecting wire or wires.
Numerous such systems of television have been patented;
indeed elementary geometrical patterns have been success-
fully transmitted by Ruhmer between Brussels and Liege,
a distance of 72 miles, his transmitter consisting of 25 sele-
nium cells, each about 5 centimeters square.
Rignoux and Fournier have developed a system of
television, involving the employment of a multitude of
cells but employing only two connecting wires between
the stations. The currents from the various circuits are
taken successively by a rapidly rotating collector arm at
<k
^—^ — •*-£&- ->
LINE
WIRES
©
Fig. 15.
the transmitting station and supplied to the two-line wires.
The principle of the receiving device is based upon the
Faraday effect. The arrangement of the apparatus at
this station is shown in Fig. 15, in which L is a source of
light whose rays are polarized by the prism P and then
traverse . a tube T containing water, or better, carbon
bisulphide. A second Nicol prism P' is so rotated about
the direction of the light ray as an axis that the polarized
light cannot pass through it, and is then fixed in this
position. If a current flows through the electromagnet E
which surrounds the tube filled with liquid, the angle of
polarization changes and the prism P' no longer prevents
1 84 TELEGRAPH ENGINEERING
the light from passing through it. Thus, a beam of light
of varying intensity, corresponding to the illumination of
the particular selenium cell connected at that instant
with the line wires, falls upon the cylinder C, which rotates
in synchronism with the collector arm at the transmitting
station. This cylinder carries a number of small mirrors
m, which are so arranged that the light reflected from each
falls on a particular part of the screen S. On this screen
is therefore formed a picture, consisting of patches of
various degrees of brightness, of the object exposed at the
transmitter. The different parts of the picture, although
projected successively, will appear simultaneous, if the
entire picture is produced within a fraction of a second.
An indefinite repetition of this process yields a persistent
picture.
In Low's system of television the received currents mag-
netically control the positions of slots which admit light
to squares on the receiving screen that are located in the
same positions as the corresponding selenium cells at the
transmitter.
7. Military Induction Telegraphs. — In times of war
crudely-constructed pole lines and often short lines of bare
wire laid on the ground are utilized in the telegraphic trans-
mission of military information. Because of the low insu-
lation resistance of such lines, and because of the difficulty
of transporting means for the production of electricity, the
ordinary simplex signalling methods are not used, but, in-
stead, signalling by means of induced currents at high
voltage is employed. Such induction telegraphy permits
of signalling over distances of about 300 miles with only
3 to 6 dry cells.
MISCELLANEOUS TELEGRAPHS 185
The circuit of an induction telegraph includes the sec-
ondary winding of an induction coil at each station, the
primary winding being joined to a local circuit with a key
and battery. A current pulse is induced in the secondary
coil whenever the primary circuit is made or broken, but
no steady current is induced either when the key is kept
open or when kept closed. Since the direction of the sec-
ondary momentary current when the primary circuit is
broken is opposite to that when the primary circuit is
closed, it will be observed that a polarized receiving in-
strument is essential for the operativeness of this type of
telegraph circuit. Using step-up induction coils, high line
voltages may be availed of with few cells, thereby render-
ing induction telegraphs admirably suited for military pur-
poses even for fairly long lines.
The United States army induction telegraph field kit
includes a polarized receiving instrument, a key, several
dry cells and an induction coil, mounted in a portable
box. The induction coil has 100 times as many turns on
the secondary as on the primary winding, and takes about
12 watts at 4 volts. The circuit of a simplex induction
telegraph is shown in Fig. 16, in which P, Pf are polarized
relays, 5, Sf are sounders, B, B' are local batteries, K, K'
are keys, and p and s are respectively the primary and sec-
ondary windings of the induction coils /, /'. Upon de-
pressing the key K, an induced current of momentary
duration will be produced in the secondary winding of in-
duction coil /, flowing, say, upward, which current in flow-
ing through the two polarized relays to ground G' at the
distant station causes their armatures to touch the sounder
contacts. Both sounders will operate as the result of the
completion of their local circuits. Although the current
i86
TELEGRAPH ENGINEERING
pulse over the line is of very short duration, the polarized
relay armatures will remain against their sounder contacts
until the key is released. The subsequent opening of key
K produces a reverse current pulse through the line and
the relay windings, which causes the relay armatures to
open their respective sounder circuits. Signalling in the
opposite direction may be accomplished similarly.
To reduce further the impedimenta during warfare, the
polarized relay and local sounder are replaced by a polar-
ized sounder in induction telegraph sets devised by G. R.
Fig. 16.
Guild for use by the United States Signal Corps. Such
sounders resemble those of the usual type except in that
the soft-iron yokes joining the lower ends of the magnet
cores are replaced by permanent horseshoe magnets,
thereby giving a definite polarity to the poles of the electro-
magnet cores. A current through the coils will cause the
armature to be more or less strongly attracted according
as the electromagnetization assists or opposes that of the
permanent magnet. The retractile spring of the polarized
sounder is adjusted so that reversal of current direction
will effect its proper operation with currents as small as
10 milliamperes. Inasmuch as these instruments may be dif-
MISCELLANEOUS TELEGRAPHS
I87
f erentially wound (shown at PS in Fig. 1 7) , they may be used
advantageously for duplex induction telegraphic signalling.
Induction telegraph repeaters are used for repeating into
simplex closed- or open-circuit lines or into another induc-
tion telegraph circuit. Fig. 17 shows the arrangement for
repeating from an induction telegraph to a closed-circuit
simplex line, and vice versa, using polarized and polarized-
repeating sounders. The position of the armatures corre-
sponds to the normal condition for no transmission of mes-
sages. The arrows a and a' indicate the direction of the
induced currents in the line circuit on the closing of the
local circuits including batteries B and bf respectively.
The armature of the polarized repeating sounder PR2 is
biased to remain on its lower contact except when a current
flows through either of its coils. The letters n and s indi-
cate the polarity of the polarized sounders which is occa-
sioned by their permanent magnets. The opening of the
Fig. 17.
armature contact of the other repeating sounder PRi re-
moves the short-circuit from the left-hand coil of repeater
PR2, thereby energizing this coil, but at the same time the
introduction of its resistance reduces the current strength
in relay R to a value insufficient to keep its armature at-
tracted. The repeating of signals in either direction may
readily be traced (see problem 5).
l88 TELEGRAPH ENGINEERING
PROBLEMS
1. Decipher the tape shown below, which represents part of a
message transmitted by the Murray multiplex telegraph.
2. If operators can perforate transmitting tapes at the rate of
only 4 letters per second, how many operators would be required to
keep the transmitters at one station of the Murray quadruple-duplex
and of the Pollak-Virag writing telegraphs supplied if their trans-
mitters are operated at 40 and 700 words (each of 5 letters) per
minute respectively?
O O OO CO O O O OOOO OOOO OO
O O O OO OO OO OO
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
OOO O O OOOOO OO O OOOO OOO O O
OOO OOOOO O OOO
O OO OO O O OOO
3. The rheostats of the telautograph are not of the same width
from one end to the other, but have a width that is calculated to
compensate for the variation of the line resistance occasioned by the
inclusion of more or less of the resistance of these rheostats. Formu-
late an equation giving the resistance from one end to any point
on the rheostat so that the line current will be strictly proportional
to the distance of that point from the reference end.
4. The resistances of a selenium cell are 30,000 and 20,000 ohms
under illuminations of 20 and 100 luces intensity. Calculate its
resistance under an illumination of i lux.
5. With the aid of Fig. 17 describe the operation of the instru-
ments for repeating from a closed-circuit to an induction telegraph
line, and vice versa.
CHAPTER VII
MUNICIPAL TELEGRAPHS
i . Fire-alarm Telegraphy. — Signalling systems are in-
stalled in cities and towns to enable the inhabitants to
notify the fire-fighting force promptly of the discovery and
location of a fire. The facts that a fire in its incipiency is
more readily subdued than after it has made considerable
headway, and that the loss of human life and property is
always imminent, render it imperative that the fire-fighting
force reach the scene of the fire and begin its activities in
the shortest possible time. Fire-alarm telegraph systems
should have street signalling stations or fire-alarm signal
boxes at convenient points throughout the territory served
that are capable of being operated by any one when an
occasion demands. In villages and towns where the
fire-fighting force is composed of volunteers, the operation
of a signal box sounds a public alarm which indicates the
location of the signal box operated, and the volunteers
hasten to their quarters for the fire apparatus and then
proceed therewith to the fire. In cities maintaining paid
fire departments, the operation of a signal box sends a
distinctive signal to a central station which is equipped
with facilities for disseminating this information to the
firemen stationed at the apparatus houses of the fire depart-
ment.
The time interval between the discovery of a fire by
an individual and the arrival of the firemen at a fire in a
189
IQO TELEGRAPH ENGINEERING
city may be divided into three periods. First, the time
required for the individual to reach the nearest street
signal box after his discovery of fire; second, the time
taken between the sending of the signal, usually called
" turning in the alarm " or " pulling the box," and the
repeating of this signal in the apparatus houses of the fire
department; and, third, the time elapsing from the recep-
tion of the signal at apparatus houses to the arrival at
the scene of the fire of those fire-fighting companies that
are expected to " turn out " or answer the particular
signal.
Of these periods, the first depends largely upon the prox-
imity of the nearest fire-alarm box; thus, in the Borough
of Manhattan of New York City the distribution of boxes
is such that the nearest box is anywhere from 100 to upward
of 800 feet from a building, depending to a certain extent
upon the nature of the businesses or residences of the
various districts. This time period is frequently reduced
by the use of supplementary or auxiliary boxes installed
in buildings and leased from private concerns, which are
designed when operated to trip automatically the nearest
street fire-alarm box, and also by the use of thermostatic
devices located in buildings and operated by the fire itself
to send signals to the office of the company giving the
service, from which point the alarm is telegraphically
transmitted to the central station. The second time period
comes within the province of municipal fire-alarm tele-
graphs, and depends upon the signalling speed of the fire-
alarm boxes, of central station repeating, and of the
signal-receiving devices at apparatus houses. Alarm trans-
mission in New York City requires, on the average, some-
what less than 50 seconds from the pulling of the box to the
MUNICIPAL TELEGRAPHS IQI
last stroke of the gong at apparatus houses. The third
time period depends upon the rapidity with which the
apparatus is turned out, its speed in advancing to the
fire and the distance it must traverse. The increasing
use of motor-propelled fire-fighting apparatus within recent
years has materially diminished the duration of this time
period.
It is apparent that the fire-alarm boxes of a municipal
fire-alarm telegraph system might be individually con-
nected to the central station by electric circuits, each ter-
minating in an annunciator drop which bears the number
of the box associated with it, and that the signalling de-
vices at the apparatus houses might also be connected to
the central station by separate circuits, thereby enabling
operators to signal particular fire companies that a fire
exists within their districts. The great cost of a large
number of such diverging circuits located on poles or in
underground conduits renders such a system prohibitive.
Instead, in fire-alarm systems, a number of signal boxes
are connected in series on one circuit, and similarly the
signalling devices at a number of apparatus houses are
connected to one circuit; in small municipalities both
types of devices are frequently joined to a single circuit.
In Manhattan there are approximately 40 box circuits
averaging 26 fire-signal boxes per circuit. While such
series-circuit systems introduce more elaborate fire-alarm
boxes, in that each must send a distinctive signal and should
be immune from interference by the simultaneous . actua-
tion of other boxes on the same circuit, the reduction of
the cost of line material and its installation renders such
systems far more economical than the individual-circuit
arrangement mentioned above.
IQ2 TELEGRAPH ENGINEERING
2. Fire-alarm Signal Boxes. — The fire-alarm boxes that
are distributed throughout a city are usually mounted
on posts located near the curb of sidewalks so
as to be conspicuous. One style of fire-alarm
post, with a glass globe for illumination at
night, is shown in Fig. i.
The turning in of an alarm necessitates
the opening of key boxes in order to expose the
"hook," the pulling of which starts the
mechanism for transmitting the alarm. Some
key boxes have trap locks on their outer
doors, and when a key is inserted it cannot
be withdrawn until released by a fire depart-
ment officer with his " release " key. Keys
to such boxes are customarily distributed to
responsible citizens of a town, each key being
numbered for identification. Other boxes have
keys permanently trapped in the locks and
covered with key guards consisting of an iron
casing with a glass cover. Breaking the glass
leaves the key accessible. With keyless boxes,
a handle protrudes from the front of the box,
as shown in Fig. i. In one type of keyless
box, turning the handle opens the door to
expose the hook for pulling, and also sounds a
local alarm on a large gong within the box
for attracting the attention of persons in the
vicinity, thereby discouraging the sending of
false alarms. With the other type of keyless box, the
turning of the handle sounds the local alarm as well as
operates the signalling mechanism without opening the box.
Fire-alarm boxes are generally designed to operate on
MUNICIPAL TELEGRAPHS IQ3
normally-closed circuits. Each signal box is equipped
with a spring-driven mechanism which, when set in motion
by pulling the hook, revolves a signal wheel that causes
the circuit to be opened a definite number of times with
definite time intervals between, thereby transmitting
to the central station a code signal indicating the number
and thus the location of the particular box operated.
Two such signal wheels located in different fire-alarm boxes
are shown in Fig. 2 at A and B. Each wheel has groups
of projections, one group representing units, another tens,
and so on, and when it revolves the projections suc-
Central Station
Signal Boxes
Fig. 2.
cessively touch a contact spring, thereby closing the circuit
which extends to the receiving relay R situated at the
central station. The normal position of the two signal
wheels is indicated in the figure, one wheel having 3 and 5
projections and the other 2 and 4 projections in its two
groups. When wheel A is set in motion, the circuit is
opened 3 times and after a pause is opened 5 times, which
action causes the bell at the central station to strike 3
times and then 5 times, a signal interpreted as 35. The
mechanism is arranged to rotate the signal wheel a certain
number of times, usually four, with one depression of the
hook, consequently transmitting 4 rounds of number 35
in a complete signal. The signal boxes are designed so
IQ4 TELEGRAPH ENGINEERING
that the mechanism when once started cannot be interfered
with by subsequent pulling of the hook, thus guarding
against mutilation of the transmitted signals by excited
persons who do not heed the usual directions appearing
on the inner cover of signal boxes to " pull the hook down
once and let go."
With signal boxes connected in series and having the
parts indicated in Fig. 2, it is possible that two boxes on
the same circuit might be pulled at about the same time,
and as both signal wheels would then revolve, the signal
transmitted by each would be mutilated by that sent by
the other, and both would be lost. Such interference
might arise, not only because of the breaking out of two
fires at almost the same time in districts served by one
circuit, but also because of two individuals seeing the same
fire from different points and turning in alarms from differ-
ent signal boxes. The latter condition is often minimized
by interlacing the signal-box circuits, so that alternate
boxes in both directions are joined to different circuits.
Both of these causes of signal interference, however, may
be eliminated by the use of signal boxes arranged so that
a box cannot transmit its signal while an alarm, originating
at another box, is being transmitted over the same circuit.
Such non-interfering signal boxes first came into use in
1870 through the invention of Game well, and have since
been perfected by Crane, Gardiner, Ruddick and others.
Ruddick, in 1889, introduced features in signal boxes
whereby, if two boxes were pulled simultaneously, neither
would interfere with the other, but both would transmit
their signals properly, one after the other, or successively.
Thus, if a box is pulled while another is transmitting,
the mechanism of the -former would operate without
MUNICIPAL TELEGRAPHS 1 95
affecting the circuit until the line is again free, and then
this box would automatically assume control of the circuit
and send its signal.
Fire-alarm signal boxes may, therefore, be grouped into
three types in accordance with the foregoing description,
Fig. 3.
namely: plain boxes, which are devoid of the non-inter-
fering and successive features, non-interfering boxes, which
have not the successive feature, and successive boxes, which
are also non-interfering. The successive non-interfering
type of fire-alarm box represents the highest development
of signalling devices on series fire-alarm circuits.
Fig. 3 shows the interior of the positive non-interfering
196 TELEGRAPH ENGINEERING
successive fire-alarm signal box made by the Gamewell
Fire Alarm Telegraph Company. These boxes are pro-
vided with a mechanism capable of giving 16 rounds
at one operation of the starting device, a single-stroke
bell for striking at the box the signal that is being trans-
mitted, a signal key for transmitting code signals, a test
switch for keeping the circuit closed while electrical or
mechanical tests are being made on the box, a protector
against abnormal currents, a lightning arrester and a
plug switch for including either the signal key or the signal
wheel in the circuit or for grounding the circuit at the box
during tests. The outer dimensions of this signal box are
18 by 13 by 6 inches.
The scheme of the mechanism and connections of a
Gamewell successive signal box is indicated in Fig. 4.
The line wires terminate at the outer plates of the plug
switch, the inner plate being grounded. The electrical
devices in the box are kept normally short-circuited by
the contacts C, which are kept closed by the door of the
signal box, and by the contacts C", which are kept closed
except when the box is actuated. When contacts C' or
C" are open, the line circuit includes the rear key contact,
the bell magnet, the "succession" magnet, and the signal
contacts C. The opening and closing of the signal con-
tacts is under the control of signal lever L, pivoted at h,
which carries a small roller R for riding over the teeth of
signal wheel W. The movements of lever L are limited
by the actions of locking lever B, pivoted at e, by catch T,
pivoted at a, and by controlling lever £, pivoted at d.
Signal wheel W and gear wheel G are mounted on the same
shaft and are driven by the main driving wheel D under
the influence of the spiral spring S, the signal wheel mak-
MUNICIPAL TELEGRAPHS
IQ7
ing 8 revolutions during one revolution of the driving wheel,
at a speed governed by an escapement and fan, not shown.
When the mechanism is at rest, the driving wheel is
locked by pawl P, which is attached to lever B, because
Fig. 4.
the pawl rests in slot p or p' of the upwardly-extending
flange of driving wheel D. When the hook H is pulled, the
locking lever B is raised, carrying with it insulating block
/, thereby opening contacts C". At the same time the
pawl is raised out of slot p and the mechanism is set in
1 98 TELEGRAPH ENGINEERING
motion, the pawl then slides over the periphery of the
flange on D. Signal lever L does not fall immediately,
because it is momentarily held by pin b or b' carried on the
driving wheel. If during this short test interval the line
circuit is uninterrupted, a current will flow through the
succession magnet and its armature A will be attracted,
consequently keeping locking pin / to the left and clear of
signal lever L. As pin b passes the downwardly-projecting
hook of the signal lever, this lever will fall and the roller
R will engage the teeth of the signal wheel, since catch T is
pushed to the left when the first tooth on the signal wheel
reaches roller 7?, and is kept in this position until the com-
plete signal is transmitted by means of the notched wheel
beneath W and, for a time during each revolution, by lever
L itself. While the signal lever is in its lower position,
pin / banks against its left end in order to keep lever E
clear of the signal lever during the intervals when the line
circuit is opened at C and the succession magnet is de-
prived of current. After the signal wheel has revolved
four times slot p' will be in position for pawl P to fall into
it, which action arrests the motion of the mechanism.
The engagement of pin b' with the right-hand end of the
signal lever raises roller R from the signal wheel and causes
the contacts C to be closed.
If, when the signal box is pulled, another is transmitting
its signal over the same line, the succession magnet will be
deprived of current at some instant during the brief period
that the signal lever is held up by pin b or bf, and conse-
quently, spring ^ is enabled to pull lever E away from the
magnet. Locking pin I then prevents the signal lever
from bearing on W, and causes contacts C to be kept
closed. As the normal line current, when traversing the
MUNICIPAL TELEGRAPHS 199
succession magnet, is not sufficiently strong to enable this
magnet to attract its armature when retracted to the full
extent, contacts C will be kept closed. Restoring pin r
bears against the shoe at the lower end of lever E once in
each revolution of the signal wheel, and moves this lever
clockwise so as to bring armature A close to the magnet.
This movement, which carries pin / clear of the signal lever,
does not cause this lever to drop, because catch T has
moved to the right during this interval, since its lip has been
pressed into the recess of the notched wheel beneath the
signal wheel W. After 4 revolutions of the signal wheel
the pawl P will drop into the slot of the flange on Z>, but
only partially, because the downward movement of lever
B is checked by pin q striking the shoulder m. In conse-
quence, the pawl is forced out of this slot, and the mecha-
nism continues in operation. At the next instant lever E
is moved by the restoring pin r so as to bring armature A
close to the magnet. If, while the armature is in this
position, it is kept attracted by the magnet, the signal
lever will fall after engaging pin b or b', and roller R will
ride on the signal wheel. The box now has control of the
circuit, and will transmit the box number. But if, while
the armature was close to the magnet, it was not kept at-
tracted, lever E would be pulled back by spring s, and the
signal key would be kept up by the locking pin /. Thus,
the box " looks in" on the circuit every little while, and
if it finds the circuit idle it assumes control of the circuit.
Should the circuit still be open after the signal wheel has
revolved 16 or 20 times, the mechanism is automatically
stopped by a ratchet-lever (not shown) and the box number
will not be transmitted.
The appearance of the non-interfering successive signal
2OO
TELEGRAPH ENGINEERING
box made by the Star Electric Company is shown in Fig: 5.
This box is equipped with a mechanism capable of repeat-
ing its signal number forty times with one winding of the
spring, a single-stroke bell, a signal key, a test switch for
testing the operation of the mechanism by the response
of the bell without sending any signals to the receiving
devices on the box circuit, a protector against abnormal
currents, a lightning arrester and a grounding switch.
Fire-alarm boxes that are wound by the act of pulling
the starting lever, termed sector boxes, are also used, the
mechanisms being driven either by springs or weights.
3. Public Alarms. — In villages or towns having volun-
teer fire brigades, the volunteers are called by the sounding
of a public alarm which is operated by electromechani-
cal devices connected in the same circuit as the signal
boxes. Fig. 6 shows a Game well electromechanical whistle-
MUNICIPAL TELEGRAPHS
201
4
Fig. 6.
Fig. 7.
202 TELEGRAPH ENGINEERING
blowing machine with a two-bell steam gong. This type
of public alarm gives satisfactory results where a steam
pressure of 80 pounds per square inch is maintained.
The weight-driven mechanism opens the whistle valve
simultaneously with the circuit openings, and returns to
its normal position every time the circuit is closed, thus
rendering the signal blasts sharp, and distinct. Com-
pressed air is also used for blowing horn alarms, the oper-
ation being effected in the same way as with steam gongs.
Electric horns are now being introduced for public fire
alarms.
Bells are frequently used for sounding public alarms in
cases of fire. A bell with its electrically-controlled strik-
ing mechanism is illustrated in Fig. 7. Bell-striking and
whistle-blowing machines may be wound up manually
or by automatic motor-driven machines called electrolifts.
4. Fire-alarm Central Stations. — The central stations
of fire-alarm telegraph systems comprise apparatus for
receiving, recording, and transmitting signals and fire
alarms, which devices may be designed for manual, semi-
automatic or automatic operation. Manually-operated
stations are frequently equipped also with facilities for
semi-automatic and automatic transmission of signals.
The gravity or storage battery for operating all the cir-
cuits of the system is located at the central office. The
size and character of fire central-station equipments for
cities and towns naturally depend upon local conditions
and upon the scope of the fire- signalling system. Typical
installations for central stations will now be considered.
At a manual central station, each signal-box circuit ter-
minates in a visual drop and a relay; the latter actuates
MUNICIPAL TELEGRAPHS 203
a bell and one pen of a multiple-pen register, Fig. 2. In-
coming alarms are received by one or more operators,
who are on duty at all times. Having heard the bell
signal and seen the record on the register tape, an operator
proceeds to transmit the alarm to the apparatus houses.
As the receiving instruments at these houses are usually
Fig. 8.
grouped on several circuits, it is necessary to transmit
the signal over all apparatus-house circuits simultaneously.
This is accomplished by fire-alarm transmitters, three
types of which are illustrated in Figs. 8, 9 and 10.
Fig. 8 represents a spring-driven detachable signal-
wheel transmitter with signal wheels that are cut to cor-
respond with those in all the fire-alarm boxes of the system.
These wheels are orderly arranged on pegs as shown, or,
204 TELEGRAPH ENGINEERING
if numerous, are placed in accessible drawers. Upon
receiving an alarm, the proper signal wheel is selected
and placed in position on the mechanism, and then the
handle is drawn to start the mechanism and transmit the
signal.
Fig. 9 shows a Gamewell one-dial four-number adjus-
Fig. 9.
table-speed weight-driven transmitter. The box number
to be transmitted is set on the dial at the front by moving
the four slotted disks relative to each other. The number
of rounds transmitted may be varied by drawing a lever
toward the right to the positions marked i, 2, 3 or 4.
This movement causes the multiple contacts at the rear
MUNICIPAL TELEGRAPHS 205
to be opened the proper number of times and at the correct
intervals, thereby transmitting the box number simul-
taneously over all the apparatus-house circuits.
The Star Electric Company's one-dial four-number
transmitter is illustrated in Fig. 10. Each digit is set by
moving a lever down to the desired number, and the num-
ber is then displayed near the top of the instrument.
Fig. 10.
These transmitters may be equipped with speed-changing
devices so that one or more rounds of signals may be
transmitted over one class of circuits at a certain speed
and then, by an automatic shifting of the mechanism, the
remaining rounds of the signals may be transmitted over
another class of circuits at a different speed.
Some circuits extending to the apparatus houses also
have a key and a relay at their central station ends, the
206
TELEGRAPH ENGINEERING
relay with a local bell enabling the reception of signals
originating at the apparatus houses.
Automatic central stations are used principally where a
fire-alarm system requires two or more circuits but is not
large enough to warrant the attendance of operators.
Automatic repeaters are used in such stations for repeating
signals that come in on any one circuit over all the other
circuits. These repeaters should possess non-interfering
features in order to avoid confusion of signals transmitted
by two or more boxes located on different circuits when
pulled at the same time. Such non-interfering repeaters
Fig. zi.
have been devised by Skelton, Kirnan, Cole and others.
Fig. ii shows an 8-circuit automatic repeater made by the
Gamewell Fire Alarm Telegraph Co.
The operation of a Gamewell repeater will be under-
stood by a consideration of Fig. 12, which shows the re-
peating arrangement and one box-circuit magnet with
auxiliary devices in the normal condition. The weight-
driven transmitting cylinder D is mounted eccentrically
MUNICIPAL TELEGRAPHS
207
on shaft S so as to move contact rollers R and R' against
or away from their respective contact springs in the proc-
ess of repeating alarms over box and gong circuits other
than that over which an alarm is being transmitted. As
Fig. 12.
many contacts may be provided as there are gong and
signal-box circuits in the fire-alarm telegraph system.
The transmitting cylinder makes one complete revolution
every time a box circuit is opened. Shafts E, F, G1 P and
Q extend to the right in front of other repeater magnets,
and carry levers before each magnet precisely as illustrated
for the one box-circuit magnet.
208 TELEGRAPH ENGINEERING
When the current through magnet M is interrupted,
armature A is drawn back by spring s, carrying lever B
back with it. This movement of B raises lever L and with-
draws pin p from the path of detent K, which is rigidly
attached to shaft S. As a result, cylinder D with its cams
C, Cf and C" is set in rotation. Gam C then acts upon
roller r to depress lever L, thereby restoring armature A
and resetting pin p to obstruct detent K at the end of its
revolution. Cam C' depresses lever T, which through shaft
F and spring b lowers locking lever / so as to engage and
hold armature A against the action of spring s while no
current traverses the electromagnet. Cam C" slowly lowers
the right-hand end of lever N, and as the opening o
reaches tip / of detent K' ', this tip is forced through the
opening by clockwork. Shaft G makes only a half revolu-
tion because tip t' ', when it reaches its upper position, is
held against the face / of lever N. After roller r' of lever
N reaches its highest position it is gradually lowered by
clockwork to its normal position, in the process of which
tip /' escapes through opening 0, thus permitting another
half revolution of shaft G. A series of latches #, one for
each repeater magnet, is mounted loosely on eccentrics on
shaft Gj so that the first half revolution of this shaft
lowers the latch, and the second half revolution restores
it. With those magnets whose armatures are kept at-
tracted because of the normal current traversing them, the
downward movements of latches H cause locking levers
I to. move down and hold the armatures, and also effect
the opening of contacts c by means of the pins pf. But
with the electromagnet of the box-circuit over which a
signal is being transmitted, the latch H was pushed back
by the outward movement of the armature so that its
MUNICIPAL TELEGRAPHS 2OQ
downward movement does not affect the corresponding
contacts c. This latch H is kept back by pin p" on H
engaging with latch H' during the further excursions of the
signalling armature. Every time the circuit is closed at
the signal box the armature is drawn up close to the cores
of the electromagnet, thereby releasing the locking lever
by the overbalancing effect of weight W. When signalling
ceases all devices are automatically restored to the normal
position. A break in any circuit will cause that circuit to
be automatically locked out by the locking lever until the
disabled circuit has been repaired. The circuit on which a
signal originates is indicated at the repeater by the drop /,
which is thrown back by the armature when the circuit is
first opened. All alarms transmitted by the repeater are
usually recorded on a register.
With systems arranged for semi-automatic operation,
incoming signals are received and recorded at the central
station, but after one round of a box number has been
signalled, the operator may cause the remaining rounds to
be transmitted directly to the apparatus houses of the fire
department.
The signal-box and apparatus-house circuits of a fire-
alarm telegraph system generally terminate at a switch-
board in the central station, upon which is located the
various devices associated with these circuits. Where
storage batteries are used for operating the circuits, a bat-
tery switchboard is installed for enabling the charging of
the cells in series, multiple, or series-multiple as may be
necessary, for switching from one battery to a reserve
battery, and for testing purposes. Such a switchboard
is shown in Fig. 10, located behind the fire-alarm
transmitter.
2IO
TELEGRAPH ENGINEERING
5- Signalling Devices at Apparatus Houses. — In fire-
alarm signalling systems having automatic central stations
or having manual stations employing a single method in
transmitting alarms, the sig-
nalling equipment at apparatus
houses comprises electrome-
chanical gongs and frequently
registers or visual alarm indica-
tors. The gongs have spring-
driven mechanisms and strike
one blow every time the circuit
is closed. The usual sizes of
gongs are 6, 8, 9, 10, 12, 15 and
1 8 inches in diameter. The
indicators are spring-driven
electromechanical devices for
displaying the box numbers in
large figures, being operated
only by the first round of
signals. Such indicators are
designed for showing either
three or four digits, each digit
being brought into view by a
wheel bearing the numbers
from i to 9 on its periphery.
The mechanism is of the step-
by-step type, and is manually
restored by the pulling of a
cord. Both gong and indicator may be combined into one
instrument as shown in Fig. 13, which depicts a 1 5-inch
electromechanical gong with a three-digit indicator.
Registers yield a record of received alarms either by
Fig. 13.
MUNICIPAL TELEGRAPHS 211
ink marks or perforations in paper tapes. Fig. 14 shows
a punching register, paper take-up reel and an automatic
time and date stamp which prints on the register tape the
exact time that alarms are received.
With systems having manual central stations and em-
ploying two different methods in transmitting alarms to
apparatus houses, two circuits enter each of these houses
from the central station, and these are called " gong cir-
Fig. 14.
cuits " and " joker circuits." The gong circuits terminate
at apparatus houses in electromechanical gongs and some-
times also in indicators, as described above. The joker
circuits terminate in single-stroke electric bells, or tappers,
having 5- or 6-inch gongs, and also frequently in registers.
With such systems one or more rounds of signals may be
transmitted at high speed over the joker circuits and then
the remaining rounds transmitted over the gong circuits
at the necessarily slower speed suitable for electromechan-
ical gongs, or vice versa.
Where routine telegraphic communication is desirable
between the central office and the apparatus houses, joker
circuits are also equipped with relays, -sounders and keys
at all stations. These circuits may be used for routine
instructions and messages when no alarms are being trans-
212
TELEGRAPH ENGINEERING
mitted, but as soon as alarm transmission commences,
telegraphic communication ceases. Such circuits, enabling
both telegraphic and alarm signalling, are called combina-
tion circuits. A scheme of connections of a signal equip-
ment at apparatus houses for use on gong and combination
circuits is represented in Fig. 15, the gong circuits being
normally open and the combination circuit normally
closed. Relay armature a, controlling the telegraphic
Gong Circuit
Sounder
Fig. 15-
apparatus, is attracted when the small normal currents
traverse the combination circuit, but armature b, con-
trolling the tapper, is attracted only when a larger current
is sent out on the line, which function is performed by
the central station transmitter in the process of trans-
mitting alarms.
6. Operation and Routine of a Fire-alarm Telegraph
System. — The operation of municipal fire departments
in receiving and responding to alarms is obviously different
in the various cities. A particular fire department, that
of Brooklyn, N. Y., which serves a population of 1,800,000
inhabitants and protects an area of 71 square miles, will
here be considered.
. MUNICIPAL TELEGRAPHS 213
There are 1800 fire-alarm boxes included in 40 circuits
which lead to the manual central station on Jay St., and
there are 4 combination and 7 gong circuits extending
from this central station to the 91 apparatus houses of the
department. Each box circuit terminates at the central
office in a relay, which controls one pen of a 3o-pen register
and a tapper. Each of these box circuits passes through
one or more apparatus houses for affording convenient
places for line testing. Two rounds of an alarm are trans-
mitted over the gong circuits by means of a four-dial
four-number transmitter, and then two rounds are trans-
mitted manually over the combination circuits by means
of a multiple key. A three-position telephone switch-
board at the central station is connected to the " Main "
exchange of the New York Telephone Company through
10 trunk lines, for receiving calls for fire-fighting apparatus
by telephone. Each apparatus house is joined to this
private branch telephone switchboard by a direct or a
party line.
An area of 4.8 square miles of Brooklyn is protected by
high-pressure service, supplied by two pumping stations.
Alarms of fire are received at these stations simultaneously
with the apparatus houses and a water pressure of 75
pounds per square inch is immediately applied to the water
mains. There are 215 telephone boxes connected directly
with the pumping stations for enabling fire department
officers to call for increased pressure or order the system
shut down.
The duties of fire companies and officers are largely
directed by an assignment book. Upon the pulling of a
box (or sending a first alarm) and the subsequent receipt
of the number of that box at the apparatus houses, certain
214 TELEGRAPH ENGINEERING
engine companies, hook and ladder companies, and chiefs
immediately respond to the alarm. Upon the receipt
of a second, third and fourth alarms from the same signal
box, other companies respond without other notification
than the receipt of the particular alarm, and further,
still other companies move from their own quarters into
those made vacant by companies responding to earlier
alarms. If more apparatus is needed than available on
the fourth alarm, special calls are made by the central
station operator. Such calls are also made in order to
supply a substitute for any company that for various
reasons may be prevented from answering an alarm sent
from a box to which that company is regularly assigned.
The operator must, therefore, be kept constantly informed
upon the preparedness of all companies and officers to
respond to immediate' call.
To illustrate the use of this method of answering alarms
upon signal, consider that box 93, located at Borough Hall,
be pulled. The location of this signal box and that of
the various fire companies in this section of Brooklyn are
indicated in Fig. 16 by small circles bearing the proper
numbers of the companies. Numbers between 30 and
50 represent battalion chiefs, numbers between 100 and 200
represent hook and ladder companies, numbers over 200
represent engine companies, numbers preceded by S rep-
resent fire insurance salvage corps, numbers 10 and n
represent deputy chiefs, C represents the chief of the depart-
ment, 6 represents a water tower, SI represents a search-
light engine and numbers preceded by FB represent fire
boats. The assignments for box 93 follow, the first line
gives the numbers of the companies and officers responding
to the first alarm from this box, the second line those for
MUNICIPAL TELEGRAPHS
215
2l6
TELEGRAPH ENGINEERING
the second alarm, etc., the sequence of the numbers of each
group being the order in which the companies are expected
to arrive at the signal box. These assignments are also
shown in Fig. 16 by the light dotted lines marked I, II,
III and IV which are drawn to include the locations of all
companies and officers that are assigned to answer the first
second, third and fourth alarms respectively sent from
box 93. The changes of company locations on the third
and fourth alarms are also indicated.
Station
Engine companies
Hook
and
ladder
com-
panies
Dep-
uty
chief
Bat-
talion
chiefs
Water
tower
Companies to change
locations
Engine
companies
H. &L.
Go's.
93
Joralemon
and Court
Streets
205, 224, 207
226, 204, 206, 256 SI
203, 208, 210
219, 279, 202
118, no
103
105
10
31,. 33
32
34
119 to 118
6
( 209 to 226 )
( 251 to 206 J
(235 to 219 )
(239 to 204 )
Alarms beyond the first are sent to the central station
by officers of the fire department or their aids by trans-
mitting, with the telegraph key at any signal box near the
fire, the numbers 2, 2 and the box number for the second
alarm, or 3, 3 and the box number for the third alarm, etc.
Any engine company may be ordered by the central-station
operator to respond to a box to which it is not regularly
assigned by transmitting over the apparatus-house circuits
the number 5, the box number and then the company
number in close succession. Such special calls may also
be made for hook and ladder companies by transmitting
the number 7, the box number and then the company
number. On their return from a fire, engine companies
and hook and ladder companies signify their preparedness
MUNICIPAL TELEGRAPHS
217
to answer another call by transmitting respectively to the
central office over the combination circuits the numbers
4, 4, 4 and the company number, and 4, 4, 4, 7 and the com-
pany number, the operator answering this signal by the
numbers 2, 3. Should a company be called out on a " still
alarm," one of its firemen informs the central operator
to this effect by transmitting 2, 2, 2, the company number
and then the number of the box nearest the scene of the fire.
In all five boroughs of New York City (280 square
miles) there are 13 deputy chiefs, 43 battalion chiefs, 181
engine companies, 93 hook and ladder companies, 10 fire-
boats and 8 hose companies; the personnel totals 6740
individuals. The number of fires and false alarms and the
resulting loss to buildings and contents in this city during
the first nine months of 1913 are given below; the average
loss per fire during this period is found to be $542.
1913
Number of
fires
Number of
false alarms
Loss in dollars
Total (Jan.-Sept.)
9660
I2Q3
"?,2it;,o87
Average per day
7C
c
19,103
7. Police Patrol Telegraphs. — Signalling systems are
installed in cities for enabling policemen to transmit code
signals for summoning assistance, calling ambulances or
patrol wagons, and informing headquarters that they are
on duty, and to communicate with their superior officers
by telephone. Such police-patrol signal systems have
many features in common with fire-alarm signal systems,
already described. Means for transmitting signals from
headquarters to convenient points in the city, for calling
any or all patrolmen to their nearest street stations for
2l8 TELEGRAPH ENGINEERING
the purpose of receiving instructions, may be incorporated
in police signal systems. In some cities police signal
systems utilize telephone instruments exclusively.
Police signal boxes resemble fire-alarm boxes in that
they include a mechanism for transmitting the box number
by means of a signal wheel, a telegraph key and a single-
stroke bell. In addition, police signal boxes have a tele-
phone receiver, a telephone transmitter and an induction
Fig. 17.
coil, properly connected together to form a telephone set.
Fig. 17 represents a Gamewell y-call police signal box
with its outer door open, and Fig. 18 shows the same box
with both outer and inner doors open to exhibit the various
parts.
When a policeman has occasion to send any one of the
seven code signals, he moves a pointer to the proper posi-
tion as indicated by the plate on the inner cover (Fig. 17)
MUNICIPAL TELEGRAPHS
219
and then pulls the crank located just below the pointer.
Thus, if the pointer of box 34 is placed in the second
position corresponding to " ambulance," the mechanism
would transmit 2 dots at slow speed followed after a short
pause by the box number 3, 4 at faster speed. If a patrol-
man transmits an " on duty " code signal and the cen-
tral station attendant wishes to converse with him, the
Fig. 18.
attendant depresses a key a prearranged number of times
immediately after receiving the code signal, which act
causes the bell at the signal box to sound accordingly,
thereby notifying the patrolman to use the telephone.
Numbered keys may be given to responsible citizens
with which they can operate the police signal boxes when
in need of police assistance without opening the outer door,
such keys when used being trapped in the locks for iden-
tifying the possessors.
Incoming signals are usually received at the precinct
220 TELEGRAPH ENGINEERING
headquarters by a tapper and a register. Calls for patrol
wagons are transmitted by the operator to the police
stables and garages, the number of the signal box being
Fig. 19.
sent out by detachable signal-wheel or special dial trans-
mitters. The equipment at the stables and garages usually
includes an electromechanical gong and indicator as illus-
MUNICIPAL TELEGRAPHS 221
trated in Fig. 13, a register with take-up reel as indicated
in Fig. 14, a tapper and a telephone set. Upon the receipt
of a call for a patrol wagon at these places, a wagon is
dispatched from the stable nearest the signal box from
which the call originated.
Fig. 19 shows the Star Electric Company's unit- type
central-office police desk with the necessary devices for
receiving code or telephone calls over box circuits, for
transmitting calls for patrol wagons and ambulances,
for calling one or more patrolmen on duty by flashlight
or bell signals to proceed to their nearest signal boxes
for receiving orders, for controlling and charging the
storage battery which supplies current to the signal cir-
cuits, and for testing the continuity and insulation of
the circuits. This cabinet is arranged for 3 box circuits,
2 flashlight circuits, i chief's circuit, i stable circuit and
i test circuit.
8. Statistics of Police and Fire Signalling Systems. -
The latest published census statistics of fire-alarm and
police-patrol telegraph systems in the United States are
for the year 1907. The following table gives data selected
from this census on signalling systems used for fire alarms
exclusively, those used jointly for fire alarm and police
signal service, and those used for police patrol signalling
exclusively, the various systems being grouped according
to population of the cities wherein installed.
Of the 38 cities with a population in excess of 100,000,
there are 28 + 8 or 36 having fire-alarm systems; the re-
maining 2 cities, Kansas City and St. Joseph, Mo. depended
entirely upon the telephone for transmitting alarms of fire.
Of the 40 cities having from 50,000 to 100,000 inhabitants,
222
TELEGRAPH ENGINEERING
39 have fire-alarm systems and Kansas City, Kans. de-
pended upon telephonic fire-alarm transmission. The cities
of Quincy, 111. and Chester and Williamsport, Pa. of
36,000, 34,000 and 29,000 inhabitants respectively, were
reported as having no fire-alarm systems.
Fire-alarm signal systems
Cities having populations of
100,000
and
over
50,000
to
100,000
25,000
to
50,000
10,000
to
25,000
Less
than
10,000
Total
Number of cities in group *
Fire-alarm systems
Fire alarms received in 1907
Signal boxes
38
28
39.581
12,151
40
35
10,700
4,268
82
69
14,372
5.387
281
231
17,688
8,700
'"568
14,175
9,895
"931
96,516
40,401
Telephone boxes
Miles of single wire
216
17,218
3,377
37
3,447
112
5.322
131
5,973
496
35.337
Manual transmitters
Automatic transmitters
30
24
16
34
14
52
46
IO3
58
73
164
286
Receiving circuits
Transmitting circuits
584
332
265
182
368
196
712
366
880
394
2,809
1,470
Combined fire-alarm and police-patrol signal systems
Combined systems
Fire alarms received in 1907
8
19.832
8,118
i,9i5
19,223
17
8
356
108
4
959
669
127
1. 154
2
4
34
20
10
1,848
93i
&
1
74
52
14
109
601
6
3
81
35
12
6l9
338
10
156
2
I
27
13
48
24,203
10,721
2,192
21,897
31
24
572
228
Signal boxes t
Telephone boxes
Miles of single wire
Automatic transmitters
Transmitting circuits
Police-patrol signal systems
Police signal systems
Signal boxes t
27
3,758
29
1,204
39
1,020
$
&
178
6,999
Telephone boxes
Miles of single wire
1,054
8,788
no
1.543
153
1,601
226
1,148
152
498
1.695
13.578
Transmitters
107
12
21
31
3
174
Receiving circuits
358
117
181
136
96
888
Transmitting circuits
191
75
1 20
76
29
491
* Population based on 1900 census.
t Combined signal and telephone boxes were in most cases reported as signal boxes.
MUNICIPAL TELEGRAPHS 223
PROBLEMS
1. Explain that if two successive fire-alarm boxes are pulled simul-
taneously, that box whose number has the lowest first digit will as-
sume control of the circuit before the other signal box.
2. Show the scheme of connections at the central office of 3
fire-alarm box circuits, each terminating in a relay and a drop,
the relays controlling the operation of a common tapper and a
3 -pen register.
3. Formulate the assignments of fire-fighting companies and
officers for signal box number 234 located at Fulton St. and Hudson
Ave., Brooklyn. The location of this box and of the various com-
panies and officers is shown in Fig. 16, the same number of com-
panies being assigned to this box as to box 93.
CHAPTER VIII
RAILWAY SIGNAL SYSTEMS
i. Classes of Railway Signalling. — Railway signals for
the conveyance of information to those engaged in running
trains or cars fall into the following classes: (a) block
signals which indicate whether or not a train may proceed
into the next track section or block; (b) train-order signals
for advising engineers when train-dispatcher's orders are
to be given them; (c) route or switch signals for authorizing
the passage of trains over junctions, crossings, drawbridges,
etc. ; (d) other signals, such as flags, lanterns and torpedoes,
for the warning of temporary dangers, and fixed signs for
indicating speed limits, location of water tanks, etc.
Classes b and d lie outside the scope of electric signalling,
the former class always being manual signals operated by
the telegraphers who take the train orders.
Block signals are used on lengths of track devoid of
switches and crossings for limiting the space between two
trains on the same track to an amount affording a proper
braking distance for those trains running over this track
at maximum speed. On single-track roads, block signals
also give proceed and stop indications to trains advancing
in opposite directions. Block signals may be manually
operated, manually controlled, or automatic. Manually-
operated block signals are operated either by engine drivers
or motormen upon reaching a block, or by attendants
stationed along the roadway who set their signals in accord-
224
RAILWAY SIGNAL SYSTEMS 225
ance with information of train movements received by
telegraph or telephone from their neighboring attendants.
Manually-controlled block signals are set by attendants, the
action of one in operating signals being under the control
of another; thus, two attendants, one at each end of a
block, must act in setting a signal. Automatic block signals
are actuated by track or trolley attachments, or are oper-
ated through an electric track circuit, the train movements
governing the signals in both cases. These arrangements
control either a local electric circuit which operates the
signal, or a valve which allows compressed air or gas to
move the signal.
Route or switch signals are the signals of interlocking
plants which comprise groups of switches and signals that
govern the movements of trains at crossings, junctions,
terminal yards, etc. The switches and signals of inter-
locking plants may be moved manually or by means of
compressed .gas or of electricity under the control of lever-
men, the individual movements for establishing a track
route following each other in a predetermined order. These
signals also act in conjunction with the block signals just
beyond interlocked territories.
2. Types of Signals. — Signals for block systems and
interlocking plants may be electric lights, semaphores
(with lights as night signals), or enclosed disk signals (with
lights as night signals) . These signals indicate in different
ways the commands: Stop — danger, proceed with caution,
and clear — proceed. With light signals, these commands
are displayed by utilizing a distinctive color for each : thus,
red is used as the danger signal, green generally as the clear
signal, and orange-yellow usually as the caution signal.
226
TELEGRAPH ENGINEERING
Semaphores are either of the two-position or three-posi-
tion type, the blade positions for the various indications
being shown in Fig. i. A high three-position semaphore
is shown at A} this signal being mounted on iron masts
placed beside the tracks or on signal bridges. A dwarf
DANGER
CAUTION
\CLEAR
Fig. i.
three-position signal is shown at B, and is mounted directly
alongside of the tracks, usually at interlocking plants.
These three-position upper-quadrant signals indicate by
their blade positions: danger when horizontal, caution
when inclined upward at 45 degrees, and clear when vertical.
Two two-position semaphore signals mounted on the same
mast are shown at C, the upper serving as the home blade
RAILWAY SIGNAL SYSTEMS 227
and the lower as the advance or distant blade of a block
signal. Both blades horizontal signify " stop," the upper
inclined downward 60 degrees and the lower horizontal
mean " proceed with caution," and both inclined down-
ward 60 degrees signify "clear." Spectacles carrying col-
ored glasses are fastened rigidly to the semaphore blades so
as to move in front of lamps, thereby displaying at night
colored light signals corresponding to the blade positions.
Enclosed disk signals consist of an electromagnet whose
armature controls the position of a wire hoop covered with
colored bunting, all enclosed in a glass-covered case. When
the magnet is energized, the colored disk is drawn away
from the aperture and a white background is visible; when
released, the disk falls into position and its color is dis-
played. Colored glass disks, similarly controlled and mov-
ing before a lamp, serve as the night signals. Such enclosed
signals, while once widely used, are now infrequently
employed.
Electric light signals assume a variety of forms depending
upon the conditions of use; three styles made by the Union
Switch and Signal Company are shown in Fig. 2. The
block signal used by the Interborough Rapid Transit
Company in the New York Subway is shown at A. The
upper or home signal displays either a red or a green light,
and the lower or distant signal shows either a yellow or a
green light, both being provided with an auxiliary miniature
semaphore signal immediately below the lenses for use in
case of lamp failures. Colored glass disks supported in
vertical sliding frames move in front of the lamp apertures
by means of compressed air, the valves being controlled by
electric track circuits (§5). The block signal used in the
Pennsylvania Railroad Tubes under the Hudson and East
228
TELEGRAPH ENGINEERING
Rivers is shown at B, the three upper lights performing the
same function as a three-position semaphore, since only one
can be illuminated at a time. The lower lamp always
Fig. 2.
remains lighted and serves as a fixed signal. Similar
signals with an additional lower lamp are used as inter-
locking signals. At C is shown a type of signal for daylight
service used by the Indianapolis, Columbus & Southern
RAILWAY SIGNAL SYSTEMS 22Q
Traction Company and by other electric railway com-
panies.
Semaphores for block and interlocking signals are some-
times distinguished from each other by their color or by the
shape of the ends of their blades. The indications of sema-
phores used with automatic block signal systems may be
normally danger or clear. A normal danger signal ordi-
narily stands at " danger," but goes to " clear " as a train
approaches it if the block governed by the signal is clear,
returning to " danger " when the train enters the block.
A normal clear signal stands at " clear " except when a
train occupies the block governed by the signal. Normal
clear signals are now preferred by signal engineers.
Mechanical, electric, electro-pneumatic and electro-gas
devices are used for actuating the semaphores and switches
of interlocking plants, and (excepting the first), for operat-
ing the semaphores of automatic block signal systems.
Electric-motor semaphores &re now more frequently in-
stalled than semaphores actuated in other ways.
The mechanism of the Style B upper-quadrant two-
position direct-current semaphore, manufactured by the
Union Switch & Signal Company, is shown in Fig. 3. The
track circuit is arranged so that the motor A and the holding
magnet B receive current while the block governed by the
signal is being cleared. When the signal subsequently
indicates " clear " the motor is open-circuited but the flow
of current through the holding magnet remains uninter-
rupted. The holding magnet is fixed to the " slot arm "
C which rocks around pivot D. This slot arm carries the
rod E which connects with the semaphore blade, and also
carries a system of links terminating in the cam piece F
which may engage the trunnions of the chain G. The
230
TELEGRAPH ENGINEERING
Fig. 3.
passing of a train out of the block causes the operation of
the semaphore motor, the rotation of which produces an
upward movement of the chain through the gear-wheels
H and /. Simultaneously, the armature of the holding
magnet is attracted, thereby holding the system of links
RAILWAY SIGNAL SYSTEMS
23I
and the cam F rigid. This cam, consequently, engages a
trunnion of the upwardly-moving chain, and the -slot arm
is carried to its upper position, corresponding to the clear
position of the semaphore. At this position, the circuit of
the motor is automatically opened at / by the slot arm,
this arm remaining in its upper position as long as the
holding magnet is energized.
The presence of a train in the block causes the release of
the holding-magnet armature and the loosening of cam F,
this action allowing the slot arm to descend by gravity to
the position shown in the figure. The pneumatic buffer
K, connected to the right-hand end of the slot arm, permits
the gradual return of the semaphore to this danger position.
Series-wound or induction alternating-current motors may
also be used with this mechanism. By the addition of
another slot arm, the same motor may operate the other
position for a one-blade three-position signal or the second
blade of a two-arm (home and distant) signal.
Trolley Wire
Signal Wire
Fig. 4.
3. Manual Block Signal Systems. — The scheme of a
manually-operated block signalling arrangement, frequently
used on single-track electric railways operating relatively
few cars, is shown in Fig. 4. A signal box, having three
electric lights, L\y L2 and Z,3, and a two-point switch S, is
located at each end of a block. No illuminated lamp at
232 TELEGRAPH ENGINEERING
either end indicates that the block is clear, and illuminated
lamps at either end denote that the block is occupied by
a car and that no other car may enter until these lights are
extinguished. A motorman, reaching signal box A and
finding no lamps lit, moves switch Si to the right, thereby
causing lamps L, L2, Z,3, L\ and L2' to be illuminated, and
proceeds into the block toward signal box B. The lights
now displayed by both signal boxes permit no other motor-
man, advancing from either direction, to enter this occupied
block. The lamp L, joined in the signal wire, indicates to
the motorman in the block that the signals are still set
against advancing cars. Upon reaching signal box J5, the
motorman moves switch 6*2 to the left, thereby extinguish-
ing all lamps" and clearing the block. It will be observed
that irrespective of the positions of switches Si and S2, if no
lamps are lit, a movement of either switch will light the
lamps at each box, or, if lamps are illuminated, a movement
of either switch will extinguish them. With 5 50- volt trolley
circuits, five no- volt lamps are connected in series when
illuminated.
With manually-controlled block signal systems, arrange-
ments are utilized whereby each operator stationed along
the roadway cannot clear his own signal for an approaching
train until it is unlocked through electrical means by the
operator located at the other end of the block, his own
signal thereby displaying the danger signal to trains ad-
vancing in the opposite direction.
4. Location of Automatic Block Signals. — A home signal
is one showing the condition of the track directly in front
of a train, and which, if in the stop or danger position, is
not to be passed except as governed by the rules of the
RAILWAY SIGNAL SYSTEMS 233
railway company. A distant signal shows the condition
of the track some distance ahead of a train, and, if in the
caution position, may be passed if the train is brought under
control, prepared to stop at the next home signal. Distant
signals should be placed a distance in advance of the home
signals permitting the fastest trains to be brought to stand-
still without overrunning the corresponding home signals.
This braking distance may be from 1000 to 3000 feet,
whereas the length of blocks is usually from 2500 to 8000
feet; the two distances depending upon traffic, train speed
and roadway conditions.
An automatic overlap system without distant signals is
indicated in Fig. 5. Each home signal controls a block
Block 1 Block 2
Fig. 5.
plus an overlap equal to a braking distance beyond the next
signal (as indicated by the dotted lines), thereby insuring
that a stopped car is always protected by a signal located
at least a braking distance behind it. The two-position
semaphores HI and #3 are shown held in the clear position,
while Hz is in the stop position owing to the presence of the
car in block 2. The objection to this overlap system is that
an engine driver or a motorman, knowing that at times
there are two signals at " stop " between him and the train
ahead, may be careless and overrun a stop signal without
speed diminution on the belief that he will have ample time
to stop, thereby courting danger.
Because of this objection, the automatic block systems
234 TELEGRAPH ENGINEERING
represented in Figs. 6 and 7 are preferred and generally
employed for double-track signalling. In Fig. 6, distant
signals Dz and A give advance indications of the positions
of home signals Hz and HZ respectively. When at " cau-
tion/' a distant signal signifies to an approaching train:
Block 1 Block 2
_J\ A_
l fl I — i — fl Car i -*> i — r—7?
D™ H^P oT^ H7!f___
Fig. 6.
expect to find the next home signal at " danger." For the
position of the car shown in the figure, signals HI, D3 and
Hz are in the clear position, A is in the caution position,
and H-i is in the stop position.
In Fig. 7, shorter blocks are represented wherein a distant
signal is mounted on the same mast with the home signal
Block 1 Block 2 Block 3
2-Position
Two*8.rm o \ r v o * ^^ o i M u r*
«g!l8AC. j^V J3v ^4V_
3 S!f 1«?L V JV^ JvL * V—
Fig. 7-
of the preceding block. The track length controlled by
each home signal is shown by the dotted lines. The
indications of the two-position two-arm semaphore signals
while a car is in block 3 are: Si and 54 at " clear," 52 at
"caution," and £3 at* " stop." The corresponding indica-
tions of three-position semaphores are shown at the bottom
of the figure.
The foregoing double-track signal systems are not
RAILWAY SIGNAL SYSTEMS 235
applicable to single-track roads, because they afford no
protection against oppositely-moving cars, but a number
of automatic block-signal systems have been devised and
installed for single-track railway operation. One such
system, called the TDB (Traffic Direction Block) System,
has been recently introduced by the Union Switch & Signal
Company, and is now in operation on a number of inter-
urban electric railways. In this automatic block system,
the distance between adjacent sidings is a block for oppo-
•PTr-x
Fig. 8.
sitely-moving cars, called an opposing block, and half of this
distance is a block for cars moving in the same direction, or
a following block. Thus, each opposing block forms two
following blocks. : «
Fig. 8 shows the location of semaphore signals in two
opposing blocks of this signal system and gives the indica-
tions of these signals as one or more cars proceed through
the blocks. Each opposing block is equipped with four sig-
236 TELEGRAPH ENGINEERING
nals, two being located at its ends and the other two being
located a distance of 500 to 1000 feet on either side of its
middle point. Each signal at a siding governs the track
to the signal at the next siding in the case of opposing car
movements, but only to the next signal in the case of
following car movements; whereas the intermediate signals
govern the track to the next signal for following car move-
ments. The track sections controlled by each signal are
indicated at A by broken lines for following movements and
by dotted lines for opposing movements. The signals may
be of either the light or the semaphore types, the latter,
with two-position indications in the upper left-hand quad-
rant, are represented in the figure. This type of semaphore
is widely adopted on electric roads, because the motorman's
view of them is not obstructed by the poles which support
the trolley wire.
An eastbound car R is approaching siding X at B, Fig. 8,
and, consequently, signal 2 is in the stop position. At C,
this car has passed out of the block to the left, thereby
clearing signal 2 and setting at stop signals i, 4 and 6.
A second car S is approaching siding X at D while the first
car R is approaching signal 3. It is seen that signal i
protects the rear of the first car and signals 4 and 6 protect
this car against opposing car movements. At E, car R,
having passed signal 4, causes signal i to clear for the
following car S. At F, car S has entered the first following
block while car R is in the second following block; con-
sequently, signals 4 and 6 still protect the cars against
opposing car movements and signals i and 3 protect against
following car movements. The first car has passed siding
Y at G into the next opposing block, it being observed
that both cars are protected from both directions. The
RAILWAY SIGNAL SYSTEMS
237
signal indications for westbound cars may similarly be
traced.
The four remaining diagrams, H, I, J and K, show the
signal indications for two cars R and T approaching siding
Y from opposite directions. At /, the eastbound car has
taken the siding, and does not affect any signals while off
the main track.
Trolley Wire
5. Automatic Block Signalling. — Automatic block sig-
nal systems may be divided into two groups: first, those
wherein trains or cars affect signal apparatus on arrival at
definite places along the roadway and, after passing these
points, leave the apparatus wholly
beyond their control while pro-
ceeding through the block, and
subsequently, when leaving the
block, again affect the apparatus
to restore it to its normal condi-
tion; and second, those wherein
the train or car is itself continu-
ously in direct control of the
signal for the block over which it
is passing, through the medium
of a track circuit. While cheaper to install, the first
group does not afford such thorough and continuous
protection as does the second group of signal systems.
Block signals of the first group were formerly used
on some steam railways, and are now giving marked
satisfaction on a number of interurban electric railways,
the latter permitting better signal actuation.
Fig. 9 shows the apparatus at one end of a block for an
automatic signal system of the first group as applied to an
Fig. 9.
238 TELEGRAPH ENGINEERING
electric railway. The arrangement is similar to the manual
block signal described in § 3, except that the switch S,
Fig. 4, is moved automatically when the car passes the
block limits. This action is accomplished when the trolley
wheel reaches the signal contactor C, Fig. 9, for the wheel
then touches the spring contacts of C and the trolley wire
simultaneously and causes a momentary current to flow
from the trolley wire through the switch-controlling magnet
M to ground at G. The consequent attraction of armature
A of this magnet permits the campiece c to turn the ratchet
wheel R through a distance of one tooth. This causes the
notched wheel N, having half as many crests as the ratchet
wheel has teeth, to turn an amount equal to the distance
from a hollow to a crest. A projection of the switch arm
S carries a small wheel W which rides on the notched wheel.
When wheel W rests in a hollow (as shown), switch S closes
its left contact, and when it rests on a crest, switch S closes
its right contact.
When both signal sets of a block are in the position
illustrated, no current traverses the signal wire with its
lamps L, thereby giving the indication that the block is
clear. When a car enters the block, the magnet is momen-
tarily energized and the attraction of its armature causes
a limited rotary movement of wheels R and N. Switch 5,
in consequence, moves. to its opposite position and closes
the right and opens the left contact. This action illumi-
nates lamp L and the other lamps connected in the signal
wire, thereby giving the stop indication to other cars ad-
vancing in the same or in the opposite direction. As the
car moves out of the block, the switch at the other signal is
similarly moved and the lamps are extinguished, thus again
clearing the block.
RAILWAY SIGNAL SYSTEMS 239
The Chapman Automatic Signal System employs con-
tactors which are returned by a spring to their normal
position after they have been moved in either direction
by a trolley wheel. The signals used with this system are
of the semaphore type and are actuated by electromagnets.
There are three magnets in each signal, two for controlling
the indication of the semaphore arm, and the third for
closing certain contacts upon momentary actuation as a
car enters a block section. The three positions of the
semaphore blade indicate : horizontal — car approaching in
opposite direction, inclined downward 45 degrees — clear,
vertically downward — car in block receding from you.
Insulating
Track Joints
j Track Rails t
*
Fig. 10.
The principle of all automatic block signal systems of the
second group is the operation of a relay whenever a pair of
wheels with their connecting axle enters or leaves a block.
The scheme of such systems for steam railroads is illustrated
in Fig. 10. A battery is located at one end of a block and
connected across the two track rails of a section, which are
separated from the rails of the adjacent sections by insulat-
ing joints. The rails serve as conductors for the current
from battery b to a track relay R, which is located at the
other end of the block and likewise connected across the
track rails. The relay controls through its contact points
the local circuit of battery B and the semaphore signal S.
When no car is in the block, relay R is energized and the
240
TELEGRAPH ENGINEERING
local circuit is closed, thereby holding the signal at clear.
When a car enters the block, the battery b is short-circuited
by the car wheels and axles, and the relay is deprived of
current. The consequent opening of the local circuit at
the relay sets the signal in the danger position. The
battery and relay are placed at opposite ends of a track
section, because this arrangement protects against broken
rails and also indicates open bonds between rail-lengths.
Either primary or storage batteries are used, and these
are located in battery wells or chutes beside the tracks.
When distant signals are used with the scheme repre-
sented in Fig. 10, polar-neutral track relays are employed,
Block 2
Block 1
Fig. ii.
their neutral armatures controlling the home signals and
their polarized armatures controlling the distant signals;
the operation of a home semaphore blade moving a pole-
changer for reversing the current in the relay of the pre-
ceding block. This system is called the polarized or
" wireless " automatic block signal system.
Each signal may be controlled by any number of track-
circuit relays, and each relay may have a plurality of
contacts. Thus, Fig. n shows the scheme of connections
for normally-clear two-arm semaphores (located as in
Fig. 7) for two blocks of a track intended for traffic in one
direction only. Each block is shown divided into two track
RAILWAY SIGNAL SYSTEMS
241
sections a and b, so as to increase the reliability of the track
circuits by reducing the effect of current leakage from one
rail to the other along ballast and ties. Track relays RI
and R2 control the home blade HI of block i, relays R3 and
RI control the home blade H2 of block 2, and relays RI, R2,
R3 and R± control the distant blade D2. The operation
of the signals for indicating the track conditions with the
passage of a train can be understood readily from an
Fig. 12.
examination of the diagram, if it be remembered that each
semaphore blade assumes the horizontal position whenever
its local circuit is opened at a relay contact. For the
position of the train indicated, the contacts of relay RI are
open and, therefore, home blade HI and distant blades A
and DZ will be horizontal.
A large variety of track circuits is utilized in practice
for different types of automatic block signalling, using
242
TELEGRAPH ENGINEERING
normally-clear or normally-danger signals on single- or
double-track steam and electric roads in connection with
overlap, non-overlap or preliminary-section systems.
The appearances of two .types of direct-current track
relays manufactured by the General Railway Signal Com-
pany are shown in Figs. 12 and 13. That shown in Fig. 12
is the Taylor tractive-type relay and has 4 contacting fin-
r
Fig. 13-
gers, each with front and back contacts ; that shown in Fig.
13 is a three-position mo tor- type relay also with 4 contact-
ing fingers, the closing of one or the other sets of contacts
being accomplished by a partial rotation of the motor
armature through the medium of an eccentric link.
6. Automatic Block Signals on Electric Railways. —
Signalling on electric railways is accomplished in a some-
RAILWAY SIGNAL SYSTEMS 243
what different manner from that employed on steam rail-
roads as just described, because the track rails are utilized
as a return path for the current required in car propulsion.
One-rail Block Signal System. — Where it is possible to
spare the conductivity of one track rail in the return of the
propulsion current, as on elevated roads where the support-
ing structure serves also as a return path, one track rail is
sectionalized and used for block signalling. Alternating
current is now usually employed for signalling with this
arrangement, requiring the use, on direct-current railways,
of relays that are responsive to alternating current but not
to direct current, and, on alternating-current railways, of
relays that are responsive only to alternating current of
higher frequency than the propulsion current.
Return Rail for Propulsion Current
A. C. Signal Mains
Fig. 14.
Fig. 14 shows the scheme of connections of the one-rail
automatic block signalling system. The transformers T
supply alternating current to the " exit end " of each track
section from the alternating-current supply mains. The
alternating-current relays Rj connected at the opposite end
of the track sections, control the operation of signals 5
through the local batteries B, as before, or through alter-
nating-current motors fed by transformers joined to the
signal mains. Each relay is shunted by an impedance to
keep direct currents from the instrument. Usual trans-
mission voltages are from 2200 to 4400, and at each block
244
TELEGRAPH ENGINEERING
are stepped down to 220 or no volts for the operation of
alternating-current semaphore motors, and to 6 to 15 volts
for the operation of the track circuits and lamp signals.
This system is used in the New York Subway, where
approximately 700 signals, 500 track circuits and 40 inter-
locking plants are used. During the morning and evening
rush hours 150 subway trains per hour pass g6th Street,
this heavy traffic demanding blocks as short as 1500 feet.
The signal mains supply 6o-cycle current at 500 volts to the
block transformers, each having two secondary windings,
one which feeds the track circuit at 10 volts, and the other
which feeds the lamp signal circuits at 50 volts. The valve-
Track Rail
A. C. Signal Mains
Fig. 15.
controlling magnets of the electro-pneumatic signal mecha-
nisms are operated by direct current at 16 volts supplied
by storage batteries.
Two-rail Block Signal System. — Both track rails of an
electric railway may be used simultaneously as a return for
the propulsion current and as conductors for the signalling
current by the employment of impedance bonds placed
between and connected across the track rails at both ends
of each track section. These bonds are shown at I in
Fig. 15, the middle points of the windings of adjacent bonds
being connected together. In other respects, the one-rail
RAILWAY SIGNAL SYSTEMS
245
and two-rail signal systems are identical; compare the
schemes of Figs. 14 and 15.
The impedance bonds have little resistance but large
inductance, for they consist of heavy windings of copper
around massive laminated-iron cores as illustrated in Fig.
1 6. For 600- volt railways the resistance of a bond may
PLAN VIEW-COVER REMOVED.
SECTIONAL SIDE VIEW
Fig. 1 6.
be from 0.0004 to 0.0015 ohm. The propulsion current, in
being carried around the insulating joints which separate
the track signal circuits from each other, flows differentially
through the bonds and, consequently, does not magnetize
their cores. Therefore, the propulsion current will not
affect the signalling apparatus. The impedance of the
bonds to the alternating current used for signalling is so
246 TELEGRAPH ENGINEERING
great in comparison with that of the relays that the
presence of the bonds will not affect the operation of the
alternating-current track relays.
The two-rail block signal system is installed on a number
of direct-current railways, a few of which are: the West
Jersey and Seashore Railroad, the Washington, Baltimore
& Annapolis Electric Railroad, the Hudson and Manhattan
Railroad, and in the electrified zones of the New York
Central, the Pennsylvania, and the Southern Pacific
Railroads.
This block signal system is also used on alternating-
current electric railways, the relays being designed not to
respond to the propulsion currents, but to respond to cur-
rents of a higher frequency used in signalling. Thus, on
25-cycle electric railways the signalling is usually accom-
plished by currents of 6o-cycle frequency. Signal installa-
tions of this type include the New York, Westchester and
Boston Railway, the Chicago, Lake Shore & South Bend
Railway, and the electrified zone of the New York, New
Haven and Hartford Railroad.
Alternating-current Track Relays. — The vane- type al-
ternating-current relay, shown in Fig. 17, made by the
Union Switch & Signal Company is widely used with one-
rail block signal systems. It consists of a C-shaped
laminated core carrying two field coils, one on either side of
the core air-gap. The pole-pieces of the core are provided
with single turns of wire short-circuited upon themselves,
called shading coils. An aluminum vane, pivoted in jewel
bearings, is arranged to move up and down in the air-gap.
When an alternating current traverses the field coils, a
shifting magnetic flux is established at the air-gap with the
aid of the shading coils, which flux causes an upward
RAILWAY SIGNAL SYSTEMS
247
movement of the vane. Contact fingers mounted on the
shaft carrying the vane are thereby brought against sta-
tionary contacts connecting with the terminals on the cover.
Fig. 17.
Fig. 1 8 shows the appearance of the centrifugal frequency
track relay made by the same concern and used on alter-
nating-current electric railways employing the two-rail
block signal system. Other types of alternating-current re-
lays for both one-rail and two-rail automatic signal systems
are available.
7. Interlocking Plant Signals. — Track switches and
signals at railroad crossings, junctions, crossovers, draw-
bridges and terminal yards are operated mechanically,
electrically or electro-pneumatically and are actuated by
the levers of interlocking machines under the control of
levermen. An interlocking machine is usually placed as
close as possible to the devices which it controls, but
numerous such machines are in use which are 6000 feet
248
TELEGRAPH ENGINEERING
distant from some of the devices controlled. The use of
mechanical interlocking machines is restricted to short
distances, say up to 1000 feet; but the electric and electro-
pneumatic machines may be used for controlling devices
at great distances. Fig. 19 shows the Unit Lever type
Electric Interlocking Machine, in combination with the
Fig. 18.
operating switchboard and indicator groups, made by the
General Railway Signal Company. This machine has
38 levers for operating switches and signals and has 14
indicators. Such indicators are used for checking the
correspondence of movement between the lever and the
device which it operates, the indications being received
after the operation of the device has been properly com-
pleted. The movement of a lever locks all levers conflicting
with its new position and operates the device which it
RAILWAY SIGNAL SYSTEMS
249
controls. This interlocking of levers is performed at the
" locking bed " located at the front of the machine, by
horizontal locking bars carrying V-shaped dogs which en-
gage notches in vertical tappet bars. Upon moving a lever,
its tappet bar is moved vertically and one or more locking
bars are moved by the dogs which engage them, and the
Fig. 19.
dogs carried by these bars move into the notches on cer-
tain tappet bars, thus locking their corresponding levers.
A simple illustration of the function of an interlocking
machine will be considered in connection with Fig. 20
which represents the position of signals and derails at a
single-track railway crossing. In this diagram i, 6, 7 and
12 are distant signals, 2, 5, 8 and n are home signals, and
3, 4, 9 and 10 are derails, all devices being represented in
their normal positions, that is, the derails open and sema-
phore blades horizontal. To permit a train to pass from
25°
TELEGRAPH ENGINEERING
A to B requires that derails 3 and 4, and signals i and 2
must be reversed, and for proper protection to this train
while on the crossing, derails 9 and 10, and signals 5, 6, 7,
8, ii and 12 must be held normal. This is accomplished
by the levers of the interlocking machine, which bear the
same numbers as their corresponding devices. Therefore,
^ an.
10
B
Fig. 20.
derail levers 3 and 4 when reversed should each lock derail
levers 9 and 10 normal, and conversely. Further, to pre-
vent levers 8 and n being reversed before levers 9 and 10
are reversed, it is necessary that levers 8 and n when
reversed should each lock levers 9 and 10 reversed. Each
distant signal when reversed locks its home signal reversed.
Finally, lever 2 when reversed should lock lever 5 normal,
and lever 8 when reversed should lock n normal. These
operations may be tabulated in the form of a chart as shown
on the next page, thus forming the locking sheet for the
RAILWAY SIGNAL SYSTEMS
251
interlocking machine. It will be observed that converse
lockings are not duplicated, for it is understood that if one
lever locks another lever normal, the opposite is also true,
that is, the latter lever locks the former normal.
Lever
When reversed locks
Reversed
Normal
I
2
2
3 4
5
3
9 10
4
9 10
5
3 4
6
5
7
8
8
9 10
9
10
ii
9 10
8
12
ii
PROBLEMS
1. At what minimum separation may two cars travelling m the
same direction be operated at full speed over a track with the signal
arrangements shown in Figs. 5, 6, 7 and 8? Express the result in each
case in terms of block lengths.
2. Describe the operation of the relays and semaphore signals of
the automatic block signal system illustrated in Fig. n as a train
advances from one track section to another.
3. A 1.3 volt primary battery supplies 0.5 ampere to one end of
a track circuit 3600 feet long, at the other end of which is a 3.5 ohm
track relay. The voltage measured from rail to rail at frequent
intervals along this track section showed a drop of 3.5 millivolts for
each 3o-ft. track length, this being due to resistance of track and
bonds, and to leakage across ballast and ties. What percentage of
the battery current traverses the relay?
252 TELEGRAPH ENGINEERING
4. Draw up the locking sheet for an interlocking machine to be
installed at a single-track railway junction at which the signals and
switches are located as shown below. The distant signals i, 2, 8 and
ii show the indications of the home signals 3, 4, 7 and 10 respectively;
12 34
signals i and 3 apply to route AC, and signals 2 and 4 apply to route
AB. Switch 5 is shown normally open, and the derails 6 and 9 are
normally set to derail. It should be noted that lever 5 of the machine
is under the immediate control of either lever 6 or 9, for lever 3 (or 4)
cannot be reversed until lever 9 (or 6) has been reversed.
CHAPTER IX
TELEGRAPH LINES AND CABLES
I. Aerial Open Lines. — Line conductors for telegraphic
signalling may be: bare wires mounted overhead at some
distance from each other on poles or towers; insulated
wires grouped together, forming a cable, and usually en-
closed in a lead sheath, either suspended at short intervals
from a steel cable fastened to poles or else drawn into
underground conduits; or cables comprising one or more
well-insulated conductors surrounded by a waterproof
covering and steel armor, as in submarine cables. These
types will be considered in the order mentioned.
For overhead telegraph lines galvanized iron of various
grades, hard-drawn copper and sometimes steel or copper-
clad steel wire are employed. The sizes, weights and re-
sistances of the conductors generally used are given in § 8
of Chap. I. The increasing adoption of copper for tele-
graph lines is due to its low resistance (about one-sixth
that of iron), its high tensile strength (45,000 to 68,000
pounds per square inch) and its non-corrosion under ordi-
nary atmospheric conditions.
Joints. — Lengths of iron line wire are usually joined by
placing the two ends side by side and winding half the
overlap of each wire spirally around the other; this is
called the Western Union joint. For joining copper line
wires the Mclntyre connector is widely used, which con-
sists of a double copper tube, of correct size to fit the line
253
254 TELEGRAPH ENGINEERING
wire. The ends of the wires are inserted from opposite
ends, one through each of the twin tubes, and the sleeve
is then twisted through three complete turns. Such joints
do not require soldering.
Insulators. — The insulators f6r supporting bare overhead
telegraph lines in this country are generally constructed of
glass, and sometimes of porcelain. The design of the stand-
ard form of insulator is shown at the left of Fig. i, the
dimensions in inches being indicated thereon. Its small
diameter, coupled with the relatively large distance along
the surface from the wire groove to the insulator pin, con-
duces to the maintenance of high-insulation resistance
despite accumulations of dirt and other foreign matter on
the insulator surface. The insulator at the right of Fig. i
shows the standard form of two-piece transposition insu-
lator. Insulators having double flanges or " petticoats " at
the bottom are sometimes used when greater insulation
resistance is desired.
The line wire when attached to the insulators is not
passed around the insulator but is laid in the groove at
one side and is tied in this position by short pieces of
wire of the same size as the line wire and which pass around
the insulator. The middle portion of Fig. i shows the
standard type of insulator pin for supporting the insu-
lators on the pole cross-arms. They are commonly made
of chestnut, locust or oak, both the shank and thread being
tapered. Wood-top steel pins and wood bracket-pins are
also used, the latter being fastened directly to the pole
(Fig. 4).
Poles. — Wooden poles are most generally used for sup-
porting aerial telegraph or telephone lines, except where
unusually large spans demand strong towers of steel or re-
TELEGRAPH LINES AND CABLES
255
inforced concrete. In this country white cedar, chestnut,
cypress, pine and redwood poles are principally used for
this purpose. These poles are from 20 to 80 feet in height,
but those from 25 to 40 feet are the more usual. The
height of poles to be used in a given locality is governed
by several conditions, such as ordinances requiring a
minimum distance of the lowest wire above the ground,
non-interference of the wires with the possible activities of
the fire department, clearance at trolley and railway cross-
ings, etc. The poles are from 5 to 8 inches in diameter at
the top, with an increase in diameter of about one inch in
every 10 feet toward the bottom. Poles are set from 5
to 10 feet into the ground, according to the height of the
pole and the nature of the soil. In many cases it is de-
sirable to treat the lower ends of the poles so as to mini-
mize decay where they are embedded in the ground. This
256 TELEGRAPH ENGINEERING
treatment consists of applying a preserving fluid, such as
creosote or carbolineum oil, applied by pressure, dipping or
by brush. Poles decayed at the ground may be repaired
by placing a rigid collarvof reinforced concrete around the
decayed portion of the poles.
The size of the poles should be selected so that the
transverse forces, due to the tension in the wires at turns
in the line and to wind pressure on poles and wires, do not
exceed the breaking stress of the pole. The pull, exerted
at the center of load at a point Lc feet above the ground,
that will break a circular-sectioned pole having a diameter
d feet at the ground line, may be expressed as
F = -S pounds, (i)
where A is the cross-sectional area of the pole at the ground
in square inches and S is the tensile strength in pounds
per square inch. Accepted values of the maximum fibre
stress S for some woods are given below:
Chestnut 6,000-10,000
Cypress 5,ooo- 8,000
White cedar 4,000- 8,000
Yellow pine 4,000- 8,000
pounds per sq. in.
In proper designs much lower values of this maximum
fibre stress are employed, thereby allowing a considerable
factor of safety.
At a turn in the line, if the horizontal angle between the
directions of the wires at either side of the pole be 6, and
the tension in each of N wires be T pounds, then the trans-
verse force acting on the pole at a height Lc feet above the
ground is
F = 2 NT cos - pounds, (2)
TELEGRAPH LINES AND CABLES 257
which assumes that the tension in the wires is the same on
both sides of the pole. The wind pressure on the pole,
having an average diameter of da feet and a height of H
feet above the ground, will be equivalent to a force of
KdaH pounds acting at the center of the pole, where K is
the wind pressure per square foot of projected pole area,
usually taken as a maximum of 8 pounds. This force act-
ing at the center of the pole may be replaced by a force
at the center of load of, say, 0.6 KdaH pounds acting at a
point distant Lc or f of the pole height from the bottom.
If the wind blows in the direction of the resultant trans-
verse force F', the wind pressure on the wires will be
— !sin-, where / is the distance between poles in feet,
12 2
and di is the diameter of each conductor over a possible
ice coating, in inches. Therefore the maximum wind
pressure on the pole and wires which may assist the trans-
verse force on the pole at a turn in the line is
F" = K (0.6 dJI + 0.0833 Nidi sin -} pounds, (3)
and consequently a pole should be selected so that
F>F' + F"
with a considerable factor of safety. If this requirement
demands a pole of unusually large diameter for an assumed
factor of safety and for a given angular change in the direc-
tion of the pole line, a smaller pole may be used if rein-
forced by the use of guy wires or braces of suitable types.
Such reinforcement is generally utilized with terminal
poles, with poles at the ends of long wire spans or with
poles near a curve or corner. Fig. 2 indicates the method
of guying a line at a road crossing.
TELEGRAPH ENGINEERING
To consider a specific example, assume a bend of 160
degrees in a 24-wire, 3-arm pole line of No. 9 B. & S. gage
copper wire, supported on white-cedar poles projecting 30
feet above the ground and spaced 130 feet apart. If the
maximum fibre stress be taken as 6000 pounds per square
inch, and the diameter of the pole at the ground is i foot,
and at the top is 8 inches, the transverse force on the
Fig. 2.
corner pole acting at the center of load (say at a point 25
feet from the ground) necessary to break the pole is
„ IT (6)2 X i,
F = a s/ r 6oo° = 3390 pounds.
o A 25
If the tension of each wire be 200 pounds, the transverse
force due to wire tension at the corner pole is
Ff = 2 X 24 X 200 cos— - = 1670 pounds,
and if the outside diameter of the ice-covered wire be
taken as 1.114 inches, thereby allowing \ inch of ice all
TELEGRAPH LINES AND CABLES 259
around the conductors, the transverse force due to wind
pressure is
F" = 8(0.6^—30 + 0.0833 X 24X130X1.114 sin—)
\2Xl2 2 /
= 2376 pounds.
Thus, the total transverse force that may act on the pole
under consideration is 1670 + 2376 = 4046 pounds, a
force greater than the assumed breaking stress of the pole,
or 3390 pounds. Therefore this corner pole must be
firmly guyed or braced in order to maintain telegraphic
service over this line in times of severe wind and sleet.
Cross-arms. — The cross-arms for a telegraph pole are
made of sound, thoroughly seasoned straight-grained tim-
ber, either creosoted or painted. The standard cross-arms
measure 3^ by 4^ inches, and may vary in length from 3
to 10 feet, depending upon the number of wires accom-
modated. These cross-arms are attached to the poles by
placing them in gains or slots cut in the poles and securing
them in position either by lag-screws or by bolts which
pass through the pole.
The strength of standard cross-arms is indicated in
the following table, which gives the results of recent
tests conducted by the Forest Service on 6-foot, 6-pin
cross-arms :
Average maximum downward
load in pounds
Longleaf pine (75 per cent heart) 10,180
Longleaf pine (100 per cent heart) 9,?8o
Longleaf pine (50 per cent heart) 8,980
Shortleaf pine 9,260
Shortleaf pine (creosoted) 7,650
Douglas fir 7,590
White cedar 5,200
260
TELEGRAPH ENGINEERING
Cross-arms are further secured by iron or steel braces, as
indicated in Fig. 3, which also shows the usual spacing in
inches of insulators and cross-arms.
Poles at line terminals or at the ends of long spans are
g a a a
9 9 a
Fig. 3.
usually provided with double cross-arms, placed on op-
posite sides of the poles and bolted together.
Lightning Arresters. — To protect pole lines against de-
struction by lightning, it is common practice to lead a
ground wire to the top of at least every tenth pole. Fig. 4
shows one arrangement employing a double-grooved in-
TELEGRAPH LINES AND CABLES
261
sulator mounted on a bracket pin. It will be observed
that a small gap is formed between the ground wire and
the line wire, over which a lightning discharge may take
place and pass to ground. The
lower end of the ground wire usually
connects with an iron pipe driven
into the ground at least two feet
away from the pole.
WIRE
2. Wire Spans. — In suspending
wires from pole cross-arms, the ten-
sion of the wire should be such that
at the lowest attainable temperature
the tension due to the weight of
the wire with possible coverings of sleet and snow and
due to wind pressure must not exceed a predetermined
value. The physical constants of various sizes of hard-
Fig. 4-
Fig. 5.
drawn copper and galvanized iron wire are given in the
following table. The values of tensile strength given
in this table should not be used directly in determining
the proportions of wire spans, but should be divided by a
proper factor of safety, say 2 to 4, so that the wire may
262
TELEGRAPH ENGINEERING
withstand excessive momentary loads to which the line
may be occasionally subjected.
Hard-drawn Copper
Modulus of Elasticity = 16,000,000 pounds
per sq. in.
Coefficient of Expansion = 0.0000095 per deg
fahr.
Galvanized Iron Wire
Modulus of Elasticity = 26,000,000 pounds
per sq. in.
Coefficient of Expansion = 0.0000067 per deg.
fahr.
B.&S.
Gage
No
Diam-
eter in
inches
Area
in
square
inches
Tensile
strength
in
pounds
Weight
in
pounds
per
foot
S.W.G.
No.
Diam-
eter in
inches
Area
in
square
inches
Tensile
strength
in
pounds
Weight
in
pounds
per
foot
9
O.II4
0.01028
630
o . 0396
4
0.238
0.0445
2I2O
0.1490
10
0.102
0.00815
525
0.0314
5
O.22O
0.0380
1820
0.1275
ii
O.OQI
0 . 00646
420
0.0249
6
0.203
0.0324
*55°
0.1085
12
O.oSl
0.00513
330
0.0198
7
0.180
0.0254
I2IO
0.0853
13
0.072
0 . 00407
270
0.0157
8
0.165
0.0214
IO2O
0.0716
14
0.064
0.00323
213
O.OI24
9
0.148
0.0172
820
0.0578
10
0-134
0.0141
670
0.0474
In determining the proper sag of a wire span, the maxi-
mum weight of the wire with sleet or ice loads must be
known. In view of the variation of climatic conditions, it
is usual to assume an ice coating of f inch thickness all
around the wire as the severest load, the weight being
0.033 pound per cubic inch. Wind pressure must also be
considered, this force being assumed horizontal and per-
pendicular to the wire. The maximum wind pressure may
be taken as 8 pounds per square foot of projected area of
the wire or of the ice cylinder; this value corresponds ap-
proximately to a wind velocity of 60 miles per hour. The
minimum temperature may be considered as — 20 deg. fahr.
and the maximum temperature as 120 deg. fahr., these
temperatures being reasonable values for the northern
part of this country.
Let wi = weight of wire and ice per foot of wire length,
TELEGRAPH LINES AND CABLES 263
and w<t = wind pressure per foot of wire length, then the
resultant force per foot will be
W = Vwi2 + Wi2, (4)
and the wire will assume the position indicated in Fig. 5.
With relatively small spans, the curve assumed by a wire
suspended between two insulators approximates with suf-
ficient accuracy to a parabola. On this assumption the sag
in feet at the lowest probable temperature will be
° = rr w
where w is the resultant force in pounds per foot of wire
length, / is the distance between the supporting insulators
on the same horizontal level in feet, and T is the maximum
allowable tension in the wire in pounds (assumed uniform
throughout the length of the wire).
The length of the wire in feet may be expressed as
(6)
If this wire were removed from the supports and laid on
the ground its length would be
L» -- ^' (7)
where Lu is the unstressed length of the wire in feet, A is
the area of the wire cross-section in square inches and E
is the stretch modulus of elasticity of the wire material in
pounds per square inch.
Inasmuch as wires are strung without ice- coverings and
usually in fair weather on other than the coldest days, it is
264 TELEGRAPH ENGINEERING "
desirable to know what sags to allow at the higher tempera-
tures so that, with the severest external loading at lowest
temperature, the tension will not exceed the maximum
allowable value. The increase of the unstressed length Lu
due to a temperature rise of / fahr. degrees above the former
temperature is Lukt, where k is the temperature coefficient
of linear expansion per fahr. degree reckoned from the for-
mer temperature. Therefore the total unstressed length of
the wire at the higher temperature will be
Lt-L.(i+kt); (8)
but when strung its length will be
where T1 is the tension of the wire at the higher tem-
perature. Also by analogy with equations (5) and (6), the
sag at this temperature is
do)
and the length of the wire is
r ;j_ ( \
Lst=l-\ -- -> (n)
3 ' 33
where w0 is the resultant force per foot of wire length with
no ice covering.
In order to find the sag Dt of the wire without ice at
any temperature in terms of the unstressed length Lu at
the lowest temperature, eliminate Ltj L8t and Tr from equa-
tions (8) to (n), and there results,
TELEGRAPH LINES AND CABLES 265
This cubic equation is of the form
Df -3 PDt -2Q = o, (12)
where P = l-[Lu (i + kt) - 1} (13)
_»
The solution of equation (12) is
(15)
when Pz > Q2, but when P3 < Q* hyperbolic cosines must
be used.
As an illustration, consider a No. 9 B. & S. gage hard-
drawn copper wire suspended between insulators 130 feet
apart, the factor of safety being taken as 2. From the
foregoing table, T = -*- =315 pounds, A =0.01028 square
inch, the wire diameter = 0.114 inch and the weight of
copper per foot = 0.0396 pound. The outer diameter of
an ice coating ^ inch thick all around the wire would be
1.114 inch, and the weight of this covering would be
— X 12 X 0.033 = 0.382 pound per foot.
4
The wind pressure would be - - = 0.743 pound per
linear foot. Whence
w = V(o.o396 + 0.382)2+ (0.743)2 = 0.854,
and the sag at the lowest temperature (say — 20 deg. fahr.)
becomes, from equation (5),
266 TELEGRAPH ENGINEERING
The length of the wire when unstressed is therefore
- — = 13067,4 = feet>
j. + 315 1-0019
0.01028 X 16,000,000
To iind the sag at 120 deg. fahr., substitute the foregoing
t T i// A\2 /8 XO.II4\2
value of LM, w0 = V 0.0396 + - - = 0.0857,
\ / \ 12 /
and / = 140 in equations (13) and (14). Thus,
P = ^p[I3°43 0 + 0.0000095 X 140) - 130] = 9.75,
and
Q •_ 3 X 130.43 (i +0.0000095 X 140) 0.0857 (i3o)3 _
128 X 0.01028 X 16,000,000
Since P3 > Q2, the sag at this temperature, from equation
05)> is
/ - /i ^ Si
Dt = 2 V9«75 cos ( - cos"1 ,
\ V-
3
= 6.24cos27°47' = 5.52 feet,
and its vertical component is
For unusually long spans, such as river crossings, wire of
steel or copper-clad steel are more suitable than of hard-
drawn copper or galvanized iron.
3. Economical Span Length. — To determine the pole
spacing conducive to a minimum annual maintenance
charge on the supporting structures of an aerial line, let
TELEGRAPH LINES AND CABLES 267
n = economic number of poles per mile,
h = minimum required distance of wires above
ground in feet,
H = height of pole above ground in feet,
Ci = cost of cross-arms, insulators and pins per pole
in dollars,
r = average interest and depreciation rate on poles,
insulators, etc.,
Wi = weight per foot of wire in pounds at maximum
sag,
T = tension in conductor in pounds at maximum sag,
and D' = maximum vertical sag in feet.
Assume that the cost of the line wire will not vary
with the pole spacing, and that the cost of the poles ready to
set varies as the square of their height, or Cp = aH2 dollars,
where a is a constant. Then the pole spacing is / = - — -
n
feet, and the height of the poles is (see § 2)
The cost of line material per mile, exclusive of conductors,
is
C = n (Ci + Cp) dollars;
consequently the annual expense per mile for maintaining
the pole line is
Ca = m | C, + a [h + H ff9)2]2 j dollars. (17)
To determine the minimum annual expense equate to zero
the differential coefficient of Ca with respect to n. Then
268 TELEGRAPH ENGINEERING
dC* _ vC 72 arw1h($28o)2 sarw? (528o)4 _
dn~~ 4Tn* 64 TV °'
or
4 aWjh&So)2 g 3<m>i2(528o)4 ,
- * " =
This equation is of the form x2 — px — q = o, and when p
and q are positive quantities the solution may be written
as * = £ + y + q. If w2 = x,
(528o)2 , ,
'
and q = 64p(cv: ..^' M
then
As an illustration, consider the following values sug-
gestive of the order of magnitude of the cost constants
for a 3-arm 24-wire pole line with poles 6 inches in diameter
at top:
a = 0.006,
Ci = 1.50,
r = 0.15.
Then for No. 9 B. & S. gage hard-drawn copper wires
covered with ice J inch thick all around and suspended
with a factor of safety of 3, at the minimum distance of
20 feet above the ground,
T = 210 pounds,
and wi = 0.422 pound per foot (page 265).
TELEGRAPH LINES AND CABLES 269
For these constants
0.006 X 0.422 X 20 (5280)2
4 X 210 (1.50 + 0.006 X 2O2)
3 X 0.006 (0.422)2 (528o)4
and q = - —^ = 226,000;
64 (2io)2 (1.50 + 0.006 X 20 ;
whence from equation (21) the economic pole spacing is
n = V 215 -f V(2i5)2 + 226,000 = 27 poles per mile.
The height of towers to be used, and the annual mainte-
nance of the supporting structure for the wires, may now be
found from equations (16) and (17) respectively, yielding
H = 29.5 feet above ground, and Ca = 27 dollars per mile.
4. telegraph Cables. — Aerial and underground tele-
graph cables are formed of any desired number of annealed
copper wires, from No. 14 to No. 19 B. & S. gage, indi-
vidually insulated with prepared paper, fibre or sometimes
rubber. These conductors are assembled in layers, form-
ing a cylindrical group or core and held in shape by one or
more spiral coverings of paper, and the whole is then en-
closed in a lead sheath or else is covered with tarred jute
and is surrounded by a cotton braid saturated with water-
proof compound. Lead-covered paper-insulated cables are
now principally used in telegraphy, and are called saturated-
core cables if the paper insulation is saturated with an in-
sulating compound, or dry-core cables if the insulation is
untreated. The saturated-core cables excel the dry-core
cables in the protection afforded in case of mechanical
injury, but have a higher electrostatic capacity, due to
the larger specific inductive capacity of the insulating com-
pound. Low capacity is especially desired in telephonic
270
TELEGRAPH ENGINEERING
transmission and therefore dry-core cables with somewhat
smaller wires (usually of No. 19 to No. 22 B. & S. gage for
local distances) are considered standard practice. In order
to exclude moisture from dry-core cables, the ends of sec-
tions when supplied by manufacturers, are always satu-
rated with paraffin or other insulating compound for a
distance of about two feet, and the lead sheath is then
hermetically sealed. The sheaths for cables may be of
pure lead, lead and antimony composition, or lead with
a small percentage of tin; their minimum thicknesses are
outlined in the following table.
Number of
conductors
Thickness of
sheath
Inch
10 tO 100
Ji-
IOO tO 2OO
/z
200 tO 400
A
The conductors of a paper-insulated cable may have a
single, double or triple wrap of manila rope paper spirally
applied, the thickness of each being from 0.004 to 0.008
inch. The thickness of the insulation around the con-
ductors of a rubber-insulated aerial or underground tele-
graph cable varies from 20 to 60 mils.
Telegraph companies usually specify that the individual
rubber-insulated conductors for a telegraph cable be im-
mersed in water for 24 hours and thereafter while still
immersed be able to withstand an alternating electro-
motive force of looo volts, applied for one minute be-
tween the conductor and the water. With dry-core cables
the finished lead-covered cable is subjected to a similar
test. The insulation resistance of each conductor is then
TELEGRAPH LINES AND CABLES
271
measured by an application of 100 volts for one minute
across this conductor and all the other wires and the
sheath, the reference temperature being 60 deg. fahr. A
table showing the variation of the average insulation re-
sistance with temperature is usually supplied by the cable
manufacturer.
Cables are also used where telegraph lines extend across
rivers, lakes and bays, or from the mainland to islands.
Such submarine cables are formed of either rubber- or
paper-insulated conductors within a lead sheath, this
sheath being covered with several layers of jute thoroughly
saturated with a waterproof compound. Cables to be
installed on rocky river-beds or in waters having rapid
currents are provided in addition with an armor of galva-
nized iron wire, which is surrounded by jute servings sat-
urated with a compound of pitch and fine sand.
The telegraph cable mileage in the United States in 1907
is tabulated below:
Location
Miles of cable
Miles of single
wire in cables
Average num-
ber of wires per
cable
Overhead
2 ego
40,066
ie e
Underground
1130
37,727
33.4
Submarine*
7760
7.7,82
2 O
Total
7488
8<?,i7<;
* Exclusive of ocean cables.
The weights and prices of the Standard Underground
Cable Company's telegraph cables, composed of No. 14
B. & S. gage conductors with fibre or paper insulation
measuring /2 inch in diameter over insulation, are given
in the following table:
272
TELEGRAPH ENGINEERING
Number of
conductors
Diameter over
sheath in
inches
Weight in
pounds per
foot
Catalog price
in cents per
foot
5
0.76
I.4I
25-1
10
0.97
1-93
33-9
20
1.16
2,. 55
45-7
50
1.63
4-23
81.2
100
2.18
6-54
133-9
150
2-55
8.45
181.5
Aerial Cable Installation. — In supporting overhead
cables on pole lines it is necessary to provide supports be-
tween poles because the cable itself does not possess suf-
ficient strength to sustain its own weight over ordinary
pole spans. The required support is furnished by solid or
stranded galvanized steel messenger wires of proper size, in
accordance with the weight of the cable and length of
span, to which the cable is fastened- by means of appro-
priate hangers at intervals of about 2 feet. The messenger
wire is fixed to the sides of poles or to their lower cross-
arms by means of suitable messenger supports. The sizes
and breaking stresses of various grades of steel messengers
are given in the following table:
Diameter
Weight in
Breaking st
ress in pounc
Is
in inches
pounds per
100 feet
Besse-
mer
Siemens-
Martin
High-
strength
Plow
Solid |
0.192
0.225
9.8
13-4
....
2,500
3.500
4,300
5.900
6,000
8,000
Stranded •
0.250
0.312
o 37"?
13.0
22.0
30 o
2,500
4,200
r 700
3,060
4,860
6,800
5,100
8,100
1 1 , 500
7,600
12,100
17,250
0-437
0.500
4O.O
52.0
7,600
9,8OO
9,000
1 1 ,000
15,000
18,000
22,500
27,000
TELEGRAPH LINES AND CABLES
273
The sags of messengers at different temperatures and
the transverse stresses on aerial
cable pole lines may be deter-
mined in the same manner as
shown in § 2. One type of cable
hanger, known as the metro-
politan, is represented in Fig. 6.
5. Underground Cable In-
stallation. --In densely-popu-
lated localities it is customary to place telegraph and
Fig. 6.
Fig. 7.
other electric cables underground. These cables are not
buried in the ground, but are drawn into finished ducts
274
TELEGRAPH ENGINEERING
or conduit from one manhole to another. When laid,
conduit having a sufficient number of ducts to allow
for future growth is placed in a trench and is partially
or entirely surrounded with concrete. Fibre and vitrified-
clay conduits are those principally installed, but ducts may
also be formed in concrete directly. Fig. 7 illustrates the
single-duct and multiple-duct types of vitrified clay con-
duit manufactured by the H. B. Camp Company. The
lengths of multiple-duct conduit are held in alignment by
dowel pins and each joint is wrapped with a layer of wet
muslin or burlap and thereafter plastered with cement
mortar. The top of conduits should not be less than 20
inches below the street surface.
The arrangement of a six-duct conduit of concrete, fibre,
multiple-duct clay and single-duct clay is shown in Fig. 8,
with dimensions in inches. The total costs per trench
foot of these types of conduit construction installed, in-
cluding repaving but exclusive of manholes, as estimated
by W. N. and C. L. Matthews, for various numbers of
ducts, are given in the following table:
Num-
Costs per trench foot in dollars
ducts
Concrete
Fibre
Multiple
clay
Single
clay
I
O 44
° 51
2
0.56
0.67
0-73
0.76
3
0-73
0.88
1.03
1.05
4
0.83
0.91
0.98
1.09
6
0.97
1.22
1-37
1 .46
8
I.I7
i-SS
1.64
1.92
12
1 .40
1.98
2. II
2.45
16
l.67
2.42
2.72
3.01
20
I-9S
2.94
3-22
3563
TELEGRAPH LINES AND CABLES
275
This table is based upon the spacings shown in Fig. 8,
but with multiple-duct vitreous clay conduit i inch of
concrete is allowed between the sections, and it assumes
that the conduit is laid in streets with granite or equivalent
paving. Oftentimes the concrete at the sides of the con-
4.
m
f!X 4>U •O'l »I t£?.:
I3CK1
.--.•
FIBRE TUBE
MULTIPLE CLAY
Fig. 8.
duit is dispensed with, thereby reducing the cost of in-
stallation.
Manholes, or conduit-openings, are located along the
conduit line at suitable distances apart, rarely greater than
700 feet, to facilitate the installation, repair and removal
of cable sections. The manholes are constructed of brick
or concrete, in sizes of 3 ft. by 3 ft. and upwards, depend-
ing on the number of cables to be accommodated. Fig. 9
276
TELEGRAPH ENGINEERING
shows a section of an oval manhole whose inside dimen-
sions are 7 ft. by 3! ft. The costs of manholes of either
construction vary from about $60 to $150 according to
their size and the nature of the ground where they are
installed.
GRADE LINE \
Fig. 9.
Cable Splices. — Aerial and underground cables are al-
most invariably spliced near poles or in manholes respec-
tively. The method of making splices in multi-conductor
paper-insulated cables is indicated in Fig. 10. Two cables
to be spliced are placed in position so that their conductors
overlap from 12 to 24 inches, depending on the number of
conductors. The corresponding innermost conductors of
the two cables are then twisted together as shown at A,
and a paper or cotton tube is placed over the joint as
shown at B. All others are similarly spliced with the
joints staggered (C, Fig. 10), and then the entire splice
is boiled out with paraffin and wrapped with muslin or
linen. A lead sleeve, whose inside diameter exceeds the
TELEGRAPH LINES AND CABLES
277
outside diameter of the cable sheaths by i or i| inches,
is then placed over the splice and is joined to the sheath
by means of wiped soldered joints.
Fig. 10.
Cable Pole Boxes. — At suburban points beyond which it
is not deemed necessary to extend underground cable lines,
and at water crossings, cables are brought to the tops of
poles and terminated in cable pole boxes, as shown in Fig.
ii. Combined fuses and lightning arresters are located
within this cable box, as shown at /, and are interposed
between the bare aerial wires and the cable conductors.
Electrolysis of Underground Cable Sheaths. — If stray
electric currents of an electric railway system, in wending
their way back to the generating station, flow out of cable
sheaths in moist locations at certain places, electrolytic de-
composition of the sheaths occurs at these places, for the
sheaths there behave as anodes in electrolytic cells. Con-
tinued electrolytic decomposition, or electrolysis, causes
the pitting of the cable sheath, and the consequent ad-
mission of moisture to the insulation around the con-
ductors within the protecting sheath. The extent of
278
TELEGRAPH ENGINEERING
electrolysis depends upon the number of ampere-hours
conducted, since, according to t araday's Law, one ampere
flowing out of a lead sheath into an electrolyte for one hour
would dissolve 3.87 grams of lead.
Fig. ii.
In order to locate the regions where this rapid corrosion
of cable sheaths takes place, tests are made at manholes
to determine the potentials of the sheaths with respect to
the adjacent ground, and the amounts of current carried
by them. By thus observing the direction and value of
the stray currents at a number of manholes, the places
where currents leave the cables and pass to the moist
ground are readily determined. Where a cable sheath is
found by test to be decidedly positive with respect to
TELEGRAPH LINES AND CABLES 279
ground or to the railway track, a temporary connection of
heavy copper wire including an ammeter may be made
from the sheath to a suitable ground, to the track, or to
a neighboring negative feeder. Readings at other places
where the sheath was positive to earth may then be re-
peated, and if conditions are improved, a permanent
soldered bond is installed so that the current may flow
from the cable along a wire instead of into an electrolyte.
Where several cables pass through a manhole it is good
practice to bond all of them together. After such bonds
are in place, another complete and final survey is made.
The use of negative track feeders of proper copper dis-
position, and possibly with negative boosters in these
feeders, reduces the stray railway currents to a large
extent.*
6. The Earth as a Return Path. — Professor Steinheil
in 1837 made the discovery that the earth may be used as
a portion of an electric circuit. It has been stated that
the resistance of the earth when used as a return circuit
for a telegraph line is very small if the line terminals are
properly grounded. To verify this statement, consider a
hemispherical ground electrode of radius a centimeters to
be buried a short distance below the earth's surface. The
resistance of the earth outward from this electrode to a
distance d centimeters is
pdr xv
-£
as expressed by Heaviside, where p is the specific resist-
ance of the earth, assumed uniform, in ohms per centi-
* See Sheldon & Hausmann's "Electric Traction and Transmission
Engineering," p. 157; G. I. Rhodes' paper, A.I.E.E., Trans. 1907, p. 247.
280
TELEGRAPH ENGINEERING
meter cube, and r and r + dr are the radii of concentric
hemispherical equipotential surfaces, in centimeters. The
distribution of resistance outward from this electrode may
be calculated from equation (22) by considering the resist-
ances over the distances, say a to 2 a, 2 a to 4 a, and so on.
Thus
2irJa
P
871-0
ohms, etc.
The following table shows the resistance values for the
various distances from the electrode, and Fig. 12 shows
the total resistance outward from the electrode for a par-
ticular case in which p = 800 ohms per centimeter cube and
a = i foot = 30.5 centimeters.
Distance in
centimeters
Resistance
in ohms
a to 2 a
o . 07958 p/a
2 a to 4 a
o. 03979 p/a
4 a to 8 a
0.01989 p/a
8 a to 16 a
0.00994 p/a
16 a to 32 a
0.0049 7 p/a
32 a to 64 a
0.00248 p/a
64 a to 128 a
0.00124 P/a
It is seen that the greater share of the ground resistance
is very near the electrode, consequently good conductivity
of the soil near the electrode is essential, but with greater
distances from the electrode the earth's conductivity be-
comes of less importance. It is also to be noted that the
resistance varies inversely with the size of the electrode,
whence the desirability of utilizing available extensive
municipal water pipes as ground electrodes.
TELEGRAPH* LINES AND CABLES
28l
Inasmuch as the resistance between two electrodes is
principally in the neighborhood of these electrodes, the
total resistance between them might be expressed as
2 7T
(23)
20 40 60 80
DISTANCE FROM GROUND
ELECTRODE IN FEET
Fig. 12.
where a and a' are the radii of the two electrodes respec-
tively, it being understood that one electrode is not perfectly
insulated from its mate. Some instances of almost com-
plete electrical isolation
of the ground at a local-
ity from the earth have
been observed. Thus, to
secure telegraphic com-
munication with Nash-
ville, Tenn., it was found
necessary to extend a
ground-wire from that
city to an effective ground
at a point several miles distant. On the other hand, large
sections of the earth between two widely-separated stations
may be perfectly insulating without materially increasing
the resistance of the ground return.
When the pipes of a community's water supply are not
available as a ground electrode, satisfactory ground con-
nections may be made by driving two or more iron pipes
about 2 inches in diameter into moist earth in the basement
of the telegraph office. Line and office connections with
such pipe grounds are of copper wire, usually larger than
No. 9 B. & S. gage, well soldered to the pipes.
In the practical measurement of ground resistance either
another permanent electrode presenting a known ground
282 TELEGRAPH ENGINEERING
resistance or two auxiliary temporary ground electrodes
or grounds are used, these test grounds being at least 15
feet distant from each other and from the permanent
main ground whose resistance is to be measured. In the
first case the series resistance of the two grounds minus
the resistance of the known ground gives to a fair degree
of accuracy the resistance of the desired ground. In the
second case, employing two auxiliary grounds in the
measurement of the main ground, the resistance between
each pair is observed. Then, if RI be the series resistance
between the main and first auxiliary grounds, R% that
between the main and second auxiliary grounds and RZ
that between the two auxiliary grounds, it follows that
the earth resistance at the main ground is
R = *i + fr-ft. (24)
2
The resistance of a ground will vary from time to time, de-
pending upon the amount of moisture in the soil in the
immediate neighborhood of the electrode. In practice
these resistance measurements are made periodically, at
least once a year.
The Western Union Telegraph Company specifies that
the resistances of various classes of grounds should not in
general exceed the following values:
Central office battery grounds o . i ohm,
Small office and test station grounds 5 ohms,
Lightning arrester grounds 15 ohms,
High-potential protection grounds 25-100 ohms.
7. Electrical Constants of Telegraph Conductors. — The
four electrical constants of a line conductor are : resistance,
inductance, capacity and leakance.
TELEGRAPH LINES AND CABLES 283
Resistance. — The resistance to direct currents of a wire
of area A square inches, at any temperature / degrees cent.,
expressed in ohms per mile, is
R = 0.02495 .£ (i + at), (25)
where p is the specific resistance in microhms per centi-
meter cube of the material at o°cent., and a is the mean
temperature coefficient of electrical resistance per centi-
grade degree reckoned from o° cent. Accepted values of
these constants for copper and iron follow:
Material
P
a
Annealed copper (stand.)
Hard-drawn copper
Galvanized iron
1.587
1.631
9.69
0.00427
O.OO4I4
0.0058
Tabulated values of the resistances of standard sizes of
telegraph wire are given in Chap. I. The conductivity of
commercial copper and bimetallic wire is usually specified
as a percentage of that of standard annealed copper.
Inductance. — The self-inductance of a single linear cylin-
drical wire, mounted at a height h above the ground which
serves as the return path, is
. r.
L = 0.000741 logio ^ + 0.0000805 n (26)
henrys per mile, where D is the diameter of the conductor
and p. is its permeability. A short table of logarithms
appears in the appendix. The mutual inductance between
two parallel ground-return wires, mounted at the same
height above the ground and separated by a distance d, in
henrys per mile, is
,, , N
M = 0.000741 logio - *— --- (27)
284
TELEGRAPH ENGINEERING
In these expressions, h, D and d must be expressed in the
same units. Therefore the total inductance of the two
similar wires for equal currents in the same direction is
L. = i(L + aO, (28)
while for equal currents in opposite directions is
2 d
or 0.00148:2 logio—
0.000161 ju. (29)
Equation (29) indicates that the inductance of wires
within a grounded conducting sheath is very small, inas-
much as the sheath, which may be considered as the return
path, is very near the conductors.
For compound conductors consisting of a steel core sur-
rounded by a copper shell, the factor /z in the foregoing
equations is replaced by the values given in the following
table for various ratios n of the conductivity of the com-
pound wire to that of a solid copper wire of the same
outside diameter, // being the permeability of the steel core.
n
Factor to replace n
O. 2
0-3
0.4
o-5
o.2g8fjLf +0.1292
o. 1012/1' + o. 204
0.0416 M' + o. 294
o. 0185 M' + 0.386
This table, derived from that given by Fowle,* assumes
steel to have 12 per cent of the conductivity of copper.
Capacity. — The capacity of a single overhead wire
utilizing ground as its return, in microfarads per mile, is
C =
0.0894
,t
(3°)
cosh"1
* Electrical World, v. 56, p. 1474.
f Sheldon and Hausmann's " Electric Traction and Transmission Engi-
neering," p. 230.
TELEGRAPH LINES AND CABLES 285
the symbols having the same significance as above. For
large values ot — , it is more convenient to use the very
approximate equation
where € is the base of Napierian logarithms and is equal to
2.7183. Logarithms to the base e may be obtained by mul-
tiplying the corresponding logarithms to the base 10 by
2.3026; that is, logex= 2.3026 logio %>
When a number of overhead wires are located near each
other, the capacity of each wire is increased by the pres-
ence of the others. For two parallel ground-return wires
suspended at the same height above the ground and sepa-
rated a distance d from each other, Heaviside gives as the
capacity of each wire in microfarads per mile:
0.0894 log^ -=-
(a*)
Their mutual capacity in microfarads per mile is
0.0894 log€
As the number of wires in close proximity to each other
increases, the formulae for their individual and mutual
* Sheldon and Hausmann's " Alternating Current Machines," p. 313.
286 TELEGRAPH ENGINEERING
capacities become more and more unwieldy for numerical
computation.*
• Thus, for a single No. 9 B. & S. gage wire, suspended 25
feet above the ground, the capacity is
n 0.0894
2.3026 log10
0.00966 mf. per mile.
O.II44
If another similar ground-return wire be placed hori-
zontally i foot distant from the first, then
A ,
= 9.25 and loge - '—^L - = 3.91;
therefore the capacity of each wire, as obtained from
equation (32), is now
„ 0.0894 X 9.25 or M
C = - -- XV / NO = 0.01178 mf. per mile.
(9.25)2- (3.91)2
The mutual capacity of the wires is found to be
Cm = 0.0050 mf. per mile.
The capacity of a single-conductor cable within a con-
centric metallic sheath, in microfarads per mile, is
;. (34)
where k is the specific inductive capacity or permittivity
of the homogeneous separating medium or dielectric, d is
the inside diameter of the conducting sheath and D is the
diameter of the conductor. If the dielectric consists of n
* Refer to Oliver Heaviside, "Collected Papers," v. i, p. 45; Louis
Cohen " Calculation of Alternating Current Problems," p. 97.
TELEGRAPH LINES AND CABLES
287
cylindrical layers having different specific capacities fe,
&2, • • • , kn, and of outer diameters dit d%, . . . d respec-
tively, the capacity of the conductor in microfarads per
mile is
C =
0.0894
D
d
(35)
The capacity of multi-conductor dry-core paper-insulated
aerial or underground cables, in microfarads per mile, are
usually as follows:
B. & S. gage number
Mutual capacity
Grounded capacity
|
14
O. IOO
Telegraph cables <
16
O OQ2
*
18
O.O8O
Telephone cables \
13
16
O.O72
O.O72
0.108
0.108
iQ
22
o . 074-0 . 080
0.070-0.083
O.III-O.I2O
O.IOS-O.I25
The mutual capacity is that of a conductor with respect
to its mate of a twisted pair, all the other wires being
grounded to the sheath. The grounded capacity is that of
one wire against all the others grounded to the sheath.
Leakance. — The reciprocal of the insulation resistance
of a line, when expressed in ohms, is called the leakage con-
ductance or leakance of the line and this constant may be
expressed in terms of a unit which is often called the mho.
The insulation resistance of a well-constructed open line
fastened to insulators that are mounted on poles or towers
may be from about 50 to 100 megohms per mile in clear
weather, but will drop to a fraction of a megohm during
288 TELEGRAPH ENGINEERING
prevailing wet and foggy weather. Thus, the leakance of
the wire at insulators, at places where the wire touches
trees, etc., due to moisture and dirt, is of the order of
from io~5 to io~8 mhos.
The insulation resistance of a rubber- or paper-insulated
wire within a sheathed cable is usually over 200 megohms
per mile (at 60° fahr.) when laid, spliced and connected
to terminals, each wire being measured against all the
rest and the sheath. Submarine cables generally have an
insulation resistance of over 1000 megohms per mile. The
leakance of a properly-installed cable is not affected by
weather conditions unless moisture enters as the result of
mechanical injury to the cable sheath.
8. Elimination of Inductive Interferences on Telegraph
and Telephone Lines. — Whenever direct currents are
established, changed in intensity and stopped, or when-
ever alternating currents are maintained, in an electric
circuit, electromotive forces are induced in all neighboring
conductors (a) due to the varying magnetic field, the in-
duced voltages being dependent upon the time-rate of
change of current in the inducing circuit and the proximity
of the wires to this circuit, and (b) due to the varying
electrostatic field, the resulting current flow being depend-
ent upon the time-rate of change of voltage in the inducing
circuit and the proximity of the wires to this circuit.
Thus, when telegraph and telephone circuits are located
in parallel proximity to the lines of large alternating-
current railway and power-transmission systems, the
latter operating at voltages up to 150,000 volts, these
circuits derive by electromagnetic and electrostatic in-
duction sufficient voltages to interfere seriously with their
TELEGRAPH LINES AND CABLES 289
proper transmission of signals. Fig. 13 shows the disturb-
ing effect on a ground-return telegraph line AB during the
brief time that the alternating current in the disturbing
wire CD is growing from zero to its positive maximum
value, the full and dotted arrows on the telegraph line in-
dicating respectively the currents produced electromag-
Fig. 13.
netically and electrostatically. The directions of these
currents change repeatedly in unison with the current in
the disturbing wire. With metallic circuits having the out-
going and return conductors close together, which is the
almost universal arrangement of telephone lines, electro-
magnetic disturbances may be eliminated so far as the
terminals are concerned by transposing the two wires of
the telephone line at the center of exposure to the dis-
Ao"
Fig. 14.
turbing wire, as shown in Fig. 14, for the same conditions
as in the preceding figure. However, electrostatic dis-
turbances, while reduced, are not eliminated, but it is
evident that such disturbances may be minimized by fre-
quent transposition of the two-line wires. When numer-
ous aerial telephone lines are mounted on the same poles a
careful consideration will yield a satisfactory arrangement
of transpositions for the elimination of mutual disturbances
290
TELEGRAPH ENGINEERING
as well as those occasioned by adjoining power circuits.
Fig. 15 shows a single aerial transposition made at a trans-
position insulator of the type represented at the right of
Fig. i.
Simple expedients for the elimination of small inductive
interferences on earth-return telegraph lines have been de-
Fig. 15.
vised and usually involve: the addition of inductance and
resistance to the line, shunting of relays with resistances or
condensers, or the provision on each relay of a neutralizing
winding which connects with one coil of a transformer
whose other coil is inserted in the line wire. Severe in-
ductive disturbances on grounded lines, however, require
better neutralization. Conductors within metallic sheaths
are shielded from electrostatic
but not from electromagnetic
induction.
Fig. 1 6 indicates one method
for diminishing electrostatic
and electromagnetic disturb-
ances on a ground-return line.
At frequent intervals along the line one coil of current
transformers S is bridged across a resistance R in the
telegraph line AB, the other coil being properly joined
in series with a neutralizing wire NN, or, if practicable,
with the disturbing wire itself. „ Also a potential trans-
former P has one coil included in the neutralizing wire,
and its other coil with a condenser C of proper capacity is
Fig. 16.
TELEGRAPH LINES AND CABLES 2QI
bridged from the telegraph wire to ground. This"neutraliz-
ing wire is placed parallel and close to the telegraph line
or lines and inasmuch as it is subject to the same magnetic
effects as the signal wires, the currents developed in it are
arranged to oppose by transformer action those developed
in the telegraph lines, thereby neutralizing electromagnetic
disturbance. Electrostatic induction is neutralized by the
potential transformer P in a similar manner.
Another method * particularly suitable for single-phase
alternating-current railway systems and not requiring an
additional conductor is shown in Fig. 17. The telegraph
Fig. 17.
wire AB parallels the sectionalized overhead trolley wire
which has alternate sections of opposite polarity, as indi-
cated, in order to minimize electrostatic induction. Each
section is fed at both ends from adjacent substations by
.means of the secondary windings s of the transformers
T, whose primary windings p are connected across the
high-tension transmission line, not shown. A car located
between substations draws some current from each sub-
station depending upon its distance therefrom, and these
currents flow in opposite directions, the greater current
over the shorter distance, and vice versa. Electromagnetic
induction is neutralized by this arrangement.
The present method of overcoming the detrimental
* Taylor's " Telegraph and Telephone Systems as Affected by Alternating-
current Lines," Trans. A.I.E.E., v. 28, p. 1202.
2Q2
TELEGRAPH ENGINEERING
effects of induction on the telegraph and telephone lines
paralleling the single-phase lines of the New York, New
Haven & Hartford Railroad, recommended by a com-
mittee including Mr. G. M. Yorke, is giving marked satis-
faction in practical operation. The generator voltage of
11,000 volts is stepped up to 22,000 volts by means of
auto- transformers A, Fig. 18, situated in the power station;
Fig. 18.
one terminal of each transformer joins with the contact
conductors or trolleys, the other joins with feeders which
extend along the roadway, and the mid-point connects to
the rails. The arrangement is similar to three-wire direct-
current distribution systems except that the direct load is
on one side of the circuit, the other side receiving its share
through the sectionalizing auto-transformers T, T situated
on sectionalizing bridges at frequent intervals over the
roadway. It will be seen that any train draws its current
from the auto- transformers on either side, the directions
of the currents in the n,ooo-volt and 2 2,000- volt circuits
being indicated by full and dotted arrows respectively.
Inasmuch as the two parts of the current taken by a train
flow in opposite directions toward this train, electromag-
netic effects on adjacent telegraph and telephone lines are
TELEGRAPH LINES AND CABLES
293
neutralized. Since the feeders may be placed in the same
general direction as the contact conductors with respect
to neighboring lines, electrostatic disturbances may also
be neutralized, although such disturbances were inap-
preciable along the electrified zone of the New Haven
Railroad.
9. Simultaneous Use of Lines for Telegraphy and Teleph-
ony. — A pair of line wires forming a metallic telephone
circuit may be utilized at the same time as one or two
ground-return telegraph lines, without interference be-
tween the two classes of service. A single telegraph line
may also be used simultaneously as a grounded telephone
SUBSCRIBER 1
SUBSCRIBER 2
Fig. 19.
COMMON-BATTERY TELEPHONE
CB
line. Such combined working is extensively employed for
gaining increased earning capacity of the wire plant.
Telephone Circuits. — Figs. 19 and 20 show respectively
the connections of the telephonic apparatus for the inter-
communication of two subscribers joined to a magneto and
a common-battery telephone system. Sound waves imping-
294 TELEGRAPH ENGINEERING
ing upon the diaphragm of a telephone transmitter vary
its electrical resistance and consequently vary the current
in the corresponding line circuit; the varying current flow-
ing through the magnet of the telephone receiver produces
a varying attraction for the iron diaphragm, the motions of
which set up sound waves in the air which are similar to
those incident on the transmitter diaphragm.
Each subscriber's set of a magneto telephone consists
of a telephone transmitter T, telephone receiver R, hand-
driven magneto or alternating-current generator G (open-
circuited normally), polarized bell P, induction coil /, local
battery B and receiver hook switch H. A subscriber's set
of a common-battery exchange does not include a gener-
ator and local battery, but has a condenser C which keeps
the set open-circuited to direct current when not in use;
the circuit for such current is closed by the hook switch
when the receiver is lifted therefrom in the act of calling
and when conversing with another subscriber. Electrical
energy for the operation of the common-battery telephone
circuit is supplied by the battery CB located at the central
office, this battery also supplying current to numerous
other similar circuits, each circuit having its own repeat-
ing coil 5. The apparatus at the central office used in the
establishment and in the supervision of the connection be-
tween the two subscribers is not shown in the figure.
The repeating coil S is similar in design to the retarda-
tion coils used with the bridge duplex telegraph circuits
(p. 71), except that the resistance of each of the four
windings is usually from 20 to 40 ohms. Coils b and c
form the primary winding, and coils a and d form the
secondary winding of a transformer when subscriber i is
talking, the reverse being true when subscriber 2 is talking.
TELEGRAPH LINES AND CABLES 295
Variations in current magnitude in one subscriber's circuit
are thus inductively transferred to the circuit of the other
subscriber.
Simplex Signalling over Telephone Lines. — The simplex
simultaneous signalling system affords the transmission of
one telephone and one telegraph message over one pair of
wires, as indicated in Fig. 21. The two wires are used as
TO CENTRAL JVV-^O °fr~^<\_ T° CENTRAL
OFFICE OF CTT S Ifa 1 1 LTT S ID OFFICE OF
SUBSCRIBER 1 X>-O/d JC^X/T SUBSCRIBER 2
Fig. 21.
a metallic telephone circuit, and both wires in parallel are
used as the line wire of a ground-return telegraph line.
The junctions between the coils b and d of the two re-
peating coils 5,5 connect with the usual telegraphic ap-
paratus at single Morse stations. When the lines and
repeating coils are properly balanced, the current for
actuating the telegraph relays divides equally between the
two-line wires in flowing from station B to A, and these
portions flow in opposite directions around the iron cores
of the repeating coils, thereby contributing no magnetiza-
tion to the cores. Consequently the telegraph currents
will not affect the telephone instruments which connect
with the repeating coil windings a and c. Inasmuch as
the points of attachment of the telegraphic apparatus are
neutral points of the telephone line, the telephone voice and
ringing currents will not affect the telegraph relays. The
simultaneous transmission of both messages is improved
296
TELEGRAPH ENGINEERING
by the shunting of condensers C around the key contacts.
It is evident that the resistance of the telegraph line cir-
cuit is only half that of one of the telephone lines.
Intermediate telegraph stations may be readily intro-
duced into the circuit of Fig. 21 by inserting two retardation
coils and joining the mid-points of their coils to the tele-
graph apparatus at the intermediate office.
In telephony, an extension of the circuit arrangement,
shown in Fig. 2 1 , whereby two telephone circuits each with
two repeating coils permit of the establishment of a third
telephone circuit, is much used for long-distance trans-
mission. This third, or so-called phantom circuit, utilizes
the two conductors of one of the side or physical circuits
as the outgoing conductor, and the two conductors of the
other physical circuit as the return (see Fig. 24), with an
obvious gain in transmission efficiency.
TO R
TELEPHONE
APPARATUS R
Fig. 32.
Composite Signalling. — Composite simultaneous signal-
ling secures the transmission of one telephone and two
telegraph messages over one pair of wires, each telephone
wire serving as a ground-return telegraph line. Pioneer
work in this field was done by Van Rysselberghe. Fig. 22
shows a modernized arrangement of the composite system,
TELEGRAPH LINES AND CABLES 297
and it will be observed that impedance coils and condensers,
for opposing respectively the alternating telephone and the
direct telegraph currents, are the principal features.
It is seen that the upper and lower telegraph currents
are confined to their respective line wires because of the
condensers c\. The condensers &i eliminate sparking at
the key contacts and also take care of the rise and fall
of the current in the telegraph circuit so as not to influence
the telephone instruments. The telephone circuit includes
both line wires and the four condensers c\. Because of the
high impedance of the retardation coils Z to alternating
currents of high frequency (telephone currents are often
considered to have a representative frequency of 800 cycles
per second), the telephone cur-
rents are prevented from enter-
ing the telegraph circuits. The
function of the retardation coils
R and condensers c is to balance
the telephone line and guard
against mutual interferences be-
tween the telephone and tele-
graph circuits. The two coils
Fig. 23.
R at each end may also be
replaced by a repeating coil of the type shown in
Fig. 21.
The following numbers indicate the order of magnitude
of the condenser capacities: c = 2 mf., c\ = 2 mf. and
c2 = 6 mf . The impedances Z and R are windings on soft
iron cores of the closed type (Fig. 23) and possess large
inductance; their resistances are respectively 50 and 30
ohms.
Telephone ringing over composited lines by the usual
298
TELEGRAPH ENGINEERING
low-frequency generators (about 16 cycles) is unsatisfactory
because the impedance of the retardation coils Z is small
to these ringing currents, resulting in chattering of the
relay armatures. Instead, calling is accomplished by
means of weak high-frequency currents (about 300 cycles)
over the lines which actuate suitable relays that control
the operation of local low-frequency ringing devices.
Phantom Circuits with Simplexed and Composited Tele-
phone Lines. — Two telephone circuits, each adapted for
simplex telegraphic signalling, as shown in Fig. 21, may
also simultaneously serve as the conductors of a phantom
Fig. 24.
telephone circuit, as shown schematically in Fig. 24. The
location of the simplex telegraphic apparatus is indicated
by the letters A, B, C and D. In a similar manner, two
telephone circuits, each adapted for composite working as
shown in Fig. 22, may also simultaneously serve as the
conductors of a phantom telephone circuit, thereby secur-
ing 4 telegraphic and 3 telephonic channels over 4 wires.
Railway Composite Signalling. — Telephonic and tele-
graphic communication may also be effected simultaneously
over a single line, both services utilizing the ground as the
return path. Such telephonic transmission over existing
TELEGRAPH LINES AND CABLES
299
telegraph lines is possible over distances up to say 200
miles, and is therefore useful principally in supplementing
telegraphic signalling on railway telegraph lines.
The arrangement of the apparatus at a terminal station
for such composite signalling differs from that used with
magneto or common-battery systems, and is shown in
Fig. 25. Several intermediate telegraph and intermediate
z
Fig. 25.
telephone sets may be operated on a line, code signalling
being utilized for telephonic calling. Portable telephone
sets may be carried on the trains so that in cases of emer-
gency one may be bridged from the line to ground at any
place, enabling prompt requests for directions or assist-
ance. At intermediate telegraph stations a condenser and
a resistance bridge the telegraph set so as to maintain the
continuity of the line for telephonic currents, and to pre-
vent the high-frequency signalling current affecting the
telegraph relay.
Referring to Fig. 25, the presence of the impedance
coil Z prevents telephone currents passing through the re-
lay, as before ; also the presence of the condenser C hinders
the telegraph currents from entering the telephone circuit.
The signalling current is produced by an induction coil /
300 TELEGRAPH ENGINEERING
with a vibrator, the coil also serving for transmission pur-
poses when talking. The signal-receiving device is a
special telephone receiver or howler h, with a heavy dia-
phragm, which is responsive to incoming high-frequency
signalling currents.
To signal another telephone station the keys K\ and KI
are depressed; in reality both keys are combined so they
will open and close together. The closing of key K\ sets
the armature of induction coil / in vibration, and the core
is repeatedly magnetized and demagnetized. The alter-
nating current induced in the other winding thereby flows
from ground, through the lower contacts of hook-switch
H and key K2, through coil / and condenser C to the line.
At the other stations this signalling current flows through
the condenser C, howler h, upper contact of key K2 and
lower contact of hook-switch H to ground, thus operating
the howler.
Having secured the distant station attendant, the keys
are released and the receiver R is lifted from the hook.
The local transmitter circuit is now completed and the
receiver is placed in connection with the line through the
condenser C and the secondary winding of the induction
coil.
PROBLEMS
1. For a factor of safety of 5 against wind pressure, what should
be the diameter of poles at the ground line for supporting 10 No. 6
B. W. G. iron wires at intervals of 100 feet along a straight path?
The poles project 25 feet above the ground and the center of load
may be considered as 5 feet from the pole-tops. Allow 8000 pounds
per square inch as the breaking fibre stress of the poles, and assume
an ice coating \ inch thick all around the conductors.
2. What sag should be allowed in zoo-foot spans of No. 9 B. & S.
gage hard-drawn copper wires while being strung at a temperature
TELEGRAPH LINES AND CABLES
3OI
of 80 degrees fahr., so that the tension in the wires with a £-inch ice
coating at — 20 degrees fahr. will not exceed 300 pounds ?
3. Determine the economic pole spacing for a pole line with
No. 12 B. & S. gage hard-drawn copper wires in which the maximum
allowable tension is specified as 100 pounds. The wires are to have
a minimum clearance of 20 feet above ground, the cost of cross-
arms, insulators, pins, etc., is $2.00 per pole, and the pole cost-
constant is a = 0.005.
4. Estimate the cost per mile installed of two zoo-conductor (No.
14 B. & S.) lead-covered telegraph cables located in a clay under-
ground conduit, with manholes 440 feet apart, each costing $75.00.
The cost of drawing the cables in the conduit and splicing the con-
ductors may be assumed as 7 cents per foot of cable.
5. Millivoltmeter readings over 6-foot lengths of a lead-sheathed
cable, taken at two successive manholes, were i.o and 0.25 milli-
volts. If the outside diameter of the sheath is 2.5 inches and the
thickness of its wall is £ inch, determine the current leaving the
cable-sheath to ground between the manholes, the resistivity of lead
being taken as 8 microhms per inch cube.
6. Two auxiliary grounds were employed in the measurement of
the ground resistance at a newly-constructed permanent ground,
and a battery in series with an adjustable resistance of r ohms was
successively bridged from one ground electrode to each of the. others.
The voltage V across the battery, the voltage drop V over the re-
sistance r and the earth potential difference E volts were observed
for each case with a voltmeter, resulting in the following data:
Quantity
From perma-
nent to first
auxiliary
ground
From perma-
nent to second
auxiliary
ground
Across the two
auxiliary
grounds
r
70
50
110
V
10.3
IO.O
II. 0
V
6.8
7.2
7.8
E
0-3
-O.I
O. 2
The ground resistance of each path is
V - V + E
V
r, whence the
resistance of the permanent ground may be computed.
302 TELEGRAPH ENGINEERING
7. Two No. 9 B. & S. gage copper wires one foot apart hori-
zontally are suspended 25 feet above the ground. Calculate the
total inductance per mile of both wires for currents in the same and
in opposite directions.
8. A single conductor 0.30 inch in diameter is surrounded by two
concentric layers of insulating material each 0.25 inch thick, the
inner and outer layers having specific capacities of 3 and 2 respec-
tively, and these are surrounded by a metallic armor. Compute the
capacity of this cable per' mile of length.
9. Draw a scheme of connections for compositing two telephone
circuits which serve simultaneously as the physical circuits of a
phantom telephone circuit.
CHAPTER X
THEORY OF CURRENT PROPAGATION IN LINE
CONDUCTORS
i. The Transmission of Current Impulses along Tele-
graph Lines. — The currents at any instant that pass
different points of a line conductor differ from each other,
and become less and less the more remote the point of
consideration is from the generator end of the line con-
ductor. This is due to the distributed nature of the four
line constants: resistance, inductance, capacity and leak-
ance. In determining the effect at any place on a telegraph
Fig. i.
line of impressing an electromotive force at one or both
of its terminals, it is necessary to consider the conditions
existing in telegraphic transmission. The nature of the
impulses to be transmitted by a telegraph line may be
inferred from graph (a), Fig. i, which indicates the sequence
and duration of the voltage applications to the line for
the -word "thumb." It is seen from this figure that
telegraphic transmission involves the propagation of long
303
304 TELEGRAPH ENGINEERING
and short unidirectional impulses of constant magnitude
hj which are variously grouped and spaced. The theory
of propagation of such irregular impulses may be con-
sidered in the following ways:
a. The impulses may be considered as made up of a
continuously applied direct current of magnitude -, upon
which is superposed an alternating current of rectangular
wave-shape of amplitude - . While this rectangular wave-
2
shape is susceptible to resolution into a Fourier's Series of
sine curves whose relative frequencies are the successive
odd numbers, it is much more convenient in the theory
of telegraphic transmission to consider a single equivalent
sine-wave alternating current rather than such a multiplicity
of harmonics which together constitute the actual impulse.
Graphs (b) and (c), Fig. i, reveal the approximation of
" equivalent" sine curves to dot and dash wave-shapes
respectively, the amplitude being conveniently taken as
2
- h. The frequencies of the equivalent alternating cur-
o
rents in the two cases correspond respectively to the number
of dots and to the number of T's which may be sent out on
the line per second, the latter frequency being ^ of the
former or dot-frequency. Neither frequency prevails for
more than several cycles, but nevertheless this alternating-
current theory of transmission leads to an approximate idea
of the propagation of telegraphic characters, especially
when the speed of signalling approaches the theoretically
attainable limit imposed by the conductor. It may be re-
marked that a somewhat similar condition exists in teleph-
ony, for in practical telephonic transmission calculations a
CURRENT PROPAGATION IN LINE CONDUCTORS 305
"representative " frequency of 800 cycles per second is
considered appropriate for a single equivalent sine-wave
alternating current, which is recognized in preference to
a constantly-varying series of complex wave-shapes that
actually constitute articulate speech. The frequency of
the equivalent telegraphic alternating current to be used in
any particular calculation depends upon the speed of sig-
nalling, the dot-frequency varying possibly from 15 cycles
or less with hand transmission to 125 cycles with automatic
transmission. The computed sinusoidal current wave-shape
at any point of the line may then be reduced to its corre-
sponding rectangular wave-shape.
0. If the speed of telegraphic signalling over a line is
much below that theoretically attainable thereon, the time
of growth and fall of the unidirectional current impulse
will be short in comparison to the duration of a dot signal,
and consequently the steady value of the current at every
place on the line will be reached within every signal. There-
fore the magnitude of the received impulses may be ascer-
tained on the basis of a maintained direct current flowing
over the line, the effects of inductance and capacity being
ignored because these constants influence only the growth
and fall of the current value. This method of treatment
may be termed the direct-current theory of transmission.
7. On the contrary, if the speed of signalling is such that
the current at any place does not nearly assume the ulti-
mate value that accompanies slower signalling during the
time of dot or dash signals, then a consideration of the
growth and subsequent fall of the current alone is of im-
portance. This consideration of occurrences during the
repeated transitional periods of application and with-
drawal of voltage on the line may be called the transition
306 TELEGRAPH ENGINEERING
theory of transmission, and is utilized chiefly in the treat-
ment of submarine cable telegraphy for computing the
shape of arrival current curves.
The transmission theories just enumerated will be con-
sidered in the order named, the first two being developed
in the present chapter while the third is discussed in the
following chapter devoted to submarine telegraphy.
Alternating-current Transmission Theory
2. Propagation of Alternating Currents along Uniform
Conductors of Infinite Length. — The impression of a
sinusoidal or harmonic alternating E.M.F. upon a localized
circuit, having resistance R, inductance L and capacity C,
initiates three reactions of the circuit as follows: (a) re-
sistance reaction (RIf), the overcoming of which produces
heat; (b) inductance reaction (I,—-), the overcoming of
\ at J
which develops a magnetic field; (c) capacity reaction
[ — / I'dt\ the overcoming of which forms an electrostatic
field; where I' is the instantaneous current value, and /
represents time. With long line circuits the electrical
constants of the circuit are distributed in space, and con-
sequently the current, while everywhere sinusoidal, has not
the same value or phase throughout the circuit.
The simplest case of alternating-current wave propa-
gation is that on conductors of infinite length, since on
such lines the effect of reflection of the waves at the distant
end can be ignored. Consider the element ds of an infinitely
long uniform line with a perfectly-conducting ground re-
turn, at a distance s from the end upon which a simple
harmonic electromotive force is impressed, as shown in
CURRENT PROPAGATION IN LINE CONDUCTORS 307
Fig. 2. A current will flow through the conductor, and at
the instant t at the element ds it may be represented by
/', and that in the adjacent elements by I' + dl' and
/' — dl1 ', the latter referring to the element more remote
from the generator. Let E', at this instant, be the poten-
tial of the line with respect to the earth at the element ds
and let the potentials of the adjacent elements above that
of the earth be E' + dEf and E' - dE' respectively. Let
R, L and C in homologous units represent respectively the
i i' i i-ai'
Ground
Fig. 2.
uniformly distributed resistance, inductance and capacity
of the line per unit length.
The difference of potential between the two ends of the
element ds is dE' and this must be equal to the sum of the
resistance and inductance reactions of the elementary cir-
cuit occasioned by the current /'. As only the reactions
of the conductor need be considered, there results for this
element
*f+— -f- •,-. <->
Since the line has capacity with respect to earth, it takes
a charging current; and since the line is not perfectly
308 TELEGRAPH ENGINEERING
insulated from ground, a slight leakage current will flow.
Therefore the current which does not continue beyond the
element ds, but which flows from the line to ground under
the voltage E', is
where g, the leakage conductance or leakance, is the recipro-
cal of the apparent insulation resistance per unit length of
line. Then
_<^-Cd-^ + E'z (2)
ds~ ' dt *g'
Differentiating (i) with respect to time, there results
^ dt* dt dt\ds
and differentiating (2) with respect to distance, there results
Substitution of the former in the latter equation gives
dl' dE'
and replacing the last term by its equivalent from (i) there
is obtained the equation of propagation of current along a
uniform line, as
the solution of which shows the current value at the point s
of the line at the time t in terms of the line constants
R, L, C and g.
CURRENT PROPAGATION IN LINE CONDUCTORS 309
Similarly, by differentiating (i) with respect to distance,
and (2) with respect to time, and then combining the re-
sulting expressions, there is obtained
dE' d2E'
Equations (3) and (4), for current and voltage distribution
respectively, are true for any length of line, and are identi-
cal, so that the solution of one of them suffices.
Since the magnitude of the current must decrease in re-
ceding from the generator end of the infinitely long line,
and since the current is simple harmonic when the impressed
electromotive force is such, and differs in phase therefrom
more and more as s increases, the following representation
of the current at any point s of the infinitely long line at the
time / suggests itself:
/'=/€-* cos (#- as), (5)
where 7 is the maximum value of the current at the genera-
tor end of the line, p is 2 T times the frequency of the im-
pressed harmonic electromotive force, e~^ is the diminution
in magnitude of the wave over unit length of circuit, a is the
phase retardation per unit distance which in degrees is
— , j8 and a being constants which depend upon the
resistance, inductance, capacity and leakance of the line,
and c being the base of Napierian logarithms.
The substitution of this assumed expression for the cur-
rent I' with proper values of a and /3 in (3) will satisfy this
equation and permit of the evaluation of the constants a
and /3. Thus, differentiating (5) with respect to time,
' = - pi€-» Sin (Pt - «s),
310 TELEGRAPH ENGINEERING
and again,
rPJ'
£- --#*/«-* COS (#- as) j
and differentiating with respect to distance,
sin (pt - as) - ftle^* cos (pt
a sin (pt -as) -ft COS (pt -as)},
JTf
— = air*8 sin (pt - as) - ftle^* cos (pt - as)
and again,
J2Tt
— = /€Hfc{ - a* cos (pt - as) - aft sin (pt - as) }
- Pie'?8 { a sin (pt - as) - ft COS (pt - as) }
= 7e-^[(/32 - a:2) COS (pt - as) - 2 aft sin (pt - as)].
Substituting these values in equation (3), there results,
^cos (pt - as) - (RC + gL) pie-**3 sin (pt - as)
* COS (pt - as) - le-P* [(ft2 - a2) COS (pt - as)
— 2 aft sin (pt — as)] = O,
or
p2CL cos (pt - as) + p (RC + gL) sin (pt - as)
- Rg COS (pt - as) + (ft2 - a2) COS (pt - as)
— 2 aft sin (pt — as) = O.
This expression can only be true if
fCL -Rg = -(0*- «2) = c? - p, (6)
and if
p (RC + gL)=2 aft. (7)
These are simultaneous equations which can be solved for
a and ft. Thus, substituting the value of a from (7) in (6)
gives the following biquadratic:
= o,
CURRENT PROPAGATION IN LINE CONDUCTORS 311
whence
(RC-
p*L2C2-p2LC + Rg].
Therefore,
(8)
and similarly
(9)
The constant /3 is called the attenuation coefficient, and a
is called the wave-length constant. Having determined the
values of a and 0, the current at any point on the line dis-
tant s from the generator at the time t may be determined
when the maximum current value is known at the end upon
which the electromotive force of frequency -2- is impressed.
At some other point on the line distant r from the genera-
tor end, the current value at the instant / is
// = /€-* cos (pt - or).
If this more distant point r be chosen so that the current
there will be in phase with that at the point s at that in-
stant, then
cos (pt — as) = cos (pt — or).
Between these points r and s there is an integral number of
complete waves, n; therefore, the wave-length is
n
Since the phase retardation can be considered over this
distance as 2 irn,
as + 2 irn = ar:
312 TELEGRAPH ENGINEERING
consequently,
r — s _
a n
As the frequency of the impressed electromotive force is
— cycles per second, the velocity of wave propagation
will be
v = -£-\ = £> (10)
27T a
In cables, because of the close proximity of the conduc-
tors to one another, the inductance is little and the capacity
large. Since 2 irf times the inductance is small compared
with the resistance of the conductors, and, in good telegraph
and telephone cables, as the conductance of the insulation is
small compared with 2 irf times the capacity, the attenua-
tion constant of such cables may be expressed in a more
convenient form by expanding the factors \^R2 + P2L2 and
^/p2C2 + g2 of equation (8) by the binomial theorem and
disregarding terms of higher order than the second as being
too small to make any appreciable difference. Then
*(>+m^(>+^]
PCR(* -i-^-i — £— 4— f?£-\
Neglecting the last term for similar reasons, the attenuation
constant becomes
CURRENT PROPAGATION IN LINE CONDUCTORS 313
If the inductance be entirely ignored, there results herefrom
by disregarding g 2 • This expression is convenient in
considering wave transmission over cables. If the leakage
conductance be taken as zero, it reduces to
3. Velocity of Wave Propagation over an Ideal Line. -
An ideal line may be considered a perfectly insulated one
employing conductors of zero resistance, for then the at-
tenuation would be nil. Thus, by substituting in (8) and
(Q)> g = ° and R = o, there results
0 = o and a = p VZC.
Therefore, the velocity of wave propagation on such a line
would be v = - —- (n)
VLC
The inductance of a straight conductor due to the mag-
netic flux surrounding the conductor, in electromagnetic
units per centimeter length, is
d-D
and the capacity thereof in electrostatic units per centi-
meter length is ^
d-D*
where D is the diameter of the wires and d is their inter-
axial separation.
314 TELEGRAPH ENGINEERING
As there are 9 X lo20 electrostatic units in one electro-
magnetic unit of capacity, the square root of the product of
these expressions in electromagnetic units is
3 X io10
Therefore, the velocity of electric wave propagation, when
the resistance and leakance of the conductors are neglected, is
3 X io10
v = ^ — — centimeters per second. (12)
With conductors in a medium like air, for which both the
permeability /* and the permittivity k are unity, the velocity
of propagation is 300,000 kilometers per second (186,000
miles per second), which is identical with the velocity of
light. For actual lines the velocity of wave propagation
is somewhat lower than this value.
4. Wave Propagation along Conductors of Finite Length.
— In the foregoing discussion of wave propagation on in-
finitely long lines, no cognizance was taken of reflection
of the outgoing waves upon arrival at the distant terminal
of the circuit. Voltage and current waves, which together
constitute an electromagnetic wave, when traversing rela-
tively short circuits having distributed capacity and induc-
tance, are partially reflected at both ends thereof with or
without phase reversal, total reflection taking place only
when the impedances at the terminals of the lines are either
zero or infinity (that is, short-circuited or open-circuited).
If a single impulse be impressed upon the circuit, a wave will
travel back and forth along the line, until it is attenuated
to practically nothing. If such waves continually depart
CURRENT PROPAGATION IN LINE CONDUCTORS 315
from one end of a line, and each wave is reflected a great
many times, alternately at the other and initial ends of the
circuit, before extinction, the current and voltage every-
where on the line will be gradually built up and ultimately
assume their final values. This steady state is approached
by successive jumps and not uniformly, although attained
in a very short time — perhaps a second. After the steady
state is reached, all the outgoing waves may be considered
together as a single resultant wave-train, and all the re-
turning waves as another single wave-train. The following
method of deriving the equations of current and voltage
distribution on lines of finite length for the steady state
displays the results physically as two oppositely moving
wave-trains, each of definite initial amplitude. By not con-
sidering the short, unsteady period immediately following
the voltage application, a simplification of operations may
be effected over the foregoing method of treatment by intro-
ducing the complex quantity, inasmuch as one independent
variable — that of time — is eliminated thereby. The
resulting expressions are complex quantities and their in-
terpretation must be made accordingly.
Harmonically varying quantities can be represented by
vectors. The length of such a vector shows the maximum
value of the quantity, and its direction indicates the phase
of that quantity. Each vector may be resolved into two
rectangular component vectors, say, one horizontal and the
other vertical. To distinguish vertical from horizontal
components, a symbol, usually^', is placed before the verti-
cal component. Thus, the expression a + jb means that b
is to be added vectorially at right angles to a. Obviously
the magnitude of the resultant vector is Va2 -{- b2, and
the angle it makes with the horizontal component is
316 TELEGRAPH ENGINEERING
tan"1 - • The interpretation of this quadrantal operator or
a
neomony isj = V— i.
By applying the operator to equations (i) and (2) and
counting the distance s positive from the receiving end of
the line, it follows that for the steady state
(13)
and
(14)
which are relations independent of time, wherein Em and
Im represent the maximum values of electromotive force
and current respectively at any point on the circuit. The
factor (R -\-jpV) may be called the conductor impedance,
and (g -\-jpC) the dielectric admittance. Differentiating
these expressions and substituting gives respectively
and
^=(R+jpL)(g+jpC)Im.
For convenience, let (R + jpL)(g + jpC) = y2, then the
equations of wave propagation along conductors become
;, .,' f-^ ' ;<«
and
^df = y2Im' (l6)
These are identical differential equations of electromotive
force and current which differ in the terminal conditions
CURRENT PROPAGATION IN LINE CONDUCTORS 317
only, and consequently the solution of one of them will
suffice.
Choosing the latter expression and multiplying through
by 2 — - j there results
d*Im dln dlm
2 ~7~z --- T~ = 2 rlm ~T~'
ds2 ds ds
which, when integrated, becomes
Replacing the constant of integration c\ by 72c22, where c^ is
also a constant, and separating the variables, there obtains
dlm
= yds.
V/ro2
Integration gives
loge [C3(lm +
where c3 is another constant of integration. Writing in
exponential form, this equation becomes
Squaring,
or -T-c22 = 2/ro — J
C32 C3
whence
/ _ *" _ tfc*
2C3 26^'
Choosing constants A and B so that
A = — and B = ^
318 TELEGRAPH ENGINEERING
the expression for the maximum value of the current at a
distance s from the receiving end of the line becomes
Im = Ae^8- B*"», (17)
where the two constants must be evaluated from the termi-
nal conditions.
Since the exponential coefficient 7 is the square root of
the product of two complex numbers, it is also a complex
quantity, and may be written
7 = 0 +ja,
where a and 0 are its two rectangular components. Then
08 +ja)» = (R +jpL)(g +jfQ, (18)
or
02 + 2ja0 +JW = Rg +jgpL +jpRC +
and remembering that j = V— i, this becomes
(02 - a2) + 2ja0 = (Rg - P2CL) +j (gpL +
This equation can only be true if
c?-f? = fCL - Rg,
and if
2a(3 = p(RC + gL).
These expressions are identical with equations (6) and (7),
and, therefore, the components of 7 have the same signifi-
cance as before; namely, 0 is the attenuation coefficient and
a is the wave-length constant, the values of which are given
by equations (8) and (9) respectively. The quantity 7 is
called the propagation constant of the line.
The maximum current value at a point on the line distant
s from the receiving end may now be indicated as
Writing for the exponential function with the imaginary
exponent the equivalent trigonometric expression e±:>as =
CURRENT PROPAGATION IN LINE CONDUCTORS 319
cos as ±7 sin as, the equation for Im becomes
Im = A<?8 (cos as +j sin as) — Bt~v* (cos as —j sin as), (19)
the first term of which, since it increases as 5 increases, may
be considered the main current wave, and the second term
may be called the reflected current wave. The amplitudes
of these waves at the receiving end are respectively A and B.
The maximum value of the voltage at the same point on
the line can be obtained by differentiating (19) or (17) and
substituting in equation (14),
Em = , /" [A f9 (cos as + j sin as)
g+jpc
+ Be~08 (cos as — j sin as)]. (20)
To evaluate the constants A and B, two conditions must
be known, as current and voltage at one end of the line, or
current at one terminal and voltage at the other terminal
of the line; thus, at the receiving end s = o, and equations
(19) and (20) give the maximum current and voltage values
respectively at this point as
Ir = A-B,
and
The fraction & +ja + g +jpC is frequently called the
surge impedance or characteristic impedance of the line.
Then
and
' (22)
The ratio of the amplitude of the reflected wave to that
of the main wave arriving at the receiving end, that is, the
320
TELEGRAPH ENGINEERING
ratio of B to A , will depend upon the character of the termi-
nal apparatus, and may be called the coefficient of reflec-
tion. This coefficient is
A Lf fS | J**.
^R+jJi + "
Representing the impedance of the terminal apparatus by
Zr, this expression becomes
Zr(p+ja)-(R+jpL) ,x
ZF&+ja) + (R+jpL)
Zr =
TR+jpL
For total absorption of the wave, m = o, and the receiver
impedance should be
R +jpL
ft +j<* '
Substituting the values of A and B in equations (19) and
(20), the complete equations for the maximum values of
current and voltage at any point of the line at a distance s
from the end to which the receiver is connected, become
respectively
as +j sin as)
«-* (cos <*s -J sin «*) (*4)
(25)
CURRENT PROPAGATION IN LINE CONDUCTORS 321
If it be desired to reckon the distance in the opposite
direction, that is, from the generator to the receiving ends
of the line, the sign of s must be reversed in equations (13)
and (14), and there result for the current and voltage at
any point distant s from the generator end of the line,
respectively,
(26)
and
Em = i E. + 7. ~ «-* (cos a* -j sin as)
where £„ and /„ are the maximum voltage and current
values at the generator end of the circuit.
The terminal conditions in any given problem are usually
specified, the voltage being considered the standard phase.
In the present notation for vector rotation a current lead-
ing the voltage in phase is written i\ + ji^, and a lagging
current is represented by it — ji^.
The foregoing equations may also be employed with
equal relevancy to calculations involving effective current
and voltage values instead of the maximum values of these
quantities. Short tables of exponential and trigonometric
functions appear in the Appendix.
5. Simplified Equations of Wave Propagation. — The
solution of the equations of wave propagation can be trans-
formed into a more convenient form, as shown by Kennelly,
322 TELEGRAPH ENGINEERING
by expanding the factors e±7S of equation (17). Thus, by
Maclaurin's series
l£ [3 [4
that is, e±7S can be expanded into two series, one containing
even powers of ys and the other having odd powers thereof.
From hyperbolic trigonometry, these series are called re-
spectively the hyperbolic cosine and hyperbolic sine, and
are written
Therefore,
i + • • - = cosh 7*,
[4
XK
... =sinh7,
Equation (17) for the current on the line at a point dis-
tant s from the receiving end may thus be written
Im = A (cosh ys + sinh 75) — B (cosh ys — sinh 75),
or Im = (A - B) cosh ys + (A + £) sinh 7*. (28)
The maximum value of the voltage at the same point
can be found by differentiating (28) and substituting in
equation (14).
Since —cosh ys = 7 sinh 75,
as
and — sinh ys = 7 cosh 75,
as
there results
(g +JPC) Em = (A-B}y sinh 7* + (A + B) 7 cosh 7*,
CURRENT PROPAGATION IN LINE CONDUCTORS 323
whence
Em = ^^\(A - S) sinh 7* + (A + B) cosh ys\ (29)
g+jpCl J
The constants A and £ of expressions (28) and (29) may be
determined from the conditions at the receiving end of the
line. Let Er and Ir be maximum values respectively of
the voltage and the outgoing current at this terminal.
Then, for s = o, since cosh (o) = i and sinh (o) = o,
Ir=A -B,
and B'
Substituting these values yields
Im = Ir cosh 7S + Er / {" sinh ys, (30)
K + jpL
and
Em = Ir ft*?a~ sinh 7* + Er cosh 75. (31)
The hyperbolic functions of the propagation constant 7
may be written, since 7 = 0 + y«,
cosh 75 = cosh (0j +y«5) = cosh /3s • cos as +j sinh /3s • sin as,
and
sinh 75 = sinh (3s • cos as -\-j cosh /3s • sin as.
Then the equations of current and voltage at any point on
a line at a distance 5 from the receiving end thereof are
Im = Ir (cosh 0s • cos as -\-j sinh 0s • sin as)
+ Er p •?" (sinh 185 • cos as +y cosh /3s • sin as), (32)
K -rJpL
and
£m = Er (cosh /3s • cos as +j sinh /3s • sin as)
+ Ir — ." (sinh /3s • cos as +j cosh /3s • sin as). (33)
324 TELEGRAPH ENGINEERING
When 5 is measured from the generator toward the re-
ceiving end of the line, equations (30) and (31) become
Im = Ig cosh ys - Eg R j" sinh js, (34)
and
Em = Eg cosh ys - Ig * ?" sinh 7$. (35)
From equation (34) is seen that for an infinitely long line,
on which the current at the inaccessible end is
/.cosh (oo) = £gsinh (oo),
whence
0+ja , .
(36)
By substituting this value in the same expression, the cur-
rent at a distance s from the generator end of such a line
becomes
Im = Ig (cosh ys - sinh ys) = Ig€~ys} (37)
which shows that the entering current decreases logarith-
mically to zero as s increases to oo . This expression is
analogous to equation (5). Similarly, on an infinitely
long line
Em = Ege^s. (38)
Tabulated numerical values of the hyperbolic sines and
cosines appear in the Appendix. The hyperbolic functions
of complex quantities may be obtained directly from tables
and charts prepared by Prof. Kennelly.
6. Current and Voltage Distribution on Lines for any
Terminal Condition. — The current and voltage relations
in circuits having distributed capacity and inductance with
CURRENT PROPAGATION IN LINE CONDUCTORS 325
given terminal conditions under a given impressed electro-
motive force will now be considered. Three cases arise,
namely: a, line open-circuited at receiver; 6, line short-
circuited at same place; and c, apparatus of given impedance
connected to the receiving end of the line.
(a) When the line is open-circuited at the receiving
end (IT = o), the current Ig°, entering it at the other end,
is obtained from equation (34) by placing Im = o. Since
sinh ys
cosh 75
there results
= tanh ys,
where Si represents the total length of the line conductor.
Upon substitution in equations (34) and (35), there re-
sults respectively the values of current and voltage at
any point distant 5 from the generator end of the line,
when the other end is open-circuited, as
7m°= Eg _ , -?°L (cosh ys tanh 7*1 - sinh 75), (40)
K +JPL,
and
Em° = Eg (cosh ys — sinh ys tanh 751). (41)
When 5 = siy these equations reduce respectively to the
current and voltage at the open end, viz:
Ir°= O, (42)
and E° -- I"— = E, sech •>*,, (43)
cosn ySi
since cosh2 7^1 — sinh2 7^1 = i.
(b) The current and voltage relations at any point of a
line which is short-circuited at the distant end are easily
E°
326 TELEGRAPH ENGINEERING
obtained, since the voltage at that end, Er, is zero. By
placing Em = o when s = si, in equation (35), there results
the current entering the circuit as
I " j*/~*
+ a
The current and voltage at any place are, therefore, respec-
tively, from equations (34) and (35),
J
(cosh ys coth 7*1 - sinh ys), (45)
Em'= Eg (cosh ys — sinh ys coth 7^1). (46)
The conditions at the short-circuited end are obtainable
herefrom by replacing s by si, whence
CSCh 7*1, (47)
| a
and Er' = o.
(c) When the character of the receiving apparatus is
specified, that is, when its impedance,
is known, the voltage and current at any point of the line
may be determined in terms of the impressed electromotive
force. By placing 5 = Si, equations (34) and (35) give the
current and voltage at the receiving apparatus; and divid-
ing the latter by the former, there results
E0 cosh 7*1 - I0 ?" sinh 7*1
_ __ _
11 — — £j<f ~~- ^
I0 cosh ysi - Ea p •? " sinh 751
K -\-jpL
CURRENT PROPAGATION IN LINE CONDUCTORS 327
from which
Zr p •? " sinh ysi + cosh 7^
'• = E° jp & + ja -- (48)
Zr cosh ysi + - — ^ sinh 7*1
g+jpc
By substituting this value in the same equations there
results respectively as the current and voltage at a point on
the line distant s miles from the generator:
0+ja
E'R+JPL*
Zr sinh 751 H --- -•*£— cosh
/3 i ^
Zr cosh 7*1 + , r " sinh 7*1
g+jpc
•cosh 75 — sinh 75
, (49)
and Em = Eg X
Zr sinh 7$! H 7— cosh
Q | "
Zr cosh ysi + — — T^T; sinh
sinh 75
• (50)
These equations may be more conveniently expressed by
choosing an angle 0 such that
=
R +jpL
and they assume the following forms:
Im = E0 _f "^ [coth (T5i + 0) cosh 7^ - sinh 75], (51)
/t -\-jpL
and
£w = £ff [cosh 75 — coth (7^1 + 0) sinh 75]. (52)
These general expressions are similar in form to those
derived under case (b) .
328 TELEGRAPH ENGINEERING
At the terminal apparatus of impedance ZP, the current
and voltage in terms of the impressed electromotive force
Eg may be obtained from equations (49) and (50) by putting
$i for S whence
Zr cosh ysi + , .
8+JpC
(53)
and
?
(54)
cosh ~
Zr
The general expressions (49) to (54) reduce to those
derived under cases (a) and (b) for lines open- and short-
circuited at the distant end by placing Zr equal to infinity
and zero respectively.
7. Effect of Impedance at Sending End. — In the fore-
going expressions the impedance, Zt, of any apparatus which
might be connected to the generator end of a line, such as
a relay on a telegraph line, has been ignored. The in-
fluence of such impedance can be taken into account by
replacing E0 in equations (49) to (54) by
Ea>- I.[R, +j(pLt - ^-)]= £/- I,Zt, (55)
where Rt, Lt and Ct are respectively the resistance, induc-
tance and capacity of the transmitting device, Fig. 3, and
I a is the current entering the line.
This current value, from (51) by placing 75 = o, is
CURRENT PROPAGATION IN LINE CONDUCTORS 329
where
which, when substituted in equation (55), yields
•p r
£„ =
"R+jpL
By replacing the value of Eg in equations (51) and (52) by
this quantity, there result respectively the complete and
Im
^////////////////^^^^^ w/////////////////^^^^^
Fig. 3.
general expressions for the current and voltage values at
any point on the line distant s miles from the generator
as
r J7'JL+1^_ cosh ys • coth (7^1 + </>)- sinh 7*
lm = tig p -- — - -
and
^ = £ / cosh 75 - sinh 75 • coth (7*1 + 0) / v
'
By placing 5 = Si in the foregoing general expressions
for current and voltage distribution on lines, the condi-
33° TELEGRAPH ENGINEERING
tions at the receiving end of the circuit are obtained;
namely,
/=
'
and (58)
T? _ _____ Eg Zr
"
(59)
These equations are together represented by the determi-
nantal expression
£' Z7
g J^r , , N
1 - - - -=- • (ooj
Zr
I O
i sinh 75 1
The equations derived in §§4-7 are applicable to all
alternating-current circuits having distributed resistance,
inductance and capacity in the steady state, and with any
terminal condition at either end. They are extremely use-
ful in solving transmission problems not only in teleg-
raphy, but also in telephony and power transmission. In
applying the equations to circuits employing two or more
line conductors, the significance of the symbols must be
properly interpreted.
8. Illustration of Sine-wave Telegraphic Transmission.
— Consider a 150- volt (effective value) alternating-current
generator to be connected to one end of a 6oo-mile simplex
ground-return aerial telegraph line of No. 10 B. & S. gage
CURRENT PROPAGATION IN LINE CONDUCTORS 331
copper wire, the line having a 3oo-ohm relay at each termi-
nal. Determine the current and voltage relations in the
circuit for a signalling speed yielding a dot-frequency of
15 cycles per second.
The maximum value of the impressed harmonic voltage
is 150 ^fi or 212.2 volts, which may be considered the
equivalent of a unidirectional voltage of 320 volts, as out-
lined in § i. The electrical constants of the line per mile
will be taken as follows:
R = 5.28 ohms, (page 29)
L = 3.10 X io~3 henrys,! For a single wire 25 feet
C = 9.54 X io~9 farads, J above ground (page 283)
and g = 2. co X io~6 mhos.
While the inductance of the relays depends upon several
conditions, its value in this calculation will, however, be
considered constant at 5 henrys; whence the impedance of
each relay at 15 cycles is
Zr = Zt = Rr +jpLr = 300 + 2 TT 15 X 5.7 = 300 +
ohms, and the absolute value is
VRr* + p*L? = v^2 + ^ = 558 ohms.
The attenuation and wave-length constants of the line are
respectively obtained from equations (8) and (9) as
j8 = 0.00331,
and a = 0.000808.
The velocity of propagation and the wave-length are re-
spectively
and
1 TT T ^
V = 88 = II^5° n1^68 Per second,
. 27T ..
X = r-r = 7770 miles.
0.000808 ' ' '
332 TELEGRAPH ENGINEERING
Further, since
Si = 600 miles,
Ea' = 212.2 VOltS,
£ +JpC = (2-0 + 0.8997) iQ-6 mhos,
R + jpL = 5.28 + 0.2927 ohms,
g+jpc
ySi = fa +jaSi = 1.986 + 0.4848^*,
sinh 7^1 = sinh 1.986 • cos 0.4848 +j cosh 1.986 • sin 0.4848 *
= 3.163 + 1.7307,
and cosh 7^1 = 3.284 + 1.6667,
it follows from equation (58) that the maximum value of
an alternating current arriving at the remote end of the
6oo-mile telegraph line is
2 (300 + 4717) (3.284 + 1.6667) + [iS2^
Ir =212.2 -^- - 2837 + (300 + 471 7')2 (635 + n87')io-6]
(3.163 + 1.7307)
212.2 , .
= - - - . = 0.0169 — 0.02067 ampere,
5070 +61577
or Ir = 16.9 — 20.67* rnilBamperes.
The absolute value of this maximum alternating-current
value is V(i6.9)2 + (20.6)2 = 26.7 milliamperes, and the
corresponding unidirectional current of rectangular wave
shape is | X 26.7 = 40.1 milliamperes.
The potential difference across the distant relay is
Er = IrZr = (0.0169 - 0.02067) (300 + 4717)
= 14.77 + i-7^y v°its.
* See tables in Appendix.
CURRENT PROPAGATION IN LINE CONDUCTORS 333
Equation (30) now enables the determination of the current
and voltage values at the other end of the line. Thus
Ig = (0.0169 — 0.0206 7) (3. 284 + 1.6667) + (I4-77 + I-7^y)
(635 + 1187) (3.163 + 1.730^') io-*
= 0.1138 — 0.01457 ampere.
The potential difference across the relay at the generator
end of the line is
IgZt — (O.II38 — 0.01457*) (3OO + 4717')
= 41.0 + 49.37 volts,
and, therefore, the voltage impressed upon the line is
Eg = Eg - IgZt = 212.2 - (41.0 + 49-37)
= 171.2 - 49.37 volts.
This value may be verified by means of equation (31).
The foregoing results are displayed graphically in Fig. 4,
V
49.8
Fig. 4.
which shows the harmonic alternating-current quantities
as vectors, the generator voltage Egf being the datum phase.
The scale of the receiving-end quantities is 5 times as large
as that of the sending-end quantities, all current Values
being expressed in milliamperes. Absolute values and
phase relations are also indicated.
334 TELEGRAPH ENGINEERING
Effect of Employing Higher Signalling Speeds. — If instead
of 15 cycles, the speed of signalling in the foregoing example
had been ten times as great as before, making the dot-
frequency of the equivalent alternating current 150 cycles,
then under otherwise identical conditions:
P = 942.5,
/3 = 0.00446,
a = 0.00597,
v = 157,900 miles per second,
X = 1052 miles,
Zr = Zt = 300 + 47107 ohms,
ysi = 2.676 + 3.5827,
and the current traversing the remote relay is found to be
Ir = i. 08 — 0.4577 milliamperes.
The absolute value of this received current is 1.17 milli-
amperes, and the corresponding unidirectional current of
rectangular wave-shape is f X 1.17 = 1.75 milliamperes.
This value is only 4.3 per cent of that obtainable when the
signalling speed is one-tenth as great. The influence of
signalling speed upon the magnitude of the received im-
pulses is, therefore, evident.
Direct-current Transmission Theory
9. Current in Leaky Line Conductors. — When a uni-
directional electromotive force is impressed upon a line
conductor, the current at every point of the line assumes a
steady value. Ignoring the short unsteady period of cur-
rent growth, the steady current value at any point on the
line distant 5 from its generator end may be determined
without considering the effects of inductance and capacity
of the line conductor. The current and voltage equations
CURRENT PROPAGATION IN LINE CONDUCTORS 335
to be satisfied are obtained by placing L = o and C — o in
equations (i) to (4) ; whence for a leaky line
^H=-RI, (61)
I
T=~SE, (62)
§-**•
and
(64)
where R is the conductor resistance per mile, and g is the
leakage conductance per mile of conductor length. Equa-
tions (63) and (64) are identical equations which differ only
in the terminal conditions, and, therefore, the solution of
one will suffice.
Choosing the former equation and multiplying both sides
by 2 — , there results
as
d?I dl
2d?-ds =
which, when integrated, becomes
Replacing the constant of integration c\ by Rgof, where cz
is also a constant, and separating the variables, there re-
sults
dl
336 TELEGRAPH ENGINEERING
Another integration yields
loge [c8 (/ + VP + tf)] = VRg.s = 0s,
where c3 is another constant of integration and 0
is the attenuation constant. In exponential form, this
equation becomes
Squaring, and solving for 7, gives
For convenience let - = A + B and c22c3 = A — B\ fur-
£3
ther, let the exponential terms be replaced by their equiva-
lent hyperbolic functions, viz. :
c±0* = cosh/35 ± sinh/Ss.
Then / = A sinh 0s + B cosh 0j. (65)
Differentiating this expression with respect to distance
and substituting the result in equation (62), there results
E=--(A cosh 0s + B sinh $s) . (66)
o
Equations (65) and (66) are the expressions for current and
voltage respectively at any point of the line, but the con-
stants A and B are still to be evaluated from the terminal
conditions.
If one source of electromotive force supplies current to
the line and this source be located at one terminal, then the
constants A and B may be determined by placing 5 = 0
and representing the current and voltage at this end by I0
CURRENT PROPAGATION IN LINE CONDUCTORS 337
and EQ respectively. Since cosh (o) = i, and sinh (o) = o,
it follows that
A - — 77
"
and B = Ig.
Substituting these values in equations (65) and (66) yields
the current and voltage respectively at any point on the
line distant 5 from its generator or sending end as
/ = /„ cosh /3s - ^ Eg sinh /3s, (67)
P
and E = Eg cosh 0s - - Ig sinh 0s. (68)
g
Connecting a receiving instrument of resistance Rr to
the far end of the line which has a length s\t the current
traversing this instrument would be
Ir = I0 cosh fa -E0 sinh fa, (69)
p
and the voltage across its terminals would be
/3
Er = E0 cosh fa — -Ig sinh fa. (70)
o
E
Since Rr = -p , it follows that the current entering the line
will be
Rr & sinh fa + cosh fa
I.-E.-B. - - - . (71)
Rr cosh fa + - sinh fa
g
If, as is usual, there is a resistance at the sending end also,
then Eg in the foregoing should be replaced by Eg —
338
TELEGRAPH ENGINEERING
where £/ is the voltage of the generator, and Rt is the total
resistance at the generator end of the line. Whence
Rr sinh fa + cosh fa
P
(Rr + Rt) cosh fa + f- + RrRt f ) sinh /toi
\g /v
(72)
Substituting this value in equation (69) gives the current
traversing the remote receiving instrument in terms of the
generator voltage as
EJ
(Rr+Rt)coshfa
(73)
RrRt-)smhpsi
Ayrton and Whitehead have shown that the best re-
sistance of a receiving instrument on a leaky telegraph line
is Q
Rr' = - tanh fa
g
irrespective of the relation between the torque exerted and
the ampere-turns applied.
10. Illustration of Direct-current Signalling on a Leaky
Telegraph Line. — Consider a simplex telegraph circuit
Rr
Fig. S.
with a 320-volt direct-current generator at one terminal,
as shown in Fig. 5. The line wire is 600 miles long of No.
CURRENT PROPAGATION IN LINE CONDUCTORS 339
10 B. & S. gage copper wire, and a 3oo-ohm relay is con-
nected at each end. To determine the currents traversing
the relays for various positions of the keys K and K',
when the insulation resistance is 0.5 megohm per mile.
In this example
Eg =320 volts,
Rt = Rr = 300 ohms,
R = 5.28 ohms,
g = 2.00 X IO"6 mhos,
and Si = 600 miles;
therefore, ft = ^5.28 X 2.00 X icr6 = 0.00324,
0si = 1.944,
sinh /3$i = 3.422,
cosh/3^ = 3.565,
| = 0.000617,
* = 1620.
g
When both keys, or their circuit-closing switches, are closed,
the current entering the line is obtained from equation
(72) as
300 x 0.000617 x 3-422 + 3-565
600 X 3.565 + (1620 + 3002 X 0.000617) 3.422
320 X 4.108
— * -- y = 0.1706 ampere,
2139 + 5734
or 170.6 milliamperes; and the current that reaches the
other end of the line is obtained from equation (73) as
T 320
/ = - —t - = 0.0406 ampere,
2139 + 5734
or 40.6 milliamperes.
=
340 TELEGRAPH ENGINEERING
The closeness of this result to that obtained in § 8 by
means of the alternating-current method for the same con-
ditions and a 15 cycle frequency justifies the use of the
direct-current method whenever the speed of signalling is
much below the theoretically attainable speed1 on the line,
as with hand signalling on open wire lines. The alternat-
ing-current method excels when dealing with long aerial
and underground cables.
When key Kf is opened, no current traverses the home
relay, but the current flowing through the relay at the
generator end of the line is obtained from equation (69) by
placing Ir = o and replacing Eg by Egf — I0Rt',
thus Ig° cosh to = & (Egf - IgRt) sinh to,
P
whence 7." = E.'
Rt sinh to + cosh to
g
or 7f° = -& . (74)
Rt + -cothto
g
Substituting the numerical values herein gives
T O 32O
IB = = 0.161 ampere.
300 + 1620 X 1.042
For satisfactory operation, therefore, the relay at the
generator end of the line must be very closely adjusted,
for it should attract its armature on 170.6 milliamperes
and release it on 161 milliamperes; thus giving a margin
of 9.6 milliamperes. This condition is improved by the
use of generators at both ends of the line, as will now be
considered.
CURRENT PROPAGATION IN LINE CONDUCTORS 341
ii. Simplex Signalling with Generators at Both Line
Terminals. — If two equal cumulatively-connected sources
of current be located one at each terminal of a line, as in
the usual simplex Morse telegraph circuit, then the con-
Fig. 6.
stants ^4 and B of equations (65) and (66) are evaluated
upon a consideration of the conditions shown in Fig. 6.
Herein Eg' is the electromotive force of each generator, Rr
is the total resistance at each terminal station, Eg and Er
are the potentials with respect to ground of the line wire
at the stations i and 2 respectively, and Ig and Ir are the
currents at these stations respectively.
When both keys are closed as shown, the current and
line voltage at station i are obtained by placing s • = o in
equations (65) and (66) respectively, whence
and E0=-*-A = Egf - I0Rr.
g
Similarly the current and line voltage at station 2 are
obtained by placing 5 = Si in the same equations, thus
Ir = A sinh fa + B cosh fa,
and Er = - - (A cosh fa + B sinh fa) = - (£/ -
o
342 TELEGRAPH ENGINEERING
The constants A and B are ascertainable from these four
equations, and are
at \
Rr - ( i — cosh fa \ — sinh fa
A = EO/ : /v 5\ ' ^
2 Rr cosh to + ( *• Rr2 + - J sinh to
and
cosh to + Rr - sinh fa + i
B = Ea' 77 T\ (76)
2 Rr cosh to + ( - -#r2 + ~ ) sinh to
Substituting these values in equations (65) and (66) results
in the current and voltage equations for any point on the
line distant s from one end, when equal generators are
connected to both ends of the line wire.
The current traversing the relays at stations i and 2 are
respectively
Ig = B,
and Ir = A sinh fa + B cosh fa
as already indicated. Upon replacing A and B herein by
their equivalents given in equations (75) and (76), these
currents are found to be equal, as might be inferred from
the symmetry of the line and terminal conditions, and have
the value
cosh fa + Rr- sinh fa + i
(77)
2 Rr cosh fa + ( lRr2 + - ) sinh fa
\p gl
When one of the keys is opened the current traversing the
relay at the other terminal station is given by equation (74).
To illustrate the advantage of dividing the total voltage
CURRENT PROPAGATION IN LINE CONDUCTORS 343
on a telegraph line, one-half being impressed at each end,
consider the same circuit as was discussed in the preceding
article. In this case a 1 60- volt generator is located at each
end of the 6oo-mile line.
The current traversing each relay when both keys are
closed is given by equation (77) as
I _/r-i6o 3-565+300X0.000617 X 3422 + i
2X300X3. 565 + (0.00061 7X30? +1620)3.422
= 0.1056 ampere = 105.6 milliamperes,
while the current traversing a relay when the key at the
opposite station is opened is given by equation (74) as
ro 160
ig = ~ - = 0.0805 ampere
300 -f 1620 X 1.042
= 80.5 milliamperes.
The comparison of the two generator arrangements for
the line under consideration is revealed in the following
table, the current values being expressed in milliamperes.
It is seen that with a generator at each end the operating
margin is 25.1 milliamperes, as against 9.6 milliamperes
at the home relay for a single generator of double voltage
at the home end of the line.
Key positions
32O-volt generator
at home end
i6o-volt generators
at both ends
Current
through
relay at
generator
end
Current
through
relay at
distant
end
Current
through
relay at
home
end
Current
through
relay at
distant
end
Both keys closed
170.6
161
0
40.6
O
o
105.6
80.5
o
105.6
O
80.5
Distant key open
Home key open
Operating Margin
9.6
40.6
25-1
25-1
344 TELEGRAPH ENGINEERING
12. Duplex and Quadruplex Signalling. — The theory
of signalling on leaky lines discussed in the preceding pages
is also applicable to duplex and quadruplex telegraph cir-
cuits if the terminal conditions are properly deduced.
The general expressions for current and voltage are equa-
tions (65) and (66), wherein the constants A and B depend
upon the conditions existing at the ends of the line wire.
The values of these constants with duplex and quadruplex
signalling are different from those pertaining to simplex
signalling, already considered.
In a polar duplex circuit, let Rp = entire resistance of
each polarized relay, Rb = resistance of each battery or of
Relay
Fig. 7.
the protective resistance in series with each generator, and
r = resistance of each artificial line, as indicated in Fig. 7
for one station. Placing s = o in equations (65) and (66),
there results
and E= -.A =
.
where - - = q for simplicity. The current and
CURRENT PROPAGATION IN LINE CONDUCTORS 345
voltage conditions at the other end are obtained by placing
s = Si, whence
Ir = A sinh 0Si + B cosh Qsi,
and£r = --U cosh fa + 5 sinh 0*)= ± (qEgf - Ir
the plus sign being taken when the two batteries or genera-
tors oppose each other as when both pole-changers are
either idle or energized, and the negative sign being taken
when the two current sources assist each other as with only
one pole-changer energized. These expressions assume the
current traversing the artificial lines to remain constant
irrespective of key movements.
Solving for A and B from the preceding four equations,
yields R q
- cosh Qsi db —2 • - sinh fa ± i
B = *E''l - \R - 2 / z R 2 8\ - ' (78)
[± i - i.pcoshto +(±f .£* -eWnhto
V / 2 \ 0 4 gl
and A=£B-qE0' (79)
The upper signs in equation (78) are employed when the
generators oppose and the lower signs are used when the
generators assist each other. Substitution of these values
in equations (65) and (66) gives the final expressions for
current and voltage in the case of a polar-duplex telegraph
circuit.
The bridge duplex and the quadruplex terminal condi-
tions may be similarly analyzed and the current and voltage
equations formed.* It is to be noted that the current
passing through the relay of a bridge duplex circuit ex-
* An excellent treatment 'of these conditions appears in a paper by
F. F. Fowle on "Telegraph Transmission," Trans. A.I.E.E., v. 30, p. 1683.
346 TELEGRAPH ENGINEERING
pressed in terms of the current Ig at the end of the line
wire and the voltage Eg' of the generator is
T aEgf -aIg(2Rb + r + a) ( .
^-
where P is the resistance of the relay, a = resistance of
each half of the retardation coil, r = resistance of artificial
line, and Rb = resistance in series with generator.
PROBLEMS
1. Determine the attenuation and wave-length constants of a
perfectly-insulated ground-return line having the following constants
per mile, when the frequency of the impressed electromotive force is
50 cycles: R = 4.25 ohms, L = 0.002 henry, and C = 0.016 micro-
farad.
2. Compute the current and voltage at both ends of an 8oo-mile
line of No. 10 B. & S. gage copper wire and having a 3oo-ohm relay
at each end. A 150- volt i5-cycle alternating-current generator is
to be considered connected in one terminal of this simplex circuit in
place of a 3 20- volt direct-current generator. The constants of the
relay and line are those given in § 8. Construct the vector diagram
of currents and electromotive forces.
3. Verify the value of Ir given in § 8 for signalling on a particular
line at a speed corresponding to a dot-frequency of 150 cycles.
4. For different key positions, determine the. unidirectional cur-
rents traversing the 25o-ohm terminal relays on a 4oo-mile simplex
telegraph line of No. 9 B. & S. gage copper wire. Assume the line to
have an insulation resistance of 0.5 megohm per mile, and that a
single i6o-volt direct-current generator located at one terminal
station supplies current to the circuit.
5. Calculate the currents traversing the relays of the line men-
tioned in the preceding problem when the 1 60- volt generator is re-
placed by two 8o-volt generators, one at each line terminal.
6. Solve Problem 3 of Chap. II, taking into account a uniformly
distributed leakance of io~6 mhos per mile for this 475-mile polar
duplex circuit.
CHAPTER XI
SUBMARINE TELEGRAPHY
i. Theory of Cable Telegraphy. — Because of the large
capacity and small leakance of submarine telegraph ca-
bles, the direct-current transmission theory 'discussed in
the foregoing chapter is inapplicable to signalling over
cables. However, the alternating-current transmission
theory already considered may be utilized for cable teleg-
raphy if the speed of signalling is such that a steady state
is constantly approached within a reasonable margin. For
practicable speeds on commercial cables this theory is
limited to cable sections of moderate length. When the
steady state is not nearly approached during each signal,
then the growth and fall of the direct-current accompany-
ing the application and withdrawal of constant voltage to
one end of the cable are alone of importance. The con-
sideration herein presented of these transitional states on
long cables, conveniently called the transition theory of
transmission, will reveal the nature of the current which
reaches the distant terminal of the cable.
If a steady voltage E is applied to one end of a perfectly-
insulated cable of length /, while the other end is grounded,
the potential at each point gradually rises until its value
at any poiht distant 5 from the sending end is
* ... ; EJ = E1-^, \ (i)
347
348 TELEGRAPH ENGINEERING
which indicates that the voltage-distance graph for the
steady condition is a straight line falling from E to zero,
as shown in Fig. i. Should this condition be altered, say
IB
•i
Fig. i.
by grounding the sending end, then the voltage there at
that instant would be zero, but at other places in the cable
would be as indicated by equation (i). The subsequent
voltage at any point is found by drawing an image of AB
toward the left, forming a curve DAB, and considering
this curve to represent a periodic function of distance;
which is, therefore, expressible by a Fourier's series of the
form
Em = F04-Fisin0 + F2sin20 + . . . +FnsinnO +
GI cos 0 + Gz cos 20 + . . . + Gn cos nO,
where 6 = — and n is any integer. To evaluate the co-
efficients, multiply both members by sin nO times the width
ds of the element and summate these elementary areas over
the distance DB, and there results
ri /»2J (*1l
Emf sin nO ds = F0 I sin nS ds + FI I sin 0 • sin n0 ds
Jo Jo
(*2l
+ • • • + Fq I sin qB • sin nB ds + • • -
Jo
ri rzi
sin2 ndds + GI I cos 0 - sin nB ds + • • •
Jo
X2l f*2l
cos q6 • sin nd ds + • • • + Gn I cos nB • sin nd ds.
Jo
SUBMARINE TELEGRAPHY 349
Since Emr = E — - E, dO = y ds, and when s = 2 1 then 0 = 2 TT,
I I
E I smnedO -- I 6 sin nd dO = FQ I sin n6 d0
JQ ffJ JQ
X27T /*2tr
sin 0 • sin w0 </0 + • • • + Fq I sin g0 • sin w0 d0
t/O
+ . - - +Fn l&xPntidO + Gi / cos0-sinw0</0 + - - •
Jo Jo
+ Gq I *cosq0 •smn8dO+ • • • +Gn I cos n6 • sin nd d6.
The terms of this expression are integrated as follows:
T2' .
I sin n0 dO = \ = o.
Jo \_ n J0
rif Tj Q ~|2ir 2
^ sin w^ c?0 = -r sin w^ -- cos w^ = ---
L^2 w Jo - n
I sLnqO'SmnOdO = - I cosfg— n\B — cos(q + n\d \dO
= i fsin (q - n) 0 _ sin (q + n) 0"]2y
2L g — » g + w Jo
When q and w are different integers, substitution of the
limits reduces this expression to zero.
rsin2 nBde = - I (i — cos 2 n0 } dd
2Jo V /
i f\ sin 2 w^12T
= - \e -- = TT.
2[_ 2W Jo
I cosqO 'SmnddO = - I Isinln + qjd + smln— q\6 \dO
_ _ i fcos (^ + q) 0 , cos (n — q) 0"[2r
2L w + g w- 1
350 TELEGRAPH ENGINEERING
This expression is zero whether the integers q and n are
equal or unequal. Therefore, by substitution,
2E 2E
— = irFn or Fn = — ,
n irn
and consequently the potential at any point of the cable
distant s from the sending end where E volts are impressed,
reaches the maximum value of
Emf = — ( Sm 0 + - Sin 2 0 + • • • + -
TT \ 2 n
•n f 2 j
or Em = —
This equation represents the voltage distribution at the
instant of grounding the sending end of the cable.
If, now, the potential distribution be left to itself, then
the diminishing voltage all along the cable must satisfy
the differential equation of propagation over a uniform line,
namely, equation (4) of Chap. X, which is
where C, L, g and R are the cable constants per unit length.
But in submarine telegraphy the inductance of cables is
very small and the leakage conductance is very low, that
is, L and g are negligibly small; so that the equation to be
satisfied reduces to
dt
the so-called "telegraph equation."
A solution of this equation suggests itself of the form
SUBMARINE TELEGRAPHY 351
where E' is the voltage at the point distant s from the send-
ing end at a time / after grounding that end. Differenti-
ating this expression twice with respect to distance there
results jsT^'j an(^ differentiating with respect to time
there results - n2bE'. Substituting these values in (4)
yields
' =-RCn2bE':
whence b = —. (6)
With this interpretation of the exponential constant,
equation (5) is a solution of equation (4), for it reduces to
equation (2) when / = o, is zero when / = <x> , and is zero
when s = o or s = I.
The fall in voltage at the point of reference during the
time / elapsing since suppression of voltage E at sending
end by grounding is
<»>
On the other hand, if the origin of time were taken at the
instant when the voltage E is applied, the rise in voltage
during the time / at the point of reference is also given by
equation (7). This expression also satisfies equation (4)
since it is the difference of two expressions which satisfy
it separately.
The growth of current in the cable at the point under
consideration is obtained by differentiating (7) with respect
to distance, and using de' = — R ds • /'. Thus, the current
352 TELEGRAPH ENGINEERING
value at a time / after applying the voltage E to the sending
end is
At the receiving end s = /, and the current is
// = — T— < 2 COS HIT — 2J ( €~n26' COS WTT J > •
But 2/cosw7r=— i + i — i + i— • • • ;
transposing the first term of the right hand member, there
results
i + 2 cos HTT = i — i + i — i+ • • • ,
and adding these two series term by term it will be found
that
cos rnr = — .
n=l
Consequently, the instantaneous current at the grounded
receiving end is
when both ends of the cable are without sending or receiving
instruments. The series
and when t is zero, the sum is — i + i — i + • • • =— J
as before, and therefore // is zero when time begins.
As the foregoing expression for // is slowly convergent
for small values of / it is more convenient, for purposes of
SUBMARINE TELEGRAPHY
353
evaluating the received current at first, to alter its form into
a rapidly-converging series by means of an equality due to
Fourier that
oo n^r
2«"?cos^
n=l
8000
7500
7000
6500
6000
6500
£ 5000
E4500
3500
3000
2500
2000
1500
1000
ARRIVAL CURVES
on
2500 Mile Cable
\
500
0 0.2 0.4 0.6 0.8 1
2
Seconds
Fig. a.
Taking bt = ^ and — " = i, equation (9) becomes
* Sir WiUiam Thomson, " Collected Papers," V. 2, p. 48; 1884 ed.
354 TELEGRAPH ENGINEERING
then using equation (6), there results
oo - (2 m + 1) V2
"' • <»>
If the key be kept depressed, the current at the receiving
jy
end will grow from o for / = o to the value •— , as obtained
Kl
from (9) by placing / = oo . The graph of current growth
will resemble curve 7, Fig. 2. When the battery is re-
moved and the sending end grounded, the current at the
other end will decay as shown by curve II, which is the
same as curve / drawn downward from the steady current
value as axis.
2. Illustration of Current Growth at the Receiving End
of a Cable. — As an example of the growth of the current
at the receiving end of a cable, consider a 25oo-mile cable
having a total resistance of 5000 ohms and a total capacity
of 987 microfarads to have 40 volts impressed upon the
sending end. Thus, Rl = 5000 ohms and Cl = 0.000987
7T2
farad; therefore b = — = 2.00, and the
5000 X 0.000987
ultimate current value -at the grounded receiving end of the
cable is 0.0080 ampere. Values of // to an accuracy of a
fraction of one per cent can be obtained by using only the
first terms of equations (9) and (10), if the latter be used
for time intervals up to one second, say, and the former
for longer intervals. For the conditions of this example,
the equations utilized are
// = aE\f^.~&.?2^e~^empea»toit< i,
f 7T/U V t
SUBMARINE TELEGRAPHY
355
and
// = 7T7(i - 2 e~bt} = 0.008 (i - 2 €~2t] amperes for/ > i.
Rl \ I \ I
The values of current at the receiving end of this cable as
calculated from these expressions (see table of exponential
functions in Appendix) for different values of t are given in
the following table, and are also shown by curve 7 of Fig. 2.
It will be observed that the application of voltage to one
end of a cable produces an instantaneous effect at the other,
but the growth of current at first is so extremely slow as to
give rise to the impression that there is at first a " silent
interval."
t
seconds
//
microamperes
t
seconds
IT
microamperes
O
O
0.8o
4794
0.05
0.0000017
0.90
5357
0.10
0.279
I.OO
5835
0.15
14.96
1 .20
6548
O.2O
93-6
1-50
7204
0.25
288
1.70
7466
0.30
599
2.OO
7707
0.40
1457
2.50
7892
0.50
2401
4.OO
. 7995
O.6O
3302
10.00
7999
0.70
4112
00 .
8000
3. Transmission of Telegraphic Signals. — The alpha-
betic code used generally for cable telegraphy is the con-
tinental Morse Code, comprising for its characters various
combinations of dots and dashes as tabulated in § 7 of
Chap. I. The transmission of a letter is usually accom-
plished by repeated applications of constant potential for
equal intervals of time to one end of the cable, the potential
TELEGRAPH ENGINEERING
differing in direction for dots and for dashes. With this
method of signalling over cables the code for alphabet and
figures is better represented as below, dots and dashes being
indicated respectively by upwardly and downwardly pro-
jecting rectangles of equal length.
c ~d e f
T • ••-•I M - Hi •• •• M M
o P Q r s t
Dashes
v w x y z
12 34
5 6 7
9 0 or 0
Taking T seconds as the duration of a dot or dash element,
the interval between elements is generally r, that between
letters 3 r, and that between words 7 T. By an analysis
of traffic matter it is found that the average letter contains
7.2 elements, including space between letters, and hence
requires 7.2 r seconds for transmission.
Signals are usually sent, therefore, as a succession of
equal rectangular voltage-time pulses differing in direction
and spaced irregularly. If the alternating-current theory
of wave propagation were applied to cable signalling, two
hypothetical frequencies for an equivalent sine wave would
be recognizable, namely: the dot-frequency, as outlined
in the foregoing chapter, and the reversal-frequency, as
SUBMARINE TELEGRAPHY
357
indicated in Fig. 3; the former being twice as high as the
latter. Kennelly* has considered both frequencies in
ascertaining the best resistance of receiving instruments
on cables, and the influence of terminal apparatus upon
signalling speed. He has shown that the receiving instru-
J.
\
Seconds
/
f
*\
\
r
Fig. 3-
ment for greatest sensitiveness should have a resistance
equal to the resistance component of the surge impedance
of the cable plus the resistance component of reactive
apparatus, if any, in the receiving circuit. The surge
impedance, from § 4 of Chap. X, being in general
f~+ja
g +JPC
or
v/f
+JPL
g+jpc'
rjr
becomes y — ohms for highly insulated cables, where
p = 2 TT times the frequency (dot- or reversal-frequency as
selected) of the equivalent alternating current. Thus,
taking a reversal-frequency of 4 cycles per second in the
numerical illustration of § 2, and with no reactive apparatus
at the receiver, the best resistance of the winding of the
receiving instrument, as found by this method, is the re-
sistance component of
* " Hyperbolic Functions applied to Electrical Engineering," 1912, Chap. 9.
358 TELEGRAPH ENGINEERING
2 7T
= V202,ooo (90°) =449 (45°)
2500
or is 449 cos 45° = 317 ohms.
Reverting to the transition theory of cable transmission, a
dot or dash may be transmitted by applying a unidirectional
voltage at the sending end of the cable for T seconds,
thereafter grounding that end; consequently the equation
for a dot or dash is obtained by subtracting from equation
(9) a similar equation in which the time / is replaced by
t — T whence
COS HIT -
In other words, a dot is transmitted by the maintenance
of voltage at the sending end for an infinite time, and after
T seconds the application of an equal opposite potential
also maintained indefinitely. The subtraction indicated
in equation (n) is most conveniently done graphically.
The curve of arrival of a dash element for a contact lasting
o.i second on the cable considered in the foregoing numeri-
cal illustration is shown by curve 7 of Fig. 4 as the sum of
curves a and b. An enlarged view of this curve is shown
by curve T, the multiplier being 5. It will be evident that
the shorter the contact the lower and flatter will be the
curve of received current for a dot or dash element.
By applying the foregoing method it is a simple matter
to construct a curve showing the received instantaneous
current for any combination of dots and dashes. It is only
necessary to plot the same dash arrival curve in the proper
places and with proper direction and then add the ordinates.
SUBMARINE TELEGRAPHY
359
Thus in Fig. 4 are also shown the forms of received signals
on this cable for the letters E, N, D, B and BT, the lower
dotted lines representing the nature of the impressed elec-
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1JL 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
Seconds
Pig. 4.
tromotive force. Curve II exhibits the cumulative action
of successive like signals for a signalling speed of —
7.2 X o.i
= 83.3 letters per minute and the result is apparently
undecipherable, but still it would be legible to an expert
recorder attendant.
In Fig. 5 is shown the received current curve for the
3<5°
TELEGRAPH ENGINEERING
same letters BT sent at the same speed on a shorter cable
having the same constants per unit length as that pre-
viously considered. The variations in this curve are very
prominent and are easily interpreted.
10000
8000
6000
4000
2000
0
2000
4000
6000
8000
0
(
£1
^
\
LETTERS BT Received
on
1250 Mile
Cable
1
\J
\
2
\J
\
/
\
£
\
\
/ ^
^
*.~—
\
s*
\
P
\
7
\
f
\
/
t-
/
\>
-
Dots
V
Dashes
T
) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.
Seconds
Fig.
The receiving instrument used in cable telegraphy over
relatively short distances (several hundred miles) is the
ordinary sensitive relay, while over long distances the
siphon recorder is used. The siphon recorder, devised by
Lord Kelvin in 1867, traces on a paper tape the curve
of current which traverses the instrument winding. This
recorder is a D'Arsonval galvanometer, the movements
of the coil of which are transmitted by means of two silk
fibres to an extremely small glass siphon. As one end of
this siphon passes transversely to and fro across the slowly-
SUBMARINE TELEGRAPHY
361
moving tape, it takes ink at the other end from a small
reservoir and exudes it upon the paper in the form of a
wavy line. To eliminate friction, the siphon is kept vibrat-
ing rapidly, by means of an electromagnetic vibrator, so
as to oscillate perpendicularly to the paper, thereby form-
ing a trace that really consists of a succession of closely
Fig. 6.
spaced dots. Fig. 6 shows a siphon recorder made by
Muirhead & Co., Ltd. The suspension piece with vibrator
is shown in Fig. 7.
Fig. 8 is a reproduction to exact size of a portion of a
message which was transmitted over the Bay Roberts, N. F.-
New York i6io-mile cable at a speed of 200 letters per
362 TELEGRAPH ENGINEERING
minute ( r= = 0.0416 second V The dotted neu-
' V 200 X 7.2 /
tral line shows that the siphon recorder in practice does
not behave as a fixed-zero instrument.
The resistance of siphon recorders is usually between 300
and 800 ohms, and their inductance about 0.2 to 0.3 henry.
Fig. 7.
The recorder will operate satisfactorily on a current as
small as 20 to 40 microamperes.
Signals are sent either manually or by means of auto-
matic transmitters such as described in § i of Chap. IV.
Fig. 9 shows a cable key with removable contact levers.
Automatic transmission by means of perforated tapes
results in greater speed and more regularity in the signals
than is possible with hand transmission; it is the method,
therefore, chiefly employed in cable telegraphy. «
SUBMARINE TELEGRAPHY
363
4. Speed of Signalling. — From the foregoing expres-
sions it will be seen that the received current is a function
of bt, consequently the time required to establish a given
current at the far end varies inversely with b or directly
One hund red f orty th ree
hr^M\r^^r^^^
Federal St. Boston Mass
Fig. 8.
CRF
with— — . Since the speed of signalling varies inversely
with the time required for establishing the necessary cur-
rent, this speed varies directly with , or it varies in-
Fig. 9.
versely with the product of the total resistance and total
capacity of the cable. Also, when C and R are kept con-
stant, the speed of signalling varies inversely with the square
of the cable length.
364 TELEGRAPH ENGINEERING
Accordingly, the speed of signalling over a given distance
may be increased by decreasing the total capacity or the
total resistance or both. The capacity depends upon the
conductor diameter, upon the distance between conductor
and metallic sheath and upon the dielectric constant of the
cable insulation. Greater separation between conductor
and armor and the use of larger wire are accompanied by an
increase in cost. Further, with very few exceptions, no
insulating material having a lower dielectric constant than
gutta percha compound has been successfully used up to
the present time in submarine cables.
The statement that the speed of signalling varies inversely
with the product of total resistance and total capacity of a
cable is called the "CR Law " and was announced by Lord
Kelvin. In other words, two cables of length /i and k
having the constants Ci, RI and C2, R?. respectively will be
similar (that is, yield the same arrival curves "under identi-
cal conditions) when
CM? = cAif. (12)
This is only true when the cable is entirely devoid of in-
ductance and leakance, has no terminal apparatus, and
is earthed at both ends. Malcolm has shown that two
cables having the constants Ci, Zi, RI, gi and C2, £2, R^ £2
and with terminal apparatus of impedances Zti, Zri and Z<2,
Zr2 at transmitting and receiving ends respectively will be
similar when
gih _ Zti _ Zri __ / x
gili Zt2 Zrf
and the size of the signals will be in the ratio of rj to i.
This generalized expression may be appropriately called
Malcolm's law. It reduces to equation (12) when the
SUBMARINE TELEGRAPHY 365
cable inductance and leakance and the terminal apparatus
are ignored.
Fig. 4 shows the graph of current received over a 2500-
mile cable without terminal apparatus for the letters BT
with contacts of o.i second. Taking 7.2 elements for an
average letter including space, the number of five-letter
words transmitted per minute over this cable, having
CRl2 = 4.935 ohm-farads or seconds, under these conditions
60
would be - = 15. Signalling at this speed
gives legible results, as evinced by the figure. The greater
legibility for the same signalling speed over a shorter cable
is manifest from Fig. 5 for CRl? = 1.234 seconds. The
maximum speed of signalling over any cable is determined
by constructing arrival curves of various words using dif-
ferent values of r and submitting these to an experienced
operator to determine the limit of legibility. On short
cables the inertia of the receiving instrument prevents the
attainment of the theoretically possible speed of trans-
mission.
The use of condensers in series with a cable at one or
both of its ends affords better definition in the received
signals. The curves of Fig. 10, calculated according to a
method given by Malcolm,* show the arrival curves for the
same cable considered in the foregoing numerical illustra-
tion, with terminal condensers. Curve / represents the
received current curve when a condenser of gV the capacity
of the cable is connected in series with the cable at one end.
Curve // represents the current curve when a condenser of
-j1^- the capacity of the cable is connected at each end. This
curve is considerably lower than the first but its decay is
* The Electrician, V. 69, pp. 315-318 and 981.
366
TELEGRAPH ENGINEERING
much more rapid. The advantage of introducing a con-
denser of ^ the capacity of the cable in series with it at
its middle point, if possible from a practical viewpoint, is
shown by curve ///. The ultimate steady current value
for all of these conditions is zero.
800
720
640
560
r
E 400
| 320
240
160
80
^
• — »>,
— ^
X
ARRIVAL CURVES
on 2500 Mile
Cable with
Terminal
Condensers
V
\
X
L
\
XJ
^v,^
1
\"
^
\
1
\
\
\
^
/
S"
^s
^
\
"^
//
X
s^
\
1
^
Ss^
^
^x
• — .
V
1
** — .
~ —
~ —
•- —
— ,
—
0 0.2 0.4 0.6 0.8 1.0
Seconds
Fig. 10.
2.0
3.0
By subtracting from curve II a similar curve following
the first at an interval of o.i second, the received current
curve for a dot of that duration will result, and is shown in
Fig, 1 1 by curve 7. A comparison of this curve with curve
T of Fig. 4 dispjays the fact that the maximum current is
attained sooner with condensers than without them, but
this maximum is very much lower; and further that the
positive current lobe is followed by a negative pulse when
using condensers.
When the letters BT are transmitted over this cable with
condensers of 98.7 microfarads at each end, the received
SUBMARINE TELEGRAPHY
367
current appears as in Fig. n, curve //, when the time of a
dot or a dash is o. i second. The result is more legible than
the curve of Fig. 4 for the same signalling speed without
LETTERS BT .
Received on 2500
Mile Cable with
Terminal Condensers
120
0 0.1 0.2 0,3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
Seconds
Pig. n.
condensers, and, consequently, the speed with condensers
might be increased for the same degree of legibility. The
use of condensers at the ends of cables also serves to stop
earth currents and to facilitate duplex cable operation (§ 7).
5. Picard Method of Signalling. — In transmitting
signals over great distances through several cables con-
nected in series the speed of signalling is very low, but if
messages are repeated at intermediate stations the speed
of signalling is higher and is limited by the speed on that
368 TELEGRAPH ENGINEERING
cable section having the largest value of CRl2. This re-
peating of messages has been done manually, but from time
to time schemes have been devised and placed in operation
to utilize automatic retransmission in order to avoid error
and loss of time. When the received signals are such that
if a straight zero line of some width be drawn on the tape
all of the lobes which correspond to dots or dashes still
project on their respective sides of this zero line, then the
retransmission of these signals may be accomplished auto-
matically by the use of suitable relays, such as the Brown
drum relay or the Muirhead gold-wire relay.
The signalling systems of Picard and Gott, using modi-
fications of the ordinary Morse code, are arrangements for
permitting the automatic retransmission of messages, even
on cables having a large value of CRl2.
In the Picard method, the signals are formed by the time
interval between two momentary oppositely-directed equal
impulses, a dash being distinguished from a dot by a longer
interval between these impulses. Thus, the impressed
I I I I J
Fig. 12.
impulses for the letters BT are roughly shown in Fig. 12.
These impulses are impressed upon the cable by means of
two polarized relays P, P' and a local condenser C, con-
nected as shown in Fig. 13. A depression of the key K
causes a momentary kick of the right-hand relay armature
against its contact stud and connects the positive pole of
the main battery B to the cable for an instant. When the
SUBMARINE TELEGRAPHY
369
key comes to rest after each dot or dash signal the other
relay armature shifts and causes the negative pole of the
battery to be connected momentarily to the cable. Be-
tween these cable impulses the sending end of the cable is
open-circuited, and the impressed charge passes through
Cable
Fig. 13.
the receiver. The receiving device is a suspended-coil
relay which has no retractile springs and is free to respond
to cable impulses. This system has been used for many
years on the three Marseilles-Algiers cables (560 miles)
belonging to the French government for Morse signalling
and also for Baudot printing telegraphy from Paris to
Algiers with automatic translating relays at Marseilles.
6. Gott Method of Signalling. — The method of cable
signalling devised by Gott utilizes the Morse code of short
applications of potential for dots and longer applications
for dashes, with successive elements in opposite directions,
and employing a sensitive relay at the receiver. Inasmuch as
a relay of definite and sufficient sensibility connected to the
far end of a long cable operated at high speed in the ordinary
way (§3) could not properly automatically retransmit unidi-
rectional impulses into another cable owing to the spreading
out of the signals received by it, the message in the Gott
370
TELEGRAPH ENGINEERING
system consists of an assemblage of lobes, alternately posi-
tive and negative, one lobe for each dot and one for each
dash, and the latter distinguished from the former by their
greater length. Fig. 14 shows the results obtained by using
280
240
200
160
120
80
|40
1 °
|40
80
120
160
•
/
f
\
GOTT SYSTEM
of Signalling
Letters BT on
2500 Mile Cable
/~*
\
/
/
\
1
]
/
\
/
\
/
\
/
\
/
\
/
\
£
/
\
\
/
\
/
/
\
\
/
\
/
^/
V
S
\
1
II
i
3
— »
n
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
Seconds
Fig. 14.
this method over a long cable. The upper line shows
the impressed voltage on the 25oo-mile cable previously
considered with terminal condensers, for the letters BT,
having dashes three times as long as dots; the curve shows
the current form received at the end of this cable and
traversing the relay; and the lower line shows the voltage
impressed upon the second cable by the relay, which is as-
sumed to respond to currents as small as 30 microamperes.
The curve is constructed by the addition of properly placed
dot arrival curves of the type shown by curve 7 of Fig. n,
and dash arrival curves obtained by adding two curves
SUBMARINE TELEGRAPHY
371
(the latter reversed) of the type shown by curve II of Fig.
10 with an interval of 0.3 second between them. It will
be observed that the second dot in Fig. 14 is very short
while the third dot is almost as long as the dashes. This
distortion of signals may render deciphering difficult, but
the method can be improved upon by giving each im-
pressed letter its theoretically best shape. Much better
results are attained over shorter cable sections.
One arrangement for automatically reversing the direc-
tion of the voltage impressed upon the cable is shown in
Fig. 15.
Fig. 15. The outer terminals of the split battery B connect
with the contacts of the polarized relay P, and the middle
tap is grounded through the primary winding of trans-
former T. The secondary winding of this transformer con-
nects with the coils of the relay. Depressing the key K
charges the cable with a polarity depending upon whichever
contact stud the relay armature is touching. Permitting
the key to resume its normal position will cause the cable
to be grounded at the sending end after each signal.
The function of the transformer is to control the relay
armature so that successive impulses will always be of
different polarity. Assuming the armature to rest against
372 TELEGRAPH ENGINEERING
its left contact, depression of the key will cause a current
to be produced in the secondary of the transformer and in
the relay coils in such direction as to hold the armature to the
left contact, thereby securing firm contact. Releasing the
key causes a current of opposite polarity to flow through
the relay coils, consequently the armature will move against
the opposite contact stud in readiness for the next signal.
For automatic retransmission, from an overland line to a
submarine cable or from one cable to another, the key may
be replaced readily by the armature of a relay.
The receiver employed with this system is a recorder
with a contact-making tongue attached to the moving coil.
This tongue plays between two contacts, alternately touch-
ing one and then the other. These contacts are connected
together and lead to a battery and sounder (or relay) and
back to the tongue, thus forming a local circuit for the read-
ing of the received Morse dot and dash characters.
7. Duplex Cable Telegraphy. — In modern practice
telegraph cables are generally duplexed so that messages
may be sent in both directions simultaneously. This
practice involves the use of an artificial cable equivalent
in capacity and resistance to the actual cable arranged at
each end of the submarine cable, as shown in Fig. 16.
Artificial cables may be constructed in a variety of ways.
The Muirhead artificial cable is widely used and consists
of zigzag tinfoil sheets, connected in series, separated by
means of paraffined paper from other sheets of tinfoil. The
latter sheets are grounded, or may be grounded through
resistances, while the zigzag sheets are so proportioned as
to have the requisite resistance and also the proper capacity
with respect to the grounded sheets.
SUBMARINE TELEGRAPHY
373
The real and artificial cables may be considered as form-
ing two arms of a Wheatstone bridge, the other arms being
formed by two nearly equal condensers C\ and €2 of from
30 to 80 microfarads capacity each, arranged in the so-
Artificial
Cable
Fig. 16.
called double block. One of these condensers should be
slightly adjustable in capacity so that with the variable
resistance, r, an accurate balance may be secured. The
siphon recorder, R, provided with an adjustable inductive
shunt, 5, is connected across the bridge, while the reversible
battery is connected from r to ground through the double
key K. The function of the inductive shunt is to make
up the deficiency in recorder inductance for maximum
arrival current, so that, according to the alternating-current
transmission theory already mentioned, the receiving circuit
reactance neutralizes the reactance component of the cable
surge-impedance. Another arrangement employs a con-
denser in series with the recorder and shunted by a resist-
ance, the inductive shunt being bridged across both
condenser and recorder.
When balance is procured, depression of one of the keys
establishes a current which divides equally in the two cir-
cuits, one through the condenser C\ and the cable and the
other through the condenser Ci and the artificial cable.
Hence the terminals a and b of the recorder have the same
374 TELEGRAPH ENGINEERING
potential and, consequently, no current flows through this
instrument. Thus, manipulation of the key does not affect
the home recorder.
If, however, a current arrives at this end of the cable,
part passes through the recorder to ground jointly through
the artificial cable and condenser Ci, while the remainder
passes through the condenser Ci directly to ground. Thus
the key at one end controls the operation of the recorder at
the other end of the cable. In this way signals may trav-
erse the cable in opposite directions at the same time
without interference. The Gott signalling method is also
applicable to duplex cable operation. Considerable care
must be exercised in adjusting the artificial lines to secure
a good balance, and such adjustment is always made with
the distant end of the cables open-circuited.
8. Sine -wave Signalling. — A method of signalling on
cables was devised by Crehore and Squier which employs
a tape transmitter for impressing half sine waves of electro-
motive force upon the cable instead of the usual rectangular
wave-forms. The battery ordinarily employed is, therefore,
replaced in this system by a low-frequency alternator. The
tape has three lines of holes, the upper for dots, the lower
for dashes, and the center line of guide holes engages with
a toothed wheel driven by the alternator shaft so that the
tape travels a definite distance for each revolution of the
alternator armature. The tape passes beneath two rollers
attached to levers, which close a local circuit at their other
ends whenever perforations move under a roller. Two
relays in this local circuit connect the alternator to the
cable in the proper way and for a proper time. The ap-
pearance of the tape and the corresponding form of the
SUBMARINE TELEGRAPHY 375
impressed voltage for the letters cab are shown in Fig. 17.
The mechanical and electrical features of the transmitter
excel those of the Wheatstone automatic transmitter.
; o o o coo
\oooooooooooooo
o o o o
This system of signalling was operated experimentally
by its inventors over actual submarine cables and resulted
in a higher signalling speed than afforded with the usual
battery system under like conditions. Recently, Malcolm*
has published the results of his analytical investigation of
this sine-wave system of cable signalling, in which he con-
cludes that (a) the received signals resulting from short
applications of any symmetrical electromotive force are
independent of the shape of the voltage wave and dependent
only upon its mean value, and (b) the impressed sine-wave
voltage produces less shock at the sending end of the cable
than the abrupt battery wave-shapes. It is not unreason-
able to expect the commercial application of this sine-wave
signalling system.
9. Design of Submarine Cables. — A submarine cable
consists of a copper conductor surrounded by a tube of
gutta-percha insulation, all of which is protected by jute
coverings and by spirally-laid metallic armor. It has been
pointed out that the speed of signalling on such cables
(ignoring terminal apparatus, inductance and leakance)
varies inversely with the product of the conductor resistance
and the capacity of the conductor with respect to the sheath.
* The Electrician, v. 72, pp. 14-17, 50-52, 131-134, 245-247.
376 TELEGRAPH ENGINEERING
A large conductor surrounded by a thin tube of insulation
may have the same product of capacity and resistance as a
small conductor surrounded by a thick tube of insulation,
but the cost will be different. To find the sizes of conduc-
tor and insulation which yield the minimum cost of cable
of given length for a specified signalling speed (that is, for a
given value of CR), the expression of total cost in terms of
conductor diameter is differentiated and equated to zero.
No cognizance will be taken of the armor and other pro-
tecting coverings as these items do not affect the electrical
characteristics of the cable, but they may be included in
determining the economic cable, if desired, without altering
the method of procedure.
The weight of a copper wire one mile long and having a
cross-section of one circular mil is 0.016 pound. If c\ be
the cost of copper in dollars per pound, then the cost of a
stranded conductor / miles long and D mils in diameter is
0.016 sD2ki dollars, (14)
where s is the stranding factor or the ratio of the copper
cross-section in circular mils to the cross-section of the
circle of diameter Z); thus, for a seven-strand conductor
having strands of equal size, s = ^.
If d be the diameter in mils over the insulation, the vol-
ume of insulation will be
12 X 528°/ (d2 - D2) = 0.0497 1 (^ - D2) cu. in.,
1,273,240
where 1,273,240 is the number of circular mils in a square
inch. Taking 8 as the density of the insulating material
in pounds per cubic inch, and c2 as the cost in dollars per
pound of this material, its cost will be
0.0497 / (d2 - D2) 5^2. (15)
SUBMARINE TELEGRAPHY 377
As the capacity of two concentric cylinders i mile long,
the inner of diameter D and the outer of diameter d, sepa-
rated by a medium of uniform specific indue tivity k, is
^ 0.0804 k . . j
C = - ^— microfarads
(§ 7, Chap. IX), and as the resistance of the stranded con-
ductor, having a resistivity of p ohms per circular-mil mile
at sea temperature, is
it follows that the product is
0.0894 Pk
K_
whence d = DeD*, (16)
r.
Substituting this value of d in equation (15) and com-
bining with^(i4), the total cost of the cable exclusive of
armor and other coverings is
(2K \
c^-l). (17)
Differentiating and equating to zero, there results
/ *K\ .?*
0.032 sDld + 0.0497 Ifa f 2 D - ^— J e D* - 0.0994 /5Z>C2 = o
IlK \ ^ 0.03 2 Ci5
or ( -rrr- — i j € " = - - — i = /^ for convenience.
V D* / 0.0994 ^5
378
TELEGRAPH ENGINEERING
It is possible to determine D from this expression in terms
of the known factors K and F, and this is best done graphi-
cally. Fig. 1 8 shows the relation of -=— - to F.
1.4
1.3
1.2
1.1
D2"
0.9
0.8
0.7
0.6
0.5
-:
^
^
/
/
^
/
7
/
/
7-
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 l.O 1.2 1.
Fig. 18.
As a numerical illustration, let it be required to design
the most economical 25oo-mile seven-strand submarine
cable for a value of CR = 0.6 ohm-mf. per mile (that is
CR/2 = 3.75 seconds). Let
Ci = 0.16
c2 = 0.80
6 = 0.037
k = 3.04
p = 51,000,
then F = 0.032X0.16X0.778
0.0994 X 0.80 X 0.037
SUBMARINE TELEGRAPHY 379
and g = o.o894 X ,V°4 X 5 =
0.6 X 0.778
From Fig. 18, for F = 0.354, — = 1.115 and, therefore, the
diameter of the stranded conductor is
~ /20,7OO X 2 .,
D = \ V;/ - = 231 mils,
V i. nc
and the diameter over insulation is
29,700*
d = 231 e(231)1 = 403 mils.
The total cost of the conductor and insulating material
as determined from equation (17) is 265,000 + 401,000 =
666,000 dollars.
Had the conductor been a single wire (i.e., 5 = i) the
cost would be less for the same signalling speed. Its diam-
eter would then have been 196 mils and its diameter over
insulation 358 mils (no correction being made for increase
in resistance due to stranding) . The cost would be $5 76,000.
Solid conductors, however, are not frequently used because
of the greater liability of fracture in laying the cable.
To make certain that the stranded cable has sufficient
insulation resistance, the foregoing diameters are sub-
stituted in the following equation:
' i
Insulation resistance = — I — = — loge— (18)
2 irJo x 2 TT D
2
megohms per mile, where a is the resistance in megohms
between opposite faces of a cube of the insulation one mile
on a side when at sea temperature but at atmospheric
* See Table of Exponential Functions in Appendix.
380 TELEGRAPH ENGINEERING
pressure. Taking o- = 28,000 in the numerical illustration,
the insulation resistance will be 2480 megohms per mile.
Under the enormous pressures existing at great depths under
water, the insulation resistance of the cable when laid is
greater than when tested in the factory. Taking 0.05 per
cent increase per fathom (i fathom = 6 feet) the insula-
tion resistance at a depth of 1500 fathoms will be 4340
megohms per mile, which is adequate. The design of
cables for specified insulation resistance is of secondary
importance to signalling speed, inasmuch as leakance rel-
atively affects the shape or amplitude of the arrival current
curve but little, so long as it remains constant.
The weight of conductor and insulation is
0.016 sD2 + 0.0497 (<P ~ D2)* <.
^^ - — tons per mile,
2000
which weight is generally less than one-fifth of the total
weight of the cable. The amount of protection on cables
depends on the depth of sub-
mergence, and is light on deep-
& compound sea cable sections and heavy
°~7 stconductor ^or ^ne shore-end sections of
-jute Yam cables. In order to facilitate
the k^ and ^covering of
cables they should be as light
as is consistent with the stresses
to which they are subjected. Weights of galvanized iron
or steel cable sheaths for various depths of cable sub-
mergence are indicated roughly by
- - r^ — ; - ^rz tons per mile.
(depth in fathoms)0'8
SUBMARINE TELEGRAPHY
381
The weight of jute, tape and preservative compound may
be from 40 to 100 per cent of the weight of the metallic
sheath. Fig. 19 shows to proper size the cross-section of
the 25oo-mile cable considered in this article, well pro-
tected for a depth of 1500 fathoms.
The electrical constants of a few long cables are given
below :
Cable
Length in
miles*
Total re-
sistance in
ohms
Total ca-
pacity in
microfarads
Anglo-American Atlantic (Valentia
to Heart's Content) . . .
2I2O
7,288
776
Second German Atlantic (Borkum to
Fayal)
22O7
^218
Pacific (Fanning Island to Fiji). . . .
Atlantic (Canso to Waterville)
Commercial Pacific (San Francisco
to Honolulu)
2354
2493
2622
10936
4895
4O7 ^
746
914
87<
* Distances over sea are more frequently expressed in nautical miles (nauts); i naut =
1.152 miles.
The cost of laying a cable is generally estimated as half
of the cost of the cable. The life of a submarine cable is
variously estimated as from 30 to 40 years; in fact, por-
tions of cables laid from 1851 to 1854 from England to
neighboring countries are still in use.
The commercial status of submarine telegraphy is indi-
cated by the fact that in 1911 there were over 2000 cables
in the world aggregating 314,000 miles of cable and repre-
senting an estimated investment of 350 million dollars.
10. Types of Cable Service and Tariffs. — There are
two types of cable service rendered at present by some of
the large telegraph companies, namely: full-rate service for
code and urgent messages requiring prompt transmission
and delivery, and deferred service to many countries for
382 TELEGRAPH ENGINEERING
messages in plain language not requiring the greatest ex-
pedition and involving transmission within 24 hours. In
addition the Western Union Telegraph Company renders
cable letter service and week-end letter service across the At-
lantic for less important communications in plain language
which should not be subjected to the delay of over-sea
mails. The following conditions and rates apply at present
(July, 1914) to the various types of service.
All Classes. Addresses and signatures are counted and
charged for, but no charge is made for name of originating
city and date. In addresses, the names of delivery offices,
countries, provinces, states, etc., are each counted as one
word regardless of the number of letters employed. The
cost of full addresses may be avoided by using code ad-
dresses, which are permitted by all governmental adminis-
trations upon payment of a fee. In plain language, words
of 15 letters or less are counted as one word. Abbreviated
words and illegitimate combinations of words are inadmis-
sible. Every isolated character counts as one word, and
words joined by a hyphen or separated by an apostrophe
are counted as separate words. Punctuation marks are
only transmitted upon the expressed desire of the sender,
and then charged for as one word each.
Full-rate service. Full-rate messages may be in code or
cipher language or in any plain language expressible in
Roman letters. Code messages, formed of regular or arti-
ficial words not making intelligible phrases, must be pro-
nounceable and must not contain more than 10 letters.
Cipher messages, formed of either unpronounceable groups
of letters or of groups of figures, are counted at the rate of
5 characters, or fraction thereof, to a word. The presence
of a code word in an otherwise plain language message
SUBMARINE TELEGRAPHY
383
subjects the entire message to the lo-letter code count, but
plain language words in cipher messages are reckoned 15
letters to a word. If unpronounceable groups of letters
appear in code or plain language messages, such groups are
subject to the 5-letter cipher count. Fraction bars, periods,
commas and decimal points grouped with figures count as
figures. Replies to a message may be prepaid by writing
before the name and address the letters RP followed by the
figure showing the number of words prepaid (this indica-
tion is charged as one word). The following table shows
the rates per word to points in some of the principal coun-
tries from New York City.
Present cable rates in cents (July, 1914)
'Argentine Republic
65
'Australia
66
'Austria-Hungary
32
'Belgium
25
Bermuda
42
61
'Brazil '.
70-249
Bulgaria!
35
AC
'Cape Colony
'Chili
86
65
Philippine Islands
Porto Rico
112-136
JChina (except Macao =127)
122
'Portugal
Cuba (except Havana =15)
2O
Roumaniaf. . .
'Denmark
•ir
'Egypt
50-58
'Serviaf
43
'France
25
Siam
'Germany
25
'Spain
'Great Britain and Ireland
25
'Sweden
38
'Greece
36
'Switzerland
'Holland
25
'Transvaal
86
Honduras
55
Turkey (in Europe)f
'India
74
'Uruguay
6<
•Italy
31
Venezuela
* Countries to which Deferred Service may be utilized at present,
f Secret language prohibited.
J Deferred service only to Pekin, Hankow, Tientsin, Amoy, Chefoo, Foochow, Shang-
hai, Tsingtau, Weihaiwei, Hong Kong, and Macao.
It is of historical interest to recall that in the early pioneer days of transatlantic te-
legraphy the minimum tariff was £20 ($100) for 20 words and £i for each additional word.
384 TELEGRAPH ENGINEERING
Deferred service. Deferred messages must be written in
one language which may be that of the country of origin
or of destination or may be in French, the letters LCO,
LCD or LCF respectively being prefixed to the address as
indicative of the type of service and the language used
(one word is charged for this indication or prefix). The
text of the message must be entirely in plain language,
numbers, except in addresses, being also written in words.
The rates for deferred service is one-half those shown in
the foregoing table to the countries therein starred, except
to Great Britain and Ireland where the rate is 9 cents per
word. Replies may be prepaid as in full-rate service but
the instruction as to the number of words prepaid must be
expressed in terms of full rates.
Cable and Week-end letter service. Cable and week-end
letters must be written in plain language of the country of
origin or of destination, the indication CLP or CLT and
WLP or WLT respectively being prefixed to the address as
indicative of the type of service and the method of delivery
beyond London or Liverpool, whether by post or telegraph.
Cable letter tolls are based on an initial charge of 75 cents
for 12 words (13 including indication) and week-end letters
on an initial charge of $1.15 for 24 words (25 including
indication), plus 5 cents for each additional word in both
cases. These charges cover cable transmission only and do
not include terminal telegraphic charges. The letters may
be mailed to the New York Western Union Cable Office, the
week-end letters being sent in time for mail delivery at this
office on Saturday evenings. The charges cover delivery
in London or Liverpool and mail delivery to all other places
abroad. With telegraphic delivery beyond these cities cable
letters are deliverable during the day following their date
SUBMARINE TELEGRAPHY 385
and week-end letters on Monday forenoon ; and the follow-
ing additional charge per word is made to points in : Great
Britain and Ireland — i cent, Holland and Belgium — 2
cents, France— yi cents, Italy— 6 cents, Germany— 9 cents,
and in other countries at the regular foreign rates. Figures
when not used as cipher are counted each group of 5 or less
as a word. Replies may be prepaid as in deferred service.
Cable letter service is likewise in operation with Cuba,
the rate between New York and Havana being one dollar
for 20 words (including prefix), plus 5 cents for each addi-
tional word. Double this rate applies to letters for other
points in Cuba. Week-end letter service is in operation
with Argentine Republic, Chili and Peru, and the tariff
between New York and these countries is $4.85 for 24
words (25 including prefix) plus 20 cents for each additional
word, the letters being delivered on Tuesday mornings.
PROBLEMS
1. Compute the values of the current received at one end of the
2129-mile Anglo-American Atlantic cable, having R = 1.591 ohms
per mile and C = 0.3645 microfarad per mile, at instants respectively
of 0.2, 0.4, 0.6, 0.8, i.o, 1.4, 1.8, and 2.5 seconds after impressing 30
volts on the cable; also plot a curve showing these values co-ordi-
nated to time.
2. From the curve of the preceding problem construct graphically
the curve of arrival on this Atlantic cable of a dot element for a con-
tact on 30 volts lasting 0.05 second.
3. Using the dot arrival curve of the foregoing problem as a
basis, construct the shape of signals received over the cable for any
three-letter word.
4. What may be the signalling speed in terms of 5 -letter code
words on a icoo-mile cable having a total resistance of 3000 ohms and
a total capacity of 350 microfarads for the same legibility of received
signals as represented by Fig. 4.
386 TELEGRAPH ENGINEERING
5. Plot the received signals for the letters HE (for T = o.i second
with 40 volts) sent^through the 25oo-mile cable considered in §§ 2 to
4 according to the Gott system. Curve I of Fig. n shows the
magnitude and shape of the dot element. Show the type of signals
retransmitted into another cable if the receiving relay is actuated by
a current of 40 microamperes.
6. Determine the economic dimensions of the conductor and
insulation of the cable considered in § 9 if the cost of insulation be
taken as 55 cents per pound, other constants remaining unaltered.
7. Calculate the weights per mile and the total cost of 7-strand
conductor and insulation for a looo-mile cable having a value of
CR = 1.05 X io~6 seconds. The cost of copper is 17 cents and the
cost of insulation is i dollar per pound. Take k = 3.1.
8. What would be the possible maximum annual net income of a
duplexed cable when continuously used for automatic transmission
of code messages averaging 8.5 letters to the word and 9 words to the
message, if the dot element T is 0.05 second and the space between
messages is 12 T (the symbol " understand"— 3 dots, dash, dot, is
frequently used between messages); the apportioned revenue over
this cable section being 8 cents per word ? Two operators prepare
tapes and feed the transmitter and two decipher the received mes-
sages; they work in 8 hour shifts and receive an average weekly
salary of 26 dollars. Allow 3 per cent depreciation on the cost of
the cable installed and terminal apparatus, which was $1,000,000.
9. How much would it cost to send the following cable letter:
CLT-RP 10 Instrument Cambridge
Give price and delivery spectrophotometer and radio-micrometer
with scale Richardbrown Brooklyn.
10. Decipher the message reproduced below which was received
over a i6oo-mile cable.
nf-AT^AAAM
f\A /VA/^V^
APPENDIX
TABLES OF TRIGONOMETRIC FUNCTIONS,
EXPONENTIAL FUNCTIONS, LOGARITHMS AND
HYPERBOLIC FUNCTIONS
387
388
TELEGRAPH ENGINEERING
TABLE I. — TRIGONOMETRIC (CIRCULAR) FUNCTIONS
H
u
Degrees
Radians
Degrees
Radians
0
o
o
I OOOO
13.5
o 2334
o 9724
o 5
o 0087
I OOOO
o 24
2377
9713
O.OI
OIOO
0.9999
14.0-
2419
97O3
I O
0175
0008
0680
1-5
02
O20O
O262
9998
9997
14-5
26
2504
2571
9681
9664
03
O3OO
9996
15.0
2588
9659
2.O
O349
9994
27
2667
9638
04
O4OO
9992
15.5
2672
9636
2.5
0436
9990
16.0
2756
9613
0088
28
96ll
3-0
3-5
06'
0523
O6OO
o6lO
9986
9982
9981
16.5
17 o
29
2840
2860
2924
9588
9582
9563
4.0
0698
9976
30
2955
9553
07
0699
9976
17.5
3007
9537
4.5
0785
9969
3i
3051
9523
08
0068
. S.o
0872
9962
32
3146
9492
09
0899
9960
18 5
3173
9483
5-5
0958
9954
33
3240
9460
6.0
IO45
9945
34
3335
9428
ii
1098
\r*8
9426
6.5
1132
9936
20 o
3420
9397
7.0
12
"97
1219
9928
9925
20 5
35
3429
3502
9394
9367
13
o(j
1C2"*
9359
7-5
1305
9914
21 O
3584
9336
8.0
1392
9903
37
36l6
9323
14
1395
9902
21 5
3665
9304
8.5
1478
9890
38
37O9
9287
It;
9888
9-0
1564
9877
39
3302
9249
16
IITQ-I
0872
•7827
9239
9-5
l65O
9863
40
3894
9211
17
1692
9856
23.O
3907
9205
10. 0
1736
9848
41
3986
9171
18
I79O
9838
23 5
3987
9171
10.5
1822
9833
24 o
4067
9135
II. 0
II. 5
19
20
1889
1908
1987
1994
9820
9816
9801
9799
24-5
25 o
42
43
4078
4147
4169
4226
9131
9100
9090
9063
12.0
2O79
9781
9048
12.5
21
2085
2164
9780
25.5
4305
9026
13.0
22
2182
9759
26.0
^6
4384
8988
8961
»
23
2280
9737
26.5
4462
8949
APPENDIX
389
TABLE I. — TRIGONOMETRIC (CIRCULAR) FUNCTIONS— (Continued)
u
U
Degrees
Radians
Degrees
Radians
27 o
0.47
0.4529
4540
0.8916
8910
37-5
o 66
0.6088
6131
0.7934
7900
27-S
28 o
'"48"
4617
4618
4695
8870
8870
8829
38.0
38 5
67
6i57
6210
6225
7880
7838
7826
49
4706
8823
68
6288
7776
28.5
29.0
50
51
4772
4794
4848
4882
8788
8776
8746
8727
39-0
39-5
40.0
'"69"
6293
6361
6365
6428
7771
7716
7713
7660
29.5
4924
8704
70
6442
7648
30 o
52
4969
5000
8678
8660
40.5
71
6494
6518
7604
7584
53
5055
8628
41 o
6561
7547
30.5
31.0
54
5075
5141
5150
8616
8577
8572
41-5
72
73
6594
6626
6669
75i8
7490
7452
31 5
5225
8526
42 o
6691
7431
55
5227
8525
74
6743
7385
32.0
32.5
56
5299
5312
5373
8480
8473
8434
42.5
43 o
75
6756
6816
6820
7373
7317
7314
57
5396
8419
43 5
6884
7254
33.0
5446
8387
76
6889
7248
33.5
58
548o
5519
836S
8339
44.0
77
6947
6961
7193
7179
59
5564
8309
44 5
7009
7133
34.0
5592
8290
78
7033
7109
60
5646
8253
45.O
7071
7071
34-5
5664
8241
79
7104
7O39
35-0
35- 5
36.0.
36.5
37-0
61
62
'"63"
64
' 6s"
5729
5736
5807
5810
5878
5891
5948
5972
6018
6052
8197
8192
8141
8i39
8090
8080
8039
8021
7986
796l
80
85
90
.00
.10
.20
• 30
.40
• 50
.60
7174
7513
7833
8415
8912
9320
9636
9855
9975
9996
6967
6600
6216
5403
4536
3624
2675
1700
0707
— .0292
The functions of larger angles are:
Function
When angle u lies between
45° and 90°
90° and 180°
180° and 270°
270° and 360°
sin u =
cos «=
cos (90° — M)
sin (90° — «)
sin (180° — u)
— cos (180° — M)
— cos (270° — u)
— sin (270° — «)
— sin (360° — u)
cos (360° — M)
390
TELEGRAPH ENGINEERING
TABLE II. — EXPONENTIAL FUNCTIONS
«
e*
e-u
u
e"
•-*
u
«
r"
0
I. 0000
I. 0000
0.50
1.6487
0.6065
I.OO
2.7183
0.3679
0.01
OIOI
0.9901
51
6653
6005
02
7732
3600
02
O2O2
9802
52
6820
5945
04
8292
3535
03
0305
9704
S3
6989
5886
06
8864
3465
04
0408
9608
54
7160
5827
08
9447
3396
OS
0513
9512
55
7333
5769
10
3.0042
3329
06
O6l8
9418
56
7507
5712
12
0649
3263
07
0725
9324
57
7683
5655
14
1268
3198
08
0833
9231
58
7860
5599
16
1899
3135
09
0942
9139
59
8040
5543
18
2544
3073
10
1052
9048
60
8221
5488
20
3201
3012
II
Il63
8958
6l
8404
5434
22
3872
2952
12
1275
8869
62
8589
5379
24
4556
2894
13
1388
8781
63
8776
5326
26
5254
2837
14
1503
8694
64
8965
5273
28
5966
2780
IS
1618
8607
65
9155
5220
30
6693
2725
16
1735
8521
66
9348
5169
32
7434
2671
17
1853
8437
67
9542
5117
34
8190
2618
18
1972
8353
68
9739
5066
36
8962
2567
19
2093
8270
69
9937
5016
38
9749
2516
20
2214
8187
70
2.0137
4966
40
4.0552
2466
21
2337
8106
71
0340
4916
42
1371
2417
22
2461
8025
72
0544
4868
44
2207
2369
23
2586
7945
73
0751
4819
46
3060
2322
24
2712
7866
74
0959
4771
48
3929
2276
25
2840
7788
75
1170
4724
50
4817
2231
26
2969
7711
76
1383
4677
52
5722
2187
27
3100
7634
77
1598
4630
54
6646
2144
28
3231
7558
78
1815
4584
56
7588
2101
29
3364
7483
79
2034
4538
58
8550
8000
30
3499
7408
80
2255
4493
60
9530
2019
31
3634
7334
81
2479
4449
62
5.0531
1979
32
3771
7261
82
2705
4404
64
1552
1940
33
3910
7189
83
2933
436o
66
2593
1901
34
4049
7118
84
3164
4317
68
3656
1864
35
4191
7047
85
3396
4274
70
4739
1827
36
4333
6977
86
3632
4232
72
S84S
1791
37
4477
6907
87
3869
4190
74
6973
1755
38
4623
6839
88
4109
4148
76
8124
1720
39
4770
6771
89
4351
4107
78
9299
1686
40
4918
6703
90
4596
4066
80
6.0496
1653
41
5068
6637
91
4843
4025
82
1719
1620
42
5220
6570
92
5093
3985
84
2965
1588
43
5373
6505
93
5345
3946
86
4237
1557
44
5527
6440
94
5600
3906
88
5535
1526
45
5683
6376
95
5857
3867
90
6859
1496
46
5841
6313
96
6117
3829
92
8210
1466
47
6000
6250
97
6379
3791
94
9588
1437
48
6161
6188
98
6645
3753
96
7.0993
1409
49
6323
6126
99
6912
37i6
98
2427
1381
APPENDIX
391
TABLE II. — EXPONENTIAL FUNCTIONS — (Continued)
u
t«
_u
€
u
t«
*-"
2.OO
7.3891
0.13534
4-50
00.017
O.OIIIOO
05
7679
12873
55
94.632
010567
10
8.1662
12246
60
99.484
010052
IS
5849
11648
65
104.585
009562
20
9 . 0250
11080
70
109.947
009095
25
4877
10540
75
H5.584
008652
30
9742
10026
80
I2I.5IO
008230
35
10.4856
09537
85
127.740
007828
40
11.0232
09072
90
134-290
007447
45-
11.5883
08629
95
I4LI75
007083
50
12.1825
08209
S.oo
I48.4U
006738
55
12.8071
07808
05
156.022
006409
60
13.4637
07427
10
164.022
006097
65
14.1540
07065
IS
172.431
005799
70
14.8797
06721
20
181 . 272
005517
75
15.6426
06393
25
190.566
005248
80
16.4446
06081
30
200.337
004992
85
17-2878
05784
35
210.608
004748
90
18.1741
05502
40
221 . 406
004517
95
19.1060
05234
45
232.758
004296
3.00
20.086
04979
50
244.692
004087
05
21.115
04736
55
257.238
003888
10
22.198
0450S
60
270.426
003698
15
23.336
04285
65
284.291
003518
20
24-533
04076
70
208.867
003346
25
25.790
03877
75
3I4.I9I
003183
30
27.113
03688
80
330.300
003028
35
28.503
03508
85
347-234
002880
40
29.964
03337
90
365.037
002739
45
31.500
03175
95
383.753
002606
50
33-115
03020
6.00
403.43
0024788
55
34.813
02872
7.00
1,006.6
0009119
60
36.598
02732
8.00
2,98l.O
00033546
65
38.475
02599
9.00
8,103.1
00012341
70
40.447
02472
10.00
22,026
000045400
75
42.521
02352
11.00
59,874
000016702
80
44-701
02237
12. OO
162,754
000006144
85
46-993
02128
13.00
442,413
0000022603
90
49-402
02024
14.00
1,202,600
00000083153
95
51-935
01925
15.00
3,269,000
00000030590
4.00
54.598
01832
16.00
' 8,886,100
00000011253
05
57-397
01742
17.00
24,155,000
000000041399
10
60.340
01657
18.00
65,660,000
000000015230
IS
63.434
01576
19.00
178,482,000
0000000056028
20
66.686
01500
20.00
485,165,000
0000000020612
25
70.105
01426
21.00
1,318,800,000
00000000075826
30
73-700
OI3S7
22.00
3,584,000,000
00000000027895
35
77.478
01291
23.00
9,744,800,000
00000000010262
40
81.451
01228
24.OO
26,489,100,000
00000000003775
45
85.627
01168
25.00
72,004,800,000
00000000001389
392
TELEGRAPH ENGINEERING
TABLE III. — LOGARITHMS TO BASE 10
No.
0
I
2
3
4
5
6
7
8
9
10
00000
00432
00860
01284
01703
02119
02530
02938
03342
03743
ii
04139
04532
04922
05307
05690
06070
06446
06819
07188
07555
12
07918
08279
08637
08990
09342
09691
10037
10380
10721
11059
13
1 1394
11727
12057
12385
12710
13033
13354
13672
13988
14301
14
14613
14922
15229
15533
15836
16137
16435
16732
17026
I73I9
IS
17609
17898
18184
18469
18752
19033
I93I2
19590
19866
20140
16
20412
20683
20952
21219
21484
21748
2201 1
22272
22531
22789
17
23045
23300
23553
23805
24055
24304
24551
24797
25042
25285
18
25527
25768
26007
26245
26482
26717
26951
27184
27416
27646
19
27875
28103
28330
28556
28780
29003
29226
29447
29667
29885
20
30103
30320
30535
30749
30963
3H75
31386
31597
31806
32015
21
32222
32428
32633
32838
33041
33244
33445
33646
33846
34044
22
34242
34439
34635
34830
35025
352i8
3541 1
35603
35793
35984
23
36173
36361
36549
36736
36922
37107
37291
37475
37658
37840
24
38021
38202
38382
38561
38739
38916
39094
39270
39445
396i9
25
39794
39967
40140
40312
40483
40654
40824
40993
41162
41330
26
41497
41664
41830
41996
42160
42325
42488
42651
42813
42975
27
43136
43297
43457
43616
43775
43933
44091
44248
44404
44560
28
44716
44871
45025
45179
45332
45484
45637
45788
45939
46000
29
46240
46389
46538
46687
46835
46982
47129
47276
47422
47567
30
47712
47857
48001
48144
48287
48430
48572
48714
48855
48996
31
49136
49276
49415
49554
49693
49831
49969
50106
50243
50379
32
50515
50651
50786
50920
51055
5H89
51322
51455
51587
51720
33
5I85I
51983
52114
52244
52375
52504
52634
52763
52892
53020
34
53148
53275
53403
53529
53656
53782
53908
54033
54158
54283
35
54407
54531
54654
54777
54900
55022
55145
55267
55388
55509
36
55630
55751
55871
55991
56110
56229
56348
56467
56585
56703
37
56820
56937
57054
57I7I
57287
57403
57519
57634
57749
57863
38
57978
58093
58206
58320
58433
58546
58659
58771
58883
58995
39
59106
59218
59328
59439
59550
59660
59770
59879
59989
60097
40
60206
60314
60423-
60531
60638
60745
60853
60959
61066
61172
41
61278
61384
61490
61595
61700
61805
61009
62014
62118
62221
42
62325
62428
62531
62634
62737
62839
62941
63043
63144
63246
43
63347
63448
63548
63649
63749
63849
63949
64048
64147
64246
44
64345
64444
64542
64640
64738
64836
64933
65031
65128
65225
8
65321
66276
65418
66370
65514
66464
65609
66558
65706
66652
65801
66745
65896
66839
65992
66932
66087
67025
66181
67117
47
67210
67302
67394
67486
67578
67669
67761
67852
67943
68034
48
68124
68215
68305
68395
68485
68574
68664
68753
68842
68931
49
69020
69108
69197
69285
69373
69461
69548
69636
69723
69810
50
69897
69984
70070
70157
70243
70329
70415
70501
70586
70672
Si
70757
70842'
70927
71012
71096
71181
71265
71349
71433
7I5I7
52
71600
71684
71767
71850
71933
72016
72009
72181
72263
72346
53
72428
72509
72591
72673
72754
72835
72916
72997
73078
73159
54
73239
73320
73399
73480
7356o
73639
73719
73799
73fl8
73957
55
74036
74H5
74194
74273
74351
74429
74507
74586
74663
74741
56
74819
74896
74974
75051
75128
75205
75282
75358
75435
755U
57
75587
75664
75740
75815
75891
75967
76042
76118
76193
76268
58
76343
76418
76492
76567
76641
76716
76790
76864
76938
77012
59
77085
77159
77232
77305
77379
77452
77525
77597
77670
77743
60
77815
77887
7796o
78032
78104
78176
78247
78319
78390
78462
APPENDIX
393
TABLE III. -LOGARITHMS TO BASE 10. - (Continued)
No.
0
I
2
3
4
5
6
7
8
9
61
78533
78604
78675
78746
78817
78888
78958
79029
79099
79169
62
79239
79309
79379
79449
79518
79588
79657
79727
79796
79865
63
79934
80003
80072
80140
80209
80277
80346
80414
80482
80550
64
80618
80686
80754
80821
80889
80956
81023
81090
81158
81224
65
81291
81358
81425
81491
81558
81624
81690
81757
81823
81889
66
81954
82020
82086
82151
82217
82282
82347
82413
82478
82543
67
82607
82672
82737
82802
82866
82930
82995
83059
83123
83187
68
83251
83315
83378
83442
83506
83569
83632
83696
83759
83822
69
83885
83948
84011
84073
84136
84198
84261
84323
84386
84448
70
84510
84572
84634
84606
84757
84819
84880
84942
85003
85065
71
85126
85187
85248
85309
85370
85431
85491
85552
85612
85673
72
85733
85794
85854
85914
85974
86034
86094
86153
86213
86273
73
86332
•86392
86451
86510
86570
86629
86688
86747
86806
80864
74
86923
86982
87040
87099
87157
87216
87274
87332
87390
87448
75
87506
87564
87622
87680
87737
87795
87852
87910
87967
88024
76
88081
88138
88196
88252
88309
88366
88423
88480
88536
88593
77
88649
88705
88762
88818
88874
88930
88986
89042
89098
89154
78
89209
89265
89321
89376
89432
89487
89542
89597
89653
89708
79
89763
89818
89873
80927
89982
00037
90091
90146
90200
00255
80
00309
90363
90417
90472
90526
00580
90634
90687
90741
90795
81
90848
90002
90956
91009
91062
91116
91169
91222
91275
91328
82
9I38I
91434
91487
91540
91593
91645
91698
9I75I
91803
91855
83
91908
91960
92012
92065
92117
92169
92221
92273
92324
92376
84
92428
92480
92531
92583
92634
92686
92737
92789
92840
92891
85
92942
92993
93044
93095
93146
93197
93247
93298
93349
93399
86
93450
93500
93551
93601
93651
93702
93752
93802
93852
93902
87
93952
94002
94052
94IOI
94I5I
94201
94250
94300
94349
94398
88
94448
94498
94547
94596
94645
94694
94743
94791
94841
94890
89
94939
94988
95036
95085
95U4
95182
95231
95279
95328
95376
90
95424
95472
95521
95569
95617
95665
95713
95761
95809
95856
91
95904
95952
95999
96047
96095
96142
96190
96237
96284
96332
92
96379
96426
96473
96520
96567
96614
96661
96708
06755
96802
93
96848
96895
96942
96988
97035
97081
97128
97174
97220
97267
94
97313
97359
97405
97451
97497
97543
97589
97635
97681
97727
95
97772
97818
97864
97909
97955
98000
98046
98091
98137
98182
96
98227
98272
98318
98363
98408
98453
98498
98543
98588
98632
97
98677
98722
98767
98811
98856
98900
98945
98089
99034
99078
98
99123
99167
9921 1
99255
99300
99344
99388
99432
09476
99520
99
99564
99607
99651
99695
99739
99782
99826
99870
99913
99957
Characteristics of Logarithms:
log 4030 =3.6053
log 403 =2.6053
log 40.3=1.6053
log 4.03 =0.6053
log 0.403 =1.6053
log 0.0403 =2.6053
log 0.00403 =3. 6053
Useful Constants:
« = 2.7182818
IT = 3.1415927
i radian — 57.29578 degrees.
i degree = 0.0174533 radian.
394
TELEGRAPH ENGINEERING
TABLE IV.-HYBERBOLIC FUNCTIONS
M.
sinh u.
cosh «.
«.
sinh w.
cosh «.
«.
sinh «.
coshw.
o.oo
0.0000
I .OOOO
0.50
0.5211
I .1276
i .00
1.1752
I-543I
OI
0100
OOOI
51
5324
1329
05
2539
6038
02
O2OO
OOO2
52
5438
1383
10
3356
6685
03
0300
OOO5
53
5552
1438
15
4208
7374
04
O4OO
. 0008
54
5666
1494
20
5095
8107
05
0500
OOI3
55
5782
1551
25
6019
8884
06
O6OO
OOl8
56
5897
1609
30
6984
1.9709
07
O7OI
OO25
57
6014
.1669
35
7991
2-0583
08
080I
0032
58
6131
1730
40
1.9043
1509
09
OQOI
OO4I
59
6248
1792
45
2.0143
2488
10
1002
0050
60
6367
1855
50
1293
3524
II
1 102
006l
61
6485
1919
55
2496
4619
12
1203
0072
62
6605
1984
60
3756
5775
13
1304
0085
63
6725
2051
65
5075
f
6995
14
1405
0098
64
6846
2119
70
6456
8283
IS
1506
OII3
65
6967
2188
75
7904
2.9642
16
1607
OI28
66
7090
2258
80
2.9422
3.1075
17
I708
0145
67
7213
2330
85
3-IOI3
2585
18
1810
Ol62
68
7336
2402
90
2682
4177
19
1911
0181
69
7461
2476
95
4432
5855
20
2013
O2OI
70
7586
2552
2.00
6269
7622
21
2115
O22I
7i
7712
2628
05
3-8196
3-9483
22
2218
0243
72
7838
2706
10
4.0219
4-1443
23
2320
0266
73
7966
2785
15
2342
3507
24
2423
0289
74
8094
2865
20
4571
5679
25
2526
03M
75
8223
2947
25
6912
4.7966
26
2629
0340
76
8353
3030
30
4-9370
5-0372
2?
2733
0367
77
8484
3114
35
5.I95I
2905
28
2837
0395
78
8615
3199
40
4662
5569
29
2941
0423
79
8748
3286
45
5-7510
5-8373
30
3045
0453
80
8881
3374
50
6.0502
6.1323
31
3J5o
0484
81
9015
3464
55
3645
4426
32
3255
0516
82
9150
3555
60
6.6947
6 . 7690
33
336o
0549
83
9286
3647
65
7.0417
7.1123
34
3466
0584
84
9423
3740
70
4063
4735
35
3572
0619
85
956i
3835
75
7.7894
7-8533
36
3678
0655
86
9700
3932
80
8.1919
8.2527
37
3785
0692
87
9840
4029
85
8.6150
8.6728
38
3892
0731
88
0.9981
4128
90
9.0596
9.1146
39
4000
0770
89
I. 0122
4229
95
9.5268
9-5791
40
4108
0811
90
0265
433i
3-00
10.0179
10.0677
4i
4216
0852
9i
0409
4434
05
10.5340
10.5814
42
4325
0895
92
0554
4539
10
11.0765
11.1215
43
4434
0939
93
0700
4645
15
11.6466
11.6895
44
4543
0984
94
0847
4753
20
12.2459
12.2866
45
4653
1030
95
0995
4862
25
12.8758
12.9146
46
4764
1077
96
1144
4973
30
13-5379
13.5748
47
4875
1125
97
1294
5085
35
14-2338
14.2689
48
4986
"74
98
1446
5199
40
14.9654
14.9987
49
5098
1225
99
1598
5314
45
15-7343
15.7661
APPENDIX
395
TABLE IV. — HYPERBOLIC FUNCTIONS.— (Continued)
«.
sinh «.
cosh M.
u.
sinh u. cosh u.
3.50
16.5426
16.5728
6.00
201.7132
201.7156
55
I7-3923
17.4210
05
212.0553
212.0577
60
18.2855
18.3128
IO
222.9278
222.9300
65
19.2243
19.2503
15
234.3576
234.3598
70
20.2113
20.2360
20
246.3735
246.3755
75
21.2488
21.2723
25
259.0054
259.0074
80
22.3394
22.3618
30
272.2850
272.2869
85
23.5072
35
286.2455
286.2472
90
24.6911
24.7113
40
300.9217
300.9233
3-95
25-958I
25-9773
45
316.3504
316.3520
4.00
27.2899
27.3082
So
332.5700
332.5716
°5
28 . 6900
28.7074
55
349.6213
349.6228
IO
30.1619
30.1784
60
367.5469
367.5483
15
31.7091
31.7249
65
386.3915
386.3928
20
33-3357
33-3507
70
406 . 2023
406.2035
25
35-0456
35.0598
75
427.0287
427.0300
3°
36-8431
36.8567
80
448.9231
448.9242
35
38.7328
38.7457
85
471-9399
471-9410
40
40.7193
40.7316
90
496.1369
496.1379
45
42.8076
42.8193
6-95
521.5744
521.5754
50
45.0030
45.0141
7.00
548.3161
548.3170
55
47.3109
47-3215
°5
576.4289
576.4298
60
49-7371
49.7472
IO
605.9831
605.9839
65
52.2877
52.2973
15
637.0526
637.0534
70
54.9690
54.9781
20
669.7150
669.7157
75
57.7878
57.7965
25
704.0521
704.0528
80
60.7511
60.7593
30
740.1497
740.1504
85
63.8663
63.8741
35
778.0980
778.0986
90
67.1412
67.1486
40
817.9919
817.9925
4-95
70.5839
70.5910
45
859.93I3
859.9318
5-oo
74.2032
74.2099
50
904.0210
904.0215
05
78.0080
78.0144
55
950.37H
950.3716
10
82.0079
82.0140
60
999.0976
999.0981
IS
86.2128
86.2186
65
1050.323
20
90.6334
90.6389
70
II04.I74
25
95-2805
95.2858
75
1160.786
30
100.1659
100.1709
80
1220.301
35
105.3018
105.3065
85
1282.867
40
110.7009
110.7055
90
1348.641
45
116.3769
116.3812
7-95
1417.787
5°
122.3439
122.3480
8.00
1490.479
55
128.6168
128.6207
05
1566.698
60
135-2114
135.2150
10
1647 . 234
65
142.1440
142.1475
IS
1731.690
70
149.4320
149-4354
20
1820.475
75
157-0938
157.0969
25
I9I3.8I3
80
165.1482
165.1513
30
2011.936
85
173.6158
173.6186
35
2115.090
90
182.5173
182.5201
40
2223.533
95
191.8754
191.8780
45
2337-537
INDEX
Abbreviations on ticker tapes, 121.
used in telegraph transmission, 28.
Added resistance of Field quad., 93.
Admittance, dielectric, 316.
Advantage of double-current duplex,
74-
using two generators on simplex
lines, 342.
Aerial cables, 269.
installation of, 272.
lines, 253.
Alarm indicators, 210.
Alarms of fire, transmission of, 189.
public, 200.
Alphabets, telegraph, 26, 121, 164,
356.
Alternating-current track relays,
246.
transmission theory, 304.
illustration of, 330.
Armor on cables, 380.
Arresters, lightning, 135, 260.
Arrival curves on cables, 353.
Artificial cables, 372.
lines, 47, 51.
calculation of, 47, 62, 67, 71.
Atkinson, Richard L., repeater, 40.
Attenuation coefficient, 311.
Automatic block signals, 225.
fire-alarm repeaters, 206.
repeaters, 37.
retransmission over cables, 368.
telegraphy, 108.
transmitter, no, 122.
Auto-transformers in eliminating
line induction, 292.
Ayrton, Prof. William E., receiver
resistance, 338.
Balanced circuit, conditions of, 52.
Balancing polar duplex, 59.
quadruplex, 93.
Barclay, John C., printing telegraph,
121.
Batteries, location on lines, 6.
primary, 20.
secondary, 21.
Baudot, Jean M.E., printer, 133, 163.
Bell-striking machines, 202.
Block signals, automatic, 237.
for electric roads, 231.
for steam roads, 239.
location of automatic, 232.
manual systems, 231.
one-rail system, 243.
TDB system, 235.
two-rail system, 244.
types of, 224.
Bonding of cable sheaths, 279.
Bonds, impedance track, 244.
Boxes, cable pole, 277.
fire-alarm, 192.
police signal, 218.
Bridge duplex, 67.
current in relay of, 345.
direct-point repeater, 79.
Wheatstone, 67, 373.
Brooklyn fire-alarm system, 212.
397
398
INDEX
Brown, Sidney G., drum relay, 368.
Buckingham, Charles L., printer, 133.
Bunnell keys, 8.
Burry, John, printing telegraph, 133.
Cable keys, 363.
letters, 382.
service, 381.
splices, 276.
tariffs, 381.
telegraphy, theory of, 347.
Cables, artificial, 372.
attenuation constant of, 312.
capacity of, 287.
constants of some, 381.
design of submarine, 375.
installation of, 272.
telegraph, 269.
Capacity of cables, 287.
line wires, 284.
Catlin, Fred, repeater, 42.
Cells, voltaic, 20.
Central stations, fire-alarm, 202.
Chapman, Winthrop M., block sig-
nals, 239.
Characteristic impedance of line,
3r9-
Cipher messages, 151.
Circuits on Northern Pacific, 158.
Clapp, Martin H., statistics, 158.
Closed-circuit Morse system, 2, 5.
Code, Barclay printing, 121.
cable, 356.
Continental, 25.
Morse, 25.
Murray multiplex, 164.
Phillips punctuation, 25.
words, 150.
Cole, Frederick W., repeater, 206.
Combination fire-alarm circuits, 212.
Common-battery telephone, 293.
Composite signalling, 296.
railway, 298.
Condensers in series with cables, 365.
with artificial lines, 52.
Conductance, leakage, 287.
Conductors, constants of, 262, 282.
Conduit, underground, 274.
Continental telegraph code, 25, 356.
Continuity-preserving pole-chang-
ers, 58.
transmitters, 50.
Copper-clad wire, 29.
inductance of, 284.
line wire, 29, 262.
Corrosion of cable sheaths, 277.
Cosines, table of, 388, 394.
Crane, Moses G., fire-alarm box, 194.
Creed, Frederick G., printer, 133.
Cr chore, Dr. Albert C., cable signal-
ling,-3 74.
duplex-diplex, 102.
CR Law, 364.
Cross-arms, pole, 259.
Current distribution equations, 308.
general, 329.
in duplex circuits, 50, 62, 69, 75.
in leaky lines, 334.
propagation over lines, 303.
ratio in quadruplex, 93.
received over cable, 352.
sources, 20.
variation in quadruplex, 92.
D'Arsonval, Dr. Arsene, galvanome-
ter, 360.
Davis, Minor M., duplex, 63.
quadruplex, 96.
Day letters, 152.
Dean, Robert L., printer, 133.
Deferred cable service, 381.
overland service, 152.
INDEX
399
Delany, Patrick B., multiplex tele-
graph, 162.
Desk, police central-office, 221.
D'Humy, Fernand E., repeater, 42.
reperforator, 114.
Diehl, Clark £., relay scheme, 95, 97.
Dielectric admittance, 316.
permittivity, 286.
Differential duplex, 46.
neutral relay, 46.
polarized relay, 55.
Diplex signalling, 86.
Direct-current transmission theory,
305» 334-
illustration of, 338.
point repeaters, 76.
Disk railway signals, 227.
Distance of transmission over leaky
lines, 32.
over perfectly-insulated lines, 4.
Distributing frames, 143.
Distributors, synchronous, 164.
Disturbances, inductive, 288.
elimination of, 290.
Dot-frequency, 304, 356.
Double-block condenser scheme, 373.
current duplex, 74.
Dry-core cables, 269.
Duplex automatic telegraphy, 113.
balancing, 59.
Barclay, printing telegraph, 126.
bridge, 67.
cable telegraphy, 372.
Davis and Eaves, 63.
differential, 45.
diplex signalling, 102.
double-current, 74.
leak, 62.
Morris, 66.
polar, 56.
improved, 63.
Duplex, Postal Telegraph Co., 63.
repeaters, 76.
short-line, 66.
signalling, theory of, 344.
single-current, 46.
Stearns, 46.
switchboard circuits, 142.
telegraphy, 45.
Western Union Co., 71.
Dwarf railway signals, 226.
Earth as return path, i, 279.
resistance, 280.
Eaves, Augustus J., duplex, 63.
quadruplex, 96.
Economic cable determination, 376.
span lengths, 266.
Edison, Thomas A., battery, 20, 22.
quadruplex, 85.
Electric railways, signals for, 231,
237, 242.
telegraphy, see Telegraphy.
Electrolysis of cable sheaths, 277.
Electromagnetic induction, 288.
Electrostatic induction, 288.
Equivalent sine curves, 304.
Essick, Samuel V., printer, 133.
Exponential functions, 390.
Faraday, Prof. Michael, law of, 278.
polarizing effect, 183.
Fibre stress in poles, 256.
Field, Stephen D., key system, 91.
Fire-alarm boxes, 192.
central stations, 202.
devices at apparatus houses, 210.
repeaters, 206.
systems, operation of, 212.
statistics of, 221.
telegraphy, 189.
transmitters, 203.
4oo
INDEX
Fourier, Jean B. /., series, 304, 348.
Fournier, Prof., television, 183.
Fowle, Frank F. , copper-clad wire, 2 84.
Freir, Samuel P., neutral relay, 96.
Frequency, dot-, 304, 356.
reversal-, 356.
Fuller, John, battery, 20.
Fuses, 135.
Galvanized iron wire, 29, 262.
Gamewell, John N., fire-alarm box,
194.
Gardiner, James M., fire-alarm box,
194.
General equations of line current
and voltage, 329.
Generators, 23.
Ghegan, John /., repeater, 42.
Gintl, Dr. Wilhelm, duplex, 45.
Gong circuits, fire-alarm, 211.
electromechanical, 210.
Gott, John, cable signalling, 369.
Gravity battery, 20.
Gray, Prof. Elisha, telautograph, 170.
Ground as return path, i, 279.
connections, 281.
resistance, 2, 280.
Grounded capacity of cables, 287.
Growth of current in cables, 351.
in relay, 14, 35.
Guild, George R., induction tele-
graph, 186.
Guying of aerial lines, 257.
Half-set repeaters, 80.
Handling of telegraphic traffic, 154.
Hangers, cable, 272.
Hard-drawn copper wire, 29, 262.
Heaviside, Oliver, earth resistance,
279.
wire capacity, 285.
High-potential leak duplex, 62.
Horton, Lewis, repeater, 42.
Howler, telephone, 300.
Hughes, Prof. David E., printer, 133.
Hyperbolic functions, table of, 394.
use of, 18, 265, 284, 322.
Ideal line, velocity of wave propaga-
tion on, 313.
Impedance at ends of line, 326.
characteristic, of line, 319.
conductor, 316.
of relays, 13.
surge, 319, 357.
track bonds, 244.
Indicators, fire-alarm, 210.
Inductance of line wires, 283.
Induction repeaters, 187.
telegraphs, 184.
Inductive line interference, 288.
shunt for recorders, 373.
Installation of aerial cables, 272.
Instrument tables, 145.
Insulation resistance of cables, 270,
288, 379.
of lines, 30, 287.
Insulators, 254.
Interlacing of circuits, 194.
Interlocking machines, 247.
plant signals, 225, 247.
Intermediate offices, 6.
Iron line wire, 29, 262.
Jacks, pin-, 139.
spring-, 138.
Joints in line wire, 253.
Joker fire-alarm circuits, 211.
Kelvin, Lord (Wm. Thomson), CR
law, 364. * C
recorder, 360.
INDEX
401
Kennelly, Dr. Arthur E., hyperbolic
functions, 321, 324.
receiver resistance, 357.
Keyboard, ticker, 119.
Keys, 8, 363.
Kinsley, Carl, printer, 133.
Kirnan, William H., repeater, 206.
Kleinschmidt, Edward E., perforator,
122.
Korn, Dr. Artur, telephotography,
175-
Lalartde, F. de, battery, 20.
Leak duplex, 62.
relays, 78.
resistance of Field quad., 93.
Leakage, line, 30.
Leakance of lines, 287.
Leclanche", Georges, battery, 20.
Legibility of recorder tapes, 359.
Letters, cable, 382.
day and night, 152.
Light-relay, 177.
signals on railways, 225.
Lightning arresters, 135, 260.
Lines, aerial open, 253.
artificial, 47, 50.
capacity of, 284.
inductance of, 283.
inductive interference on, 288.
leakance of, 287. •
resistance of, 29, 283.
telegraph, 28.
Local circuits, 4.
duplex and quadruplex, 141.
Locking sheet, 250.
Logarithms, table of, 392. "•
Loop switchboards, 141.
Low, A. M., television, 184.
Lowy, Heinrich, earth resistance,
Maclaurin, Colin, series, 322.
Magnet bobbins, windings of, 13.
Magneto telephone circuit, 293.
Main switchboards, 139.
Malcolm, Dr. Henry W., law, 364.
Mallet perforator, 109.
Manholes, 275.
Manual block signals, 224, 231.
Marino, Algeri, telephotography,
181.
Marking current, 112.
Matthews, W. N. and Claude L., con-
duit costs, 274.
Maver, William, Jr., repeater, 42.
Mclntyre, C., connector, 253.
Mecograph transmitting key, 10.
Mercadier, Prof. Ernest J. P., tele-
graph system, 162.
Messages, telegraph, types of, 150.
Messenger wires, 272.
Military induction telegraphs, 184.
Milliken, George F., repeater, 42.
Morkrum printer (Chas. L. Krum
and Jay Morton), 133.
Morris, Robert H., duplex, 66.
Morse, Prof. Samuel F. B., code, 25.
telegraph system, i.
Motor-generator sets, 24.
switchboard connections of, 147.
Muirhead, Dr. Alexander, artificial
cable, 372.
relay, 368.
Multiplex, Murray, page printer,
163.
telegraphy, 162.
Municipal telegraphs, 189.
Munier, Claude J. A., printing
telegraph, 133.
Murray, Donald, printer, 133, 163.
Mutual capacity of wires, 285.
inductance of wires, 283.
402
INDEX
Neilson, Hugh, repeater, 42.
Neomon, interpretation of, 316.
Nernst, Dr. Wallher, lamp, 177.
Neutral relays, construction of, 12.
differential, 46.
effect of current reversals in, 94.
with extra coil, 96.
Nicol, William, prism, 183.
Night letters, 152.
Non-interfering repeater, 206.
signal boxes, 194.
Open-circuit Morse system, 5.
Oscillogram of current growth, 14.
Overlap railway signal system,
233-
Paper winder, 16^ 211.
Patching cords, 139.
Peg-switch panel, 136.
Perforator, keyboard, 122.
Kleinschmidt, 122.
mallet, 109.
Permittivity of dielectric, 286.
Phantom telephone circuit, 296.
Phantoplex system, 103.
Phillips, Walter P., punctuation
code, 25.
repeater, 37, 80.
Photographs, transmission of, 175.
Physical telephone circuits, 296.
Picard, Pierre, cable signalling, 367.
telegraph system, 162.
Pins, insulator, 254.
Plugs for pin jacks, 139.
Polar direct-point repeater, 76.
duplex, 56.
Polarized block-signal system, 240.
relays, 53, 125.
sounder, 186.
Polar-neutral track relay, 240.
Pole boxes, cable, 277.
changer, 56.
Western Union, 72.
spacing, economic, 266.
telegraph, 254.
Police patrol boxes, 218.
central offices, 220.
telegraphs, 217.
statistics of, 221.
Pollak, Dr. Anloine, writing tele-
graph, 167.
Postal polar duplex, 63.
quadruplex, 96.
Power switchboards, 146.
Primary batteries, 20.
Printing telegraph, Barclay, 121.
various, mention of, 133.
Printing telegraphy, 115.
Problems, 43, 83, 106, 134, 161, 188,
223, 251, 300, 346, 385.
Propagation constant of line, 318.
Protective devices, 135.
resistances, 24, 6 1.
Protectors, 145.
Public fire alarms, 200.
Quadrantal operator, 316.
Quadruplex, Davis-Eaves, 96.
Field key system, 91.
Postal Telegraph Co., 96.
repeaters, 100.
signalling, theory of, 344.
switchboard circuits, 141.
systems, operation of, 87.
telegraphy, 85.
Western Union, 98.
Railway composite signalling, 298.
interlocking signals, 247.
operation, the telegraph in, 157.
signal systems, 224.
INDEX
403
Receiver, Barclay printing, 126.
Korn telephotographic, 177.
Pollak-Virag, 168.
Receiving instruments, best resist-
ance of, 357.
best winding for, 16.
Recorder, siphon, 360.
Wheatstone, 108, 114.
Reflection coefficient, 320.
Registers, 15, 210.
Relay current in bridge duplex,
345-
Relays, ampere-turns for, 4.
cable, 368.
construction of neutral, 12.
current growth in neutral, 14.
design of, 35.
Diehl arrangement of, 95, 97.
differential neutral, 46.
polarized, 55, 125.
leak, 78.
light-, 177.
phantoplex, 104.
polarized, 53.
resistance of, 13, 19, 56.
step-, 1 80.
track, 240, 246.
use of, 3.
windings, 16.
Repeaters, Atkinson, 40.
closed-circuit, 37.
direct-point, 76.
duplex, 76.
fire-alarm, 206.
half-set, 80.
induction, 187.
open-circuit, 42.
quadruplex, 100.
simplex, 35.
various, mention of, 42.
Weiny-Phillips, 37, '80.
Repeating coil, 294.
sounders, 40, 67, 95.
Reperforator, 114.
Resistance of artificial lines, 52.
of Field quadruplex, 93.
of grounds, 2^2.
of polarized relays, 56.
of relays, 13.
of selenium, 175.
of siphon recorders, 362.
of sounders, n.
of telegraph lines, 29.
of the earth, 279.
of wires, 283.
Resonators for sounders, n.
Retardation coils, 67.
construction of, 71.
Retransmission over cables, 368.
Reversal-frequency, 356.
Rheostats, artificial line, 52.
Rignoux, television, 183.
Ringing over composited lines, 297.
Rowland, Prof. Henry .4. /printing
telegraph, 133, 163.
Riiddkk, John /., fire-alarm box, 194.
Ruhmer, Ernst, television, 183.
Sags of wires, 262.
Saturated-core cables, 269.
Secondary batteries, 21.
Sector signal boxes, 200.
Seeing at a distance, 183.
Selenium resistance as affected by
light, 175.
Self-inductance of wires, 283.
Semaphores, 225.
operation of, 229.
Semi-automatic transmitters, 10.
Sextuplex signalling, 104.
Shading coils on relay, 246.
Shunt, inductive, 373.
404
INDEX
Side circuit, 296.
Siemens, Dr. E. Werner, printer, 133.
Signal boxes, fire-alarm, 192.
Gamewell Company, 196.
police, 218.
successive, 195.
Signalling speed on cables, 363.
types of, see Telegraphy.
Signals, railway, 224.
Silent interval in cable operation, 355.
Simplex instruments, 8.
repeaters, 35.
signalling on telephone lines, 295.
with one generator, 336.
with two generators, 341.
switchboard circuit, 142.
telegraphy, i.
Simultaneous telegraphy and teleph-
ony, 293.
Sines, table of, 388, 394.
Sine- wave cable signalling, 374.
equivalent, 304.
transmission, illustration of, 330.
Single-current duplex, 46.
line repeaters, 35.
Morse circuit, 2.
Siphon recorder, 360.
Skelton, Francis A., repeater, 206.
Sounders, ampere-turns for, 3.
construction of, 10.
polarized, 186.
repeating, 67, 95.
resistance of, n.
windings of, 16.
Spans, economic length of, 266.
wire, 261.
Spark quenching at contacts, 61, 73.
Specific inductive capacity, 286.
Speed, effect of signalling, 334.
of cable signalling, 363.
of signalling, 33.
Splices, cable, 276.
Spring jacks, 138.
Squier, Col. George 0., cable signal-
ling, 374.
Statistics of cables, 271, 381.
of telegraph systems, 159.
Steam railways, signals for, 239.
Stearns, Joseph B., duplex, 46.
Steinheil, Prof. Karl A. von, earth
return, 279.
Step-relay, 180.
Storage batteries, 21.
Strap and disc switch, 136.
Stresses in poles, 256.
Submarine cables, design of, 375.
telegraphy, 347.
Successive signal boxes, 195.
Sunflower distributor, 126.
Surge impedance, 319, 357.
Switchboards, fire-alarm, 209.
police telegraph, 220.
power, 146.
telegraph, 138.
Synchronous distributors, 164.
Tape, perforated transmitting, 108,
122, 164, 167.
siphon recorder, 361.
ticker, 120.
Tariffs, cable, 381.
telegraph, 152.
Taylor, John D., relay, 242.
Telautograph, 170.
Telegrams, 152.
Telegraph cables, 269.
equation, 350.
induction, 184.
in railway operation, 157.
lines, 253.
current propagation in, 303.
municipal, 189.
INDEX
405
Telegraph statistics, 159.
Telegraphy, automatic, 108.
cable, 347.
duplex, 45.
cable, 372.
fire-alarm, 189.
multiplex, 162.
police-patrol, 217.
printing, 115.
quadruplex, 85.
simplex, i.
simultaneous telephony and, 293.
submarine, 347.
synchronous, 162.
writing, 167.
Telephone circuits, 293.
Telephoning of messages, 155.
Telephony on telegraph lines, 298.
simultaneous telegraphy and, 293.
Telephotography, 175.
color, 181.
Television, 182.
Test grounds, 282.
Theory of current propagation, 303.
Thomson, Prof. Elihu, arcs, 181.
Ticker telegraphs, 115.
Tiffany, George S., telautograph, 170.
Time stamp, automatic, 211.
Timing of condenser discharge, 52.
Toye, Benjamin B., repeater, 42.
Track circuits, 239.
relays, 240, 246.
Traffic-direction-block system, 235.
telegraph, 150.
handling of, 154.
Transformers, use of, in eliminating
inductive interference, 290.
Transition theory of transmission,
305, 347-
Transposition insulator, 254.
of line wires, 289.
Transmission distance on leaky lines,
32-
on perfectly-insulated lines, 4.
of current over line, 303.
of signals over cables, 355.
theory, alternating-current, 306.
direct-current, 334.
transition, 305, 347.
Transmitters, automatic, no, 122.
continuity-preserving, 50, 58.
fire-alarm, 203.
Korn telephotographic, 176.
pole-changing, 56.
Pollak-Virag, 167.
repeater, 38, 40.
semi-automatic, 10.
ticker telegraph, 115.
Wheatstone, 108.
Trigonometric functions, 388.
Underground cables, 269.
installation of, 273.
conduit, 274.
Uniform lines, current distribution
on, 306.
Van Rysselberghe, Prof. Francois,
composite signalling, 296.
Vector representation, 315.
Velocity of wave propagation, 312.
Vibrator, siphon recorder, 361.
Vibroplex transmitting key, 10.
Virag, Josef, writing telegraphs, 167.
Voltage distribution equations, 309.
general, 329.
on cables, 350.
Voltages, standard, in telegraphy, 24.
Wave-length constant, 311.
propagation, theory of, 306.
Wedges for spring jacks, 138.
406
INDEX
Week-end letters, 382.
Weights of cable, 271, 380.
sheaths, 380.
of line wire, 29, 262.
Weiny, Roderick H., repeater, 37,
80.
Western Union bridge-duplex, 71.
quadruplex, 98.
switchboards, 139.
Wheatstone, Sir Charles, automatic
telegraph, 108.
bridge, 67, 373.
Whistle-blowing machine, 200.
Whitehead, Charles S., receiver re-
sistance, 338.
Winding constants of magnets, 13.
for receiving instruments, 16.
Wire, bimetallic, 29.
capacity of line, 284.
leakance of line, 287.
inductance of line, 283.
resistance of line, 29, 283.
sizes of line, 29.
spans, 261.
tensile strength of, 262.
weights of line, 29, 262.
Wright, John E., printer, 133.
Writing telegraphs, 167.
Yorke, George M., line induction, 292.
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SODDY, F. Radio-Activity ; an Elementary Treatise from the Stand-
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THIESS, J. B. and JOY, G. A. Toll Telephone Practice. 273 illustrations.
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UNDERBILL, C. R. Solenoids, Electromagnets and Electromagnetic
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URQUHART, J. W. Electroplating. A Practical Handbook. Fifth
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WADE, E. J. Secondary Batteries: Their Theory, Construction, and Use.
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WADSWORTH, C. Primary Battery Ignition. A simple practical pocket
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WALKER, FREDERICK. Practical Dynamo-Building for Amateurs.
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WATT, ALEXANDER. Electroplating and Refining of Metals. New
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WEBB, H. L. A Practical Guide to the Testing of Insulated Wires and
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WEYMOUTH, F. MARTEN. Drum Armatures and Commutators.
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WILKINSON, H. D. Submarine Cable-Laying, Repairing, and Testing.
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WRIGHT, J. Testing, Fault Localization and General Hints for Linemen.
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YOUNG, J. ELTON. Electrical Testing for Telegraph Engineers. Illus-.
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