PHILCOTECHREP DIVISION

November and December, 1954 No. 4

t.A

Editorial John E. Remich 1

Crystal Checker Leland N. Van Allen 2

NBS Research in Radio Propagation 4

Duplicating and Addressing System for Tape Relay CentersCapt. Thomas Cunningham 23

What's Your Answer? 27

Index for Vol. IV 28

Solution to September -October "What's Your Answer?" 29

PHILCO

TECHREP DIVISION

BULLETINPublished bimonthly by

The TechRep Division of Philco CorporationPhiladelphia, Pennsylvania

&litoi John E. Remich

aeritas, big &filo/ Gail W. Woodward

,Fecknical 6Vitazd Francis R. Sherman

John W. Adams

Baldwin G. Sullivan

&de*4art Office:

Technical Information SectionPhilco TechRep Division22nd St. and Lehigh AvenuePhiladelphia 32, Penna.

If any information contained herein conflicts with a technical order,manual, or other official publication of the U.S. Armed Forces, theinformation in the official publication should be used. Views expressedin this publication are the opinions of the authors and do not necessarilyrepresent those of Philco Corporation. All technical information andcircuits are presented without responsibility as to patent infringement.

Copyright 1954, Philco Corporation

editorial .

1954

by John E. RemichManager, Technical Department

As the fourth year of BULLETIN publication draws to aclose, we wish to take this opportunity to express our appreci-ation to Philco Field Engineers for their excellent cooperationin contributing the many fine articles which have appearedduring 1954.

During the past year, the BULLETIN has been converted toa bimonthly publication. In addition, a new and spritely "dress"

was adopted for the magazine with the publication of the July -

August issue. These changes, however, are mechanical ones, and

do not affect the aim of the BULLETIN, which is to bring tothe Field Engineer the latest and most helpful informationrelating to his specialty.

The year 1954 has seen a further interest an transistors, andnew developments along this line have caused an increase incommercial applications for transistorized components. In alike manner, the almost unprecedented swing to automation hasbrought the servomechanism into sharp focus. Therefore, tran-sistor and servomechanism articles have been conspicuous inthe 1954 BULLETIN issues. It is felt that the Field Engineerwill have increasing need for information concerning transistorsand servomechanisms.

We welcome your further cooperation in 1955, and wish yousuccess during the coming year.

1

CRYSTAL CHECKERby Leland N. Van Allen

Philco Field Engineer

A description of a test device which can aid field main-tenance men two ways: first, by decreasing equipmentoutages due to crystal failure, and second, by decreasing

the effort involved in checking crystals.

(Editor's Note: The crystal checker described in this articlewas specifically designed to check the activity of crystalsused in the AN/ARC-3 airborne equipment; however, achecker of this type can be used to determine the relativemerit of crystals used in other equipments if acceptablestandards, based on those described in this article, are

established.)

CRYSTALS FOR THE AN/ARC-3 air-borne VHF transmitter -receiver, whichis extensively used in U.S. aircraft, mustbe quite active to provide dependableservice. Using agencies, realizing this,require that the AN/ARC-3 crystals bechecked periodically. Such a check be-comes a major problem to a typicalmilitary organization, which may havemany thousands of crystals on hand.Checking quantities of crystals by trialin an operating set is obviously slowand impracticable, particularly whenadjustments must be made to the equip-ment for each different crystal fre-quency. The alternate method of check-ing crystals by using a test oscillatorand tuning for the signal on a commun-ications receiver is very unsatisfactoryfrom a technical viewpoint because thismethod indicates only whether a crystalwill oscillate in the test -oscillator circuit-it provides no assurance that the crys-tal will operate in actual service.

The crystal checker to be describedovercomes these disadvantages by pro-viding a quick method of checking crys-tals for relative activity, which actuallyamounts to a crystal quality check.While specifically designed for checkingcrystals in the frequency range of 5 to 9

megacycles, it can be adapted for usewith crystals of virtually any frequencyby simply using different circuit com-ponents.

The schematic diagram of the crystalchecker is shown in figure 1. The Pierceoscillator circuit was chosen because itis not frequency discriminating; i.e., itwill permit a crystal of nearly any fre-quency to oscillate.

Any triode having suitable power re-quirements, such as a 6AT6, 6J5, 6C5,1/2 6SN7, 6SR7, 6SQ7, etc., may beused. If a double triode is used, onesection may be diode -connected andused for the power -supply rectifier, thuseliminating the need for a separate rec-tifier component.

To obtain adequate meter deflection,a fairly low value grid leak resistor(10K) is used to encourage grid -currentflow. In addition, this low value ensuresthat differences in crystal activity willbe reflected as substantial variations inthe amount of grid current.

The r -f choke in the plate circuit mustoffer a high impedance to frequenciesabove the lowest -frequency crystal to bechecked (in this case 5 megacycles),

2

IMO

+150V 65moSELENIUM

.005µt RFC iy RECTI FIER

II mh 470

CRYSTALSOCKET

CRYSTAL TOBE CHECKED

10K

I K

6AT6-I-um11 Bpi

150V I I5V

6.3V

OFF

ON I I 5V

60 CYCLES

MERIT 3045 OREQUIVALENT

Figure 1. Schematic Diagram of Crystal Checker

and the grid -to -cathode trimmer is ad-justed for maximum grid current on thelowest -frequency crystal to be checked.

The power supply can be fairly sim-ple since good filtering of the outputvoltage is not necessary.

The crystal checker should be cali-brated prior to use by plugging in sev-eral good crystals and setting the meterto indicate half -scale for the crystal giv-ing the highest reading. When a crystalof unknown activity is checked, thereading obtained will then indicate theactivity of that crystal relative to 0.5 offull scale (0.5 being used as 100%, orccperfect").

Experience with this checker hasshown the following to be true: crystalshaving an activity of 60% or higher(0.3 to 0.5 on the meter scale) rarelyfail in service; those producing a read-ing from 0.2 to 0.3 of the meter scaleoccasionally do not function properly in

use; and those producing readings of0.2 or less are undependable.

With this in mind, the following inter-pretation of meter readings is suggested:

0 to 0.2-Bad0.2 to 0.3-Questionable0.3 to 0.5-Good

It is true that the use of this checkermay result in the rejection of some crys-tals which, would give satisfactory serv-ice; however, as a general rule, it is"better to be safe than sorry."

If desired, the frequency of each crys-tal may be checked, while it is operatingin the checker, by using a communica-tions receiver or frequency standardsuch as the BC -221; however, this checkis not ordinarily necesary. Crystals sel-dom change frequency unless some phy-sical damage is done to the quartz plateitself, and when this happens, an accom-panying loss of activity is almost certainto occur.

3

THE

NBS RESEARCH IN RADIOPROPAGATION

A broad program of research in radio propagation en-sures development of better systems, more accuratestandards, and more reliable propagation forecasts for

use by the Government, industry, and science.

INCREASED UTILIZATION of thespace available in the radio spectrum byalmost every phase of industry, com-merce, science, and the armed serviceshas been the determining factor informulating the program of the CentralRadio Propagation Laboratory (CRPL)of the National Bureau of Standards.Technological developments have ad-vanced the science of communicationsand electronics so that equipments nowfunction at frequencies up to 100,000megacycles. Accompanying these ad-vances is the growing need for moreinformation about the characteristics ofradio energy under diverse conditions.Thus, in order to serve these interestsmore effectively the National Bureau ofStandards is establishing a new multi-million -dollar radio research laboratory(see figure 1) in Boulder, Colorado.

As the Nation's central agency forcollecting radio propagation data, CRPLin turn analyzes and disseminates infor-mation that aids reliable global aviation,all-weather shipping and harbor control,and world-wide communications. TheLaboratory's studies of frequency allo-cation and interference affect the estab-lishment and operation of AM, FM, andTV broadcast stations. Data on ultra-high -frequency radio propagation andthe development of improved microwavemethods are important to the WeatherBureau and military aerologists for usein upper -air temperature, humidity, andwind measurements. Accurate measure-ment methods and standards maintainedby CRPL are essential to studies inmany branches of engineering and

physics. Also, many industrial applica-tions of radio require CRPL standardsand measurement techniques.

EARLY RADIO PROPAGATIONACTIVITIES

Radio propagation studies were for-mally begun at the Bureau in 1909 withthe measurement of low -frequency radi-ations. The radio signals at these fre-quencies traveled comparatively shortdistances and only along the surface ofthe earth (so-called ground -wave trans-mission). The studies were extended toinclude higher frequencies after thebasic demonstrations of ionospheric re-flection of radio waves in 1926. In theseexperiments, the radio waves were di-rected toward the upper atmosphere (50to 300 miles above the earth's surface).Here, the layers of ionized gases actvery much like mirrors and bend thehigher -frequency radio energy back to-ward the earth. Thus, by using iono-spheric reflections, it became possible totransmit radio signals over extremelylong distances.

In the subsequent decade NBS in-creased the scope and amount of itsionospheric measurements and theory,and developed techniques that were in-corporated later in military radar andradio. However, full achievement of thevalue of systematic collection of radiopropagation data was not accomplisheduntil the Combined Chiefs of Staff (U.S.Armed Forces) established the Inter -service Radio Propagation Laboratory(IRPL) at NBS in the spring of 1942.

4

Figure 1. Air View of the National Bureau of Standards Multimillion Dollar ResearchCenter in Boulder, Colorado. This structure will house the Bureau's Central RadioPropagation Laboratory. The design of the building features a central spine, with one-story wings extending perpendicularly from it on either side. The structure takesadvantage of the sloping terrain that rises from a state highway toward the Flatironsto the west. The buildings in the background, also part of the research center, are

portions of the NBS-AEC Cryogenics Engineering Laboratory.

During World War II, IRPL renderedcontinuous service to the military estab-lishments. A direction -finder study, be-gun under the National Defense Re-search Committee (NDRC), was takenover by the Laboratory. Large quanti-ties of ionospheric and other radiopropagation data were accumulated fromall over the world. With the develop-ment of radar, the need was furtherincreased for propagation informationat ultra -high frequencies and at themicrowave frequencies (greater than3,000 mc). Many groups from theArmy, Navy, and Air Force were trainedin the use of radio propagation informa-tion and techniques. Continuous liaisonwas maintained with the military con-cerning their communications opera-tions. Staff members from the British

and Canadian Navies and the R.A.F.were assigned to IRPL, and liaison offi-cers were assigned for duty with similarorganizations in Australia, New Zealand,Great Britain, and Canada.

Regular ionospheric predictions wereissued in a form that later became themonthly publication Basic Radio Propa-gation Predictions, CRPL Series D. Adisturbance warning service was alsoestablished to forecast ionosphericstorms that would interrupt radio com-munications. An extensive reporting andanalysis program was mail tained byNBS, the Carnegie Institute of Wash-ington, the Army Signal Corps, andothers active in the study of radio prop-agation. Hundreds of special propaga-tion problems of both technical and

5

strategic value to communication andintercept work were solved. The mostusable frequencies for many types ofcommunications to all parts of the worldwere determined. Accompanying prob-lems involving antenna design, powerand receiver requirements, and fre-quency allocations were also solved. Inaddition, NBS was employed in thedevelopment of VHF and UHF stand-ards, countermeasures work, and theregular standards activities carried overfrom before the war.

The service performed by IRPL andthe other propagation laboratories dur-ing the war not only increased the de-pendability . of radio but also showedthat still greater improvements in radioequipment and communications couldbe attained through continued research.This experience showed that propaga-tion information and research were vitalto the effective use of radio communi-cation, direction finding, radar, radionavigation, and other devices employingradio waves.

At the end of the war, a survey offuture work needed by the Army, Navy,Air Force, Coast Guard, FCC, and non -Government interests led to the conclu-sion that the whole field of basic propa-gation research should be centralized. Itwas realized that if the progress andservices rendered during the war werenot continued, the Nation would losemuch of the benefit derived from theoriginal effort. Moreover, the UnitedStates would be at a disadvantage incomparison with other countries, whileat the same time military and civilianradio activities would be greatly ham-pered. In addition, many Federal agen-cies, under the exigencies of wartime,had developed organizations workingnot only on applications of propagationto their problems, but also on funda-mental research along parallel lines.Centralization of basic propagation re-search common to all the user agenciesseemed, therefore, the best scheme to

meet the needs of the country in thisfield without needless duplication ofwork.

Although the need for coordinationwas apparent, the magnitude of the taskwas too complex to achieve success inone organizational step. Accordingly, onMay 1, 1946, the Central Radio Propa-gation Laboratory was established asone of the technical divisions of theNational Bureau of Standards. A RadioPropagation Executive Council, organ-ized to formulate general policy, in-cluded representatives of the Army,Navy, Air Force, FCC, CAA, CoastGuard, State Department, and the radioindustry. Besides the existing IRPLfunctions, the new Laboratory assumedthe duties of the NBS Radio Section.These included the maintenance and de-velopment of radio standards, the opera-tion of radio broadcasting station WWV(which transmits standard radio fre-quencies, time signals, audio signals,and radio , theincipient standards work on high fre-quencies, radio countermeasures, andradiosondes; all of which are related,directly or indirectly, to propagation. Ofparticular importance was the promo-tion of standards development in thethen -unexplored but rapidly growingfields of ultra -high and microwave fre-quencies.

Thus, the program of the new CentralRadio Propagation Laboratory was de-signed to include all aspects of radiopropagation research and investigationand many related activities. Experimen-tal programs of world-wide scope wereplanned. These included measurementsof radio field intensity, ionospheric ab-sorption, radio noise, solar and geo-physical effects, the structure of theatmosphere and ionosphere, and the in-fluence of the ground and troposphereon radio propagation.

The information obtained from thesestudies of radio wave propagation is

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Figure 2. The Radiosonde, OriginallyDeveloped for the Navy by the NationalBureau of Standards in 1936, Suspendedfrom a Free Balloon, Telemeters In

on Upper -Air Pressure, Tempera-ture, and Humidity. Thegeneral use by the Navy, Army, CoastGuard, and Weather Bureau for collect-ing meteorological data employed inweather forecasting, and has replaced theairplane for obtaining information of thistype. The radiosonde employs a modu-lator and oscillator, the ultra -high -fre-quency output of which is controlled byspecial resistors that are sensitive tochanges in atmospheric phenomena. Thechanges in modulation frequency are thus

measures of the phenomena studied.

analyzed and disseminated by CRPL toall interested users of radio communica-tions. The material is also employed inpreparing predictions of radio -wavepropagation conditions 3 months, 2weeks, or even 6 hours in advance. Aspart of the operation of two standard -frequency radio broadcasting stations(WWV and WWVH), CRPL dispensesradio disturbance warnings to users ofcommunications circuits over the NorthAtlantic and North Pacific areas. Fur-ther, the Laboratory has custody of theNational primary standards of all elec-trical quantities used at frequencies be-

tween 10 kc. and 100 kc., and performscalibrations in terms of these standards.

The role of CRPL in national defenseis both basic and operational. It con-ducts basic research and developmentwork for use of the armed services andtheir contractors, and provides much ofthe operational information and guid-

ance in the field of applied radio propa-gation. The radiosonde, shown in figure2, is a good example of such work. Thevalue of CRPL's program became evenmore apparent during the latter part of1950 when its activities were again di-rected toward the needs of nationaldefense and the requirements of themilitary.

CRPL prediction services were usedfor determining operating frequenciesfor both strategic and tactical operationsin all parts of the world. Both long -haul,point-to-point, and intertheater commu-cations utilized the detailed predictionsthat only the Laboratory could make,and for which the experience of theIRPL was invaluable. The Laboratoryassisted in the preparation of tables offrequencies for communications betweenfleets and naval bases, flight charts foraircraft ....communications, tables andnomograms for frequency allocations,and detailed short-term predictions forspecific areas. Warnings of sudden radiodisturbances or ionospheric stormswhich could interfere with radio com-munications were sent to the armedservices, with instructions as to whataction should be taken to maintain com-munications. Ionosphere recorders wereinstalled at field and advance -base prop-agation stations to obtain on -the -spotinformation. Analysis and testing ofnavigation and direction finding systemswere necessary to ensure the success offleet operations, aircraft missions (bothlong- and short -distance), and interceptand intelligence work. Propagation dataand standards over wide frequencyranges were required for phases of ra-dar such as search, early warning, fire

control ( ground, air, naval, antiair-craft), blind bombing, navigationalradar, beacons, identification, and dis-tance -measuring equipment.

CURRENT CRPL ACTIVITIES

Current activities are divided alongresearch lines essentially according tothe manner in which radio energy ispropagated. Responsibility for pursuingthe program is assigned to three labora-tories and a service section. The Iono-sphere Research Laboratory investigatesthe physical phenomena affecting theionosphere and radio propagation inand through the ionosphere (50 to 300miles above the earth's surface). TheSystems Research Laboratory is con-cerned with the characteristics of radio

systems depending on propagation inthe troposphere (up to about 10 milesabove the surface of the earth). TheMeasurements Standards Laboratoryperforms research and develops stand-ards and methods of measurement forall electrical quantities used at radiofrequencies. Finally, the CRPL propaga-tion prediction services correlate thewide -spread observations made by CRPLand other laboratories (both foreignand domestic as shown in figure 3) andprepare propagation predictions forusers of the radio spectrum.

These many activities have uniquelyprepared the NBS Central Radio Prop-agation Laboratory for the role ofconsultant and adviser to the Fed-eral Government on matters pertaining

Figure 3. Network of World -Wide Observatories Supplying CRPL with Solar ActivityInformation. (Numbered flags designate location of each observatory.) 1: NBS andNaval Observatory, Washington, D.C.; 2: Cornell University, New York; 3: McMath-Hulbert Observatory, Michigan; 4: Sacramento Peak, New Mexico; 5: Climax, Colo-rado; 6: Boulder, Colorado; 7: Mt. Wilson, California; 8: Greenwich, England; 9:Meudon, France; 10: Wendelstein, Germany; 11: Kanzelhohe, Austria; 12: Pic duMidi, Pyrenees; 13: Tokyo, Japan; 14: Mt. Stromlo, Australia; 15: India; 16: Sweden;

17: Italy.

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Figure 4. Gun Barrel Hill, Colorado, NBS Field Station Containing Three GiantWurtzburg Antennas. These devices are arranged to receive signals of a certain fre-quency radiated from the sun and to track the sun automatically as it moves acrossthe sky. Each antenna is tuned to receive a different frequency from the many

emitted by the sun.

to international radio communicationagreements. Members of CRPL haveserved on many international commis-sions and have given their services tomany national committees concernedwith the allocation of radio communica-tion circuits.

IONOSPHERE RESEARCHLABORATORY

Like most of the major functions inCRPL, the program of the IonosphereResearch Laboratory is based on pri-mary research in the physical laws gov-erning radio propagation. Studies ofelectromagnetic wave propagation the-ory are required to ascertain and applythe physical laws that form the frame-work for practical operating techniques.The studies also provide a basis forextrapolation of existing theories to newsituations without costly reproductionof field experiments. Closely related are

theoretical investigations of the mech-anism of radio frequency emission fromthe sun, in particular, solar noise bursts.On the experimental side, a 50 -footarray of radiometers is being con-structed near Boulder; and two otherradio telescopes are used to measuresolar emissions in the 160- and 480-mc.frequency regions (see figure 4). Theupper atmosphere physics program in-cludes an investigation of the complexmotions which this region undergoes asa result of the gravitational tidal forcesexerted by the sun and the moon. Forinstance, experiments using radio reflec-tions from the ionosphere have shownthat winds in the upper atmosphere haveperiodic variations and travel at speedsup to 300 miles per hour.

A thorough knowledge and under-standing of the nature and cause ofionization in the upper atmosphere isvitally important to the operation of the

9

CRPL prediction service. Characteristicsof the ionospheric layers are determinedat many radio sounding stations through-out the world. Some are operated byNBS; others form a network of coop-erating observatories that exchangeinformation at regular intervals. NBS-maintained field stations are located atAnchorage and Point Barrow, Alaska;Ft. Belvoir, Va.; Narsarssuak, Green-land; Ramey Air Force Base, P.R.; Ft.Randolph, Canal Zone; Guam; andMaui, Territory of Hawaii.

The propagation data received by.CRPL from a selected group of suchradio sounding stations, together withinformation from cooperating solar andmagnetic observatories, are the basis forNBS forecasts of ionospheric radiopropagation disturbances. General fore-casts, a few weeks and days in advance,are prepared from the 27 -day recurrencetendency of ionospheric disturbancesand from application of solar -terrestrialrelationships. More specific forecastsare made a few hours in advance fromstudies of variations in the earth's mag-netic field and from trends in iono-spheric and radio propagation observa-tions over a broad area. Advance fore-casts are furnished directly to represen-tatives of civilian and military govern-ment communication agencies, commer-cial enterprises, technical laboratories,and individuals. Short-term forecastsevery 6, 8, or 24 hours are furnished torepresentatives of key agencies and havewide distribution by broadcast and tele-type. Short-term forecasts for communi-cation circuits across the North Atlanticare prepared every 6 hours in the NBSforecasting center at Ft. Belvoir, Va.,and broadcast twice each hour by radiostation WWV. Similar forecasts forpaths across the North Pacific are pre-pared in the Anchorage, Alaska, fore-casting center and broadcast by radiostation WWVH.

In addition to studies of the iono-sphere directly related to the transmis-

sion of intelligence, CRPL conducts anextensive research program aimed atdiscovering how the upper atmospheremay be useful even during critical dis-turbance periods. A multifrequency ion-osphere recorder, sweeping from 1 to25 mc. in as little as 15 seconds, wasdeveloped for routine observations at allfield stations. In addition, CRPL pio-neered in developing a multifrequencyrecorder covering the low- and very -low -frequency ranges, from 50 kc. to 1.15mc. It is hoped that, through study of

the fundamental properties and basiclaws governing the practical usage oflow frequencies, an understanding willbe obtained that will permit more accu-rate prediction of the behavior of trans-mitted radio energy.

Instruments have recently been com-pleted to measure precisely the velocityof propagation of radio waves over theearth at frequencies between 100 and200 mc. Measurements will be made ofthe effects of atmospheric conditions andthe effects of reflection from terrainfeatures on the velocity. The measure-ments are expected to yield useful infor-mation on the ultimate accuracy andreliability of certain types of radio navi-gation systems.

Included in the prediction and fore-casting services of CRPL are recom-mendations of the maximum usable fre-quencies that may be employed duringany transmission period. Studies are be-ing continually conducted over long-distance paths to observe effects such asscattering of radio waves of certainfrequencies by the ionosphere or theground. These effects are additionaltools for the study of propagation con-ditions and improvement of communica-tions. A controlled radio path has beenestablished between Sterling, Va., andBoulder, Colorado (1500 miles) ; andas an experiment, a circuit was estab-lished between Sterling, Va., and CedarRapids, Iowa, using the moon to reflectthe signal. Still other studies are being

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Figure 5. NBS Model Antenna Range. This range is believed to he the largest of itskind designed to measure antenna radiation patterns in the vertical plane. Theinverted -V structure supports a self-contained target transmitter at the vertex and isdesigned to move in a 180 -degree arc. The antenna to be tested is placed at the centerof the oval -shaped grouted plane. The model techniques that are used permit aninvestigation of antenna characteristics in the 1-to-25-mc. region while actually oper-

ating at frequencies between 60 and 1500 mc.

performed in the arctic regions to findwhy and how communication on certainfrequencies is affected by the highlyactive aurora.

CRPL is also developing new and im-proved antenna systems for propagationinvestigations. A model antenna range,shown in figure 5, is used to investigateantennas in a model ratio of 60 to 1.

The ever-increasing use of radiowaves for both civilian and militarypurposes and the corresponding de-mands for useful frequencies make theproblem of frequency allocation moreand more acute. The present trend is toutilize higher and higher frequencies,and thereby extend into the microwaveregion as far as practicable. In thisregion, perhaps the chief factor limitingthe prediction of propagation conditionsis atmospheric absorption. In order toobtain data on this phenomenon, large

cavity resonators (100 centimeters indiameter) have been constructed. Theyhave a cavity Q (measurement of effici-ency) of over one million. With thisapparatus, it is possible to study molecu-lar structure through microwave spectra,ionic absorption, and the absorption ofatmospheric constituents under variousmeteorological conditions.

SYSTEMS RESEARCH LABORATORY

All of the systems research activitiesof CRPL were transferred to Boulder,Colorado, in 1951. Here the rollingplains, extending hundreds of miles east-ward from the mountain regions, areutilized in many phases of radio propa-gation research. The mountains, too, areput to use: several transmitters are lo-cated on Cheyenne Mountain, near Colo-rado Springs, which affords an almostperpendicular drop of more than 2000

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feet to the floor of the plains. The pro-gram of this laboratory is divided be-tween frequency utilization research andinvestigations of tropospheric propaga-tion phenomena.

Frequency utilization research is con-cerned with obtaining information toassist in the allocating, regulating, andadvisory activities of such agencies asthe Federal Communications Commis-sion, International Radio ConsultativeCommittee, the Armed Forces, and vari-ous other governmental and privateorganizations employing radio methodsof communication, navigation, and con-trol. Experiments have been conductedin which mobile recording units havetraveled over areas serviced in commonby several TV and FM stations to deter-mine the amount of interference offeredby each station. Other mobile stationshave been placed on top of Pike's Peakto determine the effects of antennaheights on radio -wave propagation. Theaccumulation of such noise data on ter-restrial and extraterrestrial noise fromall parts of the world is expected toassist in the prediction of noise levelsin relation to geographical location, sea-son, time of day, frequency, and phaseof the sunspot cycle. A suitable receiver -recorder has now been developed withsuch necessary special features as nar-row bandwidth; good noise figure, highstability, and multichannel recordingfeatures.

The several types of modulation avail-able for the transmission of intelligenceare also studied by CRPL because oftheir effect on both the allocation andutilization of frequencies. This programincludes a determination of information -bearing capabilities, minimum band-width requirements, and minimum sat-isfactory signal-to-noise and signal -to -interference ratios for various systems,as well as effects of choice of frequenciesand fading of signals.

Studies of the effect of irregular and

inhomogeneous terrain were originatedby CRPL to provide basic informationand theories for application to systemstudies and, in general, to promote fur-ther understanding of the physicalconcept of electromagnetic wave propa-gation in the presence of such terrain.Experimental data from other sources,such as the Armed Forces and the FCC,are integrated into the CRPL programfor study and analysis. Mobile field -strength measurements are made overvarious types of terrain at frequenciesup to 500 mc. The experiments areconducted with single or double trans-mitters employing antennas up to 30feet in length. Conventional housetrailers, such as the one shown in figure6, have been modified to carry the elec-tronic transmitting and recording equip-ment relatively shock -free over roughterrain. A series of experiments dealingwith the refraction and tropospheric re-flection of radio waves over mountainobstacles has led to a new concept con-cerning the installation in mountainousregions of TV and FM broadcastingstations.

Besides the sun and terrain, the tropo-sphere has also been found to have aprofound influence on radio propaga-tion, particularly at frequencies above50 mc. This influence is most strikingat distances beyond the line of "radiosight," where the cause of abnormallyhigh observed field -strength levels andof seasonal and diurnal (daily) varia-tions are not well understood. Experi-ments have shown the presence of reli-able signals more than 500 miles fromthe transmitter, whereas previous the-ories predict a maximum range of onlysomewhat greater than the radio horizonat the frequencies employed.

Several transmitters are installed onCheyenne Mountain (see figures 7, 8,and 9) and on Pike's Peak as part of aresearch program designed to obtainfield -strength data under all types ofair-to-air, air -to -ground, and ground -to -

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.Figure 6. Mobile Research Unit Used by the National Bureau of Standards to Meas-ure the Field Strength of Radio Signals. Mobile units such as these have been sent toPikes Peak to determine range of transmitted signals from installations in the generalarea. Others have cruised in service areas common to several transmitters to determinethe amount of interference offered by each station. The antenna (on top of trailer)can be raised to a height of 30 feet by remote control while the unit is in motion.

Figure 7. Three -Cavity Klystron Transmitter Operated by the National Bureau ofStandards on Top of Cheyenne Mountain, Colorado. This instrument is used in theCRPL tropospheric propagation research program in studying the characteristics of

signals transmitted over distances beyond "radio -line -of -sight.

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Figure 8. Transmitting Antennas at theSummit Site of NBS Field Station onCheyenne Mountain, Colorado, Employedin the CRPL Tropospheric PropagationResearch Program. The metal tower sup-ports two antenna arrays for transmittingsignals at frequencies of 100 and 198.2mc. The semipyramidal horn antenna atthe base of the tower radiates energy at afrequency of 1046 mc. This summit siteis one of two similar installations onCheyenne Mountain: the summit is 9000feet above sea level; the second site is2000 feet below it, but does not include

the 1046-mc. transmitter.

ground radio transmitting conditions.By making measurements at frequenciesbetween 100 and 1600 mc., data areobtained which permit a correlationwith the relatively large amount of exist-ing FM and TV propagation data. Thisinformation has disclosed certain radio -wave characteristics that existing theo-ries have not predicted. These data alsoserve as a basis for establishment ofmore comprehensive and exact theoriesgoverning propagation of radio energyin the troposphere.

Figure 9. Semipyramidal Horn AntennaLocated on Top of Cheyenne Mountain,Colorado. The radiator is used in experi-ments designed to determine the condi-tions of the troposphere causing reliablereception of signals more than 500 milesfrom the transmitter. This antenna radi-ates 1.6 megawatts of effective power at a

frequency of 1046 mc.

In order to study the meteorologicalconditions associated with the observedresults from the Cheyenne Mountaintropospheric propagation research pro-gram, a 500 -foot tower has been in-stalled along the transmission path nearHaswell, Colorado. Special meteorologi-cal instruments and microwave refrac-tometers developed by the Bureau areemployed on the tower to study the va-riations in refractive index of the lowerportion of the atmosphere. Some of theassociated equipment is shown in figures

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Figure 10. The NBS Microwave Refractometer Employed at a Midwestern Site NearBoulder, Colorado, as Part of a Program for Measuring the Refractive Index of theLower Atmosphere. The unit at the left includes the electronic control and recordingcircuits. The box -like unit at the right contains the microwave elements and associatedelectronic components. During a measurement, this unit is raised to the top of a

500 -foot tower.

10, 11, and 12. Tropospheric variationshave been found to have an importantinfluence on the strength and fadingcharacteristics of VHF and UHF radiosignals received at great distances. Dur-

Figure 11. Microwave Components ofNBS Microwave Refractometer Used byCRPL to Measure the Refractive Ihdex ofthe Lower Atmosphere. In normal use,these components are suspended from the

top of a 500 -loot tower.

ing recent years, several Governmentagencies have organized this type ofinformation into a form suitable for theefficient allocation of radio frequenciesin the milk) spectrum ranging around

Figure 12. Analogue Computer for Solv-ing the Radio Refractive Index Equation.This device is one of the products of theCRPL instrumentation program devotedto the development of equipment to beused in studies of the ionosphere andtroposphere. This instrument computesthe refractive index automatically fromobserved meteorological parameters, in-cluding temperature, atmospheric pres-

sure, and relative humidity.

15

50 mc. The Radio Technical Committeefor Aeronautics, for instance, has re-quested CRPL to supply informationthat will eventually lead to the allocationof frequencies for air -ground communi-cations and navigational facilities.

A program is in operation to supplybasic radio propagation data for thefrequency range of 30 to 6,000 mc. in aform adaptable for use in operationalanalysis of different communicationssystems. The Department of Defense,through one of its agencies vitally inter-ested in radio propagation informationfor the VHF and UHF portion of thespectrum, has assisted CRPL in obtain -

Figure 13. IN BS Primary Resonator Fre-quency Standard. Temperature -controlledquartz crystals are made to resonate at afrequency of 100 kc. Several of the oscil-lators are offset from 100 kc. by a smallnumber of cycles to permit comparisonmeasurements by dual electronic counters.A variable oscillator is also employed inthe comparison measurements. The ac-curacy of this system is more constantthan the rotation of the earth, the presentNational standard of time. Therefore, de-viation of the oscillator frequency (and,therefore, that transmitted by WWV )from the mean sidereal day must be com-puted. These variations are periodicallyissued as corrections to the NBS frequencystandard utilized by science, industry, and

commerce.

Figure 14. The NBS Microwave Adjust-able Frequency Standard with WhichSecondary Frequency Standards Are Cali-brated for Government Agencies, DefenseActivities, Science, and Industry. The pairof dolly -mounted racks to the right con-tain the electronic components of the

Model II ammonia clock.

ing a large amount of radio transmis-sion loss data over almost the entireUnited States. The analysis and inter-pretation of these data must take intoconsideration the seasonal and diurnalvariations occurring in the different re-gions of the world. The information willalso be related to such factors as an-tenna heights, terrain effects, meteoro-logical and climatological conditions,and antenna directivity effects.

MEASUREMENT STANDARDSLABORATORY

The Central Radio Propagation Lab-oratory is responsible for the mainte-nance and development of electricalstandards and standards of measure-ment in the frequency range between30 kc. and 100,000 mc. (see figures 13and 14). The NBS standard of fre-quency is composed of a series of quartzcrystal oscillators, each of which vi-brates at an extremely constant rate of100,000 cycles per second. The refer-ence vibrations are electrically multi-plied and divided to produce a wholeseries of standard -frequency signalsranging from a few cycles up to 100,000

16

megacycles. This range makes it possible

to conduct precise research and devel-opment programs in radio -frequencystandards. These standards are incor-porated into the measurement of quan-tities such as dielectric constant andpower factor, impedance, power, fieldstrength, attenuation, voltage, magneticpermeability, and current. In additionto the "laboratory" standards, CRPLbroadcasts standard carrier frequencies(2.5, 5, 10, 15, 20, and 25 mc.) fromWWV, shown in figures 15 and 16, andthree from station WWVH (5, 10, and15 mc.) that are utilized by organiza-tions depending on precise frequencymeasurement or control.

The need for standards of electricalquantities applicable to the constantlyexpanding field of electronics had beenrecognized for some time, but the estab-lishment of suitable standards has beencomplicated by rapid developments inthe field and the continuous extensionof the useful frequency range. Even low -frequency (audio) standards have not

yet reached the perfection generally de-sired, and standards at all frequenciesare continuously being improved. CRPLmaintains a continuing program aimedat developing basic and better transferstandards of measurement, instruments,instrumentation techniques, methods ofmeasurement, and analysis of the elec-trical quantities.

Standard methods of measuring di-

electric constant and power factor ofsolids, liquids, and gases have beenestablished by CRPL over a wide rangeof radio frequencies. Many instrumentsand comparison standards have beenand are being developed for measuringspecimens used in the NBS high -polymerprogram, the Bureau of Mines oil recov-ery program, CAA studies of antennahousings, the ASTM standardizationprogram, and for other similar applica-tions by private industry and educa-tional institutions. The expanded devel-opment of microwave equipment duringWorld War II has been responsible foradded emphasis on the study of dielec-

Figure 1.5. Exterior of NBS Radio Broadcasting Station WWV, Beltsville, Maryland.From this station, standard radio frequencies of 2.5, 5, 10, 15, 20, and 25 nc. aretransmitted continuously with accuracies of two parts in 100 million. Two standardaudio frequencies, 600 and 440 cycles, are broadcast on all radio frequencies. Tele-phone poles support the antenna system, from which signals are transmitted to all

parts of the world.

17

Figure 16. Interior of NBS Radio Broadcasting Station WWV. The banks of sixtransmitters are carefully monitored and precisely controlled to generate signals with

an accuracy of two parts in 100 million.

tric and magnetic properties of materialsat the microwave frequencies (300 to100,000 mc.). A program for the im-provement and automation of dielectricmeasurements has led to the develop-ment of refractometers for observingthe refractive index of the atmosphere,and has contributed to the study of thepropagation of microwaves. Relatedstudies have included investigationsof transmission -line characteristics, gasmeasurement, high -Q circuits (re-entrantcavities), and the calibration of capaci-tors, inductors, and special radiocomponents.

In the frequency range between 30mc. and 300 mc., standards are beingdeveloped for a variety of impedances,including single components, lumpedconstant and distributed constant net-works, and linear and nonlinear, bal-anced and unbalanced, unilateral andbilateral, active and passive devices.Impedance standards of all magnitudescurrently used are being developed. Inthe 300- to 30,000-mc. range, studiesare being made on a waveguide-discon-tinuity type of absolute standard of

impedance and reliable sliding loads foruse as secondary standards.

techniques are available formeasuring power between 10 kc. and300 mc. and within the power rangebetween a microwatt and a megawattdepending on frequency and waveform.Present measuring equipment is capableof handling mostly c -w power. Theequipment will eventually handle pulsedpower, c -w modulated and pulse modu-lated, dissipated or monitored by meas-uring devices, under matched conditionsfor optimum efficiency, .9r when fed intoany conceivable impedance. Throughoutthe frequency range, investigations arein progress on absolute and independentmethods of power measurements usingdevices such as bolometers, thermistors.and calorimeters for cross-checking ab-solute accuracy. A new microcalorimeteihas been developed for low power levels.and work is continuing on the development of a high -power water calor-imeter.

CRPL also maintains programs di-rected toward the further development

18

of attenuators of various types, notablythe waveguide-below-cutoff attenuatorsfor practically the entire frequencyrange. Reliable primary standards of r -fvoltage have been developed for useover a wide range of voltage and fre-quency; investigations are continuingfor the improvement of these standardsand the development of new, stablesecondary standards. Work is also pro-gressing toward the development of r -fcurrent standards. In cooperation withthe FCC and other regulatory agencies,CRPL maintains national referencestandards of radio field strength for thebenefit of broadcast stations and usersof dielectric heating, diathermy, andother interference -producing electrical

apparatus.At the present time, no working pri-

mary frequency standards are absolutelyfree of drift, aging, or instantaneouschanges. However, variations have beenreduced by a factor of 1000 within thepast 30 years; and a constancy of betterthan 1 part in 1 billion over a 24 -hourperiod is now available. Nevertheless,requirements in defense, research, andcommunication still exceed the perform-ance of the best primary oscillatorsoperating under precisely controlledconditions of temperature, vibration,and voltage. Experiments are currentlybeing performed on new types of stand-ards operating at higher frequencies andlower temperatures, and on syntheticallyproduced quartz crystals.

The lack of authentic comparative in-formation on the characteristics of pow-dered iron and other magnetic materialswas responsible for a research programaimed at the development of instrumentsand methods to measure accurately per-meability and loss factor. The resultinginstrument is known as an r -f perme-ameter and serves as a secondary stand-ard. It is now possible to establishspecifications for powered iron based onthe accurate results of NBS instrumentsand standards.

Standard frequency broadcasts werebegun by the National Bureau of Stand-ards in 1923 on announced schedules.The usefulness of the broadcasts hasbeen continuously extended, and theservice has been improved in accuracy,reliability, and availability in the UnitedStates and throughout nearly all the restof the world. Accurate time signals, timeintervals, audio frequencies, radio fre-quencies, and time announcements invoice and code are now continuouslyavailable on six frequencies of WWV(Beltsville, Md.) and on three frequen-cies of WWVH (Maui, Hawaii). Theyare relied on by many commercial,scientific, and governmental agencies, aswell as the Armed Forces. In additionto the normal maintenance activitiesassociated with the stations, a continu-ing improvement program is in prog-ress, typified, for instance, by theinstallation of single-sideband transmit-ters at WWV to reduce the width of thefrequency spectrum now used. Anotherexample is demonstrated by an activitylocated on Gun Barrel Hill near Boulder,Colorado. Here, CRPL has completedthe installation of a laboratory, asshown in figure 17, to monitor continu-ously radio carrier and modulation fre-quencies and field strength from radiostations WWV and WWVH. The resultsof this work should prove to be usefulin predicting frequency errors to beexpected in the carrier and sidebandsfor different communication paths, time,and carrier frequencies.

The rapid development during WorldWar II of microwave equipment has ledto its application in radar, navigationalaids, communication systems, relay sys-tems, and many defense weapons suchas guided missiles. In addition to thestandards developed for this region ofthe spectrum, research is being con-ducted on the utilization of microwavesfor atomic frequency and time stand-ards, spectroscopy of gases, and preci-sion i n terferometry.

19

-r

Figure 17. Interior of NBS Field StationNear Boulder, Colorado, Established toMonitor and Study the Signals Trans-mitted by Radio Station WW V andWWVH. The station is also used as oneof the network of ionosphere probing sta-tions maintained by, or operated in co-operation with, the National Bureau ofStandards. The C3 ionosphere recorder(right, background) is one of the basicinstruments used widely by science andthe military for investigating the outer

atmosphere by radar techniques.

The limitations of the present stand-ard of time, the mean solar day, haveinstigated a search for new methods todetermine time and frequency. The orig-inal NBS atomic clock utilized the ab-sorption characteristics of ammonia toprovide a control element in a servoloop containing a precision oscillator.The success of this initial experimenthas led to the further development ofatomic clocks utilizing cesium atoms.The latest NBS cesium beam clock nowunder development is shown in figure18, and is expected to attain an accuracyof 1 part in 10 billion.

The microwave absorption character.istics at microwave frequencies of mostgases are being utilized in spectroscopicanalysis in much the same manner asinfrared and ultraviolet techniques areemployed. A current project involves thecompilation and dissemination of newand revised information on microwavespectrum lines for use as referencestandards and for research purposes.

Optical interferometers have proveninvaluable for the precise measurementof short distances and of wavelengths ofoptical radiations. For microwave fre-quencies, work is progressing towardthe development of a precision interfer-ometer which will measure longer dis-tances (1 to 50 meters) and wavelengthsof microwave radiations with great ab-solute accuracy. The instrument will alsomake possible a highly accurate meas-urement of the velocity of light.

REGULAR PROPAGATIONPREDICTION SERVICES

The radio frequency predictions nowissued by CRPL are essentially in theform developed for the armed servicesduring World War II. However, muchprogress has been made in reducingmany of the errors. Included among theerrors and common to all systems ofpredictions are those caused by the lackof accuracy in available methods of pre-dicting solar activity, by insufficientworld-wide distribution of ionosphereobservations, and by day-to-day varia-tions of ionosphere characteristicsaround the monthly median values. Oneserious source of error, that of presen-tation, use, and interpretation of data,is being overcome by the developmentof a true map representation of basicradio propagation predictions, both forthe entire world and for the arctic re-gion. It is contemplated that the finalform of presentation Ain consist of 12maps, one for each even hour of GCT,for a given month, and for each of thecharacteristics for which predictions aredesired.

In order to prepare predictions of thebest sky -wave operating frequencies forcommunication paths all over the world,CRPL collects and analyzes ionosphericdata from 76 stations having world-widegeographical distribution. The results ofthe analyses are compiled and distrib-uted to scientists and scientific organi-zations in the United States and in many

20

Figure 18. NBS Atomic Bean Clock. A beam of cesium atoms is discharged andmade to move down the cylinder from left to right. When these atoms pass throughthe electromagnetic field set energy, they vary from a straight-linepath. Suitable instruments can be arranged to detect this variation and feed a voltageback into the microwave generator so as to make it correct itself, and, thereby, producethe correct frequency. With this system, accuracies can be obtained of better than one

part in 10 billion.

foreign countries. CRPL series F, Iono-spheric Data, is a 90 -page monthly doc-ument distributed to the cooperatingobservatories, military and civilian gov-ernmental agencies, industry, and scien-tific organizations. The series includes,in addition to ionospheric and radiopropagation data, tables of solar flares,coronal data, and sunspot numbers, ra-dio propagation quality figures, andgeomagnetic data.

CRPL series D, Basic Radio Propaga-tion Predictions, is issued monthly as anaid in determining the best sky -wavefrequencies over any path at any timeof the day for average conditions forthe month of prediction. Each issue ofthis series predicts the maximum usablefrequencies 3 months in advance oftheir expected occurrence. Included are

charts of extraordinary -wave criticalfrequency for the F2 layer, of maximumusable frequencies for a transmissiondistance of 4000 km., of percentage oftime for transmission by the sporadic -Elayer in excess of 15 mc. for a distanceof 2000 km., and other informationconcerning the sporadic -E and regular -Elayers. Methods for using the charts in-cluded in CRPL series D are given inNBS Circular 465, Instructions for theUse of Basic Radio Propagation Pre-dictions.*

Twice a month, CRPL issues the Jaseries to those who wish later informa-tion concerning maximum usable fre-quencies. Series Ja carries revision fac-tors for the advance radio propagationpredictions made in the series D publi-cation. In addition CRPL issues semi -

21

weekly the series J reports, AdvanceRadio Propagation Forecasts for NorthAtlantic Paths, to those interested in thequality of reception over these commu-nication circuits. The forecasts includean estimate of propagation quality forthe first 7 days after the issuance of theinformation and an estimate of the dis-turbed periods within the next 25 days.A similar series, series Jp, supplies in-formation for users of communicationpaths across the North Pacific. Stillshorter term forecasts are given to NBSradio stations WWV and WWVH forworld-wide transmission, and CRPL isprepared to issue reports every hour oroftener by telephone to governmentalusers requiring this special type ofinformation.

Ionospheric physics, of which theCRPL prediction services represent oneof the practical outcomes, has the wholeearth and the outer atmosphere as itslaboratory; the research "team" in-cludes scientists from many countrieswho make observations at remote loca-tions. As an agency of the Federal Gov-ernment. CRPL maintains close ties withits counterparts in other countries, as

* Available from the Superintendent of Doc-uments, U.S. Government Printing Office,Washington 25, D. C., for 30 cents. Theseries D publication is available from thesame source at 10 cents per issue or on asubscription basis for S1.00 per year (for-eign $1.25).

well as universities, research institutions,and communication companies in theUnited States and abroad. This type ofcooperative study of universal problemsof the upper atmosphere and radiopropagation will reach a peak of activ-ity in 1957-58, when at least 28 coun-tries plan intensive joint investigationsin many fields of geophysics. This pe-riod of widespread observational pro-grams coordinated in space or time iscalled the International GeophysicalYear, or IGY.

Through CRPL, the National Bureauof Standards will participate in the IGYby employing its facilities maintained athalf a dozen remote outposts. Moreover,the experience and training of its staffwill be utilized for observing the outeratmospheric phenomena. The programwill include overhead and oblique iono-spheric soundings, radar observations ofaurora, and some types of ionosphericwind measurements. Special "WorldDays." selected by an international co-ordinating agency, will be the occasionfor intensive observations of all iono-spheric phenomena, as well as solaractivity, cosmic rays. and phenomenaobservable with the aid of rockets. Theresults of this tremendous program areexpected to yield more exact knowledgeof many natural phenomena which af-fect everyday activities in science, indus-try, and commerce.

ERRATUM

September and October issue, page 7;Figure 2 is shown as having four parts. Theupper two, drawings (labels A and B) shouldhave a caption reading "Figure 1. AmplifierWith Cathode Degeneration A. SchematicDiagram B. Equivalent Circuit."

22

DUPLICATING AND ADDRESSINGSYSTEM FOR TAPE RELAY CENTERS

by Captain Thomas CunninghamSignal Maintenance Officer "SHAPE"

Teletype is today used more extensively than otherforms of telegraphy for fast and efficient handling ofmessage traffic. These facilities, which include directpoint-to-point private line services, switched exchange(TWX) systems, and tape relay, play the all-importantpart of linking our Armed Forces communications

channels throughout the world.

TAPE RELAY SYSTEMS handle the majorpart of the message traffic to overseasdestinations, using both wire and radioas transmission mediums. At the ter-minal stations of these systems, mes-sages are received in written form, eitherby messenger service or by tributaryteletypewriter circuitry. Each messagethat is to be sent via tape relay net-works is processed by the message cen-ters of these terminal stations, whererouting indicators, message identifyingnumber, the precedence, and transmis-sion instructions are added to the mes-sage. The message is then prepared onperforated tape and sent automaticallyby means of a transmitter distributor.At the distant terminal station or inter-mediate tape relay station, the messageis received on a typing reperforator,which simultaneously types and reper-forates the message on a similar tape.The advantages of such a system overmanually operated circuits are that incases where the message must be relayedthrough an intermediate station, muchtime is saved in retransmitting the orig-inal message, and operating personnelrequirements are considerably lessened.Upon reaching the designated terminalstation, the message is reproduced lo-cally in page copy form for local de-livery, or, in the case of tributary tele-type circuits, is sent on by a transmitterdistributor.

Quite often a single -message text isdirected to one or more addresses, con-stituting multiple address and book mes-sages which may require separate rout-ing at the originating terminal station orat an intermediate relay. Considerabletime may be saved in the transmissionof these types of messages if duplicatetapes are prepared in order that simul-taneous sending can be initiated overthe different routes. It is highly desir-able, therefore, that each tape relaycenter be equipped with an efficientduplicating and addressing section, quiteoften refer -red to as ZVA.

ZVA SYSTEM

Duplicating and addressing (ZVA)systems should be designed to providemaximum flexibility with the minimumof equipment. The installation describedin this article, shown in figure 1, pro-vides a means of reproducing duplicate -message tapes from either of two oper-ating positions in any quantity up totwelve simultaneously. This system iscomposed of six AN/TGC-1 packagedteletypwriter sets, two Model 19 tele-typewriter sets, and a control console.Selection of the desired number ofduplicate -message tapes to be producedis accomplished by manipulation of lineswitching keys mounted on the controlconsole. Motor control switches are alsoprovided on this unit, to activate the

23

F (NOT SHOWN)3 EACH

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POWER SWITCHES 1-12 FROM L TORLSK SWITCHES 1-12 FROM L TO R

Figure I. Installation of Duplicating and Addressing System,Showing Equipment Layout

reperforators in the AN/TGC-1 equip-ments that are to be used. Informationin the headings of messages may be in-serted or deleted from any message byswitching the reperforators either in orout of the circuit.

CONSTRUCTION

Each M-19 teletypewriter set isstrapped C2 to C3, and C4 to C5, asshown in part A of figure 2. Line con-nections are made at Cl and Cg of eachunit with their distant ends terminatedin teletype plugs. This places the Trans-mitter Distributor, Keyboard, and Typ-ing Unit of the M-19 table in series,which allows automatic or manual send-ing and also provides a page copy onthe Typing Unit for checking errors inthe tape.

The line from M-19 #1 is pluggedinto the MJ-4 jack of AN/TGC-1 set"C", and the selector switches for thisunit are set for split duplex -polar opera-tion. The neutral teletype signal fromthe M-19 is thus converted to a polarsignal for transmission to all reperfor-ator receiving relays. The polar signal

output from terminal #10 of set "C" iswired in series through all #5 and #6terminals of the line switching keys.(See part B of figure 2.) This providesa closed loop for all reperforators whenthe line switching keys are in the"down" position.

The line from M-19 #2 is pluggedinto the MJ-4 jack set of "F", and thewiring is from terminal #10 of set "F"to terminals #3 and #4 of the lineswitching keys. This provides a closedcircuit for all reperforators when theline switching keys are in the "up"position.

All reperforator receiving relays arewired to the #1 and #2 terminals oftheir respective line switching keys.Marking battery is also furnished atterminals #7 and #8 of the line switch-ing keys, as shown in part B of figure 2,in order to have the reperforators runclosed when the line switching keys arein the center position. The transmittercircuits of sets "A", "B", "D", and "E"are not used, and the selector switchesof these units are set for normal duplex -

polar operation.

24

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The power circuit is modified asshown in part C of figure 2, and themotor control toggle switches are wiredin series with the reperforator motor cir-cuit at the motor fuse.

(Editor's Remarks: ZVA systems, al-though not new in idea, have posed aconstant problem in construction. Usu-ally the chief difficulties encountered areduring switching operations, where ex-traneous characters might be typed as aresult of short intervals of circuit inter-ruption. For this reason this article wasof sufficient interest to us to warrantfurther research. Therefore, we directedrelevant questions to the Bell Labora-tories to verify the technical soundnessof Captain Cunningham's design. Thequestions, together with the answers re-ceived, are listed below.

Q. Can the line windings of twelve WE255A relays be connected in seriessuccessfully in a polar circuit with-out introducing sufficient character-istic distortion to produce marginaloperation of the equipment?

A. "Assuming a ± 15 -milliampereseries circuit, a driving source ofplus and minus 130 volts, the use ofa single winding on each relay, and60 WPM operation, characteristicdistortion effects in a circuit contain-ing twelve relays would be muchsmaller than the distortion toleranceof a Teletype Corporation typing re -perforator. For circuit conditionsother than those assumed, the per-centage change of current during theshortest signalling element to betransmitted may be calculated fromthe L/R* ratio of the circuit. If dur-ing the shortest pulse (including in-put distortion) to be transmitted abuild-up to less than 90% of steady

° The inductance of each of the two wind-ings is about 1.25 henrys at normal sig-nalling frequencies, and, since the twowindings are closely coupled, the induc-tance of the winding in series -aiding isvery nearly four times this value.

Q.

A.

Q.

A.

state current is indicated, alternativecircuitry should be considered."

Would a parallel arrangement ofthese windings be more advanta-geous?

"Parallel connection of branch cir-cuits, each branch containing a linerelay for operating a typing re -

perforator, provides a somewhat su-perior circuit. In this case, eachbranch should consist of currentlimiting resistance and a line relaywith two windings connected in se-ries -aiding. As compared with theseries circuit, the resistance of eachbranch would be increased by a fac-tor of two, and the inductance re-duced by a factor of three, so thatthe time constant would be reducedby a factor of six. The total currentfrom the driving source would beincreased by a factor of six; there-fore, the current should be limitedto 71/2 milliamperes per branch cir-cuit, to prevent excessive deteriora-tion of the contacts on the masterrelay which is driving the multiplebranch circuits."

Under normal operating conditions,can the armature of the polar relaybe depended upon to remain posi-tioned on its marking contact duringtransfer of the line winding betweentwo closed circuits, to prevent ex-traneous characters, from appearingin the message text as a result of theswitching operation?

"The armature of the 255A relay ingood adjustment will usually remainon the contact to which it was lastoperated, even though the operationflux is reduced to zero. The holdingforce is, however, normally quitesmall, and may be materially re-duced or actually made negative bypoor adjustment of the relay. Evenwith a positive holding force, the

26

combined effect of interfering cur-rents, building vibration, and thelike might cause the armature to

leave its contact momentarily duringswitching operations. For these rea-

sons it is considered sound designpractice to provide a small holdingcurrent during switching operationswhen maintenance of the markingcondition is a requirement.")

"What's Your Answer?"

This problem was submitted by Philco Field Engineer Leland Van

Allen, who noted the unusual conditions described in the problem

during one of his frequent bouts in the TV servicing field.

The schematic shows a typical circuit found in TV horizontal de-

flection systems. As shown by the presence of the voltmeter, the

damper circuit produces a 250-volt boost in the B+ voltage, thereby

making the supply voltage for the output tube 550 volts. If the circuit

is traced, it will be noted that the output tube plate current is the

same as the B+ supply current-in the case shown we have assumed

a value of 100 ma. A simple calculation will show that the B+supply power is 30 watts, and that the plate input power of the out-

put tube is 55 watts.

The problem is to explain where the additional 25 watts for the

output tube come from.

100 ma

B+300V

TO H.V.RECTIFIER

r- - - 1

I -I-L_. _ _J

HORIZONTALDEFLECTION

YOKE

(Solution next issue)

27

Index for Vol. IV Philco TechRep Division BULLETIN

Antenna Instructions, Simple Aid ToA

C

Month Page -

July -Aug. 2

Conference on Cryogenic Engineering, 1954 July -Aug. 6Cryogenic Engineering Laboratory, NBS-AEC May -June 30Cryogenic Engineering, 1954 Conference on July -Aug. 6Crystal Substitution For Radio Receiver R-19/TRC-1 July -Aug. 13Crystal Checker Nov. -Dec. 2

D

Duplicating and Addressing System for Tape Relay Centers Nov. -Dec. 23

E

Editorials:BULLETIN Plans May -June 3The Growth of Field Engineering July -Aug. 1Wanted-BULLETIN Articles Sept. -Oct. 1

Nov. -Dec. 1Electronic Clinical Thermometer May -June 18Engineering Report Sept. -Oct. 11

H

Homemade Training Slides Sept. -Oct. 2

L

Listening Device May -June 18

N

NBS-AEC Cryogenic Engineering LaboratoryNBS Research in. Radio PropagationNew Philco Training Manual

Philco Training Manual, NewP

R

May -June 30Nov. -Dec. 4Sept. -Oct. 29

Sept. -Oct. 29

Radio Propagation, NBS Research in Nov. -Dec. 4Relay, Voice Operated Sept. -Oct. 13R-19/TRC-1, Crystal Substitution For Radio Receiver July -Aug. 13

S

Servicing Syncbros and Servomechanisms:Part 1 May -June 4Part 2 July -Aug. 15Part 3 Sept. -Oct. 16

Shoran Equipment July -Aug. 23Simple Aid to Antenna Instruction July -Aug. 2Surface -Barrier Transistor:

Part 1 May -June 19Part 2 July -Aug. 7

28

Index (Cont.) Month PageT

Tape Relay Centers, Duplicating and Addressing System for Nov. -Dec. 23

Thermometer, Electronic Clinical May -June 18

Thevenin Equivalents For Vacuum -Tube Circuits Sept. -Oct. 6

Training Slides-Homemade Sept. -Oct. 2

Transistor, Surface -Barrier:Part 1 May -June 19

Part 2 July -Aug. 7

V

Vacuum -Tube Circuits, Thevenin Equivalents ForVoice Operated Relay

w

Sept. -Oct. 6

Sept. -Oct. 13

"What's Your Answer?""Double -Pole -Double -Throw Switch" Problem May -June 29

Solution July -Aug. 29

"Class -B Linear R -F Amplifier" Problem July -Aug. 22

Solution Sept. -Oct. 28

"Neon Lamp" Problem Sept. -Oct. 5

Solution Nov. -Dec. 29

"TV Deflection Power" Problem Nov. -Dec. 27

Solution to . . . September -October

"What's Your Answer?"

The action of the neon lamp can be summarized as follows:

1. The neon lamp will light as soon as the switch is closed,and will remain on for approximately 0.6 second. Sincethe voltage across the lamp is d.c., only one of the elec-trodes will glow.

2. After the 0.6 -second interval, the lamp will extinguishand remain off for approximately 2.4 seconds.

3. At the end of the 2.4 -second interval, the lamp will lightagain and remain on as long as the circuit is energized.This time the opposite electrode will glow, because thepolarity of the voltage is reversed.

The above analysis can easily be verified by calculating thetime constant involved and consulting a "Universal RC TimeConstant Chart."

29

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