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MODERN RADIO
OPERATION

J. O. SMITH (2ZL)

Associate Member, I. R. E.

326 Broadway

New York

Wireless Press, Inc.

b'.

^'^^ : ' iM

273089

Jfln 2 1 1924

CONTENTS

Chapter • Page

1. The Radio Telephone ------- i

II. Transmitting Equipment Used in Radio Telephony and Its

Operation ----__--_ 7

III. Leading High Power Broadcasting Stations - - - 14

lY. Receiving Equipment for All Purposes and Its Operation 25

V. Spark vs. Continuous Wave Transmission - - - 43

VI. Vacuum Tube Fundamentals - - - - - - 48

VII. Operating Characteristics of Vacuum Tubes - - - 52

VIII. Methods of Obtaining Plate Potentials and Types of Con-
tinuous Wave Transmitters ------ 69

IX. Continuous Wave Transmission by Amateurs - - - 77

X. Tube Transmitters in Commercial Work - - - - 118

XI. Advantages of a Counterpoise Ground in Connection with

Tube Transmitters -- - 129

XII. General Information for the Amateur - - - - 131
XIII. Radio Laws and Regulations of the United States - - 132

Preface

The single objective of this book has been the assembly and sim-
plification of valuable and instructive information for those interested
in the operation of present-day transmitting and receiving equipment.
This volume contains neither mathematics nor theory. All the informa-
tion given is in plain, understandable language and is based upon expe-
rience and knowledge gained in the actual operation of modern apparatus
of the vacuum tube type.

Acknowledgment is made of the assistance and co-operation of
Howard L. Stanley, of the Adams-Morgan Company ; Harry Sadenwater,
of the General Electric Company; and E. V. Amy, of the Radio Cor-
poration of America, in the development of several of the transmitting
circuits described in this book, by means of which many of the unprece-
dented results achieved by 2ZL station were made possible.

The Author.

CHAPTER I

The Radio Telephone

The radio telephone, that latest contribution of science, by means of
which entertainment and information may be broadcasted to thousands
of listeners at once, is assuming an increasing importance and influence
in the affairs of the people of this great country of ours. By it, instru-
mental and vocal music, speeches, lectures, and in fact all audible
sounds and speech can be made simultaneously available to thousands
upon thousands of listeners. This new branch of science has incalculable
possibilities.

The usefulness of the radiophone was first demonstrated about 1905,
but not until shortly after the close of the war was there regular use
made of it outside of the military and naval branches of the government.

The first time that the radiophone was used on a really big scale in
making information available to hundreds of thousands of listeners at
one time, was on July 2, 1921, when the boxing contest for the cham-
pionship of the world between Jack Dempsey and Georges Carpentier,
at Jersey City, N. J., was broadcasted blow for blow and round by
round, by voice, from the temporary station which. had been installed by
the Radio Corporation of America, at the Hoboken, N. J., terminal of
the Lackawanna Railroad. A careful check of the reports as to the num-
ber of listeners to the voice description of the big bout on July 2nd has
clearly established the fact that the number was very close to 300,000.
The undertaking was successful in every way and the audibility and
strength of the voice was such that the whole detailed description was
heard as far as Florida, 1,000 miles away, which is an exceptional dis-
tance for daylight transmission of the voice.

2 Modern Radio Operation

In about fifty theatres and hails within a radius of 200 miles of
the transiiiitler, amateur radio operators had installed receiving equi])-
nient and loud-speaker horns, and large audiences listened to the voice in
the air that described the big event. Admissions were charged, and the
proceeds were divided between the Navy Club, which aids the sailors of
our Navy, and the American Committee for Devastated I-Vance.

drew White and H. I*. Welker conducting; a preliminary test ot the 314 K.W.
nitter at Hoboken, N. J. by which the Dempaey-Carpentier JlBht was described
by voice to 300,000 persona

The details of the big bout were described over a telephone circuit
by J. Andrew White, editor of The Wireless Age, who was at the ring-
side, and were then retransmitted by radiophone from Hoboken.

The whole project was of great magnitude and absolutely unparal-
leled in its scope, for never before in the history of radio had anything
of the kind been attempted. That the undertaking was entirely success-
ful in every respect is a source of the greatest gratification to the author,
as he operated the Zy-> K.W, General Electric radiophone set which was
used at Hoboken, and it was his voice which was heard by the 300,000
listeners, the largest number of people ever talked to simultaneously by
one person in the history of the world.

The Radio Telephone 3

In October of 1921, the author had charge of the operation of a
temporary radiophone station, erected by the National Amateur Wire-
less Association, at the Seventy-first Regiment Armory, New York City,

■ in connection with the annual Electrical Show. This station was of
limited power, as it was intended to cover only the metropohtan district.
Prominent artists, including Miss Anna Case, of the Metropolitan Opera
Company, and Miss Sopbie Tucker, a headhner in vaudeville, entertained

4 Modern Radio Operation

large audiences via radio during the show. The annual championship
baseball games between the New York National and American League
teams were being played in New York at that time and these games
were described ]>lay by play, by voice. In every case, the broadcasted
description was only a few minutes behind the actual play at the Polo
Grounds.

In November, 1921, the author took charge of the operation of WDY
station, of the Radio Corporation of America, at Roselle Tark, N. J.,
which became famous throughout the eastern part of the United States
through its high-grade programmes rendered in "human intere^Jt" style.

That these three undertakings in broadcasting have had a targe share
in the development of the present gruat public interest in radio there is
no doubt. This interest has spread all over the country and has resulted
in the establishment of a large number of radiophone broadcasting
stations.

The number of broadcasting stations now in operation in the country
is such that it is possible for anj'one to listen to musical and other forms
of entertainment, lo official time signals, weather forecasts and reports.

The Radio Telephone 5

market quotations of all kinds, health and educational talks and much
other interesting and instructive information, provided suitable receiving
apparatus is installed.

The entertainment, information and instruction which are now being
broadcasted become, in this way, available to anyone interested regard-
less of where they may be located with respect to the transmitting station,
provided proper receiving apparatus and equipment is installed.

The broadcasting form of communication, which is distinctively
radio's, has a future of unguessed possibilities. Dr. Alfred N. Goldsmith,
professor at the City College of New York, Director of the Radio Tele-
graphic and Telephonic Laboratory at that institution. Secretary, of the
Institute of Radio Engineers, and Director of the Research Department of
the Radio Corporation of America, made the following comment recently
on the future of radio broadcasting:

"Radio broadcasting," said Dr. Goldsmith, "will provide the school,
the theatre, and the lecture platform of the future. A man will be able
to have in his own home, the news, the latest play, the opera, a lecture,
or a political debate. He will not be required to accept one of these
alternatives at any given time, but will be able to choose any of them.
since they will all be sent out concurrently on different wave lengths.

"The result on the political life of the country will be incalculable.
The United States is a particularly scattered nation, dependent almost
entirely for its unity on the rapidity of its means of communication. The
latter at present consists of the press, the periodicals, the wire telegraph
and telephone.

"The two former are by their very nature, deferred in their effect
in greater or lesser degree. The two latter are immediate, but personal,
reacting generally only between individuals. They reach a definite point ;
the radiophone covers an area. In radio broadcasting is the means of
immediate personal contact between the officials of the government and
the citizens, and between the candidate and his possible constituents. As
a result reactions to g^reat issues will be direct, swift, and unaffected by
geographical differences. Ihe nation will be integrated to a degree never
conceived of, and the resulting effect on our life and institutions is
equally inconceivable.

6 Modern Radio Operation

*The effect on the Nation's artistic life will be equally great. As
the motion pictures have stimulated people's artistic visual images, so
will the *j\Iovies of the Ether' stimulate their aural images. It can
reasonably be predicted that popular taste in music and the spoken
drama will be immeasurably uplifted."

Dr. Goldsmith also pointed out another analogy between the radio
and the movies, in that the former is a projection of a special sort of
electro-magnetic or light wave, and the latter of an ordinary light wave.

"However," he continued, "the radio telephone has certain definite
provinces. It will not, as some imagine, replace the wire telephone.
Upon the latter will always depend the basic communications in congested
districts ; just as transoceanic communication, and communication affect-
ing moving bodies and across inaccessible spaces must inevitably be the
province of the wireless. Between these two extremes is a large field
whose disposition between wire and wireless only the future can deter-
mine. But each has essential limitations which will prevent it ever
crowding out the other."

Professor Goldsmith made it clear that in its own field the ra«tio
was as completely practicable as the wire. In the matter of privacy he
explained that instruments have been invented, such as the cryptocode
machines, which send out messages in code with tremendous speed, and
decode them at the receiver. Anyone listening in would find it practi-
cally impossible to pick up the message, or if he did so, to decode it in
time to be of any use. Furthermore, these machines can alter the code
as often and as irregularly as may be desired.

In the field of radio-telephony there is being perfected an instrument
which sends out the voice so greatly distorted that an ordinary listener
tvould hear more gibberish : the receiver for which the message is
intended, hozvever, picks it up and renders it immediately intelligible.
Further, the method of distortion is continually changing, so that no
one listening in could be successful for a very long time.

CHAPTER II

Transmitting Equipment Used in Radio Telephony

and Its Operation

i\luch of the equipment used in radio telephony operates as in wire /
telephony. As a general thing this wire telephone equipment consists of
a microphone transmitter with a battery and microphone transformer at
one station and a telephone receiver at the other. The function of the
transmitting station is to produce pulsating current voltage at the output
terminals of the transformer, this current changing in frequency and
amplitude corresponding to the pitch and intensity of the sound waves
produced by the human voice. The receiver on the other hand has
imposed upon it a voltage similar to that at the output terminals
of the transmitter transformer* and produces sound waves of similar
nature which are impressed upon the human ear. In wire telephony
therefore it is the function of the electrical equipment to use the con-
ductive properties of a wire line to produce sound waves at the ear of
the listener corresponding to those at the mouth of the transmitter.

The function of the radio telephone is to utilize the properties of
the ether of space to replace the conductive properties of metallic wires
in producing audible sounds at the receiver corresponding to the audio
frequency voltage at the terminals of the speech transformer. Equip-
ment must be provided of course, for causing the speech transformer
voltage to control or modulate the flow of energy in the antenna wires
at the transmitting station and from the effect upon the ether of the
electrical energy in these wires to produce similar voltage changes at the
telephone receiver at the receiving station.

8 Modem Radio Operation

The systems of radio telephony most generally used secure audio
frequency modulation of the radiated high frequency energy by varying
it at audio frequency. The radio frequency is known as the carrier
wave. When the amplitude of the radio frequency carrier wave, which
of itself is of such high frequency as to be inaudible, is changed or
varied and the rate of change in amplitude is within audible limits, a
carrier wave of high frequency radio energy is said to be modulated.

Radio frequency is also used to secure the transmission of ordinary
spark telegraph signals, but at the receiving end is made to disappear by
the rectifying action of the detector which passes only audio frequency
currents to the receiving telephone. Obviously therefore, a detector
capable of receiving spark signals will also be capable of receiving radio
telephone signals.

There will necessarily be some distortion of speech in the case of
radio telephony, as the speech element goes through four different stages
in passing from the mouth of the transmitter to the ear of the receiver.
It is true, however, that distortions due to one stage of the process
may be compensated for by opposite distortion of another stage.

In radiophone broadcasting transmission many problems are en-
countered in properly transmitting speech and music. AA^hen a radio-
phone transmitter is to be used for speech only, there is little difficulty
in finding the proper arrangement and value of circuits and constants
which will give the desired result, but when music, both vocal and
instrumental, is to be transmitted, real problems are encountered.

For ordinary speech, a standard microphone will answer satisfac-
torily, but in transmitting music with the periods, or frequencies, of
the many tones running from one extreme of the scale to the other, the
ordinary microphone will not answer, because it has several periods of
vibration of its own. When music of one or more of these particular
periods is impressed upon it, the result is resonance and either reinforcing
or absorption of the impressed note, or tone, resulting in its being either
much stronger or much weaker than tones or notes either above or below
it in pitch when heard at another station as radiated energy. In addition,
it is apt to be considerably distorted.

Radio Telephone Operation 9

The best microphone for transmitting music is, therefore, one which
has practically no period or periods of its own, in order to minimize
absorption and distortion, and special microphones of this type, known
as condenser transmitters, are now in use in several of the big broad-

casting stations.

Condenser Transmitters

The condenser transmitter consists of two parallel plates, with air
as the dielectric between them. The rear plate is of heavy, gold-plated
steel and forms the back of the instrument. The forward plate is of
very thin steel, stretched to its elastic limit, which is used as a vibrating
diaphragm. This arrangement presents a typical air-damped vibrating
system, with high stiffness and damping provided by the air film between
the plates. The narrower the air film, the more sensitive the transmitter
to pressure upon the diaphragm.

When such a condenser is used the effect of impressing upon the
diaphragm the sound waves from human voices or from musical instru-
ments is to cause the diaphragm to vibrate, changing the capacity of the
condenser at a frequency corresponding to the frequency of the sound.
The result of this change in capacity is to produce an alternating potential
drop across the high resistance. Thus, the condenser transmitter performs
the same function as a telephone transmitter, with the important exception
that the alternating potential drop across the resistance for a given
amount of sound energy, by proper adjustment of the damping film of
air and the area of the diaphragm, can be made nearly independent of
the frequency impressed upon the diaphragm, and it is, therefore, a
highly desirable type of transmitter for radiophone broadcasting.

While practically without a period, and highly desirable for that
reason, these special transmitters are not nearly as sensitive as those
generally used and present problems of a special kind in the way of
modulation amplification. In view of it being necessary to have a certain
amount of energy at the set to properly modulate the high-frequency
output to approximately 60 per cent, of its total, and because the output of
these special microphones is too small to properly accomplish the result
directly, it is quite obvious that some method of amplification must be

Mode^^n Radio Operation

used between the microphone and the set in order to build up the output
of the microphone to a proper value. The complete layout is shown
m Fig. 1.

The circuit employed for modulation amplification, while similar to
that used for ordinary audio-frequency amplification, employs trans-

Jiiicra Mocfu/af/on
trans f. amp//f/er

Speech MocfukTfor
a/np/if/er tubes ,

Oscii/ator
tubes ,

Fig. 1. Diagrammatic layout of a radiophone transmitter of high power

formers of a special type, and the amount of output is controlled by
means of a variable resistance shunted across the secondary of the
microphone transformer, also of special type. The amount of modula-
tion can be determined by means of a modulation meter, or by audible
means, and adjustments of the variable resistance made so as to get the
best results.

The "Constant Current'' System of Modulation

Modulation of the high-frequency output of the set is accomplished
by means of modulator tubes and a speech amplifier tube or tubes. The
plate of the modulator tubes are connected to the positive side of the
high-voltage circuit through the plate circuit iron-core reactor. The
l)lates of the oscillator tubes are connected to the positive side of the
generator through the radio frequency choke. The filaments of the
oscillator and modulator tubes being in parallel, the plate circuit is
completed through the spaces between the plates and filaments and thence
through the mid-point tap of the filament-lighting transformer to the
negative side of the generator.

'jr Ao//

UtllMlOILl

P.
o

] 2 Modern Radio Operation

The grids of the modulator tubes are connected through the biasing
battery to the filament and also to the plate circuit of the speech amplifier
tube by means of a condenser of approximately .25 microfarad. The
plate of the speech amplifier tube is connected to the generator through
an iron core reactor. The grid of the amplifier tube connects through the
secondary of the microphone transformer and biasing battery to the
filament. The primary circuit of the microphone transformer passes
through the primary winding of the microphone transformer and the
microphone.

When the current through the primary of the microphone trans-
former is varied, the secondary of the transformer impresses alternating
potentials on the grid of the speech amplifier tube. These variations of
potential are in accordance with the sound waves impressed on the
diaphragm of the microphone. This variation of potential on the grid
of the speech amplifier tube results in a similar change in the amplifier
plate circuit, the amount of amplification obtained being limited to the
characteristic of the tube and the circuit employed. These amplified
variations are, in turn, impressed upon the grid of the modulator tube,
by means of the capacitative coupling. These variations cause corres-
ponding variations in the plate circuit of the modulator tubes, resulting
in a corresponding increase or decrease in the power available for the
plate circuit of the oscillator tubes. This is due to the fact that there
is practically a constant current supply for the plate circuits of both
tubes due to the action of the iron-core reactor in the positive lead from
the generator and it is due to this characteristic that the method has
been termed the "constant current" system of modulation. As a general
thing, the plate current of modulator tubes when not modulating should
not exceed 3/5 of the normal full load plate current when the tubes
are modulating.

Placing of Artists With Respect to the Transmitter

When several artists are singing or playing ensemble for broad-
casting, it is necessary that they be placed at certain distances from
the recording microphone in order that the voices or instruments may
be properly recorded as a whole. This placing of persons and voices

Radio Telephone Operation 1 3

is an important feature of conducting a broadcasting programme which
has been ignored or improperly handled more often than otherwise.
The phonograph companies have devoted years of study to this particular
phase of recording and as a result have worked out definite methods for
recording voices and instruments. The methods and placing used in
phonograph recording, however, do not work out to good advantage in
radio recording and it has been necessary, therefore, to make a special
study of recording for radiophone broadcasting. There has been great
improvement in the ensemble numbers broadcasted recently, however,
and as time goes on there will undoubtedly be still more improvement
made, until weil-balanced ensemble numbers will be broacasted ""
satisfactorily as single voices and instruments have been in the pas.

Audio fiequenoy modulation of a radio frequency, or continue

CHAPTER III

Leading High Power Broadcasting Stations

WDY, RosELLE Park, N. J.
{Radio Corporation of America)

The Roselle Park station of the Radio Corporation of America,
call letters WDY, is located in the General Electric Company's plant,
formerly the old Marconi plant in the Aldene section of Roselle Park,
New Jersey. It is about sixteen miles due west from New York City,
in the central part of the State of New Jersey.

Two steel lattice towers each 175 feet high and 20 feet square at
the base support a six- wire cage-type antenna 10 inches in diameter.
These towers are 200 feet apart. The antenna is of the multiple-tuned
type and has two cage leads, one of which is connected to the center
of the horizontal part of the antenna, being connected through a tuning
coil to ground. The other lead, which is connected to one end of the
horizontal portion of the antenna, leads down to the set in the station.
Both of these leads are of the cage type, 4 inches in diameter. This
multiple tuning of the antenna gives much greater efficiency on the
short wave of 360 meters than would be true of any other type of antenna
arrangement. The total antenna current of the station is between 8
and 10 amperes.

The power for the station is furnished by the Public Service Cor-
poration of New Jersey and goes into the power room at 2,200 volts.

Broadcasting Stations 1 5

two phase. This alternating current is used to drive the alternating cur-
rent motor-generator from which current for the direct current motor-
generator of the set itself is secured. An auxiliary motor generator set

1 of WDT station, Roselle Park, N. J,

is also installed and this draws power direct from the alternating current
supply.

The radio set is of General Electric Company manufacture. The
filaments of all tubes are lighted with alternating current which is
supplied from a special winding on the radio motor-generator set.

1 6 Modern Radio Operation

The voltage of the generator which supplies the plate potential for
the large tubes used in the set is 2,000 volts direct current. Four 250-
watt Radiotrons UV-204 are used in the set itself, two as power tubes,
or oscillators, and two as modulators. A 50-watt tube is used as a speech
amplifier in connection with a system of 5-watt tubes used as modulation

amplifiers, the latter in turn receiving their energy from several micro-
phones of special type placed about the room at desirable points. By
means of a set of resistances in the modulation amplifier circuit it is
possible ,to regulate voice and music modulation to any degree desired,
WDY is really not a radio station — it is a studio. It is of hexagonal
shape furnished in blue and gold draperies ; the carpets and rugs carry
out the same color scheme. This color scheme is also carried further
in the lighting arrangements, a large chandelier in the center of the
studio giving a soft, mellow light to the whole place.

Broadcasting Stations 1 7

By referring to the illustration it will be seen that on one side of
the studio is a Knabe-Ampico piano which is used for piano selections
and accompaniments. On the other side will be seen an Edison re-crea-
tion phonograph. The radio set used at WDY shows up clearly in the
illustration.

An interesting feature of the station is a large map of the United
States which hangs in the foyer of the studio. Tacks have been placed
on this map on points from which reports of the reception of the music
and speech from the station have been reported and examination of
this map shows that the extreme range of the station while in operation
extended from points in Eastern Canada to Porto Rico, Cuba and the
Florida peninsula and as far west as Omaha, Nebraska. The station
has not been operated recently and probably will not be used again. A
new station, to contain apparatus of the latest design in broadcasting
equipment, which will take over the previous schedules and services of
the old WDY station, as well as those of the Radio Corporation and
the Westinghouse station WJZ, at New^ark, is now being built by the
Radio Corporation in the heart of New York City.

WGY, Schenectady, N. Y.

(General Electric Company)

A radio broadcasting station, more powerful than any now sending
out programs, has been installed by the General Electric Company at
its plant in Schenectady, N. Y.

From the roof of a five-story factory building, two towers 183
feet high and spaced 350 feet apart, support an antenna at such height
as to give the wireless waves unobstructed freedom to travel equally
well in all directions.

The General Electric station operates on 360 meters under the call
letters WGY. It is equipped with the most modern of radio apparatus,
including a multiple-tuned antenna of the same design as that which,
because of its many advantages, has been installed in Radio Central, the
world's most powerful commercial station, at Rocky Point, L. I., and
at other transoceanic stations of the Radio Corporation of America.

1 8 Modern Radio Operation

A three-rom studio, where the programs are produced, is located
in a Company office building, 3,000 feet from the transmitting station.
One room is used as a reception room for the artists, where they may
sit and chat until their time on the program arrives, without danger of
interfering with what is going on in the studio. The second room is the

One of the 183-foot lowers at WUY

Studio, where a concert grand piano, a victrola, an oi^an and other
equipment for the artists are to be found. Here are a number of port-
able microphones, which are commonly known as pick-up devices, which
can be shifted about to locations best suited for the reception of
announcements, musical numbers, or whatever may be sent out. In the
room on the opposite side of the studio is apparatus for amplifying the
sound waves before they are transmitted by wire to the broadcasting
station.

2 Modern Radio Operation

A red light when the station is in operation warns persons in the
room that whatever they may say will be sent out to thousands of ears
of an invisible audience. A switchboard in the studio is within reach
of the studio director at all times. Not until he throws a switch can
anything reach the antenna. A tdephone attached keeps him constantly
informed just how the program is going out and enables him to change
the position of the artist or microphone to improve the tone quality of
the entertainment. With the exception of the small pick-up devices or
microphones and the switchboard, there is nothing in this room to
indicate it as being different from any musical studio.

In the apparatus room, the sound waves are put through a number
of steps of modulation amplification; by means of vacuum tubes, which
increases their volume thousands of times. The amplified sounds are
then put onto a wire and sent to the broadcasting station, where they
enter the modulator tubes of the transmitter.

A 220-volt alternating current line, which is but little higher than
the voltage used for lighting purposes in the home, is boosted to 30,000
volts by means of a transformer. This voltage ;s then applied to a
number of kenotron tubes, acting as rectifiers, which change the voltage
to direct current, and this rectified high-voltage is impressed upon the
plates of the modulator tubes and of a high-power oscillator tube,
which generates the power to be radiated from the antenna.

WJZ, Newark, N. J.

(Operated by the Radio Corporation of America and
Westinghouse Electric and Manufacturing Co.)

This Station is located at the plant of the Westinghouse Electric
and Manufacturing Co., at Plane and Orange Streets, near the Lacka-
wanna Railroad station, Newark, N. J.

The antenna is swung between two 120-foot guyed steel masts on
Ihe building top, so bringing the upper horizontal part about 200 feet
above the street level. The aerial "flat top" consists of 6 wires extending
between two 30- foot spreaders, and is 150 feet long. From the North-

Broadcasting Stations 2 )

west end a ]>lural wire cage down-lead drops directly to llie radio station;
from the oi)posite end a similar down-lead extends to the "multiple"
tuning coil.

Below the antenna, and 12 feet from the roof level, is a twelve-wire
counterpoise ISO feet long. The separation of the aerial from tiie
counteqKjise is thus about 108 feet, which is frequently taken as the
"effective height" of the antenna system.

The natural wave lengih of the antenna-counterpoise structure is
not far from 450 meters, so that for transmission on 360 meters (th&
normal operating wave length for broadcasting) series condensers of
0.0005 microfarad are inserted in each connection. These are placed
directly below the lead-in insulators in the interior of the station.

Two three-electrode vacuum tubes are used as oscillators for radio-
phone transmission and three somewhat similar but specially designed
high-impedance tubes modulate the radio frequency currents generated
by the other pair. The antenna, counterpoise, grid and plate leads are
all connected in the split-coil oscillation circuit to the flat spiral indue-

22 Modern Radio Operation

tance on top of Ae radio set This coil is made of flat copper strip
mounted on micarta spokes, and is grounded at the minimum potential
point recrly midway between antenna and counterpoise.

The oscillator and modulator tubes run on 2,000 volts direct current,
which is produced by a single-commutator generator driven by a direct-

cnniitcted two-phase 6(>-cycle 5 horsepower motor. Special filter circuits
are provided to suppress the commutator hum of this machine, with
ilic result that outgoing traffic of speech and music is heard with very
little extraneous noise from the dynamo. The filaments of the five
large tubes are lighted by alternating current at 10 volts, this being
drawn from a transformer. In this circuit again it has been found
necessary to provide a grounded filter arrangement to eliminate the
foreign noise of the 60-cycle alternating current used.

Broadcasting Stations 23

The three modulator tubes are connected on the plate modulation
plan and are supplied with voice frequency current from a speech
amplifier containing several three-element vacuum tubes. An ingenious
arrangement compensates for the inherent distortion which is so often
found when vacuum tube transmitters are operated at full power for

Olga Petrova formally opening the new Btudo at WJZ-

radio telephony, and the clarity of the speech and music sent out from
WJZ is limited only by the characteristics of the microphones used to
pick up the sound waves and transfer them in electrical form to the
speech amplifier.

Not the least interesting feature of the station lies in the completeness
with which its details have been worked oul. The complete radio

24 Modern Radio Operation

transmitter is enclosed in metal screening and glass, and a blower is
provided to hold the tube temperature at the best operating value. A
switchboard is mounted on the right hand side of the transmitter so
that the set may be connected to the station microphone for annoimce-
ments, etc., to the shielded pick-up device used for phonograph repro-
ductions, or to the studio which has been built on the first floor of the
factory building.

This studio is specially designed for concert work. It is attractively
furnished and is located where it is convenient of access to artists. A
grand piano and other musical instruments form part of the equipment,
and the walls are hung with heavy curtains in order to deaden echoes
and eliminate outside sounds. Different types of microphones are used
for various kinds of work, such as solos, quartettes, lectures, etc. An
interlocking system of light signals and switches connects this room wit^
the transmission station on the roof.

The radio station is also equipped with a standard Westinghouse
medium wave receiver, with a range of 150 to 5,000 meters wave-length.
During the nightly musical program which runs from 7 to 10.15 o'clock,
the 9.55-10.00 time signals from Arlington are received on this outfit,
using a long single-wire antenna, and transferred electrically to the radio
telephone transmitter. Thus the time signals themselves, with the
characteristic spark tone of Arlington "NAA," are retransmitted on
360-meter wave length for the benefit of listeners having short-wave
receivers. Obviously, there is no appreciable time lag in this transmis-
sion, and consequently, accurate Naval Observatory time is made
available in the amateur wave length range.

This station is one of a series of broadcasting stations established
by the Westinghouse company. Others are located at Pittsburgh, Pa.
(KDKA), Springfield, Mass. (WBZ), and Chicago, 111. (KYW), all
broadcasting on 360 meters.

CHAPTER IV

Receiving Equipment for All Purposes and

Its Operation

When ■ a receiving station is located within a few miles of the
transmitting station, the receiving apparatus required is of a type which
-can be easily and readily installed by anyone not familiar with or versed
in radio communication. A receiving outfit which will give satisfactory
results up to a distance of 20 miles from the transmitting station can
be bought of any dealer for about the same number of dollars. Outfits
of this type usually employ crystal detectors as the sensitive element for
making the speech and "aiusic audible and in the case of such sets it is
necessary to use the head telephone type of receivers. It is possible,
liowever, to use several of the headsets in parallel, so that several persons
can listen at one time.

It is not possible, however, to use a loud speaker horn, so that the
speech and music can be thrown out into a room for the benefit of several
listeners, when a crystal detector is used. In order to do this it is
necessary to employ a more comprehensive type of receiver, employing
vacuum tubes ?nd with the extra amplification of incoming speech and
music so obtained it is possible to reproduce the speech and music with
any degree of intensity desired.

The signals of a transmitting station diminish in intensity as the
distance from it increases. At points nearby, that is, within a 20-mile
radius, it is possible to hear the speech and music with a very small

2 6 Modern Radio Operation

set with one end of it connected to a bed spring, gas stove or other metal
object of large surface, and the other to a water, steam or gas pipe.

At distances of over 50 miles or so, it will be necessary to employ a
standard receiving set of good design, and also several steps of amplifi-
cation, to insure signals of good audibility. There is no fixed rule for
the amount of amplification which may be necessary in order to produce
good signals. As a general rule it might be stated that a crystal detector
set will answer up to 20 miles, a good receiver and detector tube up to
30 miles, and one or more stages of amplification for greater distances.

At night, especially during the cold months of the year, the range
of signals of a given station will often be several times its daylight
range. Under these conditions, due principally to dry, clear and calm
atmospheric conditions, it is frequently possible to listen to the speech
and music of a station located a thousand or more miles distant from
the listener. This uncertainty as to conditions from night to night, with
the possibility of listening to other stations situated at exceptionally
long distances, is one of the great fascinations of radio. The query
"Who did you hear last night?" has become as common as "How are
you this morning?" since the great public has come into radio.

Variation of Strength of Radio Signals.

Variation in the strength of radio station signals, both code and
voice, particularly in long-distance night communication, is a phenomenon
concerning which comparatively little is known even by advanced radio
enigneers. That signals and voice often gradually increase to unusual
strength and then fade slowly or rapidly until entirely below audibility
is of course of itself well known, but while many theories have been
advanced nothing definite has as yet been determined upon as a cause
for what has frequently been referred to as "fading." But is it fading?
Isn't it true that it is really a rising instead of a falling characteristic?
The fact that stations can be heard at night which cannot be heard in
the daytime would indicate that the range of such stations had increased
many times during the night as compared to the daylight range.

Receiving Equipment 27

It has been definitely determined that daylight restricts the range of
a station to a definite area. It has been definitely determined, further,
that as a rule, signals from distant stations are more likely to be stronger
during a night following a cloudy day than following a day of bright
stmshine.

This would seem to indicate that the daylight effect is the sole
determining factor. If this were true it might be expected that with
the coming of night the range of all stations in all directions, especially
those employing short wave lengths, would increase proportionately.
This, as is well known, does not happen.

What does happen is that the range of stations to the west of
New York, for instance, may increase greatly, while not a single station
in New England will be heard. On another night New England stations
may come through strong, and not a single station in the Middle West
be heard from. On another night signals will be strong from all
directions.

This shifting condition would seem to indicate that the condition of
the atmosphere is a main factor, but this is disproved by the fact that
It is possible to determine whether a station is located in the west, or in
New England, by the manner of the rise and fall in signal strength.

The signals from New England stations increase and decrease very
rapidly. In fact, it is a common occurrence to hear a New England
station fade completely out in the middle of a four letter word, and come
up strong again in the middle of the next word.

The rate of rise and fall in the case of Middle West s^^ations is
much more gradual. These stations fade out slowly, over a period of
10 or 12 words usually and then swing back again in the same gradual
way. This would seem to* indicate that the country intervening in both
directions between New York and New England and the West was
the controlling factor.

Why should signals fade rapidly in one case and gradually in the
other? Is it a question of distance, topography, terrain, or what? The
old theory of attributing "fading" to conditions at the transmitting
station won't stand in the face of the foregoing facts.

28 Modern Radio Operation

There are many spots on the ocean known to commercial radio
operators as dead pockets. One of these is along the New Jersey
coast, near Barnegat. Another is on the Gulf of Mexico, near the lower
Mexican coast. Why dead pockets on the ocean? The same thing is
true, however on land. For instance, the owner of an amateur radio
station at Fall River, Mass., can work stations near New York easier
than stations in New England, half the distance away. He is in a
l^ocket. New England, in fact, seems to be in a pocket by itself. It
is easier to work New England from Ohio or Illinois than from Long
Island or New York City, 75 miles away.

There are, in fact, a large number of dead spots throughout the
country, which have caused much interest and speculation on the part
of operators of amateur stations as to their definite size and effects on
signals from various directions, and much experimental work has been
done in an effort to evolve a satisfactory solution of the matter.

What were known as "fading tests" were conducted recently during
the winter months, to endeavor to solve the "fading" problem. A lot
of information has been printed from time to time as to what was
accomplished by these tests, but a solution of the "fading" problem
appears to be as far off as ever.

The only way the disadvantages of "fading" can be overcome is
by means of increased amplification. If, with certain receiving equip-
ment at one station the signals of another station swing out, or fall
below audibility, the solution is, of course, to employ additional amplifi-
cation, so that the signals will be kept at sufficient strength to be audible
while at minimum strength.

Receiving Antennas

An antenna for receiving purposes may be any one of several
types. A good type for the purpose is a single wire, about 150 feet long,
suspended between two buildings, or poles, or between a building and
a tree. The wire should be at least 30 feet above ground. Forty or

Receiving Equipment 29-

fifty feet above ground will give still better results. Where it is not
possible to stretch a wire of 150 feet, less length, down to 50 feet will

probably answer, but the strength of incoming signals will be less than
if the longer stretch were used. Several wires, in parallel, mounted on

t betler results
In receiving: than a single wire

Spreaders, can be used. These can be of any length between 50 and
150 feet. For receiving purposes, however, the number of wires in an

Modem Radio Operation

antenna need not be more than two in number, as very little will be
gained by the additional wires. However, where it is not possible to
construct an outdoor antenna of sufficient length to make it worth while,
an antenna of four or five wires in parallel can be constructed in the
attic of a detached dwelling, for instance, and fairly good results obtained.

Figr. 5. Sugrsrestion for an indoor antenna to be installed in the attic

It will probably surprise many readers to know that in building an
outdoor antenna, particularly for receiving purposes, insulated wire
should be used. The insulation will not interfere in the least in the recep-
tion of signals, but will, on the other hand, protect the conducting antenna
wires from the elements, consequently from corrosion, and this is a very
vital point in connection with the efficiency of receiving antennas.

It is well known that the high-frequency oscillations of a transmitting^
station do not penetrate the antenna wires of the receiving station to any
conceivable depth. They travel practically only on the surface, or skin,
of the wires. It therefore follows that the less corrosion, consequently
resistance, there is on the skin, or outer surface of the wires, the less
energy will be consumed in the course of the incoming signals as they
travel along to the receiving station. It must be remembered that the
amount of energy which reaches a receiving station from a distant trans-
mitting station is exceptionally small, consequently any great amount of

Receiving Equipment 31

conductor resistance at the receiving station will seriously affect the final
result at the detector. Several tests were made in England recently to
determine the effect of corrosion of antenna wires. Two antennas of
the same size were used. One had been, in use for a year and another
one of the same size and proportion, in which new copper wire was
used, was erected alongside the first one. Comprehensive tests showed
that signals when received on the new antenna were at least 25 per cent,
stronger than when the old antenna was used, the wires of which were
badly pitted and corroded.

As shown in the diagram, small porcelain insulators should be
inserted in the antenna wire where it is connected to whatever supports it.

Lightning Protection

A lightning switch should be installed on the outside of the building.
While it is practically true that an antenna is no more of a menace
during an electrical storm than a telephone wire, an electric light wire
or perhaps even the wiring of doorbells and other interior communicating
systems, the fire insurance regulations require that certain forms of
protection against lightning must be provided, in order to reduce the
possibility of danger to a minimum.

There are several ways of protecting a building where an outdoor
antenna is used. One way is to disconnect the antenna lead-in and drop
the end to the ground, outside the station. This, however, is not a good
method unless a ground pipe is provided and the antenna lead clamped
to it each time the antenna is grounded, in order to provide a path of
low resistance. When the antenna lead is merely thrown on the ground,
a high resistance still exists between the antenna and ground, which is
liable to cause a lightning discharge to jump from the antenna to other
nearby objects which may offer a path to ground of lower resistance.

Two devices for lightning protection have the approval of the Na-
tional Electric Code — the manually-operated switch and the grounded
short gap.

The manually-operated lightning switch, when thrown to the ground-
ed position, provides a practically positive protection, in that heavy

32 Modern Radio Operation

electrical surges induced in the antenna system by nearby lightning
discharges, will pass harmlessly to grotmd.

The grounded short gap operates automatically. It consists of two
electrodes held in a fixed position in a sealed chamber from which the
air has been exhausted, and it has been found that inductive currents
readily pass through the gap in the thin air in the chamber.

A good ground connection should be provided ^f or whatever device
may be installed. This can be in the form of two or three lengths of
galvanized pipe driven at least 4 feet into the ground, metal plates buried
in the ground, two or three feet below the surface, or a water pipe. The
conductor running from the lightning protective device to ground should
be not smaller than a No. 4 copper wire, copper tubing % inch outside
diameter or copper ribbon % inch wide. The conductor must be mounted
on insulators and must be at least 5 inches clear of the building. All
connections should be soldered.

There are very few cases on record of lightning having actually
caused any damage to radio stations although the number of stations in
the United States has been over 100,000 for the last two or three years,
and is about 600,000 at the present time, due to the widespread interest
of the public \i\ radiophone broadcasting. The chances of lightning
damage to a radio station are no greater than for any other building.

A well-grounded antenna is not only itself protected against the
effects of lightning, but is also a protection to the building on which it
is installed, for if lightning should strike the building the effects of it
will be minimized by the easy path to ground which is afforded by an
antenna when suitable grounding devices have been installed and properly
connected to a good ground.

Receiving Elquipment

A circuit diagram of an antenna and other connections for a crystal
detector set, which will operate efficiently over a considerable band of
wave lengths, is as follows:

V-^

Antenna

Tuning ^ariab/e Defecfor feacf
CO// concfenser / p/?0nes

-I- 1 ? h(-

Ground -•-^^^

Fig. 6. Circuit diagraan of a receiving set employing a crystal detector

A diagram for a regenerative circuit employing honeycomb coils
and a detector tube, for use on 360 meters, which is much more sensitive
than a crystal detector hook-up, is shown in the following diagram :

*-4mm^

/lead ,
p/7ones

Fig. 8. The tickler regenerative circuit using honeycomb
or duo-lateral coils. Amplifiers can be added, by insert-
ing the primary of an amplifying transformer in place

of the phones, as in Pig. 7

In the feedback, or regenerative circuit, the incoming signal is
impressed upon the grid, and, because of the feedback connection, regen-

34 Modern Radio Operation

eration of the incoming signal takes place. As energy is returned to
the grid circuit by the plate circuit with each incoming oscillation, the
process continues to build up the strength of the incoming signal. This
effect is limited only by the fact that after a certain amount of energy
has been transferred to the grid circuit the tube will oscillate, and so
become a generator of independent oscillations. In this condition it
establishes a certain period of oscillation which may be controlled by
adjustment of the circuits until its period may differ from incoming
oscillations of continuous nature (which are themselves of a frequency
so great as to be above audibility), by 500 or 1,000 cycles. Thus is
produced what is known as the "beat" note, or difference of frequency
between two high-frequency oscillations of almost, but not quite the same
frequency. It is in this way that the signals of other continuous wave
stations, which of themselves are inaudible, are made audible. The
method is known as heterodyning.

A circuit diagram for a regenerative receiver, using a vario-coupler
and variometers, for the reception of either spark or continuous wave
(C.W.) signals, including two steps of audio- frequency amplification to
which a loud-speaker horn may be attached, is shown on page 35.

It is advisable to avoid the use of regeneration, as far as possible,
in the reception of radiophone speech and music, if signal strength is
such that satisfactory results can be obtained without it, for the reason
that regeneration will cause some amount of distortion, which, particu-
larly in the case of music, is, of course, undesirable. Where speech or
music of a radiophone station is not sufficiently strong to be heard clearly
without considerable regeneration, it is desirable to employ one or two
steps of radio-frequency to amplify the incoming energy to whatever
degree is necessary for satisfactory reception. This will obviate the
distortion caused by regeneration.

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36 Modern Radio Operajtion

Radio Frequency Amplification

There are marked advantages in high, or radio frequency ampli-
fication over the low. or audio frequency method of amplifying in
reception. Audio frequency has its place in land wire communication
and in the modulation circuits of a radiophone transmitter, but when
amplification at the radio receiver is desired it is certainly not good
engineering practice to first rectify the incoming high-frequency current
and then amplify the rectified current at audio frequency. For one
thing, static and other undesirable noises are of audio frequency, and
when that form is used in reception they are amplified to the same degree
as incoming signals. When radio-frequency is used, static, induction and
other disturbances are amplified only slightly, if at all. This one big
advantage of high frequency amplification appears to be sufficient reason
for its general adoption.

There is another reason of equal importance, however.

The detector tube of a receiving circuit rectifies, and so makes
audible incoming high frequency signaU of either continuous or dis-
continuous waves. On weak signals, however, the tube will function
only to a certain point. Where signals are too weak to be detected
and rectified by the detector tube, they are lost, and no amount of audio
frequency amplification will help matters. The proper thing to do,
therefore, wJiere reason or desire exists to warrant it, is to amplify the
radio frequency of incoming signals, then detect it, and again amplify
the resultant audio frequency.

A number of textbooks contain diagrams of radio frequency ampli-
fication circuits, but while all of these will operate satisfactorily on
frequencies from 500,000 down (or wavelengths 600 meters and up),
there has been only one circuit up to the present time which will operate
efficiently on frequencies in the neighborhood of 1,500,000 (200 meters),
that being the resistance-coupled super-heterodyne circuit developed by
Armstrong and used by Godley at Ardrossan. This super-heterodyne
circuit, while affording marvellous amplification, calls for the use of
so many tubes that its use is practically prohibitive to the average amateur.

Receiving; Equipment 37

In the super-heterodyne arrangement used by Godley (which, by
the way, was not unduly elaborate), nine tubes were used for spark
signals, and an additional external heterodyne, ten in all, for C.W.
reception. This number of tubes is required because a considerable
proportion of the incoming energy is lost in the transfer coils which this
type of circuit makes necessary between the high and intermediate circuits
and again between the intermediate and low, or, audio-frequency circuit.
Roughly, this arrangement, while extremely sensitive and reliable, is
beyond the average amateur, for, in addition to first outlay for assembly
and installation, there is an exceedingly heavy drain on the facilities for
filament heating, the average current for the number of tubes used by
Godley being 10 amperes.

The new iron-core transformers which are now available to the
market have undoubtedly solved the problem of amplification at high
frequencies, having been designed to work on a broad band of frequencies,
without tuning, at which most amateur operation is carried on and also
over a wide band of lower frequencies. A detailed circuit for radio and
audio frequency amplification is shown on the following page.

Reception of Continuous Wave Signals

Operators of receiving sets, who can read Continental Code, will
find considerable entertainment in listening to transmitting stations, many
of them at distant points, which use continuous waves for amateur
message relay work. The usual and easiest way of exploring for straight
C.W. signals is to bring the receiving tube into oscillation, with about
SO per cent, coupling between primary and secondary and then tune
slowly over a wide range of wave lengths by means of the secondary
variometer or condenser. Once a C.W. signal is located, the antenna
condenser should be brought into resonance, and the plate variometer
adjusted to the dead point, which indicates absolute resonance of all the
circuits. Variation of the' coupling will then give any beat note desired.
It is possible to locate a C.W. signal, whether it is straight C.W., Inter-

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Receiving Elquipment 39

rupted C.W. (I.C.W.), or voice modulated, as some percentage of the
C.W. energy comes through without modulation. As a general thing
when listening for •spark signals amateurs carefully avoid allowing the
detector tube to come into full oscillation, bringing it up only to a
regenerative point. This is really a mistake, as the ether these days is
pretty well filled with C.W. signals and phenomenal ranges are being
covered every night.

The Super-Regenerative Receiver of E. H. Armstrong

The super-regenerative method of reception, a new invention of E.
H. Armstrong, was described and demonstrated by the inventor at a
meeting of the Institute of Radio Engineers on June 7, just as this book
was going to press. The apparatus used in the new circuit was not unduly
elaborate, neither was the arrangement of it complicated, but the amount
of amplification obtained with the new circuit, as compared to the ordinary
regenerative circuit, was amazing.

When the ordinary regenerative circuit is used, the energy can be
fed back from the plate to the grid circuit, or the incoming signal regen-
erated, up to only a certain point. In other words, if the inductance of
the plate circuit is being increased by means of a variometer, an increase
in regeneration, resulting in increased signal strength, is obtained up to
a certain point, which we may assume arbitrarily to be 50 degrees on the
variometer scale. Somewhere between 50 and 55 degrees, the ability to
further regenerate or increase signal intensity is lost, if the incoming
signal is other than a continuous wave signal, due to the fact that the
tube begins to oscillate and becomes a generator of independent oscilla-
tions, at a frequency based on the constants of the circuit. It is a
well-known fact that in the last few degrees, just before oscillation occurs,
the greatest amount of regeneration is obtained, due to the fact that the
steep part of the characteristic regenerative curve of a tube is just
being approached. The problem has been, therefore, to prevent the tube
from oscillating, so that regeneration of incoming signals might be carried
on to the limit of the tube. Armstrong, in his new circuit, has solved

40 Modem Radio Operation

this problem, and the resultant amplification is so far beyond anything
ever yet obtained as to be impossible of adequate description on the
printed page. It can be done adequately only by actual demonstration.

During the course of the lecture by Armstrong an actual demonstra-
tion was carried on, several set-ups of regenerative and super-regenerative
circuits being employed, with a small loop as an antenna. An ordinary
regenerative receiver, with two steps of audio-frequency amplification,
with a loud-speaker horn, in the last step, was tuned to WJZ radiophone
broadcasting station. The music and speech with this arrangement was
just barely audibk to listeners seated about 10 feet from the horn. The
loop and horn were then transferred to the super-regenerative circuit
and the result, as a comparison, was astounding, for the amplification
obtained was so great that the speech and music literally filled the entire
hall where the lecture was given. It was estimated by Armstrong that
the amount of amplification obtained by means of the super-regenerative
system was approximately 100,000 times greater than was possible with
the regular regenerative system. It was stated that in some cases that
amplification could be increased to the ratio of 1,000,000 to 1.

This new super-regenerative system is peculiar in one respect, in
that it does not amplify spark, or discontinuous wave signals, due to its
inherent quality of rejecting free oscillations. Its greatest field lies,
therefore, in the reception of either continuous wave or modulated con-
tinuous wave signals, which makes it of the greatest value in broad-
casting reception, or in continuous-wave telegraphy. The circuit works
best on wave lengths below 1,400 and is, therefore, one which can be
employed in its greatest usefulness on the lower wave lengths, for
commercial, broadcasting and amateur work.

It is unfortunate that complete details and values of this new
super-regenerative circuit cannot at present be given, owing to the patent
situation. In a general way, however, the results described in this
article are accomplished by means of either two or three tubes in the
circuit. Detail diagrams are shown on page 41.

It seems rather unusual to say the least, that the amazing results
accomplished with this apparatus should be based upon a circuit employ-
ing two, or at the most, three vacuum tubes. Judging by the results

Receiving Equipment

Jil T

r^^

Manner In which the variation Is Introduced Into Che positive resistance of the tuned

circuit. This is done by means of bji oscillating tube O, the srld circuit of wtiich

is connected through the tuned circuit LC of the amplifying tube R

Demonstrating the Armstrong Super-Regenerative Rpcelver

42 Modem Radio Operation

obtained during the demonstration at the Institute of Radio Engineers,
wlierein signals of sufficient audibiHty were obtained from a small loop
to flood the entire lecture hall, which, in itself, is situated in a steel and
stone building, would seem to indicate that the use of audio frequency
amplification with its many objectionable features, had at last been made
unnecessary and soon to be relegated with amateur spark transmitters, to
the past history of radio communication.

CHAPTER V

Spark vs. Continuous Wave Transmission

A great many amateurs who have used the spark method of trans-
mission for many years have been known in the past to utterly refuse to
be interested in continuous wave transmission, and to give many reasons
why C.W. transmission would never supplant, or even equal, the old
familiar spark method. It is a notable and interesting fact also that after
C.W. had been used a while by others many of these same amateurs
were the first to comment on the readily-apparent advantages of it, espe-
cially its low decrement, or rather lack of decrement, the amazing dis-
tances it would cover on small power and its great flexibility.

In the case of the spark transmitter, employing alternating current
of some frequency, it is good for one thing — telegraphing. It has fre-
quently been stated that the only way to get anywhere with a spark set
is to use power to the limit. It is true that while his intentions are of

the best, in many cases the amateur is limited in a mechanical way in
the construction of his antenna and ground system and does the best he
can instead of the best for results. The writer has personally visited
a great many amateur stations throughout the country and in almost
every case noted that the antenna and ground system was entirely inade-
quate to handle properly the amount of energy put into it by the spark
transmitter. The necessity of designing the transmitter and antenna
system for each other is an important point generally overlooked by
amateurs.

44 Modem Radio Operation

If one were to attempt to use pressure and force two gallons of
liquid into a one-gallon receptacle, something would be likely to happen.
In the case of the station using a 1 K.W. spark transmitted on a ^ K.W.
antenna, the something that happens is the emission of energy on a hun-
dred or so wave lengths, even with a loose coupling. The eflfect is the
same as in the case of a too closely coupled set — where energy is radiated
over a wide band of wave lengths.

The result, especially in congested localities, is readily apparent.
About 75 per cent, of the amateur interference (QRM)* we hear so
much about, is due to the fact that energy is being radiated over a wide
band of wave lengths, instead of on a narrow band as it should. Cer-
tainly the receiver can be tuned only to one wave length at a time, conse-
quently all the energy radiated on other wave lengths is wasted energy,
accomplishing nothing but interference with other stations that are
endeavoring to receive on neighboring wave lengths.

The legal decrement of a transmitting station is fixed at .2, and
even where, in a few cases, this feature of the radio law is complied
with, there is interference on other wave lengths when a nearby station
is endeavoring to receive signals. In the case of C.W. transmission,
the energy is practically all radiated on one wave length.

It will readily be seen that C.W. transmission eliminates practically
all the unnecessary interference caused by a spark set of reasonable
power. The fact that the signals from a C.W. transmitter can be heard
at only one place on the receiving set is one reason why many amateurs
liave objected to its use as a means of communication. These objec-
tions are based on both ends of the transaction : — the operator of the
transmitting station experiences difficulty in raising a distant station,
unless the receiver of the station happened to be set on the transmitting
wave length, and the receiving operator complains of the unusual
sharpness of tuning the received signals, which calls for niore than
ordinary care in the adjustment of circuits, etc. These objections, how-
ever, seem trivial in the face of the great advantage of C.W. transmis-
sion over the spark method, especially as they can be overcome easily.
As the power of C.W. transmitters gradually increases, as will certainly

Advantages of C.W. Transmission . 45

be true in the future, there will be less difficulty in "raising" practically
any station within working range without resorting to previous notice
and agreement.

The complaint of sharpness of tuning at the receiving end usually
dissipates quicker than last week's salary once the advantages of it are
experienced. Once the signals from a C.W. transmitter are located, the
possibilities of tuning them away from QRM and QRN (interference
and static) are there and it is a simple matter to accomplish this very
desirable result. It is quite a common thing nowadays to get a card
from some fellow hundreds of miles away saying that the "C.W. signals
were QSA (strong) and could be read through local QRM," etc., with-
out trouble. This is often true even when the antenna input of the trans-
mitting station was in the neighborhood of only 20 or 25 watts, and
the antenna current approximately one ampere. On nights when the
air is "dead" and no distant spark stations can be heard, there is
usually some distant station using straight or unmodulated C.W. whose
signals can be easily read.

When the output of a C.W. set is modulated with a buzzer or tone
wheel, the received signal can be regenerated and amplified to a much
greater extent than a spark signal, especially of the 60-cycle variety.
Another great advantage in the use of C.W. by amateurs for short
distance work particularly is voice modulation. The fact that the law
requires that work shall be carried on with a minimum of power neces-
sary to effect successful communication is a point generally overlooked,
intentionally or otherwise, by many operators of 1 K.W. spark trans-
mitters and it is a frequent occurrence to hear a 1 K.W. station using
full power to communicate with another station on the next block. This
phase of amateur radio has been repeatedly criticised, more often by
operators of spark coils and low powered transmitting sets, than other-
wise. Everyone is familiar with the tales of the interfering spark coil
station, whose operator is usually accused of being able to transmit, but
not receive, and the misuse of power by the big station is a favorite
method of counter-attack on the part of the small station operator. It
is, however, quite true, that the high-powered amateur stations are fre-

46 Modern Radio Operation

quently interrupted in relay work by small stations and spend much
precious time and use many K.W.'s of good energy trying to make
the operator of the small station understand that he is interfering — at
the end of which the operator of the small station often comes back and
informs the high-powered stations that his "signals are strong tonight."

The use of a voice modulated C.W. set obviates all such disputes.
The operator of the small station can usually understand English, even
though he never heard of Morse, and if he understands that he is creat-
ing interference is usually entirely willing to "stand by" or "go to bed."

In the case of the spark transmitter of high power (1 K.W. or more)
all sorts of mechanical and electrical difficulties are generally present.
"Kickbacks" are the bugbear of an amateur's life. The matter of insula-
tion is another matter of great importance, both in the case of interior
wiring and the antenna system. It is generally possible to insulate
interior wiring properly without great trouble, but where high voltages
are imposed upon an antenna it is a different matter. Where more energy
is impressed upon an antenna system than the system can properly take
care of brush discharges occur to such an extent as to cause aerial fire-
works of considerable magnitude, resulting in a loss of efficiency. Fre-
quently the antenna insulators break down under such unusual strain and
cause further losses and trouble.

Another phase of spark transmission which has caused amateurs
generally to sit up and take notice the country over is the stand the power
and telephone companies have taken where high-powered amateur spark
sets were operated. In many cities and towns the power companies
have recently refused to allow transmitting sets to be connected to house
lines, insisting that a separate service transformer and separate power
line be installed. The cost of installation of the separate transformer
and service asked by the power companies has been generally declared
exorbitant, and in many cases the situation has resulted in a deadlock,
the result being that the amateur has had to be content with a spark
coil, or no transmitting set at all. The other phase of the question, that
of interference on neighboring telephone lines, is a common occurrence
and one which has caused no end of hard words on the part of neigh-
bors and the telephone company concerned. While not vital to the

Advantages of C.W. Transmission 47

effective operation of the offending station, such occurrences certainly
db not add to the peace of mind of the operator.

With a C.W. set, however, unless the set is of imusually high power,
the pull on the service lines is so small as to make connection on the
regular house service lines entirely feasible and safe, and consequently
no separate service is necessary or required. Neither is there any danger
of overloading the antenna.

Unless the set is of very high power as amateur sets go, the difficulty
is liable to be in the other direction, in that the capacity of the antenna
system might be so great as to absorb energy faster than the set could
supply it. The result of such condition would be that the set would not
oscillate. Here, again, the rule that transmitters and antenna systems
should be designed for each other also holds good. In the case of C.W.
transmission, however, the matter is more favorable to the amateur
field, in that a smaller antenna system, involving less expenditure of
money for erection and upkeep, will answer every requirement of suc-
cessful transmission.

In view of the fact that practically all the energy of a C.W. trans-
mitter is radiated on one wave length, a low power set of such charac-
teristics will usually accomplish as much at the receiver as a spark trans-
mitter of many times the power, making a C.W. transmitter a com-
paratively inexpensive, safe and wonderful method of communication.

CHAPTER VI

Vacuum Tube Fundamentals

The three main elements of a transmitting or receiving tube are:

A plate.
A filament.
A grid.

When it is desired to use a tube as a generator of energy, whether
as a producer of a wave whose frequency is close to that of an incoming
C.W. signal, thereby producing a "beat" at audible frequency (hetero-
dyning), or for the purpose of supplying energy for charging an antenna
for transmission purposes, certain definite rules of tube operation must
be followed in order to obtain proper results.

In the first place, it must be understood that when the filament of
a tube of any type is brought to a state of incandescence the filament
emits electrons. As the filament, or cathode, of a tube is invariably
connected to the negative pole of a source of high voltage, and the
plate, or anode, of a tube to the positive side of the source of supply,
an electron flow takes place from the negative filament to the positive
plate and the amount of this electron flow between the two elements is
in proportion to the diflference of potential between the filament and
plate. This means, in effect, that the more positive the plate becomes
with respect to the filament, or the greater the difference in potential
between the two elements becomes, the greater will be the flow of
electrons from the filament to the plate, omitting for the moment con-
sideration of the action of the grid of the tube, to be covered later.

Tub»e Fundamentals 49

When electrons are emitted by the filament and form a path
through the space of the tube to the plate, this path becomes a conduc-
tive medium, and allows a certain amount of current to flow from the
plate to the filament. This flow is known as space current and can be
measured by means of the proper indicating instruments. The space
current is a direct result of the plate circuit voltage applied to the
tube. The circuit, therefore, begins at the positive and negative poles
of the generator, or battery, employed as a source of "high" potential,
the positive is connected to the plate of the tube, the negative to the
filament and the circuit is completed through the space in the tube
between the filament and plate which, as has been explained, is made a
conducting medium by reason of the electron flow from filament to
plate. This electron flow occurs, of course, only when the filament is
made incandescent and a source of high voltage impressed on the plate
and filament, and, as above stated, this electron flow takes place in the
opposite direction to the plate current flow. In other words, the space
current of the high potential plate-filament circuit flows from plate to
filament; the electrons flow from filament to plate. The electron flow,
which consists of a stream of negative ions released by the filament
when in a state of incandescence, while of prime importance in the
operation of a tube can be ignored insofar as ordinary operation is con-
cerned, as it is an action which takes place automatically providing the
tube is properly operated.

The control of the space current from plate to filament, however,
is of the greatest importance and this phase of tube operation in trans-
mitting sets should be carefully studied and thoroughly understood by
every operator of this type of transmitter. Excessive continual space
current through any type of tube will soon destroy the tube, or, at least,
so change its characteristics as to make it unsuitable for the purpose for
which it was intended. The amount of space current which any tube
will handle is specified by the manufacturer and allowing space current
in excess of the specified amount to flow through any tube will soon
destroy its usefulness.

Excessive plate current invariably causes heating of the plate in a
tube and if the degree of heating is so great as to cause the tube to

50 Modern Radio Operation

become bright red or white-red, the result will be that gases, which are
lodged in the metallic parts of the tube, will become liberated and
instead of a high-vacuum tube the result is a gaseous, or soft, tube. By
this is meant that the liberation of gases has changed the tube from a
"hard" to a "soft" tube, and once this occurs it will thereafter be impos-
sible to use the proper high voltage across the plate and filament of the
tube without causing excessive space current to flow, resulting in undue
heating and further softening of the tube.

When a transmitting or power tube has become gaseous, or soft,
it will be necessary to cut down the voltage of the plate-filament circuit
telow the normal amount for best output and consequently the efficiency,
or, perhaps, usefulness of the tube, has been destroyed.

The operator of a power tube should, therefore, be sure that at no
time does the normal space current of any type of tube exceed the
amount definitely specified by the manufacturer. Very little will be
accomplished by overloading a tube in the way of increased output, but,
on the other hand, this slight additional output gained by overloading
will result in rapid deterioration and ultimate destruction.

Abnormal plate current in the case of a tube transmitter is usually
the result of one or several of the following conditions.

A — Excessive plate voltage, as compared *^o the specified voltage for
the type of tube employed.

B — Excessive positive potential on th^ grid.

C — Excessive resistance in the antenna circuit.

D — Improper adjustment of the circuits.

In the case of A and B, the remedy is to follow the specifications
of the manufacturer and not exceed them.

The result of excessive resistance in the antenna circuit is the same
as that of resistance in any other circuit — limitation of current. The
current flowing in the antenna is cut down by the excessive resistance
and this condition, perhaps more than any other, is responsible for

Tube Fundamentals 5 1

operators overloading their tubes in order to push the antenna current
up to the point where they believe it should be. The obvious answer
in the case of low antenna current is, of course, the reduction of antenna
resistance, by the rebuilding or re-designing of the antenna system. As
a usual thing amateur operators use an earthed ground of some kind,
and such grounds usually have a very high resistance to high-frequency
currents, naturally limiting the output of the set.

CHAPTER VII

Operating Characteristics of Vacuum Tubes

W. C. WHITE, General Electric Co.,
in The Wireless Age

It is very desirable to operate the tungsten filaments of transmitting
tubes at constant voltage rather than constant current. The filament
life at constant voltage is approximately three times the life at constant
current.

The emission during life at constant voltage drops slightly, but this
can be easily taken care of in design if it is desired to maintain abso-
lutely full output to the end of life^ The filament current at constant
voltage decreases 5 to 10 per cent, during life. For this reason it is
not possible to obtain full life from a filament when an ammeter is used
for adjustment.

The variation of life and electron emission with filament voltage is
shown in figure 9. These curves show the poor economy in forcing a
tube, because it will be seen that to double the emission reduces the life
to one-quarter. Conversely they show the advantage of operating a
tube conservatively, for by reducing the electron emission to one-half,
which allows half the rated output, the life is quadrupled. This is even
Vsore forcibly shown in figure 10, which shows tlft variation of high
frequency output current (radiation currej^t), for a 5-watt tube in a
typical oscillating circuit, plotted asrainst filament amperes. At low fila-
ment temperature the output is entirely limited by the electron emission
whereas beyond a certain point increased emission does not appreciably
increase the output, which becomes limited by other factors in the tube.

Tube Characteristics 53

A life curve plotted on the same chart with filament current shows that,
in order to gain an increase of 5 per cent, above rated output by filament
temperature increase alone, the Hfe is decreased to approximately 40
per cent, of the normal.

In making filament adjustments the three following points should
be kept in mind:

(1) Do not materially raise the filament current to get a small increase
of output. The curves of figure 10 show the poor economy of this.
Considering operation over a period of one year it would be more
economical to operate conservatively two tubes in parallel and get
even a greater output than from one running with an excess fila-
ment temperature.

(2) For long tube life the best circuit adjustment is the one showing
the lowest value of plate current. It is for this purpose that an
ammeter in the plate circuit was suggested in a previous para-
graph. It is well worth while to experiment with various circuit
adjustments in order to get a satisfactory output with a minimum
input current. Expressed in another way this simply means getting
as high an oscillator efficiency as possible. If a milliammeter is
not available for use in the plate circuit, a miniature incandescent
lamp may be employed during adjustment and the lowest current
judged roughly by the filament brilliancy.

(3) The maximum rated filament voltage of the tube should not be ex-
ceeded for any length of time. In all cases the filament should be
maintained at as low a temperature as possible, consistent with satis-
factory results. As noted in a previous paragraph the filament cur-
rent at constant filament voltage decreases during life, therefore,
adjustment by current is sure to result in abnormal temperature of
the filament as its life progresses. All tubes are given a certain
rated filament current plus or minus an allowance at a rated voltage.
This, as above stated, can apply only to a tube when it is new, as
the filament resistance increases during Hfe. This rating denotes
or should denote the filament voltage at which the tube will give
rated output at rated plate voltage throughout its average life under

54 Modern Radio Operation

specified conditions. Therefore, it is a distinct advantage if the
user can obtain the result he desires by operating the filament at a
voltage under normal. Operation at 95 per cent, normal filament
voltage should double the life of the tube. Under many conditions
this is possible. Under some abnormal conditions the filament must
be operated at an over-voltage. Under the latter condition the
user must expect and accept a shorter tube life.

This question of rating is a difficult one, but not entirely unlike the
rating of other electrical apparatus. Consider the case of a direct cur-
rent motor rated 1 horsepower at 110 volts. This rating is fixed by a
commonly accepted set of standardization rules which govern permis-
sible temperature rises and other factors. Both the manufacturer and
the user know that probably 2 horepsower is obtainable from the motor,
but both also know that if this overload is persisted in, disastrous
results are sure to follow sooner or later and the useful life of the motor
greatly shortened. Also both know that the motor will operate at an
over- voltage, say 150 volts, but they also both know that this lowers the
factor of safety of the commutator and that a flashover or bad sparking
is almost sure to result. Eventually vacuum tube ratings will also be
fixed values, but this standardization must await a wider understanding
of the technical features involved before it reaches the same status as
in the case of highly standardized forms of electrical machinery.

In the case of the larger sizes of power tubes a fixed filament
rating is maintained principally to insure uniformity and establish a
definite tube rating. In all cases the filament should be operated at as
low a temperature as possible.

It should be remembered that the variations of life, electron emis-
sion and other factors do not bear the same proportionality to filament
current as to filament voltage. This is due to the temperature coeffi-
cient of resistance of the filament resulting in an increase of resistance
with an increase of current. Owing to this factor a 5 per cent, change
of filament voltage causes about a 3 per cent, change in filament current
in the useful range of filament temperatures.

Tube Characteristics 55

- In experimenting with different circuits and circuit adjustments it
is advisable first to operate at one-half or one-third normal voltage. In
cas; of abnormal adjustment or faulty connections the tube itself then has
a much larger factor of safety against destruction.

Fig. ■

This same precaution should also be observed when the set has not
been operated for some time. Then in case some part of the circuit has,
through accident, been changed, no harm will come to the tubes and the
voltage may be turned off and the circuit corrected.

Most well-made tubes will stand a great overload on the plate for a
few seconds, but a continuation of an abnormally high plate tempera-
ture is sure to deteriorate the vacuum.

Most transmitting tubes have a definite plate voltage rating. As
in the case of a filament voltage rating this voltage should be the value
which will give rated output throughout the average life of the tube.
It is to the interest of the manufacturer to make this voltage as high

56 Modern Radio Operation

as possible as it allows a higher power rating of the tube, but in. all
cases some factor hmits this voltage. These factors art usually elec-
trolysis of the glass of the seal, dielectric strength in the base or stem,
overheating of the metal parts or glass due to the increased energy to
the plate, or puncturing of the glass.

Fig. 10. Hadiatii

On the small types of tubes in which all the leads are brought
through a common sten, electrolysis in the seal of this stem is the
factor usually limiting the plate voltage. At plate voltages above rated
value electrolysis causes air leakage through the seal and thus unduly
shortens the life of the tube. Even at rated voltage a slight, but harm-
less amount of electrolysis takes place, which can be detected by a
blackening of the grid leads in the glass of the seal. This blackening
is due to electrolytic deposition on the grid leads which form the neija-
tive electrode for the electrolysis.

Tube Characteristics 57

At higher plate voltages where this electrolysis is more severe the
glass of the seal in the vicinity of the grid lead changes to a dark brown
color.

In a radio telephone transmitting circuit of the usual type a modu-
lator tube is employed and a buzzer is often substituted for the micro-
phone when it is desired to send out interrupted continuous waves. This
imposes very severe voltage strains on the oscillator tube and if an over-
voltage is also applied to its plate the voltage between grid and filament
may be excessive. The protective gaps described in a previous para-
graph are a safeguard against breakdown due to this voltage.

Unless the constants of the oscillating circuit are changed the plate
current will go up when the plate voltage is increased, causing the
energy loss to the plate to be rapidly increased. This, of course, is liable
to cause deterioration of the vacuum.

Puncturing of the glass occasionally is met with and is caused by
the heat of electron bombardment or dielectric losses softening the glass
or it may be caused by excessive voltage when the glass is a dielectric.

In most types of tubes, if puncturing does occur, it will take place
through the stem, between the leads inside the stem and the sleeve on
the outside which supports either the grid or plate structure. Such puncr
turing is much more liable to occur when the glass is very much heated
due to overload. It is most effectively provided against by the protec-
tive spark gap previously mentioned which should be set as close as
possible and still permit normal operation. Puncturing of the bulb
Itself is rare at plate voltages under 5000.

Some of the principal precautions to be observed in the use of power
tubes have been explained. The experimenter with the larger sizes of
tubes will find many interesting conditions and discover many new phe-
nomena. However, he must be careful and use good judgment or an
undue destruction of tubes and apparatus is almost sure to result.

Although in the past it has usually been the custom to operate the
tungsten filaments of vacuum tubes at an approximately constant cur-
rent by means of an ammeter, operation at constant voltage is to be
recommended as giving a much longer life to the filament in about the
ratio of three to one.

58 Modem Radio Operation

In operating tungsten filaments in vacuum tubes, observance of the
three following rules will greatly increase the useful life of the tubes:

(1) The most favorable adjustment of the set, of which the tube is a
part, is the one which gives the desired result with the lozvest value
of plate current,

(2) The filament current or temperature should not he materially raised
to give a slightly increased output, or signal, which is not vitally
necessary.

(3) Do not, for any length of time, exceed the maximum filament rating,
and in all cases reduce the filament temperature to as low a value
as is consistent with satisfactory operation of the apparatus.

Most tubes are designed for operation in one or two designated
positions; that is, vertically, or horizontally, with a certain side, or end,,
up. It is advisable to observe this feature, because a hot tungsten fila-
ment has a tendency to sag very slowly, and if this is not prevented, or
compensated, by operation in a certain designated position, there are
liable to be changes in the electrical constants of the tube, caused by-
changes in the distance between the electrodes.

If for some reason the vacuum in a tube becomes faulty, it is usually
noted by the characteristic glow due to ionization of the gases present.
If gases evolved from the metal parts or glass, due usually to the heat
from an overload, are the cause of this glow, it will be blue in color;
whereas, if it is due to leakage of air, it will appear purple or pink.

Occasionally a tube will- be met with which, when the filament is
energized, shows a sort of yellowish-white smoke in the interior near
the filament or it fails to come up to normal brilliancy at rated amperes

and a dark-blue powder forms on the plate and grid. Both these eflfects
are due to considerable amounts of leakage of air, but take place under
diflferent conditions.

The smoke or powder formed is an oxide of tungsten which exists
in several forms and varied in color from a very light yellow to a very
dark blue, depending upon the conditions at the time of its formation.

One limit to the possible output of a tube as an oscillator is the
amount of energy that can be dissipated safely in the form of heat. If

Tube Characteristics

it is attempted to dissipate too much energy, the glass and electrodes
will be liable to evolve gas which reduces the vacuum. If the tube is
enclosed in a small unventilated space, normal operation may overheat
the glass of the bulb and cause it to evolve gas. This is most hkely
to occur where a number of tubes are operated in parallel, thus causing
a considerable energy' dissipation in a small area.

When the filament of a power tube is operated from a direct current
source through a regulating resistance, the plate current causes an
inequality in the filame^it current. This action is represented in figure 11.

-j||ll|-MAAAAA

Fig. 11

The electron emission occurs along the length of the filament and
therefore one end of the filament will carry more total current than the
other end; this causes one end of the filament to be the hotter, which
for the same amount of emission will shorten the life. The relative
resistance values of the regulating rheostat and the filament, and also
the location of the point of connection between ^' -^^^^^^^^^nt and plate
circuits, determines the amount and direction of f ^^P ^^ ^"\ As shown
in figure 11 the plate current causes the filament t^^ minimum^ decrease
at the positive filament terminal. This is the sif ^^ ^^^ ^^^^'mode of
connection. ^ >- /

Modern Radio Operation

If, however, the filament is operated from a few cells of storage
battery, or directly from a low-voltage direct-current generator, so that
the resistance in series with the filament is small, it is immaterial whether
the return from the plate circuit is made to the positive or negative ter-
minal of the filament; the heating current in the negative side of the
filament is increased by the same amount. A considerable resistance in
series with the filament is essential to any alteration in the distribution
of the flow of plate current through the filament circuit as a safety pre-
caution. As the plate current is usually in the peighborhood of 2 per
cent, to 7 per cent, of the filament current, and as a 3 per cent, increase
of filament current halves the life of a tungsten filament, the importance
of this effect is evident.

-TL

-^^y^

[.nmimm

Fig. 12

If a low-voltage direct-current generator \z used for filament light-
ing, it is usually connected in circuit as shown in figure 12, the filaments
being directly^ropowderf to the armature leads, the adjustment of fila-
ment tempefts and varfe made by a rheostat in the field circuit of the
generator, pending upoi an arrangement difficulty may be experienced
with the ^t to the pol: i)uilding up if the filaments are left in circuit.
This is owitvrgv^hatJ fact that the cold resistance of a tqngsten filament

Tube Characteristics

is very low, only one-thirteenth to one-sixteenth of its normal operating
resistance. Therefore, if a small low-voltage direct-current generator is^
used at full load to supply tungsten filaments, the cold resistance of the
filaments may be so low that it acts as practically a short circuit on the
armature and prevents the generator from building up.

On power tubes it is preferable to use alternating current for fila-
ment excitation. The chief reason for using A.C. is that it obviates
the unbalanced condition of a D.C. filament current, as described in a
previous paragraph. It is also more practical to generate and distribute
the low-voltage high-current energy for filament operation by means of
A.C

Fig. 13

In using A.C. for filament excitation the filament terminals should
be connected directly to the transformer low-voltage terminals, the regu-
lating resistance being placed on the power side. Also the return of the
grid and plate circuit should be made to a center tap of the coil supply-
ing the filament. This mode of connection assures minimum disturbance
in the plate and grid circuits from the frequency of the filament source.
Both of these points are shown in figure 13.

Modern Radio Operation

Some points in connection with the use of tubes as oscillators will
next be taken up.

In the various diagrams of connections which are shown in this
book, each one is simplified so as show more clearly the point under
discussion. For this reason many diagrams for clearness or simplicity'
omit features which in another paragraph are shown to be advisable.

In all tube oscillator circuits there is an inductance in the plate cir-
cuit across which the high-frequency voltage is set up. Care should be
taken that this inductance is not placed between the filament energy
source and the plate energy source, as shown in figure 14-A. Both of

Fig. 14-A

Fig. 14-B

these sources have, usually, a large capacity or a certain resistance to
ground, so that a circulating current will flow through the coil and
through each source to ground. For the type of circuit shown, the cor-
rect arrangement is shown in figure 14-B. The importance of having
the circuit correct in this respect becomes greater the larger the power
and the higher the voltage used.

In arranging an oscillating circuit to deliver high-frequency energy,
it is important to reduce to a minimum the losses in the high-frequency
circuits. Not only should the wires used be of low resistance and the
condensers have low losses, but it is best to trace through the circuits
carrying high-frequency currents, to be sure that the resistance is a
minimum.

Tube Characteristics

Three common errors in this respect are shown in figure 15-A, which
represents a capacity coupled oscillator circuit. In this diagram the
high-frequency current of the oscillating circuit must pass through a
resistance path comprising the filament in parallel with its resistance,
and battery source. Also it must pass through a fuse in the plate cir-
cuit and through the plate voltage source. In figure 15-B the same
circuit is shown with these three errors corrected ; the first, by changing
the wiring so that the return of the grid and plate circuits is brought
back to the same filament terminal; the second, by change of the fuse
position, and the third, by shunting the plate circuit generator with a
by-pass condenser.

Fig. 15-A

Fig. 15-B

For miscellaneous laboratory work the capacity-coupled type of cir-
cuit is a very convenient one to set up and operate, usually giving little
trouble. However, if the circuit happens to be set up in a certain
peculiar way, very puzzling results and failure to operate may sometimes
occur, particularly if a tube of low impedance or resistance is used, or
several tubes are connected in parallel.

This arrangement is shown in figure 16-A. If, as shown in this
diagram, the leads from the coupling condenser C are connected to the
plate and grid coil terminals rather than to the corresponding tube ter-
minals, as shown in figure 16-B, very high-frequency oscillations may
occur, a second capacity coupled circuit being formed, the capacity
between the electrodes acting as the coupling condenser and the leads
between the grid and plate coils and the corresponding tube terminals

Modem Radio Operation

acting as the grid and plate inductances. This condition is accentuated
by having these leads long and the leads to the coupling capacity short.

Fig. le-A

pigr. 16-B

This unexpected production ^f ultra high-frequency oscillations is
often a very troublesome problem in high-power tube apparatus when
a considerable number of tubes are operated in parallel. The low im-
pedance or resistance of the tubes in parallel accentuates the effect.
One expedient which often aids in overcoming this difficulty is the inser-
tion of a very small inductance (a few microhenries) in one or more
of the grid leads close to a tube grid terminal.

■* ^ 1

Gap

? \r- Fuse

Figr. 17

This coil is shown in figure 17. This figure also shows fuses in
the plate circuit of each individual tube, a very desirable feature on high-
power, high-voltage tubes. This fuse should blow at two to four times
the rated plate current of the tube.

Tube Characteristics

This figure 17 also shows another desirable feature for high- voltage,
power-tube circuits. In experimental work with oscillating circuits un-
usual conditions may occur which will cause transient voltages to be
set up between the grid and the filament, which will reach peak values
many times higher than that set up in normal operation. It is imprac-
tical to design and construct a tube and its base to stand up under this
very abnormal voltage, which only occasionally occurs, due to incorrect
adjustment.

A safety spark gap should therefore be provided between the grid
and filament terminals at or near the tube socket or mounting. This gap
should be adjusted to between one-thirty-second and one-quarter inch,
depending upon the plate voltage employed and the number and type of
tubes used. This precaution should be taken on any tube or group of
tubes delivering over 50 watts of alternating current energy or operating
at a plate potential above 2000 volts.

In one of the simplest and most frequently used forms of capacity-
coupled circuit there is a precaution that should be observed.

This is illustrated in figure 18. It will be noted that the coupling
capacity C has one of its terminals connected through the grid coil to
the negative terminal of the high-voltage source. Very often this capac-
ity C is a variable air or oil dielectric condenser, and its breakdown, due
to high-frequency and high voltage, will therefore short-circuit the gen-
erator. The resultant arcing inside the condenser may also burn the
plates badly.

Fig. 18

This possibility may be prevented by the use of a second capacity
C, which should be large in capacity in comparison with the first C. The
condenser C, if it is at least one hundred times the value of the first C,

Modem Radio Operation

need not be a low-loss condenser. It is necessary, of course, that the
condenser C, safely stand the voltage of the D.C. source.

In a typical form of oscillating circuit, as shown in figure 19, the
frequency of oscillations is principally determined by the value of the
capacity C and inductance L.

As far as the natural frequency of oscillation is concerned, it will
remain constant as long as the product of L and C is constant. How-
ever, it will be found that the type of circuit shown in figure 19 will

Fig. 19

only oscillate at a given frequency in a satisfactory manner when the
capacity C is under a certain limiting value. This is explained by the
fact that certain values of high-frequency voltage are necessary on the
grid and plate. If the capacity C is very large, the tube will not supply
sufficient energy to pass enough current through C to set up across it the
necessary grid and plate high-frequency voltage. The lower the value
of resistance and the lower the losses in the oscillating circuit, the larger
the value of C that may be used and still maintain oscillations.

For the type of circuit shown in figure 19, the limiting value of
C, for the usual types of small tubes running at reasonable values of
plate voltage, is in the neighborhood of a maximum of .001 microfarad
for a frequency of one million cycles (300 meter wave-length). This is
necessarily a very approximate figure because of the many factors which
are involved, but it at least gives the experimenter an idea of what not
to use.

In the use of high-voltage direct-current generators operated singly
or in series, it has been foimd that when they are employed for supply-

Tube Characteristics

ing energy for tube-plate circuits, a considerable strain is imposed on the
insulation of the armatures. This is particularly accentuated when the
tubes are used for radio telegraphy and telephony where the load fluc-
tuates rapidly, or is switched off and on suddenly. For the usual types
of circuits, one of which is shown in figure 20, the negative side of the
generator is practically at ground potential.

-VWAAAM"^

Fig. 20

The train which is imposed on the machines is in the form of a
voltage surge which momentarily raises the generator voltage several
fold. One terminal being; grounded, the strain occurs on the insulation
between the frame or armature core and an armature conductor which
at the instant is near the positive terminal or brush.

In a radio-telephone transmitter correct wave-lengths and normal
antenna current are not, as in telegraphy, indications that the set is func-
tioning properly. Neither of these factors give any information as to the
degree of modulation. The amount of modulation is most satisfactorily
obtained by means of an oscillograph, but this is seldom available for
use when and where desired.

A simple device to indicate modulation is a miniature tungsten fila-
ment lamp in the plate circuit of the modulator tube. This should be
chosen of such a rating or so shunted that normally it burns at a dull

Modem Radio Operation

red. When the microphone is spoken into, it should flash up and the
degree of this brightening soon becomes a very good indication as to
whether the modulation is normal or not. This arrangement is shown
in figure 21.

f-mm^

ttopbfs
ifffsdif.
tutte

Fir. 21

There are so many things that may prevent a radio-telephone trans-
mitter from properly functioning while showing full radiation current,
that an indicator, as described above, is very useful.

CHAPTER VIII.

Methods of Obtaining Plate Potentials and
Types of C. W. Transmitters

ftryfy

B" Batteries

There are several means of obtaining a. proper plate potential for
a tube transmitter and the one decided upon should be the method most
desirable for the type and intended service of the set. Ordinary "B
batteries can be used for furnishing the plate potential for one "hard
receiving tube, which can be operated as an oscillator, although the

6^'/^^ y DC

Fig. 22. Circuit diagram of a simple CW transmitter

amount of current used will cause a marked drop in voltage in a short
time and completely exhaust the batteries after approximately 30 oper-
ating hours. Many amateurs, however, have made up sets of this type

70 Modem Radio Operation

for use over short distances, for both voice communication and C.W.
telegraphy. While a small transmitting set of this type will generate
sufficient power in an antenna to work over distances of a mile or so,
the use of "B" batteries is not desirable because of the necessity for
constant renewal of the batteries.

Direct Current^ or Kenotron Rectified A.C.

In the event that the main object is to carry on communication by
v^oice, two methods of -supplying plate potential, either one of which
will be satisfactory, are available : namely, direct current, from a special
high-potential generator, or rectified alternating current. The advantage
of the direct current method is, of course, that it is constant in ampli-
tude and direction and if the generator is of proper design, very little
filtering will be necessary to take out the hum of the generator, or other
^ noises, in order to provide noiseless carrier energy for speech or music.
In the case of a well-built generator, it is usually desirable to use an
iron-core inductance in each side of the circuit, of a value of approx-
imately 1 henry. Several filter condensers, of a total of at least 5 micro-
farads are connected across the line, on both sides of the chokes and
this arrangement will take care of the filtering out of all extraneous
generator noises, or noises which may come into the motor on the power
feed lines and be picked up by induction, in the generator. The actual
amount of inductance and capacity required for filtering purposes is,
of course, best determined by experiment, but the foregoing values will
serve as a guide and really should be considered as a minimum in any
type of radiophone transmitting set. When installing condensers in a
set, however, it should be definitely determined that they are built to
withstand the value of the potential in use, with special regard to high-
voltage surges which may occur. In the case of small tubes, this will
not be a serious matter, as most all types of filter condensers on the
market are built to withstand ordinary voltages. In the case of 50-watt
and 250- watt tubes, however, the matter is of great importance and due
care should be used in the selection of condensers.

When used for telegraphic communication, the energy radiated by
a C.W. transmitter employing direct current on the plates, heterodynes

Types of C.W. Transmitters 71

into a clear liquid note, the pitch of which is determined by the frequency
of oscillation of the tube in the receiving set.

In the case of tube-rectified A.C., the proper voltage is obtained by

means of a step-up transformer and the problem of filtering the current
becomes a more difficult matter, in view of the constant change of direc-

tion of the current and the resultant hum. In the case of single-phase

A.C., a rather elaborate filtering process is required, embracing several

times the amount of capacity and inductance necessary in the case of

direct current, before a good operating condition is reached, where the

hum has been practically eliminated. The great advantage of the A.C.

method over the D.C. is not only its greater efficiency, but the fact that

it makes unnecessary any rotating unit, it is ready for use at the throw

of a switch, while a motor-generator takes a little time to get going and

uses a lot of power while doing it.

On frequencies below 60 cycles, however, the rectifying method is
rather unsatisfactory for radiophone work. On the other hand, two,
three, six and nine-phase • 60-cycle current, where available, are to be
preferred in the order named, over single-phase current, it being pro-
gressively easier to eliminate the hum with an increased number of
phases.

A. C. Plate Supply

When it is desired to use a tube transmitting set only for telegraphic
communication, the voltage for the plate supply of the tube to be used
is obtained by means of a transformer. Three types of circuit, each
one of which has its advantages, can be used when A.C. is applied to
both the plate and filament of a tube, or tubes.

The use of kenotron rectifier tubes, in conjunction with a proper
filter, on an A.C. supply of a frequency of 60 cycles, will give a result
closely approximating the result obtained with direct current. When
heterodyned at a receiving station, the signals of such a set will be found
to be of good "liquid" quality, that is, most of the characteristic rough-
ness of the 60-cycle current will have been smoothed out and the resultant
heterodyned note will be fairly clear.

72 Modern Radio Operation

Another type of circuit, wliich gives a note approximately 80 per
cent, liquid, or clear, with A.C. on both filaments and plates, is the self-
rectification, also known as full-wave rectification circuit. This circuit
is shown in detail on page 95.

The third type of circuit previously referred to, which employs
A.C. on both filament and plate, is known as half-wave rectification.
In this circuit one terminal of the high-voltage transformer secondary
is connected to the filament and the other to the plate. The output
obtained with this type of circuit is good, but the note is rough and
hard to read through atmospheric disturbances. When heterodyned
the note of a circuit of this type is extremely rough and a very small
proportion of it is liquid in character. Many excellent transmitting
records have been made with this type of circuit by amateurs, however,
and it is extensively used by the amateur fraternity.

As a summary, the kenotron-rectified circuit is efficient, it can be
used for both telegraph and telephone, and when used for telegraphic
communication the note heterodynes at 80 per cent, of a liquid character.
It involves the use of at least two extra tubes, but the output is approx-
imately 40 per cent, more than can be obtained with a self-rectification
circuit, the heterodyned note of which is of practically the same quality.
For example, the output of a kenotron circuit under test, employing two
50- watt tubes as oscillators, was 4j4 amperes. Using the same secondary
voltage on the two oscillator tubes in a self -rectification circuit the cur-
rent dropped to 3 amperes. In addition, it was necessary to raise the
filament voltage one volt above normal to obtain that result. The self-
rectification circuit is not, therefore, a very efficient one, but the final
result, the eflFect at the receiver of another station, is practically the same
as that of the kenotron-rectified circuit, — which means that the expense
and operation of two additional tubes is avoided.

If it is desired to increase the output of a transmitter employing two
tubes in a full-wave rectification circuit, the addition of two tubes, one
on each side will increase the output 40 per cent. That is, if the output of
a transmitter is 3 amperes, the additional two tubes will increase it to
4.2 amperes. With the addition of still two more tubes, the increase

Types of C.W. Transmitters 73

will be 20 per cent, of the original amount, or a total of 4.8 amperes, based
on an original output of 3 amperes for two tubes. Increasing the number
of tubes will, of course, necessitate increased load capacity in the source
of plate and filament current.

When a single tube is used, with D.C. or A.C. on the plate, the
ratio of increase above specified will hold true in the case of the addi-
tion of single tubes in the circuit.

Method for Reducing Excess Plate Current
Excess plate current which no amount of adjustment of the circuits
will remedy is frequently experienced by operators of assembled C.W.
transmitters of all types. As a usual thing the trouble is more pro-
nounced and more dangerous to tube life in sets of high power, as
amateur sets go, especially when A.C. is used.

When D. C. is used on the plates for phone work, plate reactors, hav-
ing an inductance of several henries and some sort of a filter system con-
taining inductance and capacity is generally used in the high voltage lines
from the generator and this, as a rule, prevents the leakage of high fre-
quency currents through the generator windings to ground, through the
power lines.

When A.C. is used on the plates in a one-half wave or full wave
rectification circuit the system of filtering used in D.C. sets is not installed
and as a result a comparatively easy path is offered for high frequency
leakage to ground through the windings of the high voltage transformer.
It is desirable, therefore, to insert radio frequency chokes in the high
voltage leads of the transformer and if full wave rectification is used
these chokes should be inserted in the leads from the ends of the trans-
former and also in the neutral lead to the center of the transformer. In
the case of high voltages and the larger size tubes it may be necessary to
take unusual precautions in order to prevent the high frequency
currents from grounding through the transformer windings. Unmounted
duo-lateral coils, L-500, make excellent high-frequency chokes for this
purpose. One in each of the three leads where full wave rectification
is used, may be sufficient in the case of voltages up«to 1,000, but where
higher voltages than this are used, especially on the plates of the UV-204
tubes, it may be necessary to use two or three of these coils m series in
each of the leads.

74 Modern Radio Operation

In order to make these high frequency chokes permanently effective
it is desirable to prepare them by means of a baking-out process in an
oven for half an liour or so in order to be sure that no moisture is left
in the insulation of the wire. After baking they shonld be immersed in
liquid paraffin which has been heated almost to the joihng point. The
heat can then be turned off and ihe paraffin allowed to cool ; the chokes
being cut out of the paraffin after it has solidified.

The coils can then be covered with insulating tape if desired, and
this will insure a moisture-proof choke which can be depended upon to

Amateur radio plate and filament trans- R.C.A. UP-1018 Amateur radio plate and
former. Front view Rhowlng the switch- lllament tranpfnrmer. Rear view show-
board Ing the terminal board

function under any weather conditions. Where trouble has been expe-
rienced from excess plate current prior to the use of these high-fre-
quency chokes, it will generally be found that the trouble is immediately
remedied upon their insertion in the circuit, and as a general thing, the
plate current will fall below normal, while the same output of the set
will be maintained. Rearrangement of the circuit may then be made
until the output of the set and the plate current bear normal relation to
each other. The plate, or space, current should never exceed the amount
specified by the manufacturer for the particular type of tube in use. The
best operation is that where a satisfactory output is secured with a mini-

Types of C.W. Transmitters 75

mum amount of space current. If the space current is kept below the
normal, or specified amount, the life of the tube, or tubes, will be greatly
reduced.

Precautions in Starting Operation

When applying power to a tube set of any type it is highly desirable,
as a matter of safe operation, to apply in both the plate and filament
circuits about one-quarter of the normal power to be used. If, when low
power has been applied, there is no indication of trouble of any kind,
half and then full power may be applied. In the event of any trouble
becoming evident, all power should be instantly cut off and not put into
the set again until the cause of it has been found and removed. Many
sets have been completed destroyed because of failure of the operator
to use proper precautions when first applying power to it, or in failing
to cut off power the instant that trouble became evident, as trouble in
one spot will usually result in outbreaks in other parts of the circuit if
allowed to continue even for a few seconds.

Before power is first applied to a C.W. set it is advisable to insert
a 100-milliammeter in the grid-leak line and adjust the grid current to
approximately 10 per cent, of the proper amount of plate current for the
tube of tubes in use. The plate current should then be adjusted to the
minimum amount that will insure a satisfactory output. After the circuits
have been properly adjusted, the milliammeter in the grid circuit should
be short-circuited or removed.

In the case of the full-rectification circuit, where two tubes are
used, one on each side of the cycle, the foregoing values given for grid
and plate current should be followed, as they apply to both A.C. and
D.C. types of circuits. The reason is that where tubes are used on each
side of the cycle, each tube works only 50 per cent, of the time, or when
the half-cycle of current on one side acts as a positive potential on the
plate. Many operators of full-wave rectification sets have made the mis-
take of allowing excessive plate current to damage tubes in such cases, in
the belief that the proper value of plate current should be that for two
tubes. This, however, is wrong practice, for the reason specified.

76 Modem Radio Operation

Some Helpful Suggestions for Operators of Tube Sets

Following are a few helpful suggestions which may aid in deter-
mining the cause of trouble in tube transmitters:

Failure to Oscillate

Plate circuit open

Grid circuit open

Improperly adjusted circuits

Defective tubes

Filament voltage below normal

Open antenna or ground circuit

Grounded antenna

Leaky or partially grounded antenna

Antenna ammeter open

Failure to Modulate

Plate circuit of modulator or speech-amplifier tube open
Defective microphone or open microphone circuit
Improper value of grid biasing battery
Defective tubes

Shorted condenser between modulator .:nd speech amplifier
tubes.

An easy method for determining the amount of power in an antenna
is by squaring the antenna current and then multiplying the product by the
resistance of the antenna. For instance, if the antenna current were 3
amperes and the antenna resistance 10 ohms, the formula would be 3 x 3 ^
9 X 10 = 90, or 90 watts of power in the antenna. When the antenna
resistance is not known, comparative values of power may be obtained
by multiplying the antenna current by itself. A few examples are as
follows :

Amperes

Comparative
Values of Power

2x2

— 4

3x3

— 9

4x4

— 16

It will be readily seen that 3 amperes represents more than double
the power of 2 amperes, while 4 amperes represents four times the power
of 2 amperes, as the antenna resistance would be the same in all cases.
Bulletin No. 74, of the Bureau of Standards, contains an excellent and
at the same time, easy, method for determining antenna resistance.. \

CHAPTER IX

Continuous Wave Transmission by Amateurs

For a long time before the war the operators of amateur radio
stations had discussed the possibiHty and practicability of the use of con-
tinuous wave transmitters for amateur work. Many theories, data and
a few facts were submitted from time to time to prove that continuous
wave transmission on short wave lengths was both possible and impossible.

The advantages of continuous wave transmission, especially its
economy and greater flexibility as compared to spark transmission, made
its general use by amateurs highly desirable. The deterrent features
were the impossibility of easily securing the means of generating un-
damped waves, and the important fact that continuous waves on short
wave lengths were declared by many to be impractical, as it was believed
that the slightest change in the characteristics of the transmitter, or the
transmitting antenna system would cause audibility changes that would
make successful reception impossible.

After the ban on amateur transmitting had been lifted, a small sup-
ply of transmitting tubes became available and amateur experimenting
with C.W. transmitting outfits started in earnest.

Thousands of amateurs had used continuous wave transmitters on
short wave lengths during the war in various branches of the service,
consequently had become more or less familiar with the general methods
and results. As their actual experience with these sets had been more
or less confined to attaching wires to binding posts on the outside of

78 Modem Radio Operation

cabinets, they found considerable difficulty in securing and assembling
the various parts and elements necessary. But it takes brains, energy
and perseverance to be a successful amateur, and what might have proved
a tough proposition to any other class or set of human beings didn't
stop the determination of Young and Old America to possess a reliable,
practical C.W. transmitting set. And so the work went on, causing
more than one enthusiast to lose more hours of sleep than would pos-
sibly be sacrificed by the average person, that is, provided said average
person desired to continue to live. As one amateur aptly expressed it,
paraphrasing a well-known song — "The hours I spent with thee, dear
set."

But perseverance will generally win out sometime or other and
the result of the untold hours of study and work on the part of the
amateurs finally resulted in a finished product. A professional sys-
tematizer would undoubtedly suffer mental torture and anguish could
he see the numberless types and specimens of C.W. outfits in use by
amateurs today, for it would be practically impossible to find two that
look as though they were even distantly related, but the important fact
is, they work.

Starting with the basic parts, a source of plate potential, a tube,
or tubes, a home-niade coil or two and what other miscellaneous junk
could be begged, borrowed or otherwise secured, these ambitious amateurs
have always managed to get some amount of undamped energy into an
antenna.

Some of the circuits which have been tried and tried and tried were
really wonderful creations. Some were plain and simple. In fact some
were so simple as to be foolish. Others were complicated beyond
description. The writer can readily recall his early attempts to secure
reliable information on C.W. sets. To the best of his knowledge and
belief, the crop totalled something like seventy-five different circuits, all
of which were thrown into the waste basket with disgust after many
weary hours of wasted trial and effort. One of the successful circuits
tried, that worked very well on low-power sets, is shown in the fol-
lowing diagram :

C.W. Transmission

With a set using the circuit shown in Fig. 23, with* two 5- watt
tubes, plate voltage of 400, it has been found possible to put 1.5 amperes
into an antenna, in connection with a counterpoise ground. The antenna
resistance was in the neighborhood of 7 ohms, which is, of course,
rather low for an amateur station antenna, and which accounts for the
large amount of antenna current as compared with the general result
where an earthed ground is used.

Hf/i

SOfwn he//x
: s 'dfo j^ copper tub'ng

iSOSOO

DC
Cenerafor

ifOAC.
Motor

Fig. 23. Circuit diagram showing method of modulating the output

An unusual feature of the circuit is the method of modulating the
output. It will be seen that the buzzer and telephone transmitter are
inserted directly in the negative high potential lead to the filament, below
the point where it branches to grid leak and filament. This method
causes only the slightest deflection of the space milliammeter and, judg-
ing by this alone, as is generally done, it would be perfectly logical to
assume that the output was insufficiently modulated to be of much use.
Actual experience, however, has shown that this method of modulation
has great carrying power, and further does not cause the slightest voice
distortion. The speaker's voice can readily be recognized as far as it
can be heard.

A distinct improvement made in this circuit was in the adoption of
a tone wheel, driven by a six-volt battery motor, which was inserted in
place of the buzzer. Buzzers, even the best of them, sometimes sing

80 Modem Radio Operation

badly off key, but the voice of the tone wheel is always steady and even.
Further, it has no contacts to stick and cause trouble. When using
straight C.W. or the telephone transmitter, it is only necessary to stop
the wheel with the brush making contact on the metal of the wheel. It
has been found desirable to have the proportion of make and break 50
per cent. each. This can be followed, regardless of the size of the disc
used. The note can be regulated by the speed of the wheel.

It may be of interest to know that a C.W. transmitter of the type
previously described, located about thirty miles out on Long Island, has
successfully covered remarkable distances, considering the input, which
was about 75 watts. Straight C.W. signals from this set have been
reported from Canada, north of Detroit, Lewiston, Me., and points in
Missouri and Florida. A test conducted with a spark station at Colum-
bus, O., developed the highly interesting fact that the signals of the
C.W. outfit were reported at Columbus as being steadier and stronger
than the signals from a well-tuned 1 K.W. transmitter located at the
same eastern station.

Interrupted continuous wave (I.C.W.) has been tried, the methods
of interrupting having been of various kinds. In the early stages the
signal was interrupted by the buzzer, as shown in figure 23. Then a
change in the method of modulation was made ai-d a tone wheel of
brass, 4 inches diameter, with bakelite insulating studs set in its face was
mounted on the shaft of a 1750 R.P.M. synchronous motor.

This arrangement gave a musical note to the interruptions that could
be varied at will by using a variable speed 6-volt battery motor, instead
of the induction motor.

When the owner of the set grew ambitious and increased the size
and pov/er of the set, the am.ount of current flowing in the filament grid-
leak line made too much of a fuss to be handled without trouble, and
another method of modulation, shown in figure 24, was tried. This
consisted of placing the secondary of a modulation transformer in the
grid-leak line, and maklx^g it serve the double purpose of grid-leak and
modulation transformer. The secondary resistance of one type of com-
mercial modulation transformer now on the market is about 1,000 ohms.

C.W. Transmission

Other resistance was added in series with the secondary according to
the amount desired/

This method of modulation permits the handling of low potential by
the key and buzzer or tone wheel, and is a great advantage over the

Fig. 24. Circuit diagram having the secondary of a modulation

transformer in the grid leak

negative type of modulation for this reason, and it is also slightly more
efficient.

Another type of modulation used is the well-known Heising system,
wherein the grid circuit of a modulator tube is acted upon by the impulses
of a transmitter, buzzer or tone wheel through a modulation transformer.

Bwzzer,

^megohm
g'na 'eah

Fig. 25. Diagram showing the Heising system of modulation

as shown in figure 25. This is undoubtedly the most efficient method
of modulation, although it is necessary to use at least one modulator tube
for each oscillator tube.

82 Modern Radio Operation

In all the experiments so far carried on the ranges of the three
methods of transmission have been comparatively as follows:

C. W. 100 per cent.

I. C. W. 65 per cent.

Voice 40 per cent

There have been occasional times when the voice has been reported
over unusual distances, but the proportions shown above as a general
thing are substantially correct. In almost every case it seems that the
carrier energy, or straight C.W., was very strong, even when the voice
could be scarcely heard, indicating that only a small percentage of the
output of the set was being modulated. This phase of C.W. transmis-
sion is one which can be profitably studied by amateurs, for there is a
great deal to be desired in the modulation of most of the amateur radio-
phone sets now in operation.

Thousand-AIile Amateur Radiophone

The remarkable distance records made by amateur radio stations
using continuous wave transmitters with several 5-watt tubes in multiple,
are matters of common knowledge. The fact that a set, employing two
or three of these small tubes, with approximately an ampere or more of
current in the antenna, has been heard and worked by stations 1,000 or
2,000 miles away, causes no special mterest at the present time.

Experiments at 2ZL station, Valley Stream, Long Island, covering
several weeks, during 1920, with transmitting sets employing 5-watt
tubes, clearly demonstrated that the signals from such sets are subject
k) practically the same conditions as damped transmitters, where the
distance between the transmitting and the receiving station is more than
the regular daylight range of the transmitting station, especially where
the C.W. output is modulated in some manner. The foregoing, however,
applies only to general conditions.

On nights when the stations of the Eighth District, particularly those
in Ohio, were inaudible on Long Island, 2ZL, using straight or modu-
lated C.W., was also inaudible at several Eighth District stations, listen-
ing on a pre-arranged schedule. When the signals from Eighth District

C.W. Transmission 83

stations were audible on Long Island, the signals of 2ZL were copied
in Ohio. During these tests one point of considerable importance devel-
oped. On nights when spark stations in the Eighth District "swung"
so badly as to make consecutive reading of their signals impossible with
two steps of audio-frequency amplification, the straight C.W. signals
from 2ZL were reported as being good and steady, and consecutive
reading was entirely possible. Summarized, this established the fact
that, while the signals from 2ZL were subject to general conditions over
long night distances when they were heard at all they were much more
steady and reliable than spark signals. It should be remembered also,
that the input of the tube transmitter at 2ZL was about 160 watts, plate
and filament, as compared to 1,000 watts input— without counting the
energy used to run the usual non-synchronous rotary spark gap — in the
case of the Eighth District spark stations.

After the experiments with the transmitter employing the 5-watt
tubes had been carried on for several weeks at 2ZL, and the reports
of the listening stations carefully studied, it became evident that the
signals of such a small set were entirely satisfactory over distances up to
100 miles. Later on it was decided to increase the power of the set. It
was not practical, of course, to use more than three or four 5-watt tubes,
because the small added output of more tubes does not warrant the addi-
tional expense of the tubes or the extra filament and plate power.

As the only obtainable tubes of increased size over 5 watts are of
50-watt output capacity, it was decided to install a transmitter employing
tubes of that size, in accordance with figure 26. Right here is where
the writer got into the same predicament as the man who caught a wild-
cat by the tail — he sure started a fine bunch of trouble for himself. It
seemed logical to suppose that to install the 50-watt tubes it would only
be necessary to insert the new tubes and sockets, supply proper filament
and plate voltage and shoot the moon. But it was somewhat different
before a smooth working 100-watt set was finally developed.

The characteristics of the larger tubes were such that their output
was 50 watts on 1,000 volts plate pontential. Of course, it was decided,
amateur fashion, to get every single possible watt out of the tubes, so

84 Modem Radio Operation

a motor-generator — 110 volts 60 cycle A.C., 1,000 volts D.C., and also a
12-volt 80-100 ampere hour storage battery to heat the 10-volt 6J4 ampere
filaments, were procured and installed. When all was ready the outfit
was started and the key pressed. In about 1-1000 of a second two
variable condensers, a couple of choke coils, two or three meters and
some other odds and ends went to heaven, or wherever such things go
when they go up in smoke. The motor-generator was a sturdy cuss or
it probably would have gone too.

In the course of time, new parts, meters, etc., were installed and
the set )vas started up again. This time trouble broke out in a different
place. The tuning, or coupling coil, which had been made up of Litzen-
draht wire, according to expert advice, got so hot* that it ceased doing
business and burned up. A new coil was wound with heavy, solid insu-
lated wire, and it also got hot. In order to avoid losses it was decided
to wind a coupling coil with 3/16 inch copper tubing. This proved to be
a good step and no more heating was detected in the set after long
stretches of transmission with as much as 5 or 6 amperes in the antenna.

It was found that a storage battery would not answer for filament
heating purposes on tubes of this size and an A.C. transformer was
decided upon. This was a new one on the manufacturers of amateur
radio apparatus at that time and one had to be made up specially. The
final result was a transformer with secondary voltages of 8 and 10, and
a total secondary capacity of 150 watts — more than sufficient to properly
heat the filaments of two 50-watt tubes. A tap was provided in the cen-
ter of the secondary winding to minimize the effect of the A.C. hum on
the filaments. This transformer was used successfully for a time; then
it also went up in smoke, which occurrence was presumed to be due to
poor insulation. A second one went the same way in short order. It
was then decided that it was probably full of high-frequency currents,
induced directly or indirectly by the set, so a system of protective con-
densers was installed. Two were used on the primary side of the trans-
former and the middle point grounded. Two were also used across the
secondary side, with the middle points connected to the neutral tap, and
the core and framework were directly grounded. After that no further
trouble was experienced with the transformer.

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Modern Radio Opetation

In the case of the set just described the oscillator grid leak was
5,000 ohms, the negative grid battery potential 60 volts, and the
proper polarity of the 6-voIt battery on the primary of the modulation
transformer was determined, of course, by experiment. It was found
desirable to reverse the polarity of the 6-volt battery as between the
telephone transmitter and the buzzer, in order to obtain the best modu-
lation.

It was sometimes found difficult to "raise" a distant station wjien
modulating the output by buzzer, because of sharpness of tuning at the
receiving station, local interference, etc. It was therefore decided to
utilize the two tubes of the set as oscillators, and insert a tone wheel or
chopper, in the common grid-leak line. A disc of brass four inches in
diameter, one-quarter inch thick, was turned off and twenty holes, one-
quarter inch in diameter were drilled around the outside edge through

C.W. Transmission

the flat surface of the disc and bakeiite studs inserted. The face was then
turned down and the disc mounted on a 1700 R.AI.P. induction motor.
Two brushes were brought to bear on this disc, one on the flat surface and
one in a position to run over the bakeUte studs as the motor revolved.
It is readily seen, of course, that this chopping arrangement is perfect
modulation, in that it breaks up the C.W. output into groups between
which no current is flowing in the antenna, because oscillation of the set
stops as the brush runs over the studs and is renewed as it comes in con-
tact with the metal of the wheel. With the two tubes used as oscillators
and chopped in this way the apparent antenna current, as shown by the
meter, was three amperes, the same as with one oscillator and one modu-
lator. As a matter of fact, however, the full amplitude of the antenna
current was considerably in excess of that figure, probably double.

The signals of 2ZL were reported from stations at the following
points while using the set just described and 2ZL worked with a number
of them:

Palm Beach, Fla..

Miles —

Air Line

from ITJL

900

Stanbridge East, Quebec 350

Little Rock, Ark 1,025

Chicago, 111 __ 725

Detroit, Mich 500

St. Louis, Mo 850

Houston, Tex 1,286

Port Arthur, Tex 1,265

EUendale, N. D..

.1,330

Miles —

Air Line

from 2ZL.

New Orleans, La 1,079

St. Paul, Minn 1,025

Kansas City, Mo 1,080

Louisburg, Nova Scotia 550

Montreal, Quebec 350

Marion, Mass 220

Memphis, Tenn 925

Grand Forks, N. D 1,300

Minneapolis, Minn. .. 1 ,025

Using one tube as an oscillator and one as modulator the voice has
been reported from Marion, Mass. ; Boston, Mass. ; Memphis, Tenn. ;
Anderson, Ind. ; Niles, O. ; Washington, D. C. ; Rochester, N. Y. ; Pitts-
burgh, Pa. ; Cambridge Springs, Pa. ; and Montreal, Quebec, and many
other points, and two-way communication has repeatedly been carried
through successfully; 2ZL by voice and the other stations replying by
spark.

88 Modem Radio Operation

The work done when using straight or unmodulated C.W., established
new records and distances for amateur C.W. transmission, at that time,
in that daily schedules were maintained with the following points:
Savannah, Ga. (4XB) ; Salem, Ohio (8ZG) ; Canton, Ohio (8ZV) ;
Langley Field, Va. (XF-1). Occasional communication was established
with Madison, Wis. (9XM), and Minneapolis, Minn. (9X1).

On one or two occasions when communication had been established
with Western stations, it developed that no Eastern amateur spark sta-
tions had been heard at Western stations, and no Western ones at 2ZL.
The straight C.W., however, was going through without any trouble.
Slight fading was noticeable, but of a longer period and more gradual
character than in the case of spark signals.

Insofar as the dependable daylight range of the set was concerned,
distances varied with the method of transmission or modulation. Using
straight C.W., 2ZL was copied repeatedly during daylight over varying
distances up to 200 miles, the greatest distance having been Boston,
Mass. Conclusive tests to determine tbe maximum C.W. daylight range
were not made, but it is believed that with three amperes of straight C.W.
in the antenna it should be possible to communicate with stations 300
miles distant during fairly favorable daylight conditions.

With the output of the set at 2ZL modulated by buzzer, daylight
communication has been successfully carried on with stations 150 miles
distant, although the reception, of course, called for careful tuning and
generally much preliminary transmitting for adjustment of the receiving
sets. With voice modulation, during daylight, conversation with stations
seventy-five miles away has also been successfully carried on. When
the two tubes were used in multiple, with the tone wheel chopping the
grid-leak current, the received signals were several times the audibility
of buzzer or voice modulation.

As a summary, the dependable daylight ranges of a set with approxi-
mately three amperes in the antenna, can be reasonably assumed to be

as follows :

Straight C.W. 200 miles

Buzzer modulated 75 miles

Voice 75 miles

Tone wheel chopper 100 miles

C.W. Transmission 89

When these ranges and the flexibility of the set are c )nsidered, and
also the fact that the total input of the set, plate and filament, under all
conditions of transmission never exceeded 350 watts, the very great ad-
vantage of C.W. transmission over the usual spark method is readily
apparent.

As a side light on the voice transmission tests made at 2ZL, at that
time a letter was received from an amateur in a little town with a popu-
lation of 160, located thirty miles South of Memphis, Tenn., saying that
he frequently heard the phone at 2ZL station. He stated that he used a
small aerial and only a single tube as a detector. He said that he and his
people liked to listen to the phone and requested that the voice be used
often, that music be played occasionally as he and his people enjoyed
listening to it.

Wonderful and mysterious are the ways of C.W. transmission when
an amateur in Tennessee, 925 miles distant, regards a radiophone concert
for his benefit by another amateur station in the vicinity of New York as
an ordinary matter.

With the set previously described all then known amateur C.W. trans-
mission records were broken by 2ZL and 5XB stations on February 11th
and 12th, 1921. The latter is the station of the Agricultural and Mechan-
ical College of Texas, located at College Station, Texas. The transmitter
used there consists of three 5-watt tubes, the total input plate and filament
being approximately 175 watts. The overland air line distance between the
two points is 1,500 miles. The two stations were in communication oc-
casionally during the winter of 1920-21 and messages were exchanged
successfully in both directions.

A variation of the circuit shown in figure 26 to include a magnetic
speech amplifier and omission of the speech amplifier tube, as shown in
figure 27 also gave excellent results.

Another set with which interesting amateur work was done at 2ZL
station was one employing A.C. on both plates and filaments of two
50-watt tubes in a self -rectifying circuit, most of the work being done on
wave lengths below 200 meters. This 100-watt continuous wave trans-
mitter, employing alternating current on both plates and filaments, was
used at 2ZL station for several months early in 1921 for amateur mes-

90 Modem Radio Operation

sage relay work and proved to be a very satisfactory transmitter for
relay work. The circuit used was the same shown in figure 27 except
that two UV203 and slightly different constants were used.

The plate current of the set was 150 milliamperes per tube at 1,500
volts on each side of the split secondary transformer; the filament cur-
rent, sixty-five watts per tube, a total of 355 watts for both tubes (plate
current figured intermittently, filaments continuously). The antenna
current on 325 meters was three amperes.

In working the regular traffic schedules it was found possible to
work Boston, Salem and Canton, Ohio, without trouble. Mr. S. B.
Young, Dorchester, Mass. (lAE), reported that the signals of 2ZL were
steady and the audibility sufficient at all times for regular relay work.
The signals of the A.C. set were found to be more easily controlled than
the signals of the D.C. set previously used at 2ZL and there was less
trouble in picking them up than in the case of D.C. signals.

It might be well to mention here that a regular schedule was main-
tained between 2ZL and lAE stations for a period of three months while
the 100-watt A.C. set was in use at 2ZL. Even when difficulty was ex-
perienced in the reception of the lignals from lAE at 2ZL station, the
signals from the latter station were read without trouble at lAE. While
the distance between the two points is about 200 miles, the territory, has
always been known as being difficult for amateur short wave spark trans-
mission. Swinging and fading of signals between the two points are
usually very pronounced. It will be noted, however, that it was specifi-
cally reported that the signals of 2ZL station were generally steady at
'Boston and that no difficulty was experienced in their reception.

In addition to Boston, regular schedules were maintained between
2ZL station and stations 8ZG at Salem, Ohio, and 8ZV at Canton, Ohio,
over a period of several months. Mr. Manning, at 8ZG, reported that
the signals from the A.C. set were always of good audibility, and en-
tirely sufficient for regular relay work, and that the signals were pref-
erable to those from the D.C. set previously used at 2ZL because of their
steadiness and greater ease in locating and handling in reception. He
further stated that the signals of the A.C. set were being copied regu-
larly at Salem without having a detector tube oscillate or in other words

C.W. Transmission 9 i

without heterodyning. Practically the same report was received from
Mr. Ley, 8ZV, at Canton, Ohio. The circuit employed in the case of
the 100-watt A.C. transmitter at 2ZL station was selected after long
experiment as being one which is entirely practical and which can be
depended upon to work under practically any conditions.

The filaments are lighted by means of a split winding on the trans-
former. In line with the more recent practice in tube transmission, con-
stant voltage was maintained on the filaments of the tubes rather than
constant current. An A.C. voltmeter was connected to the terminals
of the tubes and the voltage kept constant at the proper rating for the
tubes employed by means of a regulating rheostat in the primary of the
filament transformer.

The value of the grid, leak resistance used in shunt to the grid con-
denser was approximately 2,500 ohms. The grid condenser was a small
mica-condenser of .0005 microfarad. Mica-dielectric condensers of .002
microfarad capacity were used in the plate circuit. Condensers of
higher or lower capacity can be used in this part of the circuit, providing
the dielectric is of sufficient strength to withstand the potential employed
in the plate circuit. The tuning inductance used was one of twenty turns
approximately i^we inches in diameter. In connection with the system
at 2ZL this arrangement gave the set a transmitting wave length of 325
meters. A short wave condenser was used for reducing the wave to
approximately 200 meters.

Some experiments were made at 2ZL to determine the practicability
of employing wave lengths below 200 meters in connection with tube
work. A separate antenna, considerably smaller than the main antenna
regularly used, was used for this short wave work. This smaller antenna
was about 60 feet long overall and consisted of four wires. Considerable
work was done on 175 meters. The antenna current on this wave
length being two amperes, it was found entirely possible to work 100
miles in daylight on this wave length without trouble with that amount
of current in the antenna. The antenna current on 150 meters was in
the neighborhood of 1J4 amperes. As practically no amateur stations
were equipped with receiving apparatus which would accommodate a
wave length of 150 meters, however, it was found impossible to make

92 Modern Radio Operation

any experiments on this wave length to determine the daylight range of
the set. When the transmitter was adjusted to a wave length of 175
meters it was found, in at least three instances, that the receiving opera-
tors had to adjust their secondary circuit variometers at zero in order
to hear the signals. When the wave was further reduced it was found
impossible to "raise" any of the listening stations. After communication
had been carried on for some time on 175 meters considerable comment
was made by other amateur stations on the desirability of working on
that wave length because of the absence of interference and very little
trouble was experienced from atmospheric disturbances on nights when
static was giving considerable trouble on wave lengths above 200 meters.
A great deal has been heard from various points to the effect that it is
difficult or impossible to secure sufficient antenna current on a wave
length of 200 meters to enable the transmitting station to work any
respectable distances. It would seem that this condition is due entirely
to the fact that many amateurs attempt to adjust C.W. outfits to a
200-meter wave on an antenna with a fundamental wave length of 200
meters, which arrangement, of course, precludes sufficient couphng in
the tuning arrangement to allow free oscillation of the set. It is, how-
ever, entirely possible to work on 175 meters with tube transmitters,
without trouble, providing the antenna system is of the proper size for
that wave length. The idea that tubes will not operate and generate
power on 200 meters is an absolute fallacy which has evidently arisen
through lack of knowledge, or because of misinformation. Tubes will
oscillate on short wave lengths just as well as on long wave lengths,
providing an antenna of the proper characteristics is used.

The Amateur Trans-Atlantic Transmissions

OF December, 1921

The story of the amateur trans- Atlantic tests of December, 1921, is so
well known, that it seems unnecessary to tell more than a condensed
story of the unprecedented accomplishment in these pages. At the first
national convention of the American Radio Relay League, held at Chicago,
during the summer of 1921, it was decided to send Paul F. Godley to

C.W* Transmission 93

Europe, with proper receiving equipment, to determine if the signals of
American amateur stations could be heard across the ocean, an approxi-
mate distance of 3,000 miles. Preliminary trials were held during
November and all amateurs were invited to participate, with the under-
standing that 1,000 miles must be covered to make any station eligible
to enter the trans-Atlantic trials on an individual basis. Twenty-seven
stations qualified and to each one a group of code letters was assigned,
as well as a definite period of transmission. Free-for-all periods for
each district were also set apart each night and all stations were invited
to participate.

The result was not at all what had been expected. Many of the

stations which had qualified in the 1,000-mile preliminaries were not
heard on the other side at all, while several stations which failed to
qualify or which had not participated in the preliminaries were heard,
either by Mr. Gbdley or by English and Dutch amateurs. One station,
2AJW, heard by Godley, employed 5-watt tubes, the input being approxi-
mately thirty watts. Several other stations which were not heard at
all by Mr. Godley were copied by English amateurs and the code- words
verified, precluding any error in reception.

A complete list of stations heard by Mr. Godley at Adrossan, Scot-
land, is as follows:

Spark :

lAAW, not yet located; ^FB, Atlantic City, N. J.

lARY, BurHngton, Vt. 8BU, Cleveland, Ohio;

\l^^' ^9nM%^r* K V 9ZJ, Indianapolis, Ind.

2BK and 2DN, Yonkers, N. Y. ,_v> t.t , . r^

2EU Freeport, L. I. ^^^' Newmarket, Ontario.

Continuous Wave:

lARY, Burlington, Vt. 2ARY, Brooklyn, N. Y.

IBCG, Greenwich, Conn. 2AJW, Babylon, L. I.

IBDT, Atlantic, Mass. 2BML, Riverhead, L. I.

IBGF, Hartford, Conn. 2EH, Riverhead, L. I.

IBKA, Glenbrook, Conn. 2FD, New York City

IRU, Hartford, Conn. 2FP, Brooklyn, N. Y.

IRZ, Ridgefield, Conn. 3DH, Princeton, N. J.

IXM, Cambridge, Mass. 2ACF, Washington, Pa.

lYK, Worcester, Mass. 8XV, Pittsburgh, Pa.

with the probability that 4G'L, Savannah, Ga., was also heard.

94 Modern Radio Operation

During the tests the following American stations were heard by
English amateurs:

IBCG, Greenwich, Conn.
lAFV, Salem, Mass.
lUN, Manchester, Mass.
IXM, Cambridge, Mass.
IZE, Marion, Mass.
2FP, Brooklyn, N. Y.
2BML, Riverhead, Long Island.
2ZL, Valley Stream, Long Island.

All the stations heard by the English amateurs used C.W. trans-
mitters during the tests. Practically every type of circuit was employed,
as IBCG used D.C. on the plates, IZE Kenotron-rectified, 60-cycle A.C.,
2FP 500-cycle A.C., 2BML half-wave rectification of 60 cycle A.C., and
2ZL full-wave rectification, 60-cycle A.C.

In commenting on the result of the tests, Mr. Godley made the
following statement:

"In glancing over the above lists one is struck by the preponderance
of the C.W. stations, and by the fact that the British heard C.W. stations
only. That can mean only one thing, that C.W. is far superior, and I
should like nothing better than to see all amateurs change over to con-
tinuous wave at once. Spark methods are horribly out of date and are
so inefficient, comparatively, as to be ridiculous, were it not that many
have invested good money in spark equipment. Station lAFV, since
the tests, has gotten three messages across to England (London) on
200 watts of C.W. Many stations of the Atlantic seaboard are reaching
to the California coast with similar powers, while the west coast stations
have been shoving signals into the Hawaiian Islands. The day is not
far distant when amateurs the world over will be exchanging greetings
in many languages, and by the same token, the day is almost here when
spark stations will be of interest as having to do with history only."

The set used at 2ZL station at Valley Stream, L. I., when signals
from the station were heard in England, employed two 250-watt Radio-
trons, UV-204, in a full-wave rectification circuit, as shown in the
accompanying diagram, Figure 27.

C.W. Transmission

A transformer, with a split secondary, supplied A.C. for plate
potential, at 2,200 volts for each tube, 4,400 over all. The filaments
of the tubes were heated with A.C., by means of a transformer, also
with split secondary. The value of the grid leak resistance used in
shunt to the grid condenser was 20,000 ohms, and the capacity of the
grid condenser .002.

Fig. 27. Circuit diagram of the 500-watt full-wave rectification set
of 2ZLi Station, which transmitted signals to En^and

The antenna at 2ZL is an inverted L, 85 feet high at the end away
from the station and 65 feet high at the station end. The flat top is
120 feet long. The leads, four in number, are from the low end. The
fundamental wave length of the antenna is 210 meters. The antenna
points southwest-northeast, with the leads on the southwest end. The
fact that the station was heard in England and at Monterey, Calif., at
practically the same time, seems to indicate that there are no directional
effects. A counterpoise ground system is used, consisting of eight wires
on spreaders, directly under the antenna, and fanned out at both ends
beyond the antenna. The antenna current is 10 amperes on 325 meters,
7 amperes on 250 meters and 5 amperes on 200 meters.

Modem Radio Operation

Antenna system ol 2ZL, Station-

Three Well-Known Amateur Stations

The three amateur stations, IZE, 8ZG and 9ZG {formerly 9AKR),
all equipped with 100-watt Kenotron outfits, have become so well known
on the air that a detailed description of them and their accomplishments
will undoubtedly be of interest.

The transmitting sets used at these three stations are identical. A
750-watt transformer, with UO-volt, 60-cycle primary, has three wind-
ings, one providing high voltage, approximately 1,200 volts for the plates
of the Kenotron tubes, another supplies 10 volts for heatin;^ the filaments
of the Kenotrons and the third provides 10 volts for the filaments of
the oscillator tubes. All windings have central taps. Two Kenotrons,
UV-2I7 and two oscillators, UV-203, are used in each of the sets.

The station of Irving Vermilya, at Marion, Mass., IZE, is shown
in the illustrations. The station is operated by remote control. The
antenna of the station is of vertical fan type, of 20 wires, suspended
from two poles approximately 90 feet high. A counterpoise ground.
also of 20 wires, suspended under the antenna, is used.

C.W. Transmission

The vertical harp type of a

The C.W. signals of IZE station have been reported from Cristobal,
Canal Zone on the Pacific side of the Isthmus, and this station was one
of those heard, and the code letters verified, by amatenr stations in
England during the recent trans-Atlantic amateur tests.

In addition to these extreme and exceptional night distances, the
station has carried on regular communication with the Eighth and Ninth
districts. The daylight range of the station, with straight C.W., is
approximately 150 miles. A magnetic modulator is used for voice com-

96 Modem Radio Operation

munication and distances up to 75 miles are r^^iarly covered during
daylight by voice. A separate receiving antenna, consisting of a long.
single insulated wire laid on the ground, enables duplex operation with
other stations. The normal antenna current of the station is 5.2 amperes
on 375 meters.

8ZG, Salem, Ohio
The station of A. J. Manning, Salem, Ohio. 8ZG, has made many
exceptional transmitting records during the winter months. The set
was installed on October 19, 1921, and on the same night signals from
8ZG were heard in the First, Second and Ninth Districts, and a complete
message which was transmitted from 8ZG to 2EL, Freeport, L. I., was
copied at Havana, Cuba.

On the night of November 12. 8ZG and 5ZA. at Roswell, New
Mexico, were in communication for an hour, exchanging traffic, — an
overland distance of 1,400 miles. On January' 6 the signals of 8ZG were

C.W. Transmission

reported as of good audibility by 6ALP, at Long Beach, Calif., an
approximate distance of 2,100 miles.

A magnetic modulator is used at 8ZG and a daylight rat^e of 100

and counterpoise

miles is regularly covered by voice. The dependable daylight range of
the set for telegraphing, using straight C.W., is 200 miles, and the regular
night range 400 miles. The antenna current of the station is normally
4 to 5 amperes, on 375 meters.

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C.W. TrtinsinissioiT

9ZG, Mt. CARROL^ Ilu

The third station of the group, that of A. C. Mertz, Motmt Carroll,
111. 9ZG {formerly 9AKR), in the northwestern comer of the State,
has been heard several times on both coasts. As in the case of 8ZG, this
station was reported from exceptional distances the first night it was
operated, and communication was established with 8AWP, Syracuse,
N. Y.; 5ZA, Roswell, New Mexico, and 9AMB, Denver, Colo., through

t Kenotron Trananiitter of 9ZQ Station, Mt. Carroll, ;

considerable static. During January the signals of 9ZG were reported
from several points on the Pacific Coast and also by stations in Massa-
chusetts and Rhode Island. The dependable daylight range of 9ZG
is 200 miles, using C.W. for telegraph communication, and voice com-
munication, using a magnetic modulator, is regularly carried on over
100 miles. The normal antenna current of the station is 4.2 amperes,
on 375 meters.

1 04 Modern Radio Operation

1600-Mile Amateur Radiophone of Station 5ZA,

RoswELL, N. Mex.

The 100-watt C.W. transmitter used by Louis Falconi, Roswell,
New Mexico, Station 5ZA, has made some remarkable records for
amateur transmission, having been reported from points in every state
in the country, Canada, ^lexico, Honolulu, and by ships on both the
Atlantic and Pacific oceans.

This transmitter was built for four 50-watt tubes and one 5-watt
speech amplifier. For C.W. all power tubes are connected as oscillators
for phone, two as modulators and two as oscillators, with a 5-watt speech
amplifier. The circuit has a common plate-antenna coil and a separate
grid coil, which coil is variable in coupling to the plate antenna coil, and
is adjustable in inductance. By making the grid coil adjustable in coup-
ling and inductance, variable condensers can be eliminated and the set
that much simplified. The Heising method of modulation is used. The
set is designed so that almost any wave from 200 to 400 meters can be
instantly used and the results seem to be equally efficient on all waves.
The only disadvantage experienced with a C.W. transmitter is the trouble
in raising the station desired, unless that station happens to be right on
the wave being used. With the set at 5ZA, however, which can be
instantly tuned to any wave, it is only necessary to estimate the wave
the station wanted is listening on, change the set to that wave and call.
After the station has answered, the wave length can be changed to the
usual working wave.

To date only two 50-watt tubes have been used. With both power
tubes as oscillators, the antenna current is 4-}^ amperes on 200 meters
and 5 amperes on 375 meters, using 1,000 volts D.C. on the plates, the
space current being 225 milliamperes. When using the phone, with one
power tube as a modulator and one as an oscillator, the antenna current
is 3y2 amperes without speech and 4 amperes when the microphone is
spoken into. The plate current is 150 milliamperes without speech and
goes to 250 milliamperes with speech. All reports indicate that the
modulation is fairly complete .and the speech clear.

C.W. Tranamisaion 105

The set is mounted as a unit on an aluminum frame, with a front
panel of bakeHte, 18 x 24 inches. Everything is mounted on the frame-
work except the motor-generators, key and microphone. The unit is
rigid and easily moved about.

Referring to the back view of the set, the inductance is plainly seen
at the top. The large coil is on a tube 5j^ inches in diameter. It is
threaded five turns to the inch and 40 turns of No. 8 hard drawn bare

Front view of the transmitter Itear view of the transmitter

copper wire are wound on the tube. For connections, lengths of the
same wire J/j inch long are soldered to every other turn. Two such
rows of contacts are soldered on, one for the antenna connection and
one for the plate connection. Plugs are made out of brass rod, bored
to fit the short lengths of wire contacts and handles of bakelite or hard
rubber fitted so that the adjustments can be made while power is on.
The grid coil is on a four-inch tube and has fifty turns of No. 14 silk-
covered copper wire tapped every ten turns and the laps brought to a
switch fitted to the end of the tube. The switch shaft is made very long
so as to project from the side of the set. thus allowing the same handle

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C.W. Transmiasion 107

to adjust the coupling and also the inductance of the grid coil, making
it unnecessary to reach inside the set to adjust the grid coil inductance.
The grid coil slides on two brass rods attached to the big coil. The
rheostat under the inductance is in the primary of the filament trans-
former. The filament transformer, which is under the rheostat, is
homemade, with sufficient capacity to light four 50-watt tubes and also
the amplifier tube. The socket assembly is also homemade and has places
for four power tubes on a single bakelite base, with inter-grid chokes
and protective gaps built in. Details as to the rest of the apparatus can
be obtained from the diagram.

When first placed in operation, trouble was experienced with flick-
ering of the filament voltage due to the voltage drop on the power line
when the generators took power. Unfortunately the power line was not
of sufficient capacity for the work and thus caused the flicker. That
made the note very bad, giving it a squealing effect. The hook-up shows
how this trouble was cured. A relay was connected in the negative lead
of the 1,000-volt D.C. line and arranged so that every time the relay
closes, a small resistance in the primary of the filament transformer is
cut out, thus allowing the filament voltage to rise every time the key is
closed and juice flows from the high voltage generator. By making the
resistance variable, any drop can be taken care of in that manner, a
heavy drop requiring a greater resistance, of course, than a slight drop.
By proper adjustment, however, an absolutely steady filament voltage
can be obtained.

Another arrangement used, which is unique, but very satisfactory,
is the method of connecting the chopper. It is placed in the ground lead
and a small inductance shunted around the chopper. The chopper then
alters the wave by a few meters so many times per revolution and any
note can be obtained. This method of chopper modulation has proven
quite effective and has good carrying qualities.

The power for the set is furnished by two generator sets, each giving
500 volts and 400 milliamperes. Allowing 100 milHamperes per tube, it
is seen that the power unit is just large enough to feed four 50-watt
tubes for C.W.

1 08 Modem Radio Operation

Although using only two 50-watt tubes to date, the results have been
remarkable, both with speech and C.W. The speech amplifier, however,
has just recently been installed and the results reported on the voice
operations were made during a few short periods of operation. The
following stations have been worked by voice and no trouble experienced,
the stations reporting signals as of good audibility and modulation O. K.

Miles Miles

9BHE, Glen EUyn, 111 1,000 9TI, MUbank, S. D 900

6AWP, Santa Anna, Calif 700 9PI, Eureka, S. D 900

6ZG, Los Angeles, Calif 750 9AVZ, Pierre, S. D 850

9ZJ, Indianapolis, Ind 1,050 9AEQ, Shenandoah Iowa..™ 700

mA7TT T711 Ji M n Q7c: 9AAS, Owensboro, Ky 975

9WU, Ellendale, N. D 875 ggL, MiUon, Iowa 750

9AAS, Owensboro, Ky 975 9AAY, Chicago, 111 1,050

9AIG, Sioux Falls* S. D 800 9ZG, Mt. Carroll, 111 1,000

In the case of the above stations two-way communication was carried
on and in most cases 5ZA was the station called.

Using straight C.W. two-way communication has been carried on
with the following stations: 2ZL, XFl, NMW, 8VY, 8XF, 4FT, 8ZG,
8ZZ, 8XV, 8XH, and others closer. The foregoing are all over 1,000 miles
distant from 5ZA. The voice has been reported as follows — a few
maximum distances only being given :

Miles

S tenen, Saskatchewan, Canada 1 ,400

8YR, Miami University, Oxford, Ohio 1,150

8BYN, Detroit, Mich 1,275

The voice of 5ZA has been heard in 25 States, Canada and Mexico.
The C.W. has been heard in all States, Canada, Mexico, Hawaii and
on both oceans.

Station 5ZA and the experimental station of the Navy Department,
at Washington, D. C, NOF, have also carried on a two-way communi-
cation by voice. The reception at 5ZA was perfect and the same seemed
to be the case at NOF, as no difficulty was experienced in understanding
the speech from 5ZA. The distance between the two points is approxi-

C.W. Transmiuion 109

mately 1,600 miles and the two-way voice communication sstablished a
record for amateur power and wave lengths such as were used by both
stations. '

Amateur Station 6XAD, Avalon, Catalina Island, Calif,

Probably the most remarkable distance work ever done by any

amateur station of equal power using four 5-watt tubes is the station

6XAD, Avalon, Catahna Island, Calif., owned and operated by Lawrence

■ Mott, Major, Signal Division O. R. C, U. S. Army, and President of

the Continuous Wave Association of America.

The antenna syatera ot 6XAD

The consistent long-distance work done by Mr. Mott has attracted
the attention of the regular army and quite recently the Chief Signal
Officer of the Army, Major Genera! George O. Squier, had several of
the Signal Corps engineers make a comprehensive study of the station,
including its equipment, geographical surroundings and accomplishments,
in order to determine, if possible, the reason for the unparalleled results
obtained.

The antenna itself, of flat top design, is supported on two masts,
one sixty feet and one ninety-four feet high. There are seven wires in the

C.W. Transmission

111

antenna, standard Navy wire of seven strands, supported on an eight-foot
spreader at the low end and on a sixteen-foot spreader at the high end,
thus giving double spacing at the free end. Two-inch copper ribbons run
along the spreaders, and each antenna wire is soldered to these strips,
thus minimizing losses as much as possible.

The counterpoise ground of the station is of the same material and
size as the antenna itself, and is stretched tightly nine feet above and
parallel to the ground. The counterpoise is, of course, well insulated.

^-i-i

j/c y. - Ac.

Pig. 30. Circuit diagram of the 20-watt half-wave rectification tube transmitter at

6XAD Station, Avalon, Calif.

In addition to the counterpoise, an earthed ground is used, consisting
of 240 metal plates, each three by four feet, buried three feet under-
ground. These plates are connected together by one-inch copper ribbons,
leading in turn to a twelve by twelve-foot copper sheet buried five feet in
the ground, directly under the operating table. In addition to these copper
sheets, there are copper ribbons radiating out thirty degrees from the
antenna. In order to insure a good earth ground connection the year
round, metal stand-pipes have been put in and into these salt water is
pumped every few days, thus insuring a moist condition of the ground
over the whole area of the station. These metal standpipes are three
inches in diameter and lead down to the buried metal sheeting at regular
distances.

1 12 Modern Radio Operation

The station is equipped with the following transmitting and receiving
apparatus.

The transmitter employing four 5-watt tubes, Radiotrons UV-202,
is used principally for I.C.W. on 220 meters. The average antenna
current is 2.6 amperes. It is with this set that practically all the unusual
distance work of the station has been done.

icb the tucep Clonal

Another transmitter employs two 50-watt tubes for C.W. on 370
meters. The average antenna current is 4 amperes.

Another transmitter employs two 50-watt tubes for I.C.W., on 240
meters. Considerable experimental work has been done with this station
in connection with some forthcoming tests which are to be made with
Australia.

Receiving equipment: Grebe CR-5, which has been used in all the
unusual long-distance work of the station; a specially designed two-step
Western Electric amplifier ; a Kennedy long-wave receiver used in con-
junction with a Grebe two-step audio- freuency amplifier.

A specially designed motor-generator set, capable of delivering up
to 1,500 volts D.C. with llO-volt 60-cycIc drive, is used to supply plate
potentials for the various transmitting sets.

C.W. Transmission

113

The stations which have been worked by 6XAD are as follows:

3ALN, Washington, D. C.
3AQR, Hershey, Pa.
5HK, Oklahoma City, Okla.
5ZA, Roswell, N. M.
GAWP, San Francisco, Calif.
6JX, San Francisco, Cahf.
6ZZ, Douglas, Arizona
7LY, Bozeman, Montana.
7YJ, Corvallis, Oregon
7ZU, Polytechnic, Montana.
8AWP, Syracuse, N. Y.
8AXK, Cincinnati, Ohio
8JL, Cleveland, Ohio
8ZAC, Barnesville, Ohio
8BRL, Crafton, Pa.
8LX, Crafton, Pa.

9DVA, Denver, Colo.

9AIF, Sioux Falls, S. D.

9AIG, Sioux Falls, S. D.

9ZN, Chicago, 111.

9AJA, Chicago, 111.

9AMB, Denver, Colo.

9NX, Wichita, Kansas

9ZAF, Denver, Colo.

9WD, Chicago, 111.

9DTM, Topeka, Kans.

9AQR, Kansas City, Mo.

9X1, Univ. of Minnesota, Minn.

9XM, Univ. of Wisconsin, Madi-
son, Wise.

9XAQ, Univ. of Colorado, Boul-
der, Colo.

In the case of several stations in the Third and Eighth Districts
these stations either worked or heard 6XAD after daylight had been
in the east for approximately an hour.

The number of stations which have reported the signals of 6XAI)
is so great that it was not possible to include a detailed Hst of them.
Included among them, however, were stations in Vermont, Massachu
setts. New York, New Jersey, Pennsylvania, Virginia, District of Co
lumbia, Georgia, Oklahoma, New Mexico, California, Arizona, Montana.
Washington, West Virginia, Ohio, Kansas, Missouri, Nebraska, North
Dakota, Colorado, South Dakota, Wisconsin, Illinois, Minnesota, Ontario
and Saskatchewan, Canada.

Unusual Long Distance Work by Amateur Stations

That all types of C.W. transmitters are efficient seems to have been
established recently when three-cornered communication between ama
teur stations 2ZL, 5ZA and 8ZG was maintained; this communication
breaking all distance records for two-way work by amateur radio sta
tions. Each station taking part in this work used a different type of
tube transmitter.

1 1 4 Modern Radio Operation

Stations 2ZL and 8ZG, at Salem, Ohio, had exchanged traffic and
it was noted that conditions for long distance work were good. About
11.30 P. M. 8ZG heard signals from 5Zx\, and called, and 5ZA answered.
Traffic was then exchanged between 5ZA and 8ZG, an air-line distance
of 1,400 miles, and among the traffic sent from 5ZA was a note to 2ZL,
saying that 5ZA was hearing 2ZL well. All the traffic sent to 8ZG had
been heard at 2ZL including the note. As soon as 8ZG had finished with
5ZA, the former station called 2ZL and passed along the note. 2ZL
immediately called 5ZA and the latter answered, reporting the signals
of 2ZL as of good audibility there. Once communication had been
established, several messages were exchanged without difficulty. The
airline distance between the two points is 1,800 miles.

All the stations concerned in this exceptional work used tube trans-
mitters, but as stated before, of different types. At 8ZG, the station of
A. J. Manning, a 100-watt Kenotron set is used employing two Keno-
trons UV217 and two UV203 Radiotrons. The set used by Louis
Falconi, at Roswell, is of 100-watt output capacity, employing two Radio-
trons UV-203, with D.C. plate voltage supply. The set at 2ZL employs
two Radiotrons UV-204, in a full-wave rectification circuit, A.C. being
used on both filaments and plates.

Reports have been received that the signals of 2ZL were clearly
heard at Tuscon, Ariz., Station 6AMT, Nogales, Ariz., WJK, Taft, Calif.,
and 6GZ, Los Angeles, Calif., during the time 2ZL and 5ZA were in
communication, a maximum overland airline distance of 2,500 miles.

A 5-Watt Vacuum Tube Transmitter Employing
AN Electrolytic Rectifier*

A 5-watt vacuum tube transmitter, employing an electrolytic recti-
fier for the A.C. supply for use on the plate, is shown in detail in the
following circuit diagram.

This set has given satisfactory results, both with voice and C.W.
The voice range is 25 miles, but it has been reported at '^Z miles. The
C.W. range is in the neighborhood of 150 to 200 miles.

•Geo. L. Gates, in The Wireless Age.

C. W. Transmission 115

If the constructor has no apparatus at all the set would cost about
thirty dollars to duplicate, but as the average amateur no doubt has
some old apparatus he can easily build one considerably cheaper. The
expense is itemized below:

Transformer core $ .30

1 lb. No. 22 enameled wire 75

2 lbs. No. 28 enameled wire 1.50

x^eavi s vi iLis ^.....^..^^.^a.^*.*— • x\f

20 Mule Borax. ^ 12

Aluminum strips .25

5-watt Radiotron — 8.00

Socket 1.00

Grid Leak ^ - 10

Grid condenser ~ 10

Choke coil 50

Variable condenser 4.25

Inductance 25

H. W. A 7.00

Buzzer 2.00

Microphone 2.50

Modulation transformer 50

$29.22

The transformer is, probably, the hardest part of the set to build,
but if properly constructed it will give much better results than a motor
generator or B Batteries, besides being lower in cost of construction and
upkeep. The core is made of stovepipe iron which is cut in the shape
of an L. The size of the core when completed is 7 x 5 x % inches.
About 150 pieces of stovepipe iron 7x5 will be needed. Almost any
hardware concern carries the iron and will cut it to your specifications.
The primary and secondary can easily be wound on a lathe made from
a breast drill. The primary has 425 turns of No. 22 enameled wire. The
secondary has 2,550 turns of No. 28 enameled wire. No center tap is

116

Modern Radio Operation

taken. The filament winding has 40 turns of No. 22 enameled wire.
The filament winding is tapped at the twentieth turn. It is important
to separate each layer of wire with a layer of paper. The primary and
filament are wound on the same leg while the secondary is wound on
the opposite leg.

The rectifier is of the aluminum-lead type which gives very good
results. The rectifier consists of eight Mason pint jars, eight lead strips
5 X ^ inches and eight aluminum strips 5 x ^ inches. The solution is

Fig. 31. Five-watt transmitter with electrolytic rectifier

made up of a half pound of 20 Mule Team Borax dissolved in ten
pints of water. In filling the jars with the solution care should be taken
that none of the sediment remains in the jars. The jars should be filled
about three-quarters full. The diagram shows the order in which the
plates are connected together.

Although there is, locally, a noticeable hum if no filter system is
used, the modulation is not distorted. This hum can only be heard a
short distance from the transmitting station. The hum may be reduced
considerably if a Ford coil secondary is used as a choke coil.

The modulation transformers put out by the various manufacturers
are very good, but a Ford coil will give good modulation and is consid-
erably cheaper. The vibrator should be tightened up so as to insure
good contact. The fixed condenser shunted across the secondary should

C.W. Transmission 1 1 7

be of about .001 mfd. capacity. The grid leak is a Venus pencil No. 2B,
which may be connected from the grid to the filament to afford a sHght
increase in radiation, though the modulation is somewhat distorted.

The primary of the inductance is wound with No. 18 bell wire on a
31/^-inch cardboard tube. The coil has 26 turns and is tapped at thr
thirteenth turn for the filament lead. The secondary has 8 turns of the
same size wire without taps. The windings should be separated about
a half inch.

Any standard radiation ammeter with low reading scale may be
used. If the constructor wishes he may substitute a 3-volt flashlight
bulb for the ammeter with fair results. Of course, the flashlight bulb
will not tell when the maximum radiation is obtained, but the set will
give good results if tuned only with the flashlight bulb.

A few words concerning the operation will no doubt be useful. The
plates of the aluminum-lead rectifier must be formed before the rectifier
will work. A simple way to form the plates is to connect in a 50-watt
incandescent bulb and let the 110-volt 60-cycle current run about ten
hours. The plates will form faster if a larger bulb is used, though the
slower the plates are formed the better the results.

In applying the high and low voltages to the transmitting tube the
filament should always be lighted before the high voltage is turned on.
The high voltage should never be left on the plate of the power tube
unless the filament is lighted as the high voltage will tend to break down
the construction and insulation inside the tube.

In order to make the set operate the key in the grid circuit must be
closed when voice modulation is desired. The set is tuned by turning
the variable condenser until the flashlight or ammeter shows the greatest
reading. The beauty of this circuit is that it requires no skill to tune
the set and is therefore easily kept in operation. The microphone should
always be disconnected from the battery when not in use as the carbon
granules will become packed and the modulation will become distorted
or entirely eliminated.

CHAPTER X

Tube Transmitters in Commercial Work

Duplex Ship and Shore Radiotelephony
For the first time in the history of maritime radio, docking instruc-

■

tions were given verbally to the captain of a big trans-Atlantic liner by
the manager of the line, seated in his office in New York, while the
ship was 360 miles at sea. This pioneer work in radio communication
was accomplished by utilizing one of the latest developments of radio
engineering, duplex radio-telephony, in conjunction with the usual land-
line telephone.

While the America of the United States Lines was 360 miles east
of New York, Thomas H. Rossbottom, general manager of the steamship
company, picked up the ordinary telephone on his desk and asked central
to connect him with the S. S. America, at sea. His line was connected
through to the Deal Beach, N, J., station, and thence by radio to the ship.

Within ten minutes after the call was made Captain William Rind,
of the America, was on the telephone. After an exchange of greetings,
Captain Rind told Mr. Rossbottom the speed he was making, and the
time he expected to reach Quarantine. Mr. Rossbottom in reply gave his
instructions to Captain Rind concerning the special arrangement which
had been made with the public health officials at the Quarantine Station
for the passing of the vessel after the sunset hour.

Mr. Rossbottom and Captain Rind conversed for several minutes.
Mr. Rosbottom used the telephone at his desk, the one that is normally
used in his daily business, and without any special appliances.

Commercial C.W. Sets 1 19

Tiie interesting feature of a shipboard duplex installation is the fact
that the antenna is being used to radiate several hundred watts of power
while at the same time the radio receiver detects and makes audible the
extremely small amount of energy that is being picked up from the distant
transmitting station. Much research has been done to allow this simul-

taneous transmission and reception to be carried on and a ship equipped
with apparatus of this nature may communicate with any subscriber on
land who has an ordinary telephone in his home.

Radio telephony, heretofore limited to a simple operation — reception
or transmission — has been revolutionized as a result of these tests. Up
to this time the radio telephone has been handicapped by conditions
similar to those of the ordinary apartment house speaking tube. It has
been necessary for the operator to throw a switch when he desired to
talk after listening, or vice versa. This prevented a landline telephone
from being linked up with the radio telephone system, as it is not practical
to provide a control or "send-receive" switch at each land phone.

With the advent of the duplex wireless equipment, however, a con-
versation may be carried on through the ether as simply and as naturally
as between land telephones.

1 20 Modern Radio Operation

The equipment installed on the America consists of three maim
units — the Kenotron or power panel, the vacuum tube transmitter and
the radio receiver. Power is supplied to the Kenotron panel in the form
of low-frequency, low voltage alternating current and after being trans-
formed into a high voltage is rectified by Kenotron tubes into direct

Ziuplex radio telephone equipment on the S. S. ^nutira

current at a very high voltage. This high voltage is fed into the Radio-
tron powjr tjbes, where it is transformed into radio- frequency energy.
Other Radiotron tubes are used to control, or modulate, the high-
frequency current.

This duplex radio-telephone service will be made available for
general use by the public just as soon as the demand for it warrants-
the installation of proper apparatus afloat and ashore.

Commercial C. W. Sets 1 2 1

Recent developments and improvements which have been made in
both the transmitting and receiving apparatus of radio telephony are
of a nature which will insure the secrecy of all voice communications,
and equipment of this type will undoubtedly be used when this new serv-
ice is made available to the public. An eavesdropper, in endeavoring to
^*listen-in" on a secret communication of this kind hears only a buzz —
somewhat resembling the sound made at an ordinary receiver by a nearby
arc light, or a leaky power line. Not a single word is intelligible except to
those for whom the conversation is intended, through the agency of spe-
cial receiving equipment.

Tube Transmitters in Ship-to-Shore Work

Several tube transmitters of medium power have recently been put
into service by the Radio Corporation of America for ship and shore
work. One is installed at Marion, Mass., and operated from Chatham,
Mass., on Cape Cod, call letters WCC, wave-length 300, 425, 600 and
2,200 meters, and the other at Bush Terminal, Brooklyn, N. Y., call
letters WNY, wave-length 300, 425, 600 and 1,80C. These tube transmit-
ting sets are of three-kilowatt capacity, employing three 1 K.W. tubes as
oscillators and two high-capacity Kenotrons for rectifying the 12,500
volts A.C. supply. The normal range of the Cape Cod station is 1,800
miles daylight. This station is used for ship and shore message work,
broadcasting traffic on regular schedules and also transmits press on reg-
ular schedule on a wave-length in the neighborhood of 2,200 meters in
connection with the "Ocean Wireless News," the daily newspaper of the
sea.

These new stations of the Radio Corporation are connected by direct
wires to the main traffic office at 64 Broad Street, New York, from
which point the trans-oceanic stations of the Radio Corporation are also
controlled.

These new tube sets, the first to be used in ship-to-shore work, are
built upon an iron framework seven feet high, 32 inches wide and 36
inches deep. Three panels of dilecto provide mountings for. the neces-
sary control switches and indicating instruments. Three Radiotron tubes

122 Modem Radio Operation

UV205 are used in the set, in vertical position, each tube being of 1,000
watts output capacity.

Tbe sets have been designed to work on a line carrying 220 volts,
60 cycles, single phase, this voltage being stepped up to 12,500 volts.

A self- rectifying circuit, which has recently been developed by the
engineers of the Radio Corporation, has also been employed in the
operation of these sets, the tubes acting as oscillators and rectifiers at the
same time. In this circuit a transformer with a secondary voltage of
25,000 was used, the secondary being provided with a middle, or neutral
tap, resulting in full-ivave rectification, each tube working alternately
on the two halves of the cycl'..

Commercial C.W. Sets 123

A 2-K.W. Kenotron Tube Set for Panama

A 2-K.W. tube transmitter built recently by the General Electric
Company for the Radio Corporation of America is now installed and
in operation at Almirante, Panama.

The set consists of equipment for supplying direct current at 12,500
volts for the plate supply of the Radiotron tubes, and for converting
this power into radio frequency. Power is supplied to the transmitter
at 440 volts, single phase, 60 cycles, and stepped up to high voltage by
means of a transformer, the output of which is fed into the rectifying
system.

The rectifying system consists of two 2 K.W. Kenotron tubes
which supply 12,500 volts D.C. to the plate circuits of the Radiotron
generators. The ripple in the output of the rectifying system is smoothed
out by means of a suitable filter system. The radio frequency power is
generated by a system consisting of two 1 K.W. Radiotrons with the
necessary grid and plate coils, together with an antenna loading coil.
Provision is made for controlling the power by a power change switch
which alters the voltage on the primary of the plate transformer. The
filaments of all tubes, Kenotrons and Radiotrons are operated on A.C.
through transformers, which step the supply voltage down to the oper-
ating voltages of the filaments.

The set is equipped with a wave-changing switch which, by a single
operation, changes the transmitted wave to any one of three lengths —
600, 1,000 and 3,000 meters. The switch automatically selects prede-
termined points on the loading, plate and grid coils. Provision is also
made for transmitting on interrupted continuous (I.G.W.) as well as on
continuous waves (C.W.) This is accomplished by means of a motor-
driven interrupter in the grid circuit of the Radiotron tubes, which starts
and stops oscillations in the antenna at audio frequency, approximately
1,000 interruptions per second.

The rating of the transmitter is based on the power input of the
antenna circuit, instead of on the output of the power equipment as is
usual with spark transmitters. The rating of the tube transmitter is

r
If

Commercial C.W. Sets 125

the product of the antenna resistance times the antenna current squared,
equalling two kilowatts. While it cannot be predicted exactly what the
range of this set will be, it is expected that it will equal, if not exceed,
the range of a 50 K.W. spark transmitter. As an example of its initial
effectiveness, the set, as installed in Panama, is now carrying on reliable
and satisfactory communication with New Orleans, La., twenty-four
hours a day.

Front and rear view ol the 1 K.W, iilalo tranamltter. SM-Watt transmitter side view

Two New Types of Tube Transmitters for Commercial Work

Two new types of tube tiansniitters, one of 1,000 watts and the
other of 200 watts output capacity, manufactured for the Radio Corpora-
tion of America by the General Electric Company, are being installed on
many vessels on both coasts and also on the Great Lakes. These new
types of transmitters embrace all the latest developments in equipment
of this kind. Both types of sets can be used for telegraphy by means
of C.W. or LC.W., and also for voice communication.

126 Modern Radio Operation

The 200-watt model employs a number of Radiotrons, UV203, as
oscillators and moditlatDrs, and has control switches for voice, C.W. or
I.C.W. When using C.W. or I.C.W. all tubes are used, of course, as

oscillators. This new type of transmitter is rated at 200 watts when
used for telegraphy or at 100 watts when used for voice communication.
This rating is based on the power output of the antenna.

The larger model, employing four Radiotrons, UV204, gives 1
K.W. output to the antenna when used for telegraphy, and 500 watts of
modulated energy when used for voice communication.

Commercial C.W. SeU 127

Both models are equipped with motor-driven choppers for I. C.W.
and with wave length changing switches for the following wave lengths :
300, 450, 600, 750, 800, 1,000 and 2,000 meters. Both of these sets are
equipped with remote control apparatus.

Front and rear views o( an English type ^ K.W. tube tranamliter
The normal daylight range of the 200-watt model for voice is 50
to 75 miles ; for I.C.W. 75 to 100 miles ; and for C.W. 300 to 400 miles.
The normal daylight range* o'f the 1,000-watt model for voice is 150 to

1 28 Modem Radio Operation

200 miles ; for I.C.W., 200 to 300 miles ; and for C.W., 800 to 1,200
miles. These figures are based upon tests made overland; the receiver
consisting of a detector and two-stage audio-frequency amplifier.

High-Power Tube Transmitters

The power and consequent range of commercial tube transmitters
are being steadily increased. Tubes of 1 K.W. output are now on the
market as regular equipment. Tubes of 5 K.W. output capacity are
being r^ularly used in broadcasting by the General Electric Company.
Still larger tubes, of 20 K.W. output capacity, employing an extremely
high voltage on the plate, are now being manufactured for commercial
use and it is more than likely that they will be used regularly in the
trans-Atlantic work of the future. There is now in service at the Car-
narvon, Wales, Marconi station, a battery of 48 high-power tubes, the
output of which is equal to a 200 K.W. alternator — approximately 4
K.W. each. This station communicates regularly with Australia.

CHAPTER XI

Advantages of a Counterpoise Ground in Connection

With Tube Transmitters

In the case of land stations, there are three types of earth for a
rjround, — excellent, medium and poor. The first designation covers soil
of marshy nature, especially contiguous to bodies of salt water and which
is, as a result, itself salty in nature, oifering an excellent earth. Moist
ground of other type also falls partly within this classification, and
where a radio station is built upon earth of this type the usual arrange-
ment of buried plates, pipes and wires will answer satisfactorily and the
resistance of a well-constructed ground system in earth of that kind
will be sufficiently low as not to warrant the construction of a counter-
poise ground system. In fact, it has developed in several instances that
when a counterpoise ground system is built directly over moist ground,
considerable leakage of energy to the earth takes place resulting in less
efficiency of the transmitter than if the regular earth ground were
used. Where the earth is of such a nature as to be a good conducting
medium the regular system of plates, pipes, wire and wire mesh, buried
far enough so as to be in continually moist earth, should be used.

In the case of the second and third classifications, it will undoubt-
edly be advisable to build a counterpoise ground, consisting of approx-
imately double the amount of wire of the antenna itself. The counter-
poise can be suspended on spreaders high enough oflF the ground to
clear an automobile, or a person walking and should be suspended under

1 30 Modern Radio Operation

the antenna and also beyond it at both ends. The ends, outside of the
antenna, should be fanned out. Where an earth ground of the second or
third classification has been used, change to a good counterpoise system
will undoubtedly resuh in doubling the antenna current, an increase of
four times the amount of energy flowing in the antenna system. As
actual radiation is proportional to the amount of energy flowing in the
antenna circuit, the great increase in energy in the antenna system so
obtained will naturally result in the actual radiation of a greater amount
of energy which, after all, is the ultimate object for which a transmitter
is used.

Counterpoise ground

The resistance of the average amateur antenna ground circuit, when
an earth ground is used, is likely to be anywhere between 20 and 50
ohms. The use of a counterpoise will frequently reduce this resistance
to 7 or 8 ohms, or even less, according to the size and shape of the coun-
terpoise and also depending upon its immediate surroundings. Trees,
large metal objects or telephone wires, if in the field of the antenna or
ground, will frequently keep the resistance at an abnormal value. It is,
therefore, highly desirable, that both antenna and counterpoise ground
are kept clear of and away from all structures or wires not necessary
for the support of the antenna system.

CHAPTER XII

General Information for the Amateur

There are at the present time approximately 25,000 amateur radio
transmitting statiojis in the United States, and probably eight receiving
stations to every transmitting station, making a total of 200,000 amateur
stations. The large majority of these stations use only a small amount
of power for transmitting ; consequently, their range is small. There are
organizations of amateurs which include primarily those who are inter-
ested in the relaying of messages from one station to another, and during
the cooler months of the year, when the air is clear of static, it is fre-
quently possible to relay messages through such stations clear across the
country within a few hours. As a general rule such messages are relayed
over fairly well established lines of communication, including the most
efficient stations operated by the best amateur operators of the country.
The National Amateur Wireless Association, which includes in its mem-
bership most of the leading amateurs of the country is one of the organ-
izations which maintains a national traffic organization and relays mes-
sages to all points of the country without charge. The stations which are
a part of this relay system of the National Amateur Wireless Association
include many of the leading amateur stations which employ tube trans-
mitters, and, because they use C. W. transmitters, exceptional results are
obtained, the range of these tube stations frequently exceeding 1,000 miles.
During the warm months of the year, when there is considerable disturb-
ance from atmospheric electricity due to thunderstorms, repeated tests
have proved that tube transmitters can work successfully through
heavy static caused by thunder showers, while spark stations of the same
power could not be heard.

One of the problems of amateur activities is that of interference
between stations. This is largely the result of the use of spark trans-
mitters which radiate their energy over a wide band of wave lengths. In
the case of continuous wave transmission the energy is radiated on sub-
stantially one wave length, thereby eliminating to a great degree the ob-
jectionable interference caused by spark stations. The character of trans-
mitted energy is such that the effect at the distant receiver is much greater,
power for power, than a spark set, principally for the reason that the
undamped wave transmitter permits the use of highly refined and efficient
methods of reception.

CHAPTER XIII

Radio Laws and Regulations of the United States

The owner of an amateur radio transmitting station must obtain a
station license before it can be operated if the signals radiated therefrom
can be heard in another State ; and also if such a station is of sufficient
power as to cause interference with neighboring licensed stations in the
receipt of signals from transmitting stations outside the State. These
regulations cover the operation of radio-telephone stations as well as
radio-telegraph stations.

Station licenses can be issued only to citizens of the United States,
its territories and dependencies.

Transmitting stations must be operated under the supervision of a
oerson holding an Operator's License and the party in whose name the
station is licensed is responsible for its activities.

The Government licenses granted for amateur stations are divided
into three classes as follows :

Special Amateur Stations known as the "Z" class of stations are
usually permitted to transmit on wave lengths up to approximately 375
meters.

General Amateur Stations which are permitted to use a power in-
put of 1 kilowatt and which cannot use a wave length in excess of 200
meters.

Restricted Amateur Stations are those located within five nautical
miles of Naval radio stations, and are restricted to J4 kilowatt input.
These stations also cannot transmit on wave lengths in excess of 200
meters.

Experimental stations, known as the "X" class, and school and uni-
versity radio stations, known as the "Y" class, are usually allowed
greater power and also allowed the use of longer wave lengths at the
discretion of the Department of Commerce,

All stations are required to use the minimum amount of power nec-
essary to carry on successful communication. This means that while an
amateur station is permitted to use, when the circumstances require, an

Radio Laws and Regulations I 33

input of 1 kilowatt, this input should be reduced or other means provided
for lowering the antenna energy when communicating with near-by sta-
tions in which case full power is not required.

Malicious or wilful interference on the part of any radio station, or
the transmission of any false or fraudulent distress signal or call is pro-
hibited. Severe penalties are provided for violation of these provisions.

Special amateur stations may be licensed at the discretion of the
Secretary of Commerce to use a longer wave length and higher power than
general amateur stations. Applicants for special amateur station licenses
must have had two years' experience in actual radio communication. A
special license will then be granted by the Secretary of Commerce only
if some substantial benefit to the science of radio communication or to
commerce seems probable. Special amateur station licenses are not is-
sued where individual amusement is the chief reason for which the ap-
plication is made. Special amateur stations located on or near the sea
coast must be operated by a person holding a commercial license. Ama-
teur station licenses are issued to clubs if they are incorporated, or if any
member holding an amateur operator's license will accept the responsi-
bility for the operation of the apparatus.

Applications for operator's and station licenses of all classes should
be addressed to the Radio Inspector of the district in which the applicant
or station is located. Radio Inspectors' offices are located at the follow-
ing places :

First District Boston, Mass.

Second District New York City

Third District Baltimore, Md.

Fourth District Savannah, Ga.

Fifth District New Orleans, La.

Sixth District San Francisco, Cal.

Seventh District Seattle, Wash.

Eighth District Detroit, Mich.

Ninth District Chicago, 111.

No license is required for the operation of a receiving station, but
all persons are required by law to maintain secrecy in regard to any mes-
sages which may be overheard.

APPENDIX I.

Detailed Values of the Component Parts of the
Armstrong Super-Regenerative Receiver

The Super-Regenerative Circuit recently developed by E. H. Arm-
strong, will give results which far surpass those obtained with any other
circuit using the same number of tubes. It is especially adapted to the
reception of radio telephony and is undoubtedly the universal broadcast
receiving set of the future.

It is unnecessary here to go into the action of an ordinary regenera-
tive receiver as this is now clearly understood by practically .everybody.
It is, of course, well known that a signal, or speech, can be increased
by regeneration up to a certain point, where the tube breaks into oscilla-
tion. In the super-regenerative circuit the benefit of the limit of regenera-
tion is secured by the use of an additional oscillator tube, which alternately
stops and starts the oscillations of the detector tube, so that regeneration
can be carried to the limit.

The action of the super-regenerative circuit consists in varying the
negative resistance of the circuit, with respect to the positive, or vice
versa, so that the negative resistance is alternately greater and less than
the positive, but with the average resistance positive. Such a circuit will
not of itself produce oscillations and during the periods when the negative
resistance is the greater the current in the circuit will reach exceedingly
high values. The general operation of the super-regenerative circuit is
practically the same as that of the ordinary regenerative circuit.

A detailed diagram, with definite values of all parts of a three-tube
super-regenerative circuit, using one tube as an audio-frequency amplifier,
will be found on the following pages.

1. This condenser is a 43 plate variable condenser of .001 M, F.
capacity. A smaller or larger condenser will be equally satisfactory, the
only change being in the wavelength range covered.

2. This is the loop coupling coil. By referring to the drawing it
will be observed that this coil is wound in three sections. In the actual
set 30 turns of No. 20-38 Litz was used, but No. 22 d.c.c. may be used
with practically the same results.

3. This coil is the grid tuning coil, 25 turns of 20-38 Litz were
used. Here again No. 22 d.c.c. may be used with good results.

4. This is the plate, or tickler coil. It consists of a rotor of a vari-
ometer. The fixed winding of the variometer is removed from the frame
and the outside part merely forms a support for two tubes. These tubes,,
which may be of laminated wood, bakelite or cardboard, are fastened to
the variometer housing with small pieces of brass suitably bent and
drilled.

5. The value of this condenser need not exceed .005 M. F. With
this capacity as maximum the set will cover a wavelength range of 190-
500 meters.

6. This condenser is a fixed paper condenser, the value may be any-
thing above .01 M. F.

7. This is the negative "C" battery, used to regulate the potential of
the grids of both tubes. The value of the battery voltage must be changed
to suit the particular tubes used, and the "B" battery voltage. Two to
four small flashlight cells are suitable.

8. This is an "A" battery potentiometer, to permit fine regulation of
the value of the grid potentials. If desired this may be eliminated and
the regulation eflfected entirely by the battery No. 7.

9-10-11. Filament rheostats of any type.
12-13-14. Hard vacuum tubes such as UV-201.

15. This is a 1250 turn Duo-Lateral coil, mounted.

16. This is a 1500 turn Duo-Lateral coil, also mounted, with rather
close coupling to coil No. 15. The coils should be so placed that the out-
side of the winding connects to the plate and grid when they are arranged
for oscillation.

17. This is a .003 M. F. fixed mica condenser and with coil No. 16
gives a frequency of the order of 7,000 to 8,000 cycles. This frequency is
sufficiently high to be readily filtered out and at the same time low enough
to give good amplification results.

18. This is a separate "C" battery for regulation of the negative
potential of the oscillator tube. It is not necessary in some cases, though
frequently with certain tubes, both negative "C" batteries must be varied
to obtain proper results. One or two small flashlight cells are suitable.

19-20-21-22-23. These units comprise the filter system. They are
iixed condensers otf .00181 M. F., and the inductances are of 2.28 henries.

24. Primary of audio-frequency transformer.

25. Secondary of audio-frequency transformer.

26. Negative "C" battery for use with audio- frequency transformer
when the plate voltage is above 100 volts. This battery should have a
voltage of 3 to 4^^ volts.

27. Filament control jack, first stage type.

28. Filament control jack, last stage type. Both these jacks may be
dispensed with if it is desired to do so.

29. Six-volt storage battery.

30. 44-88 voh "B" battery.

31. 44-88 volt "B" battery depending on the tubes used and the value
of battery No. 30. In other words both batteries No. 30 and No. 31 must
be varied to give best results.

32. Battery for plate of amplifier tube. This may be as great as
300 volts or more depending on the amount of power required and what
the tube will stand.

The foregoing values should give the reader a fair idea of the method
of constructing and operating the receiver. No rigid iron bound rules
must be followed ; the descriptions are given more with ah idea of guiding
the line of thought, and not to dictate the method to be followed.

For full constructional data and operating instructions for this and
the other super-regenerative circuits, the reader is referred to the new book
by George J. Eltz, "The Armstrong Super-Regenerative Circuit," which
contains specific values for the several types of super-regenerative cir-
cuits, as furnished by E. H. Armstrong. This book can be obtained
through the Wireless Press, Price $1.00.

APPENDIX II.

During the summer of 1922 some very interesting experiments in
transmission on wavelengths considerably below 200 meters have been
carried on by a few stations in the Second, Third and Eighth Radio
Districts. Not much definite information is available at present, but it is
known definitely that communication has been maintained over consider-
able distances during times when very bad conditions, because of static
and interference existed on 200 meters, without any appreciable difficulty
having been experienced on the shorter waves. In fact, it is believed
that these experiments have pretty definitely established that the transmis-
sion curve for a given power takes an upward bend after the 200 meter
point has been passed. Contrary to what has been generally believed, the
greatest difficulty in maintaining communication on 125 and 150 meters
has not been at the transmitting end, but at the receiver, where a special
type of receiver, well shielded, was required. At the transmitting end,
there has been little, or no difficulty in getting a considerable amount of
power into the antennas of the stations participating in this unusual work.

At 2ZL station. Valley Stream, L. I., the transmitting antenna con-
sisted of four vertical wires, in a 5 foot square cage, the total height being
50 feet above ground. A counterpoise was used, consisting of 7 wires, 20
feet long, directly under the cage and about 7 feet above ground. It was
possible to tune the transmitter, consisting of two 250 watt Radiotrons
UV 204, in a full- wave A.C. rectification circuit, to 150 meters, without
the use of a series condenser. The antenna current on this wavelength
was 5 amperes. With the use of a series condenser of a value of .0003,
the wave was reduced to 125 meters, and the antenna current on this
wavelength was 4.2 amperes. By adding still more capacity in series,
the wavelength was reduced to an even 100 meters, with 3 amperes in
the antenna.

Comprehensive experiments, to determine the range, variation in
signal strength and other matters of interest are being carried on.

THE SOUND METHOD FOR
MEMORIZING THE CODE

For success in telegraphing the let-
ters must be learned by the sound.

Each letter has a distinctive cadence
or rhythm which is easily memorized
by a few hours' practice.

The charts attached give the key to
the rhythm of each letter of the tele-
graph alphabets. It forms no picture
in the student's mind, but instead a
sound IS memorized, like a bar of
music.

The chart is particularly valuable in
learning to receive, which is many
times more difficult than learning to
send. An hour a day devoted to memo-
rizing the distinctive rhythm of each
letter will enable the student to send
or receive a message in a few weeks.

The beginner is strongly advised not
to practice with charts or books which
show the actual dots and dashes.
Once a picture of each letter is formed
in memory it will be found difficult to
send or receive in the telegraph alpha-
bet properly — by sound.

WIRELESS PRESS, INC.

Dept. B.

326 Broadway^ New York

Study the Code Anyvi^here

THIS NEW WAY

of Learning the Code

is the easiest, quickest and most thorough ever devised for

learning without instruments
If you want to learn the code —

If you want to "cinch" the signals you can't remember easily —
If you want to help some one else learn the code —

GET ONE OF THESE CARDS
Don't try to teach the Ears through the Eyes

This system teaches the signals as they come through the

Head Phones

Contains both Continental and American Morse —
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$2.75^Postaf(e outside U. S. SOc. extra

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e^irelejj'MMi'j
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Title Author Price

Piractical WirelMs Telegrraphy Elmer B. Bocher 9ZJZ5

Vacuum Tubes in WireloAH Communication Elmer E. Bucher 2J85

Wireless Experimenter's Manual Elmer E. Bucher SJBS

How to Pass U. S. Govt. Wireless liicense Examinations Elmer E. Bucher .76

How to Conduct a Radio Club Elmer E. Bucher .7ft

The Alexanderson Syi»t<>m for Radio Telegraph and Radio Telephone

Transmission Elmer E. Bucher 1.26

Practical Amateur Wireless Stations — Compiled by J. Andrew White, Editor of Wireless

Agre 76

Radio Telephony' Alfred N. Goldsmith, Ph.D. 2.50

Prepared Radio MenHurenients B. R. Batcher

Radio Instruments and Measurements h 1*76

Elementary Principles of Wireless Telegraphy (In two volumes) R. D. Bangray

Volume 1 1.75

Volume 8 1.76

Acqulrlnir the Code E. P. Gordon .60

Sound Method of Licarnlni: the Code J. Andrew White JSO

Practical Aviation (Inciudlnit: construction and operation) Major J. Andrew Vdiite 2.26

Military Signal Corps Manual Major J. Andrew White 2.26

"What Tou Want to Say and How to Say It" By W. J. Heman

In French, or Spanish, or Italian, or German . .k 26

In Russian JSO

Thermionic Tubes in Radio Telegrraphy and Telephony J. Scott Tair^art 8.00

Continuous Wave Wireless Telegraphy i W. H. Ecdes 8.00

Principles of Radio Communication J. H. Morecroft 7.50

Wireless Telegraphy and Telephony li. B. Turner 7.00

Wireless Telej^raphy — With Special Reference to Quenched Gap System Jjeggett 12.00

PMnciples of Radio Bngineeringr Lauer and Brown $3.50

Spanish Edition, Elementary Principles of Wireless Telegraphy

(complete) R. D. Bangay 3.25

Thepmio-nlc Vacuum Tubes Van der Bijl 6.00

Thermionic Valve and Its Development in Radio Telegraphy and

Telephony J. A. Fleming 6.00

The Oscillation Valve, The Elementary Principles of Us Application to

Wireless Telegraphy R. D. Bangay 2.75

Telephony Without Wires Philip R. Coursey 5.00

The Wireless Telegraphists Poclcetbook of Notes, Formulae and

Calculations J. A. Fleming 3 50

Wireless Telegraphy and Telephony, First Principles, Present

Practice and Testing H. M. Dowsett 3.60

Handbook of Technical Instructions for Wireless Telegraphists

J. C. Hawkhead and H. M. Dowsett 2.50

Spanish Edition Handbook of Technical Instructions Hawkhead and Dowsett 3.00

Standard Tables and Equations in Radio Telegraphy Bertram Hoyle 3.25

Wireless Transmission of Photographs Marcus J. Martin 2.00

Calculation and Measurement of Inductance and Capacity W. H. Nottage 1.75

Short Course in Elementary Mathematics and Their Application to

Wireless Telegraphy S. J. Willis 1.75

Selected Studies in Elementary Physics (A Handbook for the Wireless

Student and Amateurs) E. Blake 2.(X)

Magnetism and Electricity for Home Study H. E. Penrose 2.25

Alternating Current Work (An Outline of Students of Wireless

Telegraphy) A. M. Shore 2.00

Pocket Dictionary of Technical Terms Used in Wireless Telegraphy Harold Ward l.(X)

Useful Notes on Wireless Telegraphy (set of five books), (paper) H. E. Penrose 2.00

Book No. 1. — District Current, 67 pages 50

Book No. 2. — Alternating Current, 50 pages 50

Book No. 3. — High Frequency Current and Wave Production, 65 pages 50

Book No. 4.-1% Kw. Ship Set, 76 pages 50

Book No. 5.— Tlie Oscillation Valve, 52 pages 50

My Electrical Workshop Frank T. Addyman 2.50

Experimental Wireless Stations P. E. Edelman 3.00

High Frequent Apparatus, Design, Construction and Practical Application. .T. S. Curtis 3.00

Textbook on Wireless Telegraphy Rupert Stanley

Volume 1. — General Theory and Practice 5.00

Volume 2. — Valves and Valves Apparatus 5.00

How to Make a Transformer for High Pressure F. E. Austin .75

How to Make a Transformer for Low Pressure P. E. Austin .75

The Operation of Wireless Telegraphy Apparatus A. B. Cole .35

Wireless Construction and Installation for Beginners A. P. Morgan .35

Lessons in Wireless Telegraphy A. P. Morgan .35

Experimental Wireless Const ruction A. P. Morgan .35

Home Made Toy Motors A. P. Morgan .35

Hawkins Practical Library of Electricity, 10 volumes Per volume 1.00

Hawkins Electrical Dictionary 2.(X)

Marconi- Victor Records — 6 Records — 12 Lessons — For Learning Code Quickly 6.00

THE WIRELESS PRESS, Inc.

Dept. B

326 BROADWAY NEW YORK

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