are accustomed to working together. In the face ofcrises, the human tendency is usually to do the re-verse, it being so easy for central agencies to ignoreestablished but not well-known organizations, and at-tempt to cope with an emergency by calling workersfrom right and left to some new location. As a matterof fact, this tendency was beginning to make an ap-pearance even as long as two years ago when the funda-mental plan of the NDRC was under discussion. Hadthe tide then setting in been allowed to run on for somemonths unimpeded, the result inevitably would havebeen a literal army of uprooted scientists in Washing-ton and other central points, sitting around idly wait-ing for vast amounts of research equipment which hadbeen placed on order, but was not much nearer ma-terialization than that, to be installed in hastily con-structed laboratories. This would have been the easyand disastrous way. Fortunately the creation of theNDRC came in time to stem such a tide.Another present problem, and it is the last with which I

shall trouble you, is one which by its existence suppliesevidence that real progress has already been madein some of the research programs thus far initiated. Ithas to do with shortening the time gap between provenlaboratory research results and the stage where massproduction can be undertaken. Some of the laboratoryresults already achieved hold such promise that everyday which intervenes before their widespread utiliza-

tion becomes a serious matter. Obviously the problemsto be met here cover a wide range of equipment and ma-terials-as wide as that marked out by the scientificresults themselves-and since they involve large-scalemanufacture, the whole plan must be carefully workedout with other official agencies, particularly the Officeof Production Management and the armed services.I am sure, however, that we are prepared to meet andsolve these problems, and rather than be concernedwith the difficulty of making progress along this ave-nue, I think all who are guiding the work of the NDRCwould exclaim to the ranks of scientists and techni-cians, "Bring on your results, the more the better, andwe will guarantee them a speedy passage to the firingline! "

In the foregoing, I have attempted merely to sketchthe setup of organized civilian research and develop-ment created for the war emergency. Obviously, it isonly a part of the total effort which is being mobilized.It would be unfair to thousands of scientists and engi-neers to infer that the main results were dependent onthe work of these agencies.The scientific departments of the armed services are

being greatly enlarged; industrial laboratories are turn-ing more and more of their efforts to direct and indirectwar work and engineers everywhere are active. Funda-mental and applied science are on the march.

CBS International Broadcast Facilities*A. B. CHAMBERLAINt, MEMBER, I.R.E.

Summary-This paper describes the present significance of inter-national broadcasting; its growth and present status in both the Easternand Western hemispheres; factors governing service to Columbia's newLatin American international network consisting of sixty-four stationslocated in eighteen different countries; the many problems attendantupon successful relaying of programs to these many points; facilitiesfor this service, including new studios, frequency-modulation program-relay circuits, and two complete 50-kilowatt transmitting plants locatedat Brentwood, Long Island, New York; features of design and operat-ing performance characteristics of the transmitting apparatus, includ-ing thirteen directive antenna arrays and their associated transmissionlines. A typical international radio relay receiving-station installationand the importance of properly engineering such facilities, will alsobe briefly discussed.

INTRODUCTIONR ADIO broadcasting means the dissemination of

radio communications intended to be receivedby the public, directly or by the inteimediary

of relay stations. In the broadest sense, this appliesboth to short-wave and medium-wave broadcasting..The chief difference between the two lies in the publicinvolved. Whereas medium-wave broadcasting is in-tended to be received by a public located in the coun-

* Decimal classification: R550. Original manuscript receivedby the Institute, August 4, 1941. Presented, Toronto Section,March 24, 1941; Boston Section, March 28, 1941; WashingtonSection, May 12, 1941; New York Meeting, September 3, 1941.

t Chief Engineer, Columbia Broadcasting System, Inc., NewYork, N. Y.

try originating the broadcast, short-wave broadcastsare designed for the public of one or more other coun-tries than that of origin.The Columbia Broadcasting System is, at the pres-

ent time, constructing two new 50-kilowatt interna-tional broadcast stations and thirteen directive an-tenna arrays near Brentwood, Long Island, a sparselypopulated location, approximately 37 miles east of theNew York studios.

Before discussing the purpose and technical aspectsof this modern short-wave transmitting plant, it wouldbe well to review briefly the history and present-daysignificance of international broadcasting.

HISTORY AND SIGNIFICANCEBroadcasting by short-wave began experimentally

during 1924. In the United States, this service was thenknown as "experimental relay broadcasting." Con-siderable activity took place in other countries atabout the same time, notably in Holland, England,and Germany. The development of this service movedalong slowly until the early 30's, when it became moreactive in both England and Germany. At about thistime, the Empire Broadcasting Service of the British

Proceedings of the I.R.E.118 March, 1942

Chamberlain: CBS International Broadcast Facilities

Broadcasting Corporation was inaugurated.' It wasnot, however, until about 1935 that the importance ofinternational broadcasting became fully recognized bythe various countries using it and the race for fre-quencies and high-power facilities began. During 1936and 1937, the number of stations tripled, the totalnumber being more than three hundred. Today thereare more than one hundred stations of this class inSouth America alone. In 1937, England, Germany,Italy, the United States, and a little later, other coun-tries including Japan, began transmitting a large num-ber of foreign-language programs utilizing Spanish,Portuguese, French, German, and English languagesfor the most part. Many of the European transmis-sions were directed toward the Americas, particularlyLatin American countries. It is not the purpose of thispaper to discuss propaganda broadcasts or any othersubject in this catagory, but as a result of recent his-tory, the significance of international broadcastinghas been well established.

During 1940, executives of the Columbia Broad-casting System visited eighteen Latin American coun-tries and made arrangements for sixty-four or morebroadcast stations in these countries to become associ-ated with a new CBS international network. It issignificant to note that this message was carried to, andleft with, the various countries visited.

The solidarity and, to a great extent, the security of the Westernhemisphere will depend upon the amount of sympathetic under-standing prevailing among the peoples of all the American nations.

That is why we are now building new radio facilities; facilitieswhich will be devoted entirely to the development of a closer friend-ship among the twenty-one neighbor republics of America; dis-seminating information, music, education, and entertainmentthrough the magic of short-wave radio.

This journey was undertaken to determine, on thespot, what could be done to further good-neighborpolicy with South and Central America and the WestIndies. The investigation demonstrated conclusivelythat transmitting North American programs to LatinAmerica by short waves was not enough since mostpersons in those countries listen to their local stationbroadcasts just as they do in the United States.

For this reason, CBS has contracted with medium-wave outlets in twenty countries to carry regular day-by-day broadcasts of specially built programs. Thenew network already consists of thirty-nine medium-wave and twenty-five short-wave stations, the latterto serve interior points.While the primary purpose of the new far-flung net-

work is to promote better relations with Latin America,the commercial radio possibilities of these countrieswill also be developed, thus promoting an exchange ofgoods as well as an exchange of ideas.2'3 In the United

""The Empire Short-Wave Station-Daventry" and "Receivingthe Empire Station," British Broadcasting Corporation publica-tions, 1939.

2 Philip L. Barbour, 'Open questions in inter-American broad-casting," Annals Amer. A cad. Pol. and Soc. Sci., vol. 213, pp. 116-124; January, 1941.

3 William S. Paley, "Radio turns south," Fortune, vol. 23, pp.77-79, 108, 111-112; April, 1941.

States, international broadcasting is a commercialradio service and, in this respect, is unlike similarservice from other countries which is, in most cases,government controlled.

CBS INTERNATIONAL BROADCASTING

CBS has been transmitting short-wave programssince 1930. During the first few years this operationconsisted of experiments of a technical nature. Net-work programs were transmitted on irregular schedules,using composite, comparatively low-powered single-frequency equipment and a nondirectional antenna.In 1932, W2XE, the former call letters of WCBX,known to many radio experimenters and amateurs,installed a new 1000-watt station, and in 1937, a10,000-watt station, which, combined with a few direc-tional antennas, greatly improved service.

Technical developments continued and program ex-periments commenced in earnest. The new station wasnot capable of competing favorably with the morepowerful and very extensive facilities used by others,particularly those of foreign countries. During the pastfew years, in addition to station WCBX, located atWayne, New Jersey, CBS has also programnmed anaffiliated 10-kilowatt international station, WCAB,formerly W3XAU, located near Philadelphia. Thesetwo stations will soon be replaced by the two 50-kilo-watt stations now under construction. The new sta-tion call letters are WCBX and WCRC.

Engineering and economic studies, made to improveCBS short-wave facilities, began several years agoand have continued on to this date. They have nowreached the stage where a large number of engineersare devoting full time to the subject. Facilities arebeing provided to improve greatly the service to LatinAmerica and Europe. In addition to short-wave broad-casting, it is necessary that the new facilities be capableof relaying programs from New York to Mexico City,Buenos Aires, Rio de Janeiro, Santiago, Bogota, Lima,Havana, and other distant cities. This requirement hasa great deal to do with planning, for instance, with thenumber and arrangement of directive antenna arrays.

In general, it has been necessary to select an ade-quate transmitting site and location; to have a suffi-cient number of transmitters of adequate power; tohave available for use, one or more frequencies in eachof the bands assigned to international broadcasting,6 to 6.2, 9.5 to 9.7, 11.7 to 11.9, 15.1 to 15.35, 17.75to 17.85, and 21.45 to 21.75 megacycles, by worldradio allocation agreements as consummated at themost recent Telecommunications Conference held atCairo, Egypt, in 1938. Stations WCBX and WCRCwill operate on one or more frequencies in each of thebands. It was also necessary to decide upon the designof the transmitting equipment which, from a conti-nuity and dependability of operation standpoint, mustbe arranged with a maximum degree of flexibility andcapable of rapid changes in operating frequency. As

119

Proceedings of the I.R.E.

mentioned previously, the necessary number and typeof directive antenna arrays had to be selected to fulfilltransmission requirements best.

WCBX-WCRC NEW FACILITIESIn addition to the thirty CBS studios now located in

New York City, new studios are being constructed toserve the new international stations. The most modernstudio construction practices known to the broadcastart will be utilized. The audio facilities will be designedand operated in accordance with standard CBS prac-tice.4From the new studios, programs will be sent to the

WABC master control, located on the twenty-thirdfloor of the Columbia Building. From this point, theywill be transmitted to three 330- to 340-megacyclefrequency-modulation radio relay transmitters lo-cated on the roof of the sixty-two story Salmon TowerBuilding. These transmitters will excite unidirectionalantennas, each having a gain of 10 decibels or more inthe direction of Brentwood, Long Island, New York.

Similar antennas, for receiving purposes, will beused at Brentwood. Special receiving, amplifying, andother control equipment, will be used to demodulatethe signals and transmit them to the main transmitterbuilding located about one mile from the receiving site.Due regard has been given to the proper location ofboth transmitting and receiving equipment for opti-mum results. This proposed operation is experimentalin nature and will allow CBS engineers to pioneer inthis high-frequency relay broadcast field. The per-formance of this system must be stable, completely

4 H. A. Chinn, 'Broadcast studio audio-frequency systems de-sign," PROC. I.R.E., vol. 27, pp. 83-87; February, 1939.

r -

I r-~~ 1 -

r--- ---- r-~ ----- -

E} AUDIO AUDIO|I AMPLIFIER &;I I AMPLIFIER &

MODULATOR MODULATOR_ n _ _ _ 1

CIS*D 6 R RCA RCA RCA732-PI

303-A 303-A 303-A

FILTER

RCA GR 732R RC CrOSCILL DIST. TR 306TA 30

MEASURING EQUIPMENT FREQUENCY METERS MOD

Fig. 1-Block diagram of the WCBX-WCRC monitoring facilities.

reliable, and suitable for continuous operation overlong periods of time.

THE BRENTWOOD INSTALLATIONThrough special arrangements with the Mackay

Radio and Telegraph Company, the site of theirBrentwood main transmitting plant will be used, wherethere are now already in operation twenty-two medium-and high-powered radiotelegraph transmitters. Mac-kay is now using many directive antenna arrays ontheir 1200-acre site which, for short-wave transmission,is excellent from the standpoint of topography, ac-cessibility, and availability of public-utility services.It is removed from populous centers, airports, and air-ways.A new fireproof, single-story wing, 40X60 feet, with

basement, is now being added to the existing Mackaytransmitter building, to house the new equipment.

Primary power supply is available from two dif-ferent sources over alternate routes to the Mackay-CBS substation, from which three underground, 2300-volt cables run to the transmitter building, a distanceof 0.66 mile. The three power feeders have a com-bined capacity of 1800 kilovolt-amperes.

Audio, measuring, and monitoring facilities havebeen designed by Columbia's engineering staff and in-clude the very latest methods of satisfying the require-ments of this project. The basic principles that mustbe considered in the functional design of a moderntwo-channel transmitting plant's audio and monitor-ing system will be used. Because of the nature of thisservice, the frequency- and modulation-monitoringapparatus arrangement, Fig. 1, is more complex thanthat usually found at standard broadcast stations.

Compression of volumerange, modulation "peak-chopping, " high-frequencypre-emphasis, and variablelow- and high-pass filters,will be available to obtainoptimum results. The de-

] gree of their use will dependupon transmission condi-tions and other variable fac-

I _tors.

UT _N

)ULATION MONITORS

TRANSMITTERSTwo custom-built, 50-kil-

owatt international-broad-cast-station equipments ofthe latest design, conceivedthree years ago, are nowbeing manufactured for thisinstallation by the FederalTelegraph Company. Thesefacilities are being con-structed in accordance withspecifications originated by

120 March

Chamberlain: CBS International Broadcast Facilities

the engineering department of CBS.Each of the two transmitters will be ca-pable of full output power to the trans-mission line, at 100 per cent modulation,over the entire frequency range of 6 to EXCITER --o

22 megacycles. It has been possible only NO.I <sorecently to obtain such powers in prac-tice at the higher radio frequencies.One of the major requirements of this

service is the ability to shift instantane- IIIously from one operating frequency to EXCITER AThanother. These transmitters are de- NO.2signed so that this can be accomplishedin a simple, positive, and reliable man-ner. There are several methods of accom-plishing this operation.5 CBS engineers EXCITER-_LOchose the method to be described after NOcarefully weighing the advantages and xc(

EXCI'disadvantages of various systems. TRAIIn order to accomplish an instantane- SWIT

ous change in frequency, there are pro-vided three complete radio-frequencysections from the crystal-oscillator unitto the 50-kilowatt power-amplifier out-put. Fig. 2 is a block diagram illustrat- g.ing the arrangement of all major ap-paratus units. This system allows the technicians whooperate the apparatus to preset the operating fre-quency of one radio-frequency section while the othertwo radio-frequency sections are being operatedsimultaneously.Each transmitter will be capable of operating on any

one of a total of twelve frequencies. Initially, ninecrystals will be provided for the frequency control ofeach radio-frequency section, a total of twenty-sevencrystals being required for the specific frequencies as-signed to WCBX and WCRC, 6060, 6120, 6170, 9650,11,830, 15,270, 17,830, 21,520, and 21,570 kilocycles.

Actually, the apparatus for these two stations willconsist of two and one-half transmitters. All of theradio-frequency equipment with associated power sup-ply and control facilities will be provided in triplicate,and the high-level class AB modulators and high-voltage power supplies in duplicate. Thus the twostations may be expanded by the addition of a thirdmodulation and power-supply unit which, with ac-cessories, will give CBS a third complete 50-kilowattransmitter, should a third station be required at somefuture date. The equipment will be installed to accom-modate this probable future expansion.The entire equipment is alternating-current-oper-

ated, utilizing specially designed water-cooled tubes,automatically regulated power supplies, and with allcircuits fully protected automatically. The apparatusis arranged so that complete accessibility to the in-

5 R. J. Rockwell and H. Lepple, "A push-button-tuned 50-kw.broadcast transmitter,' Elec. Eng., vol. 60, pp. 55-57; January,1941.

I

ELECTRICALLY CONTROLLEDAND INTERLOCKED MODULATOR

SWITCHES2-Block diagram of the WCBX-WCRC power amplifier

and modulator selector system.

terior of the transmitter units is provided for ease ofmaintenance, thus insuring maximum continuity ofservice. The operating personnel is safeguarded inevery respect.

Performance characteristics will be in accordancewith the most modern and best practices known to theart of broadcasting. They conform, in every respect,with the standards of good engineering practice pro-mulgated by the Federal Communications Commis-sion.

TABLE ITRANSMITTER PERFORMANCE SPECIFICATIONS

Carrier frequency range 6 to 22 megacyclesCarrier power 6 to 22 megacycles 50 kilowattsModulation capability 100 per centAudio-frequency response

40 to 10,000 cycles per second (1000 cycles persecond reference) ± 0.5 decibel

Audio-frequency distortionRoot-mean-square total harmonics-100 per centmodulation-S0 to 7500 cycles per second Less than 5 per cent

Carrier noise levelRoot-mean-square total, unweighted (100 per cent

modulation reference) 100 to 5000 cycles persecond -60 decibels

Below 100 and above 5000 cycles per second -50 decibelsCarrier shift0 to 100 per cent modulation Less than 3 per cent

Carrier frequency stability Within ± 0.0025 per cent

Circuits are conventional in design for the most part.There are a few noteworthy departures, including theline-type tank-circuit arrangement of the power ampli-fiers, the method of matching the power-amplifier out-puts to the transmission lines, and the arrangement formultifrequency operation.A water-cooled "resonating frame" type of line output

circuit will be used with each of the three 50-kilowattpower amplifiers. It consists of a copper pipe from eachanode parallel to each other for a lineal distance of

1942 121

Proceedings of the I.R.E.

TRANSMISSION LINES TO ANTENNAS NOS.

5 6 7

SWITCHES ARE MECHANICALLY INTERLOCKED IN VERTICAL SEQUENCE

AND ELECTRICALLY INTERLOCKED IN A HORIZONTAL SEQUENCE

Fig. 3-The WCBX-WCRC antenna-switching system.

about 35 feet with a center-to-center separation of 12inches. This length is required for 6-megacycle opera-tion. The piping will extend directly below the tubesthrough a hole in the floor to the basement and thereextend horizontally in a shielded interlocked compart-ment.

Inductive coupling will be used between the output

Fig. 4-An azimuth chart centered on New York City.

circuit of the final stage and the line to the antenna-switching system. Mechanically this will consist of atransmission-line (or frame) loop mounted in a hori-zontal plane directly above, and running the fulllength of the tank-circuit frame. This coupling loopwill be electrically grounded directly at its center.

Variation of coupling will be accomplished bymechanically varying the horizontal dis-tance between the two conductors formingthis loop. This movement will carry themfrom a point directly above the individual

i5S2 ° lines of the tank frame, toward each otheruntil they are but 2 or 3 inches apart. Thusthe coupling is decreased, both by movingthe coupling-loop conductors away fromthe tank-frame conductors and by decreas-ing the area within the coupling loop. Thedistance between the horizontal plane inwhich the tank-frame conductors are lo-cated and that in which the coupling-loopconductors are located will remain con-stant.The movement of these conductors will

be manual by means of a large handwheelcrank located on the front panel of thepower-amplifier unit and mechanicallycoupled with the mechanism controllingthe position of the coupling-loop conduc-tors.Tuning the tank frame to a particular

frequency will be accomplished by varyingits length by means of a short-circuitingbar, the position of which may be continu-ously varied along the full length of thetank frame. This short-circuiting bar will

122 March

Chamberlain: CBS International Broadcast Facilities

Fig. 5-Population density and radio-set ownership map of South America.

consist of suitable sliding contacts, arranged to gripthe line with sufficient pressure, with the short-circuit-ing conductor between them. This arrangement will becarried on standoff insulators mounted on a travelingcarriage moving on tracks below the line.A large threaded shaft or worm approximately 2

inches in diameter will be located at the center of andbelow the line, supported by bearings spaced approxi-mately 4 feet on centers. This worm extends the fulllength of the line and the carriage (with short-circuit-ing bar) is attached to it by a nut (split on one sideto pass the bearing supports) of sufficient length toride over the receded bearings. Thus the position ofthe carriage can be controlled by rotation of theworm.

At the end of the line, away from the power-ampli-fier unit is located a 3-phase, reversible, 2-speed motor,

which drives the worm by a V-belt coupling. At theend of the line near the power-amplifier unit a flexibleshaft is attached to the worm and this is used to drivea counter, on the front panel, so that the exact posi-tion of the carriage can be read on the counter.To select any one of the six frequency bands the

carriage will be run at high speed as follows: A 6-posi-tion rotary selector switch on the power-amplifier panelis set to the position desired and a motor-startingbutton pressed. Six "position" switches located alongthe carriage track may be placed at any location todetermine the operating positions for the six fre-quencies. The rotary selector switch, in selecting oneof these switches, determines the direction in whichthe motor must turn and pressing the motor-startingbutton closes the contactor to run the motor (at highspeed) in that direction. When the carriage arrives At

1231942

Proceedings of the I.R.E.

1000 FEET

Fig. 6-Ground plan of CBS and Mackay antenna arrays, Brentwood, Long Island, N. Y.

the "position" switch selected and operates it, the con-tactor falls out and the motor stops.A pilot light on the panel lights during the time the

motor is running to show the operator the change isbeing accomplished. An interlock relay prevents 12-kilovolt plate voltage being applied to the amplifierduring the process.

Safety limit switches are located, at each end of theline to cut the motor and prevent damage in case oneof the "position" switches fails to stop the travel.These limit switches have associated pilot lights on thepower-amplifier panel to inform the operator of themiscarriage. Pressing the start button will bring thecarriage back from the end of the line to a selectedposition without the necessity of going into the base-ment to run the mechanism by hand.

Vernier adjustment of the carriage position is ac-complished by a nonlocking, spring-return, single-pole,double-throw, manual switch on the power-amplifierpanel which operates contactors to run the carriage ineither direction at slow speed (actually half speed); thisadjustment may be made with power on. The manualslow-speed control of the motor is independent of the

high-speed position-selecting control except that inter-locking contacts prevent their being operated at thesame time.A second pair of pipe lines will also connect to the

power-amplifier anodes and run parallel to the pipesjust described, but will be enclosed in a separatelyshielded compartment. This line circuit will be short-circuited at the proper point to resonate it with thefundamental frequency. A fifth pipe will run betweenthis short-circuited pair to provide a path to groundfor the even-order harmonics and thus result in moreefficient operation of the power amplifier. The short-circuiting bar for adjusting the length of the harmonic-attenuation line has an identical control system tothat of the output tank-circuit line. The rotary selectorswitch and starting button are common to both sets oflines so that one operation serves for both setting theoutput tank and the harmonic lines.

Voltage regulators, power transformers, modulationtransformers, reactors, and other associated equip-ment will be located in a basement directly beneaththe apparatus with which they are associated.

124 March

Chamberlain: CBS International Broadcast Facilities

00

Fig. 7-WCBX-WCRC antenna No. 7 (9650 to 11,830 kilocycles) 4-section horizontal broadside array.

TRANSMISSION LINESOne of the major considerations is the switching

facilities to be used for interconnecting any of thethree 50-kilowatt-amplifier output lines with any de-sired combination of the thirteen transmission lines.Thirty-nine specially designed switches are requiredfor this purpose. Fig. 3 illustrates the system to beused. These switches, manually operated, will be inter-locked mechanically and electrically, in order to in-sure proper operation and protection to apparatus. Asthe voltage on the lines will be high during peaks ofmodulation (14,000 volts, root-mean-square) specialinsulators with properly designed fittings must beused. This is also true of the transmission-line andantenna insulators, all of which have been designedfor operation at 400 kilowatts peak power, at 22 mega-cycles, with a liberal safety factor included. Theseswitches are so arranged as not to unbalance the im-pedance of the lines, and thus reduce to a minimumloading difficulties, reflection losses, and undesiredradiation. Voltage-breakdown tests have been made todetermine the comparative merits of various insulatordesigns when operated at high voltages under prac-tical operating conditions.8More than 100,000 feet of copper wire will be used

for the open 2-wire balanced transmission lines. Eachof the lines will have a characteristic impedance of

6 Andrew Alford and Sidney Pickles, "Radio frequency highvoltage phenomena," Elec. Eng., vol. 59, pp. 129-136; March, 1940.

about 550 ohms. It is interesting to note that 20 tonsof No. 0 B & S gauge copper wire will be requiredfor the transmission lines and antenna elements, sup-ported from 536 wooden poles and 10 steel towers.This gives one a general idea of the scope of the an-tenna system.

Special networks will be installed on the transmis-sion lines for the purpose of performing a variety ofservices, including the matching of impedances, thecontrol of phase relationships, the division of power,filter action, the filtering of harmonic frequencies, andthe simultaneous transmission of two frequencies overone transmission line.Some of the functions of these networks could be

carried out using lumped inductance and capacitance,but it has been found more practical to utilize net-works made of sections of transmission line of thesame construction as the feeders themselves. The latterare preferable mechanically and economically, notonly because they are more rugged and stable whenexposed to the elements, but also because their per-formance may be calculated with a greater accuracy.The parameters on which their electrical propertiesdepend are linear dimensions which may be measuredon the job, in feet and inches, more simply and moreaccurately than the inductance of a coil or the capaci-tance of a condenser could be measured under similarcircumstances.Some of the networks that will be used are known

1942 125

Proceedings of the I.R.E.

z

-i

ul

(Ax

xO

rL

16E,TNWE IHORIZONTAL ANGLE - DEGREES

Fig. 8-The horizontal radiation characteristic of antenna No. 7 (9650 kilocycles).

as the "re-entrant" type, which consist of two sec-tions of transmission line joined at their ends in sucha way as to form a closed loop.7

It will be necessary to use conjugate sections on thetransmission lines. Two sections are conjugate whenthe standing-wave (Emax/Emin) voltage ratio createdon a flat line by one section is corrected by a secondsection, so that a given frequency is passed withoutchange of voltage ratio.A further and more important use of conjugate sec-

tions is to employ them in two pairs, the first pairpasses frequency F1 without introducing a ratio, butis so designed as to introduce a predetermined ratiofor frequency F2 for the purpose of matching the lineto the load. The other pair passes frequency F2 with-out change of line ratio, but matches impedances forfrequency F1. Thus, the line will be matched to theload for two frequencies simultaneously and permitsone antenna to be fed with either one of the two fre-quencies, or by the two simultaneously, if a suitableline input network is employed to isolate the lines fromeach transmitter properly.One of the antennas for transmission to Europe will

be used simultaneously byCBS and Mackay, the formerusing 6120 kilocycles and the latter 6935 kilo-cycles. The first is a modulated 50 kilowatt car- 2rier and the second a 50-kilowatt continuous-wavecarrier.A re-entrant 2-stage conjugate filter will be used '

to isolate the two transmitter output circuits and ,to maintain proper impedance relationships be- cztween the power-amplifier outputs and the line La

that feeds the antenna array.78 A network of this >

type consists of four filters. Two on one side of 5the network are designed to block frequency 6935 0kilocycles. The other two filters on the oppositeside of the network block frequency 6170 kilo-

7 Andrew Alford, "High frequency transmission line net-works," Elec. Comm., vol. 17, pp. 301-310; January, 1939.8Andrew Alford, "Coupled networks in radio-frequencycircuits," PRoc. I.R.E., vol. 29, pp. 55-70; February, 1941.

cycles. The first two filters areconjugate at frequency 6170kilocycles while the other twoare conjugate at frequency6935 kilocycles.These networks will be in-

stalled near the transmitterbuilding in order that only asingle long transmission linewill be required to carry thetwo frequencies to the antenna.This feeder is about 3800 feetlong. The economic advantagesare obvious as this plan elim-inates the requirement of twoseparate long transmission linesand two separate antennaarrays.

Several of these networks have been successfullyused by Mackay at Brentwood. Their use has beenentirely trouble-free and excellent constancy of ad-justment has been obtained with a minimum of main-tenance attention.

Experience has shown that a 5 per cent separationbetween frequencies of two transmitters is sufficientfor satisfactory operation of these networks. The de-gree of filtering obtainable under these conditions issuch that the attenuation of the undesired frequencyamounts to about 40 to 50 decibels. The power loss isnot more than 0.2 to 0.3 decibel.

DIRECTIVE ANTENNA ARRAYSThe engineering, mechanical, and economic con-

siderations affecting the choice of directional antennadesign were given detailed study by a group of en-gineers. After giving due attention to all service re-quirements, including direction, distance, and areas tobe served, many plans were considered and one ofthese adopted.

Fig. 4, an azimuth chart centered on New YorkCity, indicates the true bearings to the various world-wide areas proposed to be served. Fig. 5 shows the

R ILE :

~~~~~~~~~~Ground:: -- - - - - -- - - - -- - - - - -- - - - -

0 10 20 30 40 50 60 70 80 90VERTICAL ANGLE - DEGREES

Fig. 9-The vertical radiation characteristic of antenna No. 7(9650 kilocycles),

126 March

Chamberlain: CBS International Broadcast Facilities

concentration of urban populationand receiving sets in South America.

These, and other factors, re-sulted in the decision to erect,initially at least, 13 unidirectionalarrays, 30 antenna-array-fre-quency combinations, in accord-ance with Table II.The radiation characteristics of

a directive antenna array of this,and other horizontally polarizedtypes, depends upon the topogra-phy, arrangement, physical di-mensions, number of elements, dis-tance between the elements, dis-tance between the radiator and thereflector, height of the elementsabove ground, the phase and dis-tribution of the current, the mag-nitude of power in each of the ele-ments, and the operating fre-quency.9The Brentwood antennas will

(SHOWN AS APPLIED TO A SINGLE SECTION ARRAY. TWO OF THESESWITCHES ARE REQUIRED ON EACH 2 SECTION REVERSIBLE ARRAY)

Fig. 10 WCBX-WCRC remote-control radiator-reflector reversing system used on an-tennas Nos. 9, 10, and 11 for transmission to Europe or Mexico Central America.

9 G. C. Southworth, "Certain factors affecting the gain ofdirective antennas," PROC. I.R.E., vol. 18, pp. 1502-1536; Sep-tember, 1930.

TABLE IIDIRECTIONAL ANTENNAS TO SOUTH AMERICA AND WEST INDIES

Beam Verticaltenna Kilo-nc Direction Width Angletenna

clo True (6 deci- (maxi- Gaint General DirectionNue- cles (reofN bels mumber$ (E of N) down) radius)Degrees Degrees Degrees Deci-

bels1. 17830 171* 14 14 15 Argentina-West Coast

21520 12 12 16 South America21570

2. 17830 155* 14 14 15 Brazil-East Coast21520 12 12 16 South America21570

3. 11830 171* 30 18 11.5 Argentina-West Coast15270 22 14 13 South America

4. 15270 171* 14 17 15 Argentina-West Coast17830 12 14 16 South America

5. 11830 155* 30 18 11.5 Brazil-East Coast15270 22 14 13 South America

6. 9650 171* 14 18 15 Argentina-West Coast11830 12 16 16 South America

7. 9650 155* 14 18 15 Brazil-East Coast11830 12 16 16 South America

8. 6060 166 41 18 10 South America61206170

Directional Antennas to Eurosse or Mexico and Central America9. 17830 52* or 232* 28 14 12.5 Europe or Mexico

21520 24 12 13 and Central America21570

10. 11830 52* or 232* 30 18 11.5 Europe or Mexico15270 22 14 13 and Central America

11. 9650 52* or 232* 28 18 12 Europe or Mexico11830 22 15 13 and Central America

12. 6060 54 14 18 15 Central Europe61206170

13. Same 220 41 18 10 Mexico and CentralAmerica

* Adjustable ± 10 degrees.t Reference antenna 0.50X horizontal dipole in free space.1 30 antenna-array-frequency combinations.

consist of stacked horizontal broadside arrays, withparasitically excited reflectors. They comprise rows of2, 4, or 8, 0.5 X to 0.64 X elements, placed side by side, intwo rows stacked one above the other, with a verticalseparation between rows of 0.50 to 0.64 X. The reflectoris 0.20 to 0.22 X from the radiator. The height aboveground of the bottom row of elements depends uponthe frequency for which the antenna is designed andis usually more than 0.5 X. Fig. 6 shows the arrange-ment of CBS and Mackay antennas on the Brentwoodsite ground plan.

Fig. 7, is a drawing of a typical array, antenna num-ber 7, designed for operation on 9650 or 11,830 kilo-cycles, having a calculated gain of 15 decibels at thelower and 16 decibels at the higher frequency. Fig. 8indicates the horizontal and Fig. 9 the vertical radia-tion characteristics of this array.

Field tests, with small-scale models, give resultswhich corroborate the antenna-design calculations andthus, it is believed that anticipated performance willbe realized in practice.

Reflectors are used to obtain an additional gain ofalmost 3 decibels in the forward or desired directionof radiation. This is equivalent to doubling the carrierpower of the transmitter, with the additional ad-vantage of reducing backward radiation, which, on thehigher frequencies, sometimes results in impairing thequality of reception due to echo effect. The signal,when radiated both forward and backward, arrives atthe receiving antenna over two different great-circlepaths of different lengths, thus producing this phe-nomenon. Echo sometimes arises, even when uni-directional radiation takes place, because of the signalarriving at the receiver once, and a second time,approximately 7 of a second later, after it has traveled

1942 127

Proceedings of the I.R.E.

Antenna No. 3 Antenna N

15270 kc 9650

Gain 13 dbl Gain 15

Bearing 171 0T $ Bearing 15!

Beam Width 220 Beam Width

Beam Power 1000 kcw Beam Power

HORIZONTAL RADIATION CHARACTERISTICS(BEAM DIRECTION ADJUSTABLE * 10o)

Fig. 11-Simultaneous transmission to Latin America from WCBX and WCRC.

all the way around the world and been received again.Three of the antennas, numbers 9, 10, 11, may be °

reversed 180 degrees by remote control, and used for The best transtransmission to Europe or to Mexico and Central limited usefulnesAmerica. This is accomplished by interchanging the available for thistransmission-line and reflector-line matching stub with band. In generathe radiator and reflector, using two double-pole, night transmissi(double-throw switches, a switch for each section of the the higher frequantenna. Two switches will berequired for each of these re-versible arrays. Fig. 10 indi-cates some of the details ofthis arrangement.

Figs. 11 and 12 show typical Antenna No 4simultaneous transmission to 17830 kcvarious points of the world andrepresent typical combinations Gain 16 dblof antenna arrays as they willbe used in practice. These are Bearing 1710 Tmerely horizontal polar dia-grams applied to an azimuth Beam Width 120map centered on New York.The contours do not indicate Beam Power 1990 kwcoverage nor absolute field-in- 90tensity values but show the .directions of maximum radia-tion. ---

The tuning and adjusting ofthe directive antenna arrays,with their associated transmis-mission lines, is a complex taskthat requires the services ofexpert engineers who are ex-

perienced in this field andthoroughly familiar with thetheory and measuring tech-nique involved. Proof-of-per-

lo. 7 formance data, based on field-intensity measurements, will

kc be obtained at the Brentwoodsite, using as a reference an-

db tenna a 0.50 X horizontal di-pole located at various heights

5o T above ground. The array andreference antenna will be fedh 14o the same amount of power

1580 kw while rapid comparisons inperformance are observed atthe distantly located relay re-ceiving stations. Empiricalobservations will also be madeand these data evaluated.This subject is beyond thescope of this paper and willbe treated in a future paper,based on the results of thiswork which will take manymonths to complete.

)PERATING CONDITIONSsmitting and receiving apparatus is ofss unless a number of frequencies ares service, at least one or more in each1, the lower frequencies are good forons over paths of complete darkness,encies for daytime transmission, and

Antenna No. 10

15270 kc

Gain 13 db

Bearing 52 0 or 232 0 T

Beam Width 220

Z ~2P 1 < Beam Powor 1000 kw

HORIZONTAL RADIATION CHARACTERISTICS(BEAM DIRECTION ADJUSTAIBLE * loo)

Fig. 12-Simultaneous transmission to Europe (or Mexico) and theWest Coast of South America.

128

the intermediate frequencies, 15- and 11-megacyclebands, for transitionary periods of time; i.e., when thetransmission path is partly in darkness and partly indaylight. Because several variable factors greatly in-fluence the propagation characteristics of short waves,it is necessary to use the frequency best suited for anexisting condition of transmission and upon the properchoice of frequency depends to a large degree thesuccess or failure of a short-wave broadcast or relay.The frequencies selected for daily operation, i.e.,

the station operating schedule, are determined byexhaustive study of (1) the United States NationalBureau of Standards radio wave propagation data,10 (2)field-intensity-measurement data, (3) professional re-ception reports such as those compiled by the BritishBroadcasting Corporation receiving station at Tats-field, England, (4) frequency measurements made bythe Union Internationale de Radiodiffusion ControlCenter, formerly located at Brussels and more recentlylocated at Berne, Switzerland, (5) reports from CBSrepresentatives abroad, and (6) correspondence fromshort-wave-station listeners.The Union Internationale de Radiodiffusion Control

Center frequency measurements are very useful forpredicting sources of interference from other short-wave stations. They indicate, quite accurately, thenumber and identity of stations operating in each ofthe frequency bands. The 6- and 9-megacycle bandsare exceedingly crowded at present resulting in con-siderable chaos and interference. It is hoped that withthe conclusion of present unsettled conditions, worldradio conferences will again convene, and this situa-tion be improved. The recent inter-American radioconference held at Santiago, Chile, made noteworthyprogress in this direction.

10 T. R. Gilliland, S. S. Kirby, N. Smith, and S. E. Reymer,"Characteristics of the ionosphere at Washington, D. C.," monthlyreports published in the PROC. I.R.E., vols. 25-29; 1937-1941.

INTERNATIONAL RECEIVING STATIONIt is necessary that the receiving-station facilities,

the signals from which are used for rebroadcasting, becapable of performance equal to those of the trans-mitting station. Either space- or phase-diversity uni-directional antenna systems should be employed, andthe entire receiving-station facilities properly en-gineered. A great deal of information has been publishedon this subject and will not be detailed here.""2"3

CONCLUSIONThe present and proposed service by international

broadcast stations of North America, including expan-sion of existing facilities and construction of new sta-tions, will undoubtedly accelerate interest in this serv-ice."4 Transmissions from the United States to LatinAmerican countries will soon be equal to or betterthan those now received from other countries. Thenew WCBX and WCRC transmitting stations willincrease the intensity of CBS signals to Latin Americaand Europe, based on a conservative estimate, by atleast 20 decibels. This is equivalent to a hundredfoldincrease in the power of the existing facilities.

ACKNOWLEDGMENTSincere thanks and appreciation are extended to Mr.

Andrew Alford and associates of the Mackay Radioand Telegraph Company, and to my associates in theCBS General Engineering Department, for their co-operation and assistance in obtaining much of thematerial presented.

1 A. A. Oswald, "The Manahawkin musa," Bell Lab. Rec., vol.8, pp. 130-134; January, 1940.

12 J. B. Moore, "Recent developments in diversity receivingequipment," RCA Rev., vol. 2, pp. 94-116; July, 1937.

13 H. T. Friis and C. B. Feldman, "A multiple unit steerableantenna for short-wave reception," PROC. I.R.E., vol. 25, pp. 814-917; July, 1937; Bell Sys. Tech. Jour., vol. 16, pp. 337-419; July,1937.

14 Raymond F. Guy, "NBC's international broadcasting sys-tem," RCA Rev., vol. 6, pp. 12-35; July, 1941.

The Velocity of Radio Waves Over Short Paths*R. C. COLWELLt, MEMBER, I.R.E., H. ATWOODt, ASSOCIATE, I.R.E.,

J. E. BAILEYt, STUDENT, I.R.E., AND C. 0. MARSHt, ASSOCIATE, I.R.E.

Summary-The velocity of radio waves was measured directly inthe following manner. Two radio stations were set up on frequencies of3492.5 and 2398 kilocycles, respectively. One station was fixed whilethe other was portable. The fixed station sent out pulses which were re-ceived at the portable station. A thyratron control set off return pulseswhich came back to the base station. At the base station the two pulsesappeared upon a cathode-ray oscilloscope with a sweep of 22,800 inchesper second. The separation of these pulses gave the time for the pulsesto travel twice the distance between the stations plus the time requiredto pass through the receiving apparatus. By taking the portable stationto two positions one 0.73 kilometerfrom the base and the other 3.67 kilo-meters, it was possible to eliminate the time lag in the receiver and so tofind the exact time of propagation. Each station was in sight of theother. The average of 180 measurements was 2.985 X 101" centimetersper second.

* Decimal classification: R111.1. Original manuscript receivedby the Institute, July 17, 1941.

t West Virginia University, Morgantown, West Virginia.

Tp HE VELOCITY of radio waves in air is alwaysassumed to be the same as the velocity of light.Exact measurements over long distances are sub-

ject to the uncertainty that the real path of the wavescannot be determined. If, however, the path of the waveremains in the line of sight, it is reasonable to assumethat it will follow the straight line connecting the twopoints. The distance between the two points can bemeasured but the time interval becomes so small thatordinary measuring devices cannot be used. However,very short intervals of time (1 microsecond) may bemeasured upon a cathode-ray oscilloscope with a fastsweep.

Proceedings of the I.R.E.March, 1942 129