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THE HISTOHY AIID DEVELOPMENT OF RADIO STATION W,R,C. U
l>y William A. McCool
AN" INITIATION REqUIREMKNT
THE I,IAHTLAND BETA CHAPTER OP TAU BETA PI ASSOCIATION
THE HISTOHY AND DEVSLQPMEUT OF HADIO STATTOIT W.H.C. I^^ WASHIlTaTOU, D.C.
2. General History.
5. Electrical Tranacrlt^tlona.
7. Control Hoora and Control Qoeratlon.
8. Remote Control.
9. Transmission Links,
Comport /-e o^ Fiaciio Qt/y
In this paper, practicp.lly all the readily obtainable facts con-
cerning the history and developnent of Hadlo Station ff.H.C. are presented
briefly in most part. It is -unfortunate that the facts concerning the history
of the station could be obtained only from a few Individiials, vho have been
employed by the station since its beginning; the author has thorou^ly discus-
sed the subject with them and the results sie given in the following pages. Hb
records of the station's activities have ever been kept, except those purely
business ones, riiich are confidential to tlie station and would prove uninter-
Therefore, the majority of the material presented deals with the
station in its present status. Much emphasis has been placed on the transmit-
ter and control room, including much technical data. T!here are two reasons for
thisj first the author is extremely interested in that phase of broadcasting,
and second, mudi material was available aJon^^ these lines.
No figures on operating costs, original costs, or any other busi-
ness or commercial data could be obtained, the reason being obvious.
Ko actual photogr^ihs of the station are presented because none
were available and It ws.b not permitted to take any. A few pictures have been
added In an endeavor to give a more concise idea of the material, even thou^
most of thera sxe not of W.R.C. A schematic diagram of the transmitter is
ehOT-n; it is an exact replica of the blue-print furnished with the installa*-
Radio Station W.R.C. .of Washington, D.C. was planned in the
Spring of 1923 and financed by the Radio Corporation of America, It was of-
ficially inaugurated to the "air-lanes" in August, 1923, There were two under-
lying factors which created the necessity of a broadcasting outlet in Washing-
ton: first, an inducement to the public to buy radios, the sustaining product
of R.C.A. at that time,* secondly, to furnish programs directly from the na-
tion's capital, since it was the chief seat of government in the Onited
In 1926, the National Broadcasting Company assumed the management
of W.R.C. and in 1952, they bought it outright; however, during that time,
N.B.C. and R.C.A. had incorporated into one organization and virtually, the
station has never chang'ed hands since its beginning.
Station W.R.C, including transmitter and studios, was constructed
in the Rigga-Thompkins Building at 14th Street N.W. and Park Road. The call-
letters at that time were significant: "W", as the initial letter for all^sta-
tions on the regular broadcast bandj "R.C." for Radio Corporation. The call-
letters do not stand for Washington Radio Corporation, as commonly believed
W.R.C. began operation on the assigned broadcasting frequency of
650 kilocycles with a power output of 500 watts. With the inauguration of
Station W.M.A.L., W.R.C. relinquished that frequency to that station and con-
tinued operation on 950 kilocycles, by permission of the Federal Radio Com-
mission. It has maintained operation on that channel up to the present time.
The initial program included an address by Major-General J. G.
Harboard, who was at that time president of the National Broadcasting Co,
This program was announced by Milton J. Cross, who is now a well-known an-
nouncer on the N.B.C. net-works.
W.R.C. has always been the point of originatibn of all broad-
casted addresses by the President of the Onited States.
During the first year, the station operated only 3 or 4 hours per
day, including a fev; remote pick-ups for special occasions. Opon the comple-
tion of a year of successful operation, night programs were begun. During the
course of the following three years, the broadcasting time was finally in-
creased to 13 hours per day, which quota of time has continued up to the pre-
In 1924, the first programs from TIST.J.Z. in New York were broad-
cast through the transmitter of W.R.C. via Postal Telegraph cables. A short
time later, programs were received from as well as sent to both W.J.Z. in
Hew York and W.B.Z. in Boston.
In February 1928, the studios were transfered to the National
Press Building, on F Street, adjacent to the Fox Theatre; the studios are
still on this location, but of course many refinements have been made.
The original staff of ^.R.C. consisted of only eight members; the
present staff, not including those emploj^ed directly by N.B.C, consists of
45 members. W.R.C. boasts of having on its staff at one time such noted an-
nouncers as: Norman Brokenshire, John B, Daniel (deceased), and Ted Husing.
The original studios of W.R.C. were located, with the transmit-
ter, in the Riggs-Thompkins Building at 14th Street f3.W. and Park Road. At
that time, little was known of proper studio design; however, the walls were
soundproof and the floors were covered with thick carpet to silence foot-
In 1928 the studios were located in the National Press Building
with the business offices. By this time, some progress had been made by rad-
io engineers in the field of studio design and the ne<7 studios were built
with all these latest refinements and are still in use at present. There are
one large studio and two small ones, each of which was designed to have a
maximum reverberation time of 1 second and a minimum of .4 second. It is a
desirable feature of a studio to have a variable reverberation time, so that
the studio can be suited to the particular type of program being broadcast.
Since this refinement was not perfected until quite recently, the studios at
W.R.C. are not equipped for it. However, at Radio City, the' reverberation
time is varied by means of electrically controlled panels, which at the same
time may present surfaces with variable sound reflection coefficients at will
of the operator. The desirability of this quality can be proven in the large
studio by a clap of the hands at certain places, resulting in reverberations
having a reverberation time well over one second; this is not a good test
but it does show that there is the possibility of producing sounds having a
reverberation time beyond the lijnits for which the studio was designed.
It has been proven by the Fxperimental Research Department of
N.B.C. that the ideal studio dimensional proportions are 2, 5, and 5 -
height, width, and length, respectively^ the studios of W.R.C. have been
deslgned to meet these specifications. They were also designed to have an at-
tenuation of at least 60 decibels, bi-directionally j this feature is of ut-
most importance and Is accomplished by the use of sound absorbing materials
on the walls and ceiling and of floating load bearing walls, floor, and ceil-
ing. This latter refinement gives the studio the effect of being semi-detach-
ed from the building. It is also important that the window between the stu-
dio and the control room present an attenuation equal to that of the walls;
this is accomplished by using three separate panes of glass of thicknesses
5/lG", 1/4", and S/8"; this combination with a thin vacuum between the
panes gives the desired results.
The studios are sound-proofed against external noises by means of
a special wall and ceiling construction, for which purpose a special acoustic
celotex, having small air pocket holes in its surface, is used. The floors
are covered with thick carpet to deaden foot-steos as well as to reduce the
Actual control of a broadcast begins in the studio; a small con-
trol unit having key switches, signal lights, and an intercommunicating tel-
ephone to the control room, enables the announcer to switch the microphones
at different positions on or off, and to keep the operator in the control
room advised on the progress of the program. All microphone and control cir-
cuits are carried- in lead covered cables behind the wall sound-proofing.
Connection boxes are set along the baseboard for microphone outlets, Kach
studio is eaulpped with its nwn aniplifier, since with the tyties of micro-
phones now in use the signal ■oroducei la so weak that It reoiuires Inmiediate
amnlifl cation before it can be sent to the control room.
Advertising in radio ■broadcp.stinjfdid not strjrt on a large scale
at W.R.O. until 1938 or 1929, Before tliat time, the station itself operated
at a loss; but since R.C.A. Tauilt W.R.C. for the purpose of furnishing an in-
centive to the p-ubllc to "bvy R.C.A. radios.
During the first few years of operation, the artists were paid
directly by the station, but later they performed free of charge in that the
publicity they would obtain from the service of the station was sufficient re-
compense. It was not long until radio artists were sponsored for the purpose
With the initiation of network programs, sponsors had to buy time
on the air to advertise a product. From that time on, the development of ad-
vertising In radio broadcasting, especially in the network programs, has ad-
vanced by leaps and bounds.
Just prior to the beginning of the regular network hook-ups, 'S7.R.C.
had a fair portion of its dally program sold for advertising purposes. Later on
as the demejad for befeter talent increased, the present economic crisis began in
1929, and it was at this time that W.R.C. began to eniploy electrical transcrip-
tions on a big scale for local progrsms in conjunction with short advertise-
ments, viiich method Is used instead of a regular sponsored program.
It must be remembered that advertising is practically the only sus-
tainence that W.R.C. h^s. It follows that the greater volume of advertising,
the greater the service that is rendered to the public by the station throu^
the broadcasting medium rnd consequently, a benefit to both: the station can
afford better progrras with tiie capital furnished and the public can therefore
derive more enjosment from tlaem.
In 1950 it was found necessary to add equipment to the station
for the broadcasting of electrical transcriptions; since that time their use
has become an integral part of the daily program of W.R.C., in fact the pro-
gram from 7 A.M. to 9:15 A.M. every morning consists of nothing but electri-
cal transcriptions and advertisements. It was at tliis time that the present
economic depression was at its peak. Since the beginning of their widespliad
use, they have caused much undue criticism against their being broadcast}
from an engineering standpoint, they are fairly comparable to network broad-
casts since both have their own peculiar fallacies, both in volume range and
frequency range. The electrical transcription method of broadcasting enables
a smaller station, which can not conveniently obtain the services of high-
grade performers, to broadcast from records made by these highly-paid artists,
Thus the cost of a perfoi^ance by such artists is speed out over a large num-
ber of duplicaterecords made and distributed to the smaller stations, thus e-
nabling them to offer programs of a quality and appeal which they would other-
wise be unable to afford.
In the past few years, the quality of electrical transcriptions
has improved immensely; the frequency range of the present type is from 100
to 4000 cycles per second, with a standard speed of 78 r.p.m.
When broadcasting electrical transcriptions, the method used, is
simply to use an electrically driven phonograph turntable with an electrical
pickup unit playing from the record and feeding directly to the speech ampli-
fier in the control room, thus modulating the carrier current in the usual
way. Magnetic type pickups are still being used, although much more efficient
types have been developed. The turntables are driven by synchronous motors.
equipped with counter-balance weights to insure correct and constant speed,
There are two turntables and two pickups, both of which are located close
enough to the control panel that both can be operated by one man.
The microphone is an Instrument for changing the energy produced
by air-vibrations into electrical energy. As small as it may be, it plays an
important role in radio broadcasting. Its developement at W.R.C. has been
practically the same as any other station. Of course some stations were able
to take advantage of microphone refinements as they were developed, while
others were not, due to financial difficulties; it was the good fortune of
W.R.C. to be one of the former, since its owner and operator was the creator
of the majority of the refinements.
The first microphone to be used by W.R.C was the single-button
carbon typej it had high gain, high noise level, and a very limited frequency
response and was very inferior to the type which soon followed it. This wag
the double-button carbon microphonej it was vastly superior to the former
type and is still used today, with certain refinements of course, for certain
types of broadcasting. The carbon microphone is characterized by an Inherent
noise called "carbon hiss" which makes it undesirable for good broadcasting.
It was not long after the opening of W.R.C, that the R.C. A.. engi-
neers began to concentrate particularly on the developement of a new type of
microphone free from this objection. Their first product was the condenser
microphone. The principle involved in it is comparatively simple: it consists
of a sensitive condenser plate, acted upon by the varying pressure of sound
waves, thus varying its capacity.
The next developement of the R.C .A. engineers was the dynamic
microphone, operating on the principle of a moving coil in a magnetic field.
The velocity or ribbon microphone soon followed j it utilizes the principle of
a thin ribbon, which presents an edglirible impedance to sound waves, placed
between two permanent magnets. This latter type is by far the best produced
■to date. Recently, the R.C.I. . engineers produced a new type, operating on the
inductor principle; it has been adopted by N.B.C. as the standard model for
field work and is rapidly replacing the double button carbon microphone for
portable work. In general, concerning the developement of the micropione, the
increased efficiency, both in tone quality and frequency range, is followed
ty decreased electrical output; thus, higher gain amplification is demanded
to bring the energy levels up to the ordinary transmitting levels of the wire
links. To rectify this condition, preamplifiers must be added to the micro-
THE COMTHOL ROOM AND CONTROL OPERATION.
The control room is probably the most vital part of the broadcast
station; all prograxas must be routed through it before they can be broadcast,
whether they originate tn the studios, from the network, from the field, or
from the electrical transcriptions. It is the duty of the operator to see that
the program regardless of its source is sent to the transmitter at the proper
energy level and at the correct time. All this seems quite complicated, but
the accompanying diagram of the control room shows simply the functions of
each part; it must be remembered that this is not a schematic diagram. Follow-
ing the circuit from left to right, the input of the first amplifier may be
connected either to an outside (field) pick-up point, or to the studio micro-
phones of which two are shoiim combined in a mixer, (more or less may be used) .
The actual switching would not be accomplished with a knife switch, as shown
In the diagram for the sake of simplicity, but by means of a telephone key
or plug- in jack arrangement in which the transition from one circuit to an-
other is made without a long break. The output of the amplifier is connected
to an artificial line which drops the transmission level. This line presents
an impedance of 500 ohms in both directions. The amplifier has the same output
Impedance, while the input impedance is matched for the type microphones be-
ing used; however, the matching requirements are not highly critical, A level
indicating device is bridged across the input of the artificial line; this
indicator is designed to give correct readings when connected across e 500
ohm circuit of the type shown. The output of the artificial line feeds a mon-
itoring amplifier, but the main circuit passes through a switching system to
the input of two or more( 8 are used in this case, but not shown) line ampli-
fiers containing two stages of amplification each. One of these amplifiers
/v. B.C. CiP^/^r^o/ /ioorry a^ M^Z/r^^r-e^ /_,J\
CHEGKII^G THE MAZE OF WIRES
ThG operator is identifying and tccting the wiring for
tho termination of trunk linoc to tho studios and operating rack of
tho nov; NBC studios in Radio City.
feeds the local transmitter at 14 th Street and Park Road; another feeds the
network whenever the occasion warrants It; another feeds ^.M.A.L.; each is
installed in duplicate. The purpose of splitting the circuit by means of one-
way repeaters at this point is to permit local announcements to be made by
short-circuiting the network amplifier, thus confining whatever is said in
the studio only, to the transmitter of W.R.C. The operation is practically
the same when programs are being received from the network. The function of
the artificial line, which may seem an unnecessary loss device between the
preliminary and line amplifiers, is to provide an intermediate low-impedance
circuit with constant level, suitable for measurement purposes, and unaffect-
ed by the addition of ordinary bridging impedances.
The electrical operation of the interlocked studios may be under-
stood from an inspection of the relay circuits. The details are shown for
only one studio, the circuits for the other two studios being precisely sim-
ilar, Thg output of the artificial line goes to two fixed contact points of
a telephone relay. The winding of this relay is supnlied with 12 volts when
the announcer's switch in the studio is closed. If the "B" main relay is op-
en, the other terminal of the "A" relay winding is connected to the positive
side of the 12-volt battery, which is grounded. The same action supplies cur-
rent to a red light in the "A" studio or the control room, visible to both
operator and announcer, warning both of them that their studio is connected
through to the line amplifiers. If "B" studio is in use, then it is impossi-
ble to connect the "A" studio to the audio-frequency bus which leads to the
line amplifiers, since the "B" relay keeps the "A" relay coll from being en-
ergized. Thus there is no possibility of putting two studios on the air si-
multaneously. The studio which is not in use receives a green light from the
studio which is in operation. If neither studio is in use both lights are
dark. In this condition, also, the audio-frequency bus supplying the line
eiinpllfiers is short-circuited ty an auxiliary relay. Were this not done the
Input of the line amplifiers would be open when neither studio was "on the
air", with the result that if these amplifiers had their filaments lit,
cross-talk pick-up vrould be likely to go out on the lines.
In the diagram only two studios are shovm for the sake of slm-
p llcity; as mentioned before, there are three studios, one large and two
Tl^^ control room at W,P..O, Is more than a control room for a
single station; it is one of the control uolnts of the "^latlonal Broadcasting
Co. for both tJie- "Blue" and "Hed" networks. There are eight stations includ-
ing W.M.A.L. which receive network Tjrograms all of which are routed through
W.R.C.'s control room. Essentially, it is a booster station ^or these other
broadcast stations in that the anrollfiers raise the transmission level of the
network programs to a point where they can be satisfactorily sent on. Of
course at the same time, the control' room Is Tierfomiing its nrimary functions
iai the operation of w.a.C.
Teleohone links from any noint in Washington where a broadcast Is
likely to originate (such as nlsiht-clubs, centers of Tjolltical activities,
the White House, etc.) are connected to the control rtanel.
Local Tjrograms of W.3.C. Tjroper are boosted to the transmission
link level by two amplifiers; the first is the Impedance coupled tyoe using
the followlrvR; tubes: 2-841, and 1-210; the second amollfler is transformer
coupled and uses the following tubes: 1-841 and 1-210. The latter one Is the
type used for the network service.
Batteries are used entirely for the -oower sun-nly of the amollfi-
ers in the control room. The nlate voltage Is obtained from ""B" batteries
having a voltage rating of 440 volts; the filament guTjnly is obtained from
- ■ :::^^
A' co/^moi. ROOM.
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CONTROL ROOA/f LAVOUr
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"A" batteries having a rating of 350-400 amti ere -hours; at X3 volts; the bias
voltage sTiOTDly is obtained from "C" batteries (the "':" batteries are the dry
tyne vhila the others are wet), having a voltage rating of 33^ volts with
various ta-os for securing lower bias voltages. The "A" and "B" batteries are
charged by generators; in the first case, the generator has a rating of SO
volts at 50 amoeres, but is used at 14^-15 volts at the rated current; the
second, is rated at 600 volts but used at 440 volts. Obviously, the """ bat-
teries are not charged.
The control room personnel consists of five men; a supervisor,
3 operators, and a maintalnence man. Mr. Johnson is the chief engineer of
the entire engineering staff of W."a,C. and Mr. Merryraan is the field engine-
If the broadcast originates at some point away from the station
as in the case of a football game or other event, the microphones and usually
a speech amplifier are installed at the field and special wire telephone lines
are run to the control room. Generally, the existing telephone lines are rent-
ed from the telephone company. For broadcasts, where telephone lines are not
accessible, a portable short-wave radio-phone rtansmitter of low power, opera-
ting on a frequency of 34.6 megacycles per second is used, only for short dis-
tances, however. When the portable transmitter is used the prograa is picked
up by a short-wave receiver in the control room and then amplified to the level
of the transmitter link.
The first transmission link to be used by W.R.C. was furnished by
Postal Telegraph Co., extending from New York to Washington; later on the
link extended to Boston, The resulting programs of this network were very un-
satisfactory in that the audio frequency transmission characteristics of the
link were poor; but it did afford an outlet in Washington for more programs
and at the same time give W.J. 2. and W.B.Z. a linkage with the nation's capi-
tal. With the formation of the Mati nal Broadcasting Company, in November 1926
W.R.C. became a part of the regular "red" network with W.E.A.F. as the key
station. The program service was now transmitted from New York by special
broadcasting circuits supplied by the American Telephone Company. These cables
which are still in use were entirely underground and gave considerable im-
provement to the service both from a standpoint of noise level and frequency
range, yet far from ideal conditions; the noise level measures approximately
35 decibels, with a usable volume range of S7 decibels, 60 decibels being at-
tained with a symphony orchestra broadcast. The frequency range extended from
80 to 5000 cycles per second and the curve obtained within these limits is
flat within 1 decibel; this frequency range is better than the average broad-
cast receiver on the market today.
The transmitter is approximately two miles from the control room
In the National Press Building, Programs for both W.R.C. and W.M.A.L. are
routed through this control room. The wire link betlceen the above mentioned
points is far superior to that from New York. This two mile link has a usable
volume of 50 decibels and a frequency range from 50 to 8000 cycles per second.
As a result, the superior quality of local programs can easily be detected by
even the layman, when monitoring on a laboratory model receiver. As far as
present research has been able to determine, the frequency range between
5000 and 8000 cycles per second has great importance in producing naturalness
.and good tone quality; however, beyond 8000 cycles per second, little effect .
can be detected by the human ear. Below 50 dycles per second few tones are
produced and therefore are of little importance relatively. As a comparison,
the pipe-organ has the greatest frequency range of any musical instrument,
16 to 16,000 cycles per second; these limits are beyond those to which the
human ear is sensitive.
The first transmitter used by W.R.C. was orlj^iually designed for
shin-'board comraunication -DTirDOses, It was "built "by B.C. A. and later redesigned
esTseclally for broadcasting ourooses, with a power out-out of 500 watts. Accord-
ing to the usual iDractice, the transmitter was installed In duplicate — that is,
two senarate machines, one for regular operation and one for emergency.
These transmitters were used continuously until 1932, when an B.C. A.
Victor Tyoe 1-C model transmitter was installed; it has been in use ever since.
The old transmitters were torn down and the parts were us 3d to construct anoth-
er with a T30wer out-out of 500 watts. This reconstructed job is now being used
for the emergency transmitter.
At Tjresent, the transmitter is operated on an assigned frequency
of 950 kilocycles with a carrier power of 1000 watts in daytime and 500 watts
Pull modulation with the nominal outtrut rating of 1000 watts is
pro&iced by an InDut of about zero level (12^ millivolts). The Innut imped-
ance is 500 ohms. It is well to observe, here, that in accordance with the
conventional form, when specifying the outnut rating, no account Is taken
with regard to the flegree of raodulstion. This rating is the measure of unmod-
lated carrier wave only; however, when modulated 100^ the instantaneo-'as Deak
reaches 4 kilowatts. The tubes and circuit are so designed to -Derralt continu-
0U9 Operation at full lOO^ modulation.
This tyrje of transmitter and eq-uitiraent can be adjusted for maxl-
nium perforrnance and efficiency on any frequency within the "broadcast band,
ranging from 1500 to 550 kilocycles. However, the crystal was supplied to op-
erate on the assigned frecraency of 950 kilocycles; therefore, with any change
of freouency a new crystal must be obtained.
The transmitter is designed to operate from a 220 volt, 3 phase,
3 wire, 60 cycle -nower sunttly from the line. The -nower siiDT^ly unit consists
of two 3 unit semi-enclosed motor-generator sets. The first of these is the
filament and bias sutjolies, which consists of a 70 ampere 19 volt generator
and a 550 volt .9 kilowatt generator driven by a 5 horsepower motor. The low
voltage generator su-onlies all tube filaments excent the UX-866 rectifier
tubes and the speech amolifler tubes. The 550 volt generator su-Dnlies the
bias voltage for all tubes except those contained within the crystal oscil-
lator unit and the speech amplifier; in addition, this latter machine sud-
plies the field excitation for the remainder of the generators including the
machines for the filament aad plate supplies. With a 220 volt 60 cycle line,
this motor-generator set rotates at 1750 revolutions per minute.
Both units have a remarkably low percentage of voltage ripple in
their output when nominally loaded; they were eepecially constructed for ra-
dio transmitter BOwer auoT)ly purooses and present a very neat and -oleastng
The second unit Is a 3 unit high voltage motor-generator set con-
sisting of two identical 3000 volt 4.5 kilowatt generators driven by 14.5
horse-oower motor. In oneratlon, these generators are connected in series and
rated at 7.5 kilowatts at 6000 volts. The armatures in each are identical and
interchangeable, each being insulated for maxiraura high voltage so that only
one armature, which will fit each ma<dilne, need be carried for a snare. This
unit, with the same power supply from the line, rotates at 1750 revolutions
per minute. Different voltages can be obtained; 1500, 3000, and 6000 volts.
Each machine is completely enclosed and protected by means of Tierforated metal
This equipment must be operated from a well regulated "Dower line.
A supTJly in which the line voltage variations exceed plus or minus 5^ is con-
sidered unsuitable for broadcast transmitter siio-Dly service and requires some
form of automatic regulating equltsment. However, the line suoply used does
not vary sufficiently to warrant the use of auch equipment: It was found in
a two weeVr test run that the line voltage varied only nlus or minus 4 volts
at a maximum.
A Tjump for the cooling system and the crystal oscillator supply
rectifier are operated from the line instead of the generators. A 110 volt
single nhase lighting circuit sutTOlles the crystal heater tiower. Batteries
are used to sun-oly the filaments of the tubes in the srieech amplifier; but
the circuit is so arranged that this filament suoply can be obtained from
the motor-generator If the batteries should fail.
The following tubes are emoloyed In the trsuiaraitter:
2 - UX-2X0 1 - UV-203-A
4 - UX-865 1 - irV-a49
3 - TJX-860 2 - UX-280
2 - UX-866 1 - tJV-1652
The -posltlona of each are shown In the echeraatlc diagram.
The carrier frequency is generated hy a crystal controlled master
oscillator, amplified "by five siiccesslve stages of radio freqruency power am-
olification, and delivered to the antenna throiagh a transmission line. The mod-
ulating freffiiency, or audio frequency, passes throu^ one stage of power am-
nllflcation to the modulating circuit. Modulation talces place in the fourth
radio frequency stage. The succeeding radio frequency oower anrolifler acta as
a linear amplifier. Such a system of modulation Is "by convention, called "low
The Tsower gupijly for operating the radio system is nrimarlly a
fully automatic and Interlocked system, but provision is made for interrupt-
ing the sequence of starting for test or adjustment •Dumosss at several ■oolnts.
Some of the features of the control system are: water pressure actuated device,
temperature indicators, overload "protection with "both manual and remote elec-
trical reset, filament and "bias undervoltage interlocks, water under-pressure
and excessive temoerature interlocks together with the -oroper secfuential
starting and stotroing of cooling water, filament, bias, and t>late voltage.
The most refined methods of carrier frequency control known at
the time of the construction of the transmitter have "been utilized, which -oro-
vides exceptionally accurate carrier frequency stability. Means are Brovided
for maintaining the mean carrier frequency of the transmitter to within plus
or mimiB 50 cycles of the aasi^ed value.
Utere are two separate duplicate crystal controlled master oscil-
lators, each associated with two screen grid buffer ainpliflers. These are
built into cormact units with essential meters and controls in view and are
accessible froip the front of the transmitter panel. In order to insure perma-
nent and reliable adjustment, the internal parts of the units are completely
enclosed in metal shields. The tubes can be readily removed for reDlaceraent
purposes by withdrawing the vmits from the front panel. These two units are
capable of instantaneous switching from the front panel of the transmitter so
that either can be used at a moment's notice.
The various devices used for safety of the operating personnel
and protection of the apnaratus Include the following:
1- water t> res sure gauge and Interlock, which prevent injury be-
cause of water failure.
2- water temperature, or thermostatic cutout, which protects a-
gainst excessive one rating temperatures,
3- filament undervoltage relay.
4- "bias undervoltage relay.
5- overload circuit breaJrar with maimal and electrical reset.
6- sequence interlocks which protect each successive operation In
either starting or stoTralng.
7- thermal overload relays in each mo tor- gene rat or driving motor
8- fuses In main and all branch circuits.
9- disconnect switches in various plate suDply leads.
10- automatic high voltage disconnect and neutralizing change-over
11- switches on all doors which remove bias and plate voltages, thus
protecting operating personnel from accidental contact with dangerous voltages.
13- visual indicators as a guide to all Important circuit conditions.
13- sequence interrupting switches which provide manual control of
successive stages of operation for test and adjustment purpoaes.
A two wire transmission line Is used for coupling the antenna to
the power amollfier. This system provides a very efficient coupling; When
properly terminated and ad^st'ed, radiation from a traasnilgslon line la negli-
gible and the efficiency of transfer ia very high,. In addition, through proper
design radio frequency harmonic sunpreaslon Is acconrolished.
AUDIO FHEqUENCY CHABACTEHISTICS.
The aaidio frequency response curve from audio Input terminals to
speech amplifier through the tranamltter and Into the antenna, as measured by
rectified antenna current methods, is substantially flat. By substantially
flat, is meant that this frequency response curve will not vary more than
tdIus or minus 2 decibels from a straight line between 30 and 10,000 cycles
ner second, or more than plus or minus ^ decibel between 100 and 5000 cycles
The transmitter employs what Is known as "low level" modulation.
In this system, the audio circuits are simple, and with resrject to raalntain-
ence and tube costs, quite economical corroared to hlf;h level randulatlon. In
this low level system, the radio system is modulated In one of the low nower
stages where 100^ modulation of the transmitter outnut can be obtained. A
100^ modulated system has a great many advantages over the older tynes when
only 30^ to 50^ modulation was obtained, by reason of the fact that the peak
output for 30^ modulation, as In the former case, reaches 400^ of normal car-
rier out-out , i^ere as, the tjeak outtjut for 50^^ raodiilation, as In the latter
case, would be but 225^ or less of the carrier out-out. Thus, the average out-
put from a 100^ modulated transmitter Is considerably greater than the aver-
age output of transmitters ooerating at lower -oercentages of modulation. Nat-
urally, this increased outwit of rjower into the antenna gives a greater range
of usedfulness to the station, greater area of coverage, and a greater ratio
of signal to interference level.
The power amplifier tube in the final stage re (^l res water cool-
ing. A-pproximately 10 gallons -oer minute are circulated through the system,
propelled by a motor driven centrifugal puinp. This cooling water is cooled
by being circulated through a copper radiator fitted with couoer cooling
fins through which air Is blown by means of a fan attached to the same motor
shaft, which drives the rrump. ifflien not being circulated, the water partly
drains into a 15 gallon expansion tank which reduces the level of the water
in the tube jacket, thus allowing the tube to be changed easily. A visual wa-
ter flow indicator is provided, the return water being forced through a jet
visible through the glass windows in the indicator. The top of the tank is
vented to relieve trawoed air which collects in any circulating hot water sys-
tem and which is a constant soro'ce of danger to a tube jacket if not relieved,
since a bubble of tran-oed air circulating past the jacket may effectively cause
localized heating with consequent tube damage. The dissipation rating of this
system is 4 kilowatts; it is designed with a large factor of safety and will
effectlvely cool the tube even though the transmitter "be operated In the most
unfrivorable flliraatlc conditions, ijrovided that the cooling unit Is installed
where it can obtain a good strorjly of air.
Before a program coming from the control room via the telenhone
link can "be tiut in the Irrout of the transmitter, It must first go through the
equalizer and then through an amollfier. Identical to the ones used In the
control room, In order to boost It un to the level reouired by the Inout of
the roeech amolifier of the transmitter. This equitsment is included on the
control T)anel beside the transmitter. This T)anel also includes f?ufflclent e-
qulpraent, such as a micronhone for station announcements, a turntable and a
plck-UT) for electrical trans sciTDt ions, etc. ; this Is all Icent on hand to use
in case of emergency.
A small exoerimental short-wave transmitter la O'oerated Inter-
mittently, but at T)re3ent it is of no commercial value. It otjerates on an
assigned frequency of 34.6 megacycles, the same as the portable transmitter
used in the field.
Testing equipment is used to check the frequency of the transmit-
ter daily; this is absolutely necessary so that the frequency can be Irept with
in the Federal Communications Somralssion limits of the assigned frequency.
Modulation can be checisd by the osclllof^raT>h, a small instiTjment
mounted on the control -oanel; it OTierates on the tudncl-ole of vibrating hot
wires, the vibrations being -oroduced by the modalatlons of the carrier and
made visible through a system of rotating mirrors.
The emergency tran3mitter Is tested about once a week with a
broadcast of electrical transcriptions after mlinlght. Should the regular
transmitter fall at any tl.-ne. It takes one man only 15 seconds to switch
the Tirograra over to the emergency transmitter; with two men, only 6 seconds.
A receiver Is in o-oerqtlon at all times to -olck utd any S.0.3,
Calls from 9hiT)s at sea.
The T)ersonnel required for the cr:?e ration of the transmitter con-
sists of three onerators, working In B hour shifts.
W.R.C. has been using the eame antenna since its "beginning. It Is
situated directly above the transmitter on the roof of the Riggs Bank Building.
The antenna was designed and built with this trail ding.
The towers are mounted on concrete coliimns, 8' souare and extend
40' underground; they were at the time of their construction standard equip-
ment of the American Bridge Construction Co. They are called the bridge tyoe
of design and will stand wind un to ISO miles Der hour. The distance from tow^
er to tower is 225'.
The antenna itself has an effective height of 180' . It is of the
"T" tyoe construction, consisting of 4 main wires. The transmission line to
the antenna has a matched imne dance with that of the final stage of the trans-
The transmitter can be tested on a pure resistance dudin^ antenna.
/V.£f,C-i^^/f/^ tf^rf&m/H'^rj arr-^enrra a^ &e.///7^0re^ LS.
The obJectiTe in writing this paper will certainly have been at-
tained, if it is as interesting to those who read it, as it ^as to the author
in its preparation and writing. The author regrets the discreptancies in the
treatment of the different phases of the station, but as already explained,
the absence of some material was unavoidable.
practically all the men contacted In obtaining the material for
this paper were engineers. Each one was particularly accomodating and most
interesting to converse with; however, there was only one college graduate
In the grouo.
Mr. PhlliT3 Merryman, field engineer and control sucerviaor.
Mr. Fred Shawn.
Mr, Callahan, conjniercial srupervlaor,
Mr. B, E, Stahl, o-oerator at the transmitter.
Mr. S. E, TTewnian, pnerator at the transmitter.
Book of Inatructioaa for the 3. C.A.Victor Type 1-C Transmitter.
R. C.A.Victor Bulletin 31.
Broadcast Control Crjeration, by Carl Dreher,
THE H. C.A.VICTOR TTPS 1-D TRMSJHTTEH,
Even thOTigh W.H.C. does -not use this tyne transmitter, it is a lat-
er model of the one they now have In use. A review of It shows very tdalnly
the Improvements and their advantages. This material is -oresented to show in
a contrasting way how transmitter design has advanced in the t>ast few years.
It is Interesting; to note the elimination of the generator -oower surroly by
the incorporation of transformers and rectifying tuhes as the source of D.C.
The R. G.A.Victor 1-D transmitter has a carrier tjower of 1000 watts
and requires a 220 volt 3 -ohase 60 cycle line surroly. Long time regulation of
line voltage should not exceed 5^ and rapid variation should not exceed 15^.
The TDOweP consuntption is 5700 watts. The transmitter will ooerate on any sdbc-
ified frequency from 15X to 550 kilocycles. Full modulation is produced by an
^nput. of about zero level (13^ milliwatts); the Innut Imroedance is 500 ohms.
The carrier has a stability of better than plus or minus 50 cycles per second
from the assigned frequency. The audio characteristic curve is flat within
olus or minus 2 decibels from 30 to 10,000 cycles tjer second. The hum level
measures 60 decibels below the signal for lOOi mndulation. The radio harmonics
•oroduced meets the requirements of the Federal Comraunl cat ions Commission. It
is designed to operate satisfactorily in any aiablent temperature in the range
of 15 to 45 C, a'nd to ot>erate with a 400-600 ohm line or with an antenna sys-
tem having a resistance between 10 and 90 ohms, and a reactance of not over
The following tubes are required for normal operation: 4 R.C.A.843,
1 R.C.A.865, 3 U7-203-A, 2 UV-845, 4 UT-204-A, 2 UV-849, 6 UV0872, and 1 R.C.A.
The schematic disgraia needs some explanation. The circuits are
simple yet completely effective . The transmitter is constructed in t'TO .sec-
tions — a 250 watt exciter aiad a high level arapllTier unit. In the exciter
unit is the crystal oscillator, two buffer stages, and the intermediate po-
wer amplifier. Two audio stages, and all power sun^nly equipment are also
contained in this unit. The power amplifier section contains the power amp-
lifier and modulator with its own power supply.
The crystal oscillator uses a newly developed circuit found to
provide excellent stability and to permit changing tubes 'vithout greatly af-
fecting the frequency. The crystal is operated lightly to preclude the pos-
sibility of fracture and to insure stability well within the Communications
Commission's limit of 50 cycle deviation. The crystal oscillator tube is the
R.C.A,-845, with a heater type cathode, minimizing the possibility of hum or
From the oscillator stage, the radio frequency is amplified by a
screen grid buffer tube, the UX-865, followed by a QV-SOS-A, which in turn
drives the intermediate power amplifier. This intermediate stage employs a
pair of DV-203-A type tubes in push-pull, to supply grid excitation to the
power amplifier. This stage, like the preceding ones, operates as a Class
"C" amplifier, and uses 4 DV-204-A type tubes in parallel push-pull. The po-
wer amplifier tank coil may be coupled directly to an antenna system or to a
transmission line. In case no line is used, a harmonic suppression network
attenuates the radio frequency harmonics which are otherwise reduced effect-
ively by the line. The use of push-pull amplification and electrostatic
shielding in addition to the other devices, provides for an absolute minimum
of harmonics and thereby reduces interference with other radio services and
assures compliance with Federal regulations.
The audio frequency circuits operate tn a push-pull arrangement
throughout. The first two stages are placed in the low power section, the
last in the T>ower amplifier unit. The first audio stage employs a '^ai^ of
R.C.A.-843 type tubes in push-pull. Class "A". The second audio stage is ar-
ranged to use 2 □V-845 type tubes. Class "A". This stage then energizes the
final audio amplifier which modulates the last redio frequency stage. The
1000 v/att modulator system consists of a pair of DV-849 type tubes in push-
pull. Class "B", coupled through a specially designed transformer to the
plate circuit of the 0V-204-A, Cle:ss"C" stage.
All radio frequency amplifier stages are self-biased. This in-
sures proper operation and again provides for simplicity of design. Provi-
sion la made for limiting the plate current in the event of loss of excita-
tion. A 250 volt Rectox unit, with suitable filtering, furnishes plate volt-
age for the crystal oscillator and also bias for the second audio stage.
Plate voltage for the following three stages of radio frequency amplification
is supplied by a single phase rectifier using two OV-872 type mercury vapor
rectifiers, A SO volt dry rectifier unit biases the fitst audio stage and al-
so supplies the field of the monitoring loudspeaker. In the power amplifier
section, a single OV-872 type rectifier tube, in a heavily loaded circuit sup-
plies bias for the DV-849 type tube modulators, Plate voltage for the modula-
tors and radio frequency power amplifier is derived from a three phase, half-
wave rectifier using DV-872 type tubes. The power supply is obtained from an
auto-transformer in each section provided with taps to compensate all voltages
when the power line voltage changes. There is no necessity for individual ad-
justment of filament or bias voltages.
In the 250 watt section, a master rheostat controls all filament
voltages, and this is set initially to the correct value. The input power to
this section is fed through an auto-iraneformer with variable taps for shift-
ing from 110 volts to 220 volts or to compensate for voltage changes. The
1000 watt section contains a three phase auto- transformer with a tapped pri-
mary controlled by a panel switch. Two starting switches are provided on
each section, one for filament and bias and oscillator plate on the 250 7/att
unit, the other for all plate voltages. Time delay relays prevent application
of plate voltage before the filaments have been properly heated. For normal
operation, the switches on the right hand unit are closed and all control is
antomatlcally shifted to the two switches on the left hand unit.
Protection is afforded by a quick acting over-load relay in the
low power rectifier output circuit. Instantaneous overload relays are located
in the primary circuit of the high power rectifier, fuses being used in other
circuits. Relays are mounted on vibration-proof panels. The meters are furni-
shed to indicate filament voltage, rectifier voltages, D.C. grid currents of
the intermediate amplifier and power amplifier, tank cun-ents of the interme-
diate power amplifier and power Eimplifier, antenna current, dummy antenna cur-
rent, and the plate voltage. Sixteen meters are used, with change svritches
for obtaining all plate current readings. Pyranpl filter condensers, the new-
est and smallest type with the highest safety factor, are used throughout.
The dummy antenna is switched into the circuit or out by a panel
control. The monitoring loudspeaker obtains its audio input from the second-
ary of the ffiodulation transformer through a potentiometer. The speaker then
indicates correctly any distortion taking place in the power amplifier, mod-
ulator, or audio amplifiers. In the same part of the circuit a small Rectox
unit and raicroammeter are connected to indicate percentage of modulation.
The cathode ray modulation meter operates from a c:)il coupled to the power
amplifier tank circuit. No rectifier is required. D.C. potential Is obtained
from the transmitter rectifier. The tube is placed in a shielded compartment
and the electron "gTJn" is double shielded. Timing deflection is furnished by-
coils energized from a 60 cycle cource.
The transmitter has complete individual shielding of radio fre-
quency circuits. With the exception of the power amplifier tank coil, every
radio stage is placed within individual metal boxes. The amplifier tank coil
is placed for convenient adjustment and ia electrostatically shielded. This
results in reduction of harmonic radiation and is an additional protection
against static discharges picked up by the antenna.
Controls for tuning and neutralizing are all placed in line, and
are normally operated by a plate. After initial adjustment, these are remov-
ed from view, so that there is no tendency to change the proper settings. At
the same time, the controls are readily accessible. The controls are ccnnect-
ed with the actual tuning devices by means of "dental cable" so that the var-
iable condensers can be placed for shortest electrical connections within the
As stated before, the transmitter employs Class "B" modulation.
This type was first investigated 'bf Ley Barton, an R.C .A.Victor engineer. The
arrangement provides for high level modulation but with the modulator tubes
operated as Class "B" amplifiers, instead of Class "A", The radio frequency
amplifers are all Class "C, the highest efficiency type. The modulator effi-
ciency is also high, approaching that of the radio amplifier. Hence smaller
tubes are used with lower operating costs; by proper design of the modulation
transformer and the use of tubes with suitable characteristics, the amoutit of
distortion was made equal to, or less than, that of a low level system. It is
for that reason that the transmitter used by W.R.C. has low distortion, and
yet high efficiency, ty using the Class "B" modulation of high level.
One of the major problems occurring in the operation of a broad-
casting station is the difficulty of setting the volume control to produce the
correct level of modulation. It is desirable to maintain the average degree of
modulation as high as possible in order to produce the best volume of signal
at the receiving set and to cover up the static and electrical noise picked up
at the recieving location. Nevertheless, if the modulation tends toexceed IOO5S
distortion will be produced which will spoil the fidelity of the transmitted
program. The improved fidelity of receivers causes harmonic distortion to be-
come increasingly more noticeable and objectionable.
Operators have been forced to depend u-ion indicating devices far
from satisfactory to determine the modulation percentage. The most primitive
method, that of observing the deflection of plate meters, indicates only when
distortion has already taken place . There is no way of knowing what the modu-
lation is, If there Is no distortion, thus, a transmitter ooerated this w^.y
will tend to have either too high or too low modulation. Some transmitters
have been equipped with a modulation meter actuated ty a rectifier coupled
to the output circuit; such a meter can not follow the rapid variations pro-
duced by audio waves, and at best, serve as guides to the operator, experi-
enced in interpreting their readings
To rectify this condition, R.C.A, has produced a cathode ray mod-
ulation Indicator, which is employed in W.R.C.'s transmitter. Producing a fig-
ure briglit enough to be seen 20 feet away, in a daylight illuminated room,
this instrument makes continuous observation possible and practical. The size
of figure, 2-^ by4 inches, enables the operator to inspect the indicator accur-
ately from a distance. The cathode ray indicator reproduces high frequency
modulation as correctly as that of low frequency, and indicates the amplitude
of both positive and negative modulation peaks. In the transmitter, the cath-
ode ray tube is located behind a 'protective glass In the upper portion of the
power amplifier unit. Upon the glass cover are ruled five lines, indicating
the zero axis, the positive and negative peak values for 100^ modulation and
unmodulated carrier amplitude. The oscillogram (illustrated) indicates both
parts of the modulated wave, and when the peaks touch the outside lines, and
meet the middle, complete modulation is taking place. Lesser degrees of modu-
lation is shown by the peaks extending part way to the outside lines, and not
meeting at the middle. Over-modulation is indicated by a break in continuity
of the figure at the zero line or br flattening of the peaks.
There are four adjustments to the cathode ray indicator for the
adjustment of focussing, brilliancy, sensitivity, and for changing the sweep-
ing deflection. Excitation for the instrument is obtained by coupling to the
amplifier tank coil. The spot size can be altered, and for precise work, can
be reduced to a diameter of 1 millimeter. So sensitive is the tube that it is
influenced by terrestlal magnetism and a small magnet is used to compensate
for the deflection of the beam by the earth's magnetic field. It indicates a
symmetrical modulation br unequal amplitudes of positive and negative peaks.
The frequency on which a transmitter operates is governed by a
crystal In the oscillator circuit. Quartz plates having a suitable tempera-
ture coefficient are used for the crystal. It is mounted in a holder, which
in turn is placed in a heat insulated compartment. The latter is heated by
a resistance unit and the temperature is controlled by a mercury thermostat
in combination with a low current relay. The' heater, thermostat and crystal
holder form a thermal circuit arranged with suitable thermal filtering so
that the temperature variations of a very low order only are permitted. The
crystal circuit is designed that the external circuit produces little effect
on the frequency, A screen grid buffer stage followed by neutralized buffer
amplifiers prevents the possibility of frequency variation caused 'by the modu-
lated stage. A small vernier condenser permits accurate adjustment of the car-
rier frequency without changing the setting of the thermostat. The crystal it-
self is driven lightly. A spare crystal unit, including crystal, holder, oven,
thermostat, and indicating thermometer, is located at the bottom, front of the
exciter unit and is maintained at operating temperature in case of emergency.
Both crystals may be lifted out for inspection without disconnecting wires.
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FRSQUENCY CHAPA CTERi^TfC Cl/f?l/£:
APP£APAf^CE OF WAV£ O/V CATHOOE PAV IND/CATOR
LAMPS AND EXCITER-
WITH OTHEft SWITCHES
I ON,TH[S STARTS TRANSMITTER
FILAMENT AND PLATE
Pane/ /lrran^erT7GJ7/- of Traa^rri/^^'^^ ^ O
IHE R. C.A.VICTOR 'ERAHaaTTJiS