502 IRE TRANSACTIONS ON MILITARY ELECTRONICS October
Two Decades of U. S. Army MobileHigh-Frequency Communications*
H. C. HAWKINSt
Summary-This paper is an historical account of the trend in de- were assemiibled in a one an(l one-half ton four wheelvelopment of U. S. Army high-frequency mobile radio communica- (Irive paniel truck. This truck towed a one-toli cargotions of medium power in the period 1940 to 1960. Starting with one trailer which contained a five-kilowatt engine-drivenof the first really mobile sets of this power level, in a wide variety ofinstallation configurations to meet World War II requirements, it generator for stationi power. This set, pictured in Fig. 1,relates the progressive fulfillment of higher traffic handling capabili- became knowni as Radio Set SCR-299. The transmitterties in both single and multivehicle installations. The increasing de- provided 400 watts Al and 325 watts A3 operation overmand for smaller but higher capacity equipments indicates the the frequency range of 2.0 to 8.0 Mc.course which future development efforts should follow. The receiving equipment covered the frequency range
of 1.5 to 18.0 Mc in six bands. Both the BC-312 and theTv HI," development trend( in medium-power high- BC-342 were single coniversioni superheterodyne re-T frequenlcy mobile radio commiiuniicationis sets for ceivers capable of receiving telegraph and voice nio(lu-
I. S. military use over the past two decades can be laited signals. lRadio Receiver B('-342 operated from aconsidered more of an evolution process rather thani a power source of 115 volts ac, whereas Radio Receiverbreak-through. 'I'he evolutioni can best be followed by a BC'-312 operated from a power source of 12 volts dc.chronological account of the efforts made to improve the Service test of the S('R-299 showed that this set wascommuinicationis capability of these sets. not considered satisfactory in all respects since it did notThe first military meditumii-powered high-frequency meet all the re(luiremiienits stated in the military char-
communiications set with a measure of imiobility was acteristics and lacked the high (legree of mobility re-Radio Set S('R-197, which imiade its atppear.ance in the quired. However, it was app)roved for training purposeslate thirties. I'his set covered a frequency range of 1.5 to until a more completely suitable unit became available18.0 Mc, and had an output power of 400 watts Al emis- amid was obtainable. IProcuremenelt of a limiitedl iiumibersion (telegraphy by mleanis of oni-off keying of the radio was made.frequency carrier) but with grid modulationi, A3 emlis- Shortly therafter the Unite(d States became a comi-sion (telephony by meatns of double sideband, full batant in World War II. The urgent need for the typ)e ofcarrier, amplitude mlo(dulationi) was limiiited to about 75 communicationis afforded by the SCR-299 m.ade it nec-watts output. It was not a truly mobile set since it could essary that some of its other shortcominigs be tolerated,operate onily when stationiary. Two van-type vehicles, so large niumbers of this set were procured and shippedwhose nianetuverability, left somethinig to be desired, to various combat zones.housed the radio and power equipipeet. In the meantimne, the Signal Corps Laboratory was
Inspired by the results of the Louisiana manieuvers of making an intenise effort to improve the equipment in1940 and( the blitz type of warfare then underway in respect to both mlobility and formi factor. The distinietiveEl'urope, military characteristics were written for a radio appearance of the SCR-299 had proved to be an im-set with a high (degree of mobility and the capability of imiediate invitattioni to particular atteintioni by enemlyprovidillg voice commliuniicationi over a 100-mile range aircraft.while in motioni.The Signal ('orps Laboratory undertook the develop-
menit of such a set. 'I'he commillercial field was searchedfor a suitable transmiiitter having the compactness andpotentialities re(Ituire(l for the desired inistallattion.Several types were purchase(l froni different miianufatc-turers and giveni thorouigh road and ranige tests.The transmitter selecteI was the Hallicrafters HT-4
which latter, atfter modification, becaieii knowni as RadioTranisimitter B('-610.
I'his transmiiitter, together with then standard mili-tary commiiiiuniicationis receivers BC-312 and BC-342,
* Received by the PGMIL, July 11, 1960.t USASRDL, Fort Moinmotith, N. J. Fig. 1-Radio Set SCR-299.
1960 Hawkins: Two Decades of U. S. Army Mobile High-Frequency Communications 503
In order to disguise the radio set and( at the saime time a frequency range of 2.0 to 18.0 AIc for transmiiissioni, andimprove mobility, it was decided to install the equip- 1.5 to 18.0 Mc for reception.ment in a slip-iin type of shelter which could be carried Using the same type of shelter as in the SCR-399, theby a two and one-half ton 6X6 cargo vehicle. The high-speed telegraph station required two HO-17's, oneshelter was designed to have the shape of the covered for the transmiiittinig equipmiienit and one for the receivingcargo area of the vehicle and, when the truck's tarpaulini and conitrol equipmeiit. 'I'wo two-and one-half ton 6X6was in place, it could not be distingtuishe(d at a distance cargo vehicles were use(l to tranisport the equipment,fromii any other cargo truck. 'T'he two and( one-half ton each of which towed a one-toni cargo trailer containiillg6X6 truck provi(led increase(l mobility over the one and( PowNer Ulnit PE-95.one-half ton 4X4 vehicle. Moreover, the removable The transmiiissioni capability of this set was severalshelter would allow use of the truck when the radio set hundreds of words per miniute, but the actual amount ofcould be placed on the ground and operated in a fixed traffic which could be handled was limiited by the pro-location. ficiency of the operators in preparing perforated tape forNo improvemeit of great significanice was made in the transmiiissioni as well as reading and transcribinig the
communiicationis effectiveness, except that the frequenlcy received inked tape.range of the transmiiitter was increased to cover the About thirty Radio Sets AN/MRC-1 were deliveredrange of 2.0 to 18.0 I\lc. Different mountinig arrange- to various theaters of operation before the end of anyments were made for the receivers and control equip- hostilities in World War II.menit so that all componienits of the radio set couldI be Before the completion of Radio Set AN/MRC-1, in-removed and set up for operation without the shelter. vestigation was undertakeni in the Signal Corps Labora-The basic set, shown in Fig. 2, received the iioiiemicla- tory to deteriiiie the most effective mieanis of incorpo-
ture Radio Set SCR-399 in 1943. The sam1e set, without rating a facility for radioteletype in a set of the AN/the shelter and without a trailer for the power unlit, was MRC-1 type. The results of the investigationi indicatedcalled Radio Set SCR-499. This set afforded a flexi- that the frequency shift method of radioteletype tranis-bility of mounitinig arrangemenits which permitted instal- mission could readily be adapted to this set, so thelations in a variety of vehicles, includinig the armlored equipment design was immiiiediately started.half-track personniel carrier, the amiphibious "Duck," Componenits of Radio Set AN/MRC-1, with an im-Cargo Glider CG-4A, and somle comlponienits of the set provement in the two-kilowatt radio frequency amipli-were even installed in the quarter-tonl 4X4 "Jeep" for fier, were used with Radioteletype Equipment AN/use by airborne units. TRA-7, which was designed and built specifically forWhile the SCR-399 and SCR-499 did contribute to a this application, to form Radio Set AN/MRC-2. This
large degree to successful communiicationis and coni- set provide(l a single 60-word per minute channiiel oftinued in use long after the war, there was also a iieed radioteletype in the same frequenicy range and( powerstated for a set with greater capabilities both as to level as Radio Set AN/MRC-1 which it ultimatelytraffic handling and power output. The desigii of a high- replaced. Three shelters of the HO-17 type house thespeed CW telegraph set with a power output of two kilo- transmittiiig set, the receiving set, and the operatingwatts was undertaken. center, as pictured in Fig. 3.
This set, designated Radio Set AN/MRC-1, required Radio Set AN/MRC-2 was scheduled for use in thethe development of a two-kilowatt radio frequenicy plannied invasioni of Japan in 1945, and a numiiber of setsamplifier which was designed and fabricated at the were shipped to some Pacific islands and put in opera-Signial Corps Laboratory. Components of Radio Set tion before Vl-J day.SCR-399 and Boehme high-speed telegraph equipmentwere assenibled into a complete operating station having
.2RM-R S -3 ,i" . Fig. a
Fig. 2-Radio Set SCR-399A, inistalled as a niobile stationi. I ig. 3-Radio Set AN'/MRC-2.
504 IRE TRANSACTIONS ON MILITARY ELECTRONICS October
The facility afforded by the availability of Radio- comfort and operating conveinieiice as is found in theteletype Fquipment AN/TRA-7 made possible the teletype set.installationi of a frequency shift radioteletype service in The sudden demand(ls of limited war and brush-firethe Presidenitial train in the fall of 1945. Later, in the combat which have beeni a threat since the end of Worldspring of 1946, a radioteletype set employing miodified War 11 imposed mobile conmmuinications re(luireilmelntscomponents of the AN/TRA-7 was installed in the which the sets previously (lescribed were not capable ofPresidential planie. This is believed to have been the first fulfilling. I'he type of set iieeded was one of high traffictime that frequency shift radioteletype was employed in capacity which could be air transported and lanided inan airborne installation. the area of activity. A multichannel teletype facility was
Shortly after the war, effort was concenitrated on required which could handle the expected volume ofimproving the communiications effectiveness of the so- traffic and also be capable of working into the Armycalled "100-mile" sets, SCR-299 and SCR-399. The Command and Adminiistrative Network.radioteletype facility provided by the AN/MRC-2 was Two different sets were built iniitially, in anl effort tothen considered a logical choice, so a redesign of the satisfy these requiremenits. One, CommiluniicationisSCR-399 was undertatkeni to provide a single vehicle Central AN/GRC-98, provided a four-channel fre-radioteletype set. In accomplishing this, the AN/TRA-7 quenicy shift time division multiplex system. The other,etluipuileilt was used as in the AN/\MRlC'-2. TI'he niew Communications Central AN/TSC-16, vas a single side-designi provide(d all the facilities of Radio Set AN/ band set with greater traffic cap)acity.MRC-2 with the exception that there was a reduction of The first of these sets was hastily assemrbled of partspower fromi two kilowatts to four hundred watts. Not- available in depot stock or readily available froml coim-withstanding, successful corniiiiuniicationi was obtaiined mercial sources. It used transmijittinig componienits ofover distances of up to 1000 miles during tests. A new the old AN/MRC-2 with Telegraph Terminial Setdesigni of shelter to house the equipment, together with a AN/FGC-5 for time division multiplex. The second,rearrangemiienit of set componienits, provided greater AN,/TSC-16, was built unider contract oni an expeditedoperator comfort and( increased operating efficiency. basis. It employed, among other items, a ten-kilowatt'I'his mobile radioteletype station is called Radio Set single sideband transmiiitter which, with a tone teletypeAN/GRC-26, and( is shown in Fig. 4. terminal for frequency division multiplex, provided
Several changes have been mad(le in Radio Set AN/ sixteeni teletype and two voice channels. The physicalGRC-26 since the basic set was first built. Different size and weight of both of these sets are excessive forletters of issue were assigned for each of the various the type of operation intended, since loadinlg in aircraftsteps representinig improvements in the equipment. In and landinig at a required location are handicapped bythe current model, AN/GRC-26D, are found some of both.the results of developmenit effort since the end of World A more recent assembly of componenits developedWar II. These include Radio Transmitter T-368/URT, particularly for military use is containied in Communiica-Radio Receiver R-390/URR, Frequency Shift Con- tions System AN/TSC-17. This equipmenit providesverter CV-116/URR and Modulator MD-239/GR, simultaneous twin single sideband transmiissioni andwhich have replaced older items of lesser reliability and reception in the frequency range of 1.5 to 30.0 Mc. 'I'heefficiency. set is contained in two van-type vehicles and one truck
For applications where teletype operation is not mounted shelter as pictured in Fig. 5. Although greaternecessary, the basic functions of Radio Set SCR-399 are flexibility of operation is possible, the same limitatiolnspreserved in Radio Set AN/GRC-41. This set is used imposed by AN/GRC-98 and AN/TSC-16 regardingprincipally by the Air Force for ground-to-air communii- air transportability apply in the case of the AN/TSC-17.cation. As in the AN/GRC-26D, which it resembles inoutward al)pearance, the older coiimuniicationis equip-menits, such as the BC-610 transmitter and BC-342receiver, have been replaced by the newer equipmentdevelopmienits. The shielter offers the samie degree of
Fig. 4-Radio Set AN/GRC-26 (stanidardized). Curbside view ofcomiplete assembly, showing equipmienit as inistalled on vehicle(2- ton); with antennas down, windows and( hatch closed, it isprepared for operation. Fig. 5-Communications System AN/TSC-17.
1960 Fobes: Multichannel Radio Communication Within the Army 505
The course that the future development effort should mobile set with moderate traffic handling capability.follow in mobile communications systems of this type Future development can fulfill these needs. The advan-is clearly indicated. The need still exists for a relatively tages of single sideband emission as a means of communi-small, compact, yet powerful strategic communications cation have been told and retold many times, so thatsystem which can provide the facilities equal to a it is to be expected that adoption of this type of trans-large, fixed, global communications equipment. With mission by all services will ring down the curtain onthe current advances being made in related fields, it is many of the older tactical communications sets. Devel-believed that the realization of a suitable design can opment plans have existed for some time for a familysurely be achieved. of single sideband sets in the 25-, 50- and 100-mileThe single vehicle communications set of the class for U. S. Army tactical use. The fruition of these
AN/GRC-26 type must also undergo further evolution Signal Corps developments should assure mobile com-to satisfy current demands for a light and compact munications reliability not heretofore known,
Multichannel Radio Communication Within the Army*LAWRENCE G. FOBESt
Summary-Combat communications equipment is a highly spe- be stated as a fact even though it cannot be charged tocialized weapon in its own right. USASRDL has been an important any one group, reason, or service [1].factor in the development of combat communications and in the es- Extensive Army maneuvers in 1939 and 1940 alertedtablishment of an industrial design capability for such equipment.
An example is given by tracing the growth of Army multichannel the Army to the need of special communication forcommunication systems from the radio-link equipment of the Tu- combat operations. Funds were appropriated in June,nisian campaign, through "backbone" radio relay employment exem- 1940. This permitted implementation of a series ofplified by radio sets AN/TRC-l, AN/TRC-24, and AN/TRC-29, five-year plans which had been drawn up by USASRDLinto tactical-mobile systems giving area coverage using AN/GRC-50, (pronounced "Usa-sard-el"), Fort Monmouth, which53, 59 and 66 equipment. thenoced "UsignalCort aboraorThe fundsImportant milestones of concept and technique changes illustrate was then called the Signal Corps Laboratory. The fundsthe continued progress towards reliable tactical radio communica- were very modest indeed, but the request was initiallytions. considered to be a fantastic requirement for communica-
INTRODUCTION tions.To meet these new requirements, the laboratory ex-
versary of the founding of the Unitednnial Anni panded from a modest 250 civilian employees and aversar Co temfouning thetUnitednStates har handful of officers (in June, 1940, about 50 people wereSignl Copsephaizesthatcomunictionhasavailable for communications). It was also necessary to
long been recognized by the Army as playing an impor- enlarge facites ndaionaugurte alag developmntotant role. enlarge facl*ties and inaugurate a large development
oweve r, until very recent ti
mes, a high co m m unica-program. By October, 1942, the adjustment was nearly
However, until very recent times, a high communica- copeeuo h oeeto nefcetdvlptioncaact geeal.eerdtoalredsac complete upon the movement of an efficient develop-tioncapcitgeeraly eferedto lage isptch ment team into new quarters. These quarters became
pouch, a fast horse, and a brave rider. Even World War kno as Co nal Lartory,hosi te com-I communications were characterized by motorcycle mni on por omSignal Laboratories
dispatchriders. ~~~~~munication portion of the Army Signal Laboratoriesdevelopment effort.When war became immiiient in 1938-1939, Congress A atiigh p mv e o
made a considerable effort toward preparing for develop- troswudb*h itnusigfaueo olmen an prducio ofmiltar wepos sch s ar-War II and that the troops would soon outrun wireplanes, artillery, small arms, etc. There was not, how-X9. . 9 X ~~~~~~systems, programmed both a highly mobile long-rangeevr a geea reonto of th.atthtcma radio set, the famed SCR-299, and a radio-relay system.communications equipment could be a highly specialized
weapon in its own right. This lack of appreciation of theRAILNKNTOUINimportance of specializedl military communication can
* Received by the PGM IL, July 11, 1960. The first radio-relay system (originally called radio-t USASRDL, Fort Monmouth, N. J. link equipment) was accumulated in the fall of 1941,
