Copy 3 I 0A AL

DEPARTMENT OF THE ARMY FIELD MANUAL

Co A, lst Bn, 137th lnfFIELD RADIO

RELAY TECHNIQUESCOMMANDING OFrPC2D R&W PLAT, CO A1ST BN, 137TH INFPO BOX 106ARKANSAS C!Ty, KANSAS 67006

HEADQUARTERS, DEPARTMENT OF THE ARMYAUGUST 1957

FM 11-8

FIELD MANUAL HEADQUARTERS,DEPARTMENT OF THE ARMY

No. 11-8 WASHINGTON 25, D. C., 22 August 1957

FIELD RADIO RELAY TECHNIQUES

Paragraphs PagesCHAPTER 1. INTRODUCTION

Section I. General ........ _.....-.. 1,2 3II. Radio relay systems....... 3, 4 4

CHAPTER 2. EMPLOYMENT OFRADIO RELAYSYSTEMS

Section I. Tactical applications _ 6-8 8II. Typical use in area-type

wide-front situations__ 9, 10 14III. Equipment capabilities

and limitations .........- 11,12 18CHAPTER 3. SYSTEM PLANNING

Section I. General ......................--... 13-16 19ni. Wave propagation ........ 17-19 23

III. Siting techniques ... _ 20-26 31IV. Computing radio relay

paths .......... __....... _ 27-32 38V. System reliability.... 33-35 48

CHAPTER 4. FREQUENCYSELECTION

Section I. General .---........ 36-40 56II. Division and corps-level_- 41 43 59

III. Army level --. n CR 5E 68CHAPTER 5. .. A

Section I. 5Tr 437Th INF 56-58 87

IL --------- K59-6 674r

TAGO 1284C-Au 1

Paragraphs PagesCHAPTER 6. MAINTENANCE

CONSIDERATIONSSection I. General .---............---_ 68-70 96

II. Preventive and correctivemaintenance ........._. 71, 72 97

III. Overall and sectionaliz-ing tests for troubleclearance ....... _... 73-77 100

CHAPTER 7. ANTIJAMMINGSection I. Characteristics of jam-

ming operations ....... 78-80 108II. Antijamming instruc-

tions .....---......... 81-84 109CHAPTER 8. FIELD :EXPEDIENTS

Section I. General .................... 85, 86 113II. Connections and antennas 87-93 114

III. Power source expedients 94, 95 119IV. Operational expedients. 96-101 120

APPENDIX I. REFERENCES ___. _ ___ 126II. CHARACTERISTICS

OF TYPE RADIORELAY EQUIP-MENT .........- --......... 130

III. PHYSICAL SECURITY........ 139IV. GLOSSARY OF TERMS ........ 144

INDEX ...................... ---............... ......... 151

2 TAGO 12240

CHAPTER 1

INTRODUCTION

Section 1. GENERAL

1. Purpose and ScopeThe purpose of this manual is to provide tac-

tical and certain technical information for staffplanners and those technicians within the fieldarmy concerned with the installation and opera-tion of radio relay systems. The tactical em-ployment of radio relay equipment together withits applications and use with wire facilities toattain an integrated communciation system is in-cluded. General information is given on theapplication of radio relay, system planning, radio-wave propagation, siting and installation, fre-quency selection, noise and interference suppres-sion (antijamming), field expedients, systemmaintenance, and related subjects.

2. ReferencesPublications, training films, and other refer-

ences pertaining to the subject within the scopeof the manual are listed in appendix I.

TAGO 1284C 3

Section II. RADIO RELAY SYSTEMS

3. Generala. A radio relay system consists of a series of

radio stations operating in tandem on frequen-cies above 30 megacycles (mc). When used inconjunction with carrier or other multiplexingequipment, a radio relay system provides com-munication channels for telephone, teletypewriter,and facsimile. When wide-band equipments areused, channels suitable for electronic data andtelevision transmission also may be realized.

b. Every radio relay system has two terminals-one at each end of the system. Radio terminalsets often are installed as part of, or adjacent to,the carrier terminal. The maximum distancebetween radio terminal sets (without intermedi-ate radio relay sets) is governed by the type ofequipment used.

c. Radio repeater sets are installed where neces-sary to retransmit the signals from the precedingterminal or radio repeater. These stations gen-erally are isolated from other communicationinstallations. The block diagram of a typicalradio relay system is shown in figure 1.

4. Use of Radio Relay Systemsa. Radio relay systems may be used as a pri-

mary communication facility, or used to supple-ment and complement an existing cable andopen-wire carrier system. Specifically, radiorelay systems may be-

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(1) Used tactically to establish initial trunkline communications in a rapidly movingsituation and later supplemented bywire if the situation permits.

(2) Used as a single-channel radio circuit.(3) Used as a multiple-channel primary

facility; the number of channels willdepend on the type of equipment used.

(4) Used as a multiple-channel system tosupplement a wire system or to extenda wire system.

(5) Used as an integral link in a wiresystem.

(6) Used in combination with multiplexingequipment to provide a combination oftelephone, telegraph, facsimile, and(with certain equipments) television or

telemetering data transmission over asingle radio path.

(7) Used in lieu of wire for long lines trunkservice.

b. Radio relay systems have the following ad-vantages:

(1) They provide command control (talk-like-a-telephone) communications.

(2) They enable communication over rela-tively long distances.

(3) Installation time is much less than thatrequired for wire trunks.

(4) They are highly adaptable to wide-front, fast-moving tactical situations.Once antennas are erected and orientedand connections made to end equipments,

6 TAGO 1284C

the system is ready for preliminary ad-justment (system lineup) and operation.

(5) Where wire installation is impractical,communication can be rapidly estab-lished over otherwise impossible terrain.

(6) They are less susceptible to directenemy action and sabotage.

(7) Maintenance man-hours are greatly re-duced (when compared to the mainte-nance of long wire trunks).

c. Radio relay systems have the following dis-advantages:

(1) Radio terminal and radio repeater sta-tions are frequently installed in loca-tions, such as hilltops and other hard-to-reach places, where logistical supportfrequently is difficult.

(2) Radio relay circuits are susceptible toenemy interception and direction-findingactivities.

(3) Communication may be disrupted orseriously impaired by enemy jamming.

(4) Lack of sufficient frequency channelsmay restrict the number and length ofsystems that may be installed.

(5) Antennas frequently must be elevatedabove surrounding cover, thus possiblymaking station locations known to theenemy or to enemy agents.

TAGO 1284C 7

CHAPTER 2

EMPLOYMENT OF RADIO

RELAY SYSTEMS

Section I. TACTICAL APPLICATIONS

5. GeneralBecause of the inherent versatility and flexi-

bility of radio relay equipment, there can be noset rules or yardsticks laid down for a stereotypedapplication of such systems to tactical communi-cations. In each instance, the amount of radiorelay equipment to be used will be dictated bythe Signal Plan which, in turn, results from theestimate of the signal situation made by thesignal planner.

6. Specific Considerationsa. Radio relay circuits always are operated

point-to-point; that is, from terminal to terminalor, if radio repeaters are used, from terminalthrough the repeaters to terminal.

b. Normally, the superior headquarters willprovide the entire radio relay system, includingthe terminal equipment at the subordinate head-quarters plus necessary repeaters. Signal plans

8 TAGO 1284C

must provide for radio terminal sets to be at-tached to subordinate units, particularly whensuch units are not authorized terminals organ-ically. Attached terminal teams remain underthe command of their parent organization andare employed by the higher headquarters con-cerned.

c. Communication planners also must con-sider-

(1)The type and quantity of radio relayequipment available.

(2) The characteristics and proposed possi-ble uses of the equipments. (Generaloverall applications are given in ch 1.Equipment characteristics are listed inthis ch and in app II.)

(3) The usability of assigned operating fre-quencies.

(4) The advantages and disadvantages ofradio relay as compared with wire com-munication facilities (par. 4).

(5) Capabilities of existing and proposedwire systems.

(6) Integration of the radio relay systemwith the wire system.

(7) Where communications systems are ad-jacent or intersect, repeater stations maybe consolidated. This will simplifylogistical support and security require-ments and will reduce the number ofpersonnel.

(8) The possibility of air-transporting radio

TAGO 1284C 9

relay equipment to provide communica-tions for special situations such as areadamage control following an atomicstrike.

(9) The possibility of using radio relay asa keying-line facility for remote opera-tion of radio teletypewriter circuits, orremote operation of high-frequency (hf)radio transmitters.

d. Specific information for use in computingand selecting radio relay paths and sites is cov-ered in chapter 3. Frequency selection and meth-ods for determining operating frequencies arein chapter 4.

7. System Procedures

Reliable radio relay operations can best berealized when based upon standing operating pro-cedures (SOP). An SOP must be clear, detailed,and should include as a minimum, but not belimited to, the following:

a. Pre-operation.(1) Signal operations instruction (SOI) ex-

tracts of the prearranged message code,the map-coordinate code, and the unitauthentication system will be issued tothe team chief. Arrangements must bemade in advance to insure timely de-livery of new extracts as required.

(2) Each radio relay team chief will beissued tactical maps covering the proba-ble area in which the team will operate.

b. Tactical Employment. During operations

10 TACO 1284C

any orders for tactical employment must be givenin code, using the SOI extracts. The team chiefwho receives the message must authenticate thetransmission. Conversely, the person originatingthe instructions also should be required to au-thenticate.

c. Clear-Text Information. Transmission ofthe following types of clear-text information overorder-wire circuits (engineering channels) mustbe prohibited:

(1) Radio relay station locations.(2) Movement instructions to stations.(3) Identification of stations with units.(4) Instructions regarding future tactical

deployment.d. Changes in Circuitry. Information regard-

ing changes in a circuit must be transmitted inboth directions-from higher to lower head-quarters and vice versa. Orders regardingthe system will come from the terminal servicingthe higher headquarters.

e. Equipment Considerations.(1) Circuits must operate exactly on as-

signed frequencies.(2) Correct antennas must be used.(3) Transmitting and receiving antennas

must be oriented properly. When twoor more systems utilize the same site, allreceiving antennas should be in onegroup and all transmitting antennas inanother group. Each of the groupsshould be physically separated by therecommended distance.

TAGO 1284C 11

(4) Proper system lineup procedures mustbe followed in accordance with instruc-tions outlined in equipment technicalmanuals or other official instructions.

(5) No changes in frequencies, except withinprescribed limits, should be made with-out approval of the frequency allocationauthority.

8. System Flexibilitya. General. Radio relay systems are extremely

flexible and furnish a variety of communicationcapabilities. These systems may be used in thefollowing ways:

(1) To extend the lines of communication ina fast-moving situation, mobile equip-ments may be employed in jumpteamoperation. These teams can displace toforward, rear, or lateral locations priorto the actual displacement of head-quarters, thus insuring continuous com-munications. By maintaining communi-cations at the original command post(CP) with duplicate radio relay equip-ment or with wire systems, the circuitsmay be passed to the new CP when thecommand passes.

(2) A radio relay system may be insertedinto a wire system without reducingwire capabilities. Where terrain suchas large bodies of water or deep andrugged valleys make wire construction

12 TAGO 1284C

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impractical or impossible, radio relay

(3) Many radio relay equipments areadapted so that channels may be dropped

munication. These facilities may be

Figused to provide lateral circuitso relay pointce

oimpractical or impossible, 2). Radio relay

() Many radio relay equipment of older type also canre

TAGO 12840 13

be so adapted, if additional carrierequipment is provided.

(4) Through proper arrangement of ter-minal equipments, channels may be re-routed without termination over for-ward or lateral area systems. This pro-cedure is known as strapping-throughand provides point-to-point circuits oversystems normally used for trunkservice.

b. Adaptation of Equipment. Radio repeatersets may be arranged to function as two terminalstations. This adaptation may be used whenthere is not sufficient terminal equipment avail-able to provide circuit requirements. When usedin this manner, however, additional carrier andringing equipment is required.

Section II. TYPICAL USE IN AREA-TYPEWIDE-FRONT SITUATIONS

9. GeneralIn all cases, the communication requirements

determine the number and type of circuits neededfor interconnecting units or area communicationsubcenters. The estimate of the signal situationand the resulting signal plan should indicate theapplication and scope of the radio relay system.

a. After determining system requirements, adetailed terrain analysis, with particular empha-

14 TAGO 1284C

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minals, will indicate the number of radio repeatersets required for each circuit. Whenever possi-ble, physical type relief maps should be used inplanning terminal and relay sites. Line-of-sightpaths over reasonable distances will eliminate re-quirements for radio repeater sets.

b. Equipment transmission yardsticks are cov-ered in the technical manuals accompanying theequipments.

10. Tactical Applications

Figures 3 through 5 indicate typical applica-tions of radio relay systems at division, corps,and field army levels. Due to the flexibility andversatility of radio relay equipment, it must beclearly understood that these are but a few of thepossible applications for these systems. Theactual number of applications is limited only bythe ingenuity and initiative of the signal or com-munication planner and equipment capabilities.

a. Figure 3 shows a division type radio relaysystem in conformance with latest divisional con-cepts.

b. Figure 4 shows one application for a corpstactical system.

c. Figure 5 shows a typical field-army 12-channel radio relay system. The number of areacommunication subcenters varies in accordancewith the communication requirements.

16 TAGO 12840C

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Section III. EQUIPMENT CAPABILITIES AND

LIMITATIONS

11. Methods of OperationCertain radio relay equipments may be used

without multiplex equipment to provide a singlevoice channel over the radio path. Such single-channel 1-hop systems may be operated in oneof three methods.

a. One-way operation without a break-in fea-ture, referred to as simplex operation, requiresonly one radio frequency.

b. One-way operation with a break-in feature,referred to as half-duptex operation, requires twofrequencies. Both simplex and half-duplex opera-tion involve push-to-talk operation at the ter-minals.

c. Simultaneous 2-way transmission, calledfull-duplex or duplex operation, requires two radiofrequencies. This method does not involve push-to-talk operation.

12. Operating FrequenciesOperating frequencies for radio relay equip-

ment vary according to type and are shown inthe chart, figure 6. Additional characteristicsfor radio relay equipment are covered in appen-dix II.

is TAGO 12840

CHAPTER 3

SYSTEM PLANNING

Section I. GENERAL

13. System Planninga. System planning includes the overall layout

of radio relay circuits, locations of sites, choiceof equipment, and frequency allocation and as-signment.

b. The factors to be considered in planningradio relay systems are-

(1) Circuit requirements as determined bytariff studies and/or previous experi-ence.

(2) Capabilities of the radio relay equip-ment in conjunction with the associatedmultiplexing terminals.

(3) Propagation characteristics and terrainfeatures over which the radio systemwill operate.

(4) Siting of radio sets and antennas.(5) Power-balance calculations such as re-

quired inputs, noise levels, and poweroutputs.

(6) Interference reduction by frequency se-lection.

TAGO 1284C 19

(7) Advantages gained by using cross-polarization, separate masts, and an-tenna directivity.

(8) Field methods of minimizing inter-ference.

(9) Limitations of spiral-four cable in aradio system.

(10) Availability of frequencies for assign-ment.

c. A radio relay system consists of two radiorelay terminals and as many radio repeaters asare required (consistent with the technical capa-bilities of the equipment) to span the distancebetween the two terminals. A hop is the terraindistance separating a radio transmitter from thereceiver that receives its transmission. A pathis that part of the atmosphere through which theradiated wave passes. A direct path is one thathas no intervening obstacles and is said to be aline-of-sight. An indirect path is any path otherthan a direct path between two stations (par. 96).

14. System Considerationsa. A radio relay system may be used directly

for primary trunks, or as a link in an existingwire system. The installation may be temporaryor permanent. With some types of radio relayequipment, channels may be dropped betweenterminals and made available at some intermedi-ate point (fig. 2).

b. The permissible number of hops depends onthe type of equipment. Distortion, noise, and thepossibility of circuit failure due to inoperative

20 TAGO 12840

equipment increase as the number of hops in-creases.

15. Multiplexing Equipment Connections

a. Terminal Connections. Through the use ofmultiplexing equipment, channels may be broughtout as either 2-wire or 4-wire circuits. Thesecircuits are connected in the normal way to sig-naling equipment and switchboards or to carriertelegraph equipments.

b. Through Connections. Where systems areto be extended, through-connections betweenmultiplexing equipment are made on a 4-wirebasis. The standard signal levels specified inthe equipment technical manual should be re-tained.

c. Baseband Connections. In interconnectingradio relay and wire carrier systems, the base-band connection must be made on a 4-wire basis.Baseband connections between certain equipmentsmay require limited lengths of coaxial, spiral-four, or other special cable. Baseband connec-tions, as well as the required signal levels, arecovered in appropriate equipment manuals(app I).

16. Separation of Radio Terminal from Carrierand Multiplex Equipment

a. At the terminal installations of systemsusing wire carrier (such as the CF-1 or theAN/TCC-3), carrier equipment may be locatedwith the radio terminal equipment or centralizednear the telephone switching central.

TAGO 1284C 21

b. At division and lower levels, carrier equip-ment usually is married to the radio equipmentin the same vehicle. Such arrangement main-tains the tactical identity of the radio carrierterminal, and reduces emplacement and tear-downtime. It requires construction of a greaternumber of wire lines, however, between theAN/TRC carrier terminal and the telephoneswitchboard.

c. At higher echelons (corps and above), car-rier equipment frequently is centralized near thetelephone switching central. This permits greaterflexibility of employment for the available carrierequipment, and reduces the number of wire linesrequired. In such installations, spiral-four orother suitable broad-band wire facility is usedto feed the radio terminal output to the carriers,but the wire lines to the switchboard are greatlyreduced in length.

d. For systems using their own multiplex (ex-tremely wide-band) units, the multiplex set mustbeat the radio terminal. The 4-kilocycle (kc)carrier channels can be extended from the radioterminal to the telephone switching center by 2-wire system, 4-wire system, or by wire carrierwith terminals at these two points.

e. If the radio terminal is separated from theswitching center as outlined above, a voice-frequency engineer channel between the two loca-tions will be required for efficient maintenance ofthe system.

22 TAGO 1284C

Section II. WAVE PROPAGATION

17. Generala. The radio frequencies from 30 to 300 me

represent the very high frequency (vhf) rangeand the frequencies from 300 to 3,000 me, theultra-high frequency (uhf) range. The proper-ties and phenomena associated with radio wavesin the vhf band and the lower part of the uhfband are similar; therefore, when used in thismanual, the term vhf will refer to this range offrequencies.

b. Radio propagation in the vhf range is con-fined to ground waves-waves that travel nearthe earth's surface. Sky-wave transmission, bymeans of reflections from the ionosphere, willsometimes occur in the vhf band-particularly atfrequencies between 50 and 100 mc. Studies onscatter propagation using the ionosphere andtroposphere as a reflecting medium for vhf anduhf are presently being conducted and show pos-sibilities of a signal radiating several hundredmiles. Because ground waves attenuate rapidlywith distance, useful transmission in the vhfband between radio sets generally is limited torelatively short distances (25-35 miles), unlessexceptionally good antenna sites on high hillsare available at both ends of the path. An ex-ception to this rule sometimes occurs where highobstacles are located at the approximate centerof a transmission path (par. 19c).

c. The distance, range, and performance esti-mates given in technical manuals generally are

TAGO 1284C 23

based on standard propagation. Recent experi-ence in oversea theaters indicates that meteoro-logical conditions, such as temperature and hu-midity of the troposphere (par. 18), sometimesgive rise to what is termed guided propagation.This phenomenon may greatly extend the dis-tance over which usable field intensities are re-ceived. Such conditions are most frequently foundwhere radio sets are located near the shore of anocean or other large body of water and may bepresent for either long or short periods of time.

18. Wave Propagation Phenomenaa. General. The path of travel for radio waves

in the vhf range is the troposphere. The tropo-sphere is the layer of atmosphere directly ad-jacent to the earth's surface. It extends upwardapproximately 6 miles. The temperature nor-mally decreases about 10 .centrigrade( C.) permile, with increasing altitude; the temperatureat the upper boundary is about -- 50 ° C. Abovethe troposphere is the stratosphere, in which thetemperature remains relatively constant at ap-proximately --50 C. Because of changes inmoisture content and temperature at the tropo-sphere, certain wave propagation phenomena,such as reflection and refraction occur.

b. Refraction. Propagation of radio waves inthe troposphere is materially influenced by thedistributions of temperature, pressure, and watervapor. The variation of these qualities withheight decreases linearly in a standard atmos-phere. (The condition most nearly approximated

24 TAGO 1284C

WAVE FRONT

ANTENNA .. OPTIC

FMII-8-21

Figure 7. Refraction.

in the temperate zone has been accepted as thestandard atmosphere.) Radio energy emittedfrom a transmitter antenna may be representedby a series of concentric spherical wave fronts orradial lines called rays (fig. 7). Since the refrac-tion index normally decreases with height, theupper portions of these wave fronts move withhigher velocities than the lower portions, andconsequently the wave path may be representedby rays curved slightly downward toward theearth. As a result, under average conditions, thedistance to the radio horizon is 331/3 percentgreater than: the optical line-of-sight distance.This curvature of the rays by the atmosphere iscalled. refraction.

c:, Reflection. Over line-of-sight path, TR (fig.8'):, the radio wave at receiver R is the vector sumof: the radiations arriving by way of both thedirect. and reflected ray paths. The intensity ofthe! reflected ray path depends primarily on howeffective the earth or sea acts as a reflecting body.

TA.Go 1284C 25

TRANSMITTERT DIRECT RAY RECEIVER

O r _ t REFLECTION

REFLECTION POINT

TM 687-f

Figure 8. Reflection.

Over water and salt flats, for instance, the reflec-tion is essentially 100 percent. Over land areaswith gentle rolling country and some vegetation,the reflection is approximately 10 percent. Thephase lag of the reflected wave with respect tothe incident wave at the point of reflection is, forall practical purposes, 180° . Although the angleof reflection is small, the distance traveled by theincident and reflected ray is greater than thatof the direct ray.

d. Diffraction. The mechanism by which radiowaves curve around edges and penetrate intothe shadow region behind an opaque obstacleis called diffraction. This effect is importantbecause it allows a limited extension of the line-of-sight path length (fig. 9). This extension ofthe line-of-sight path is indicated by the distanceTR-the hop length.

e. Results of Wave Propagation Phenomena.As the receiving antenna is raised above groundlevel, the received signal strength rapidly in-creases because of decreasing diffraction until

26 TAGO 1284C

*LIN OF SIGHT

DIFFRACTIONREI$ON

TR-HOP LENGTH FMtI-P-23

Figure 9. Diffraction.

the grazing point is reached (fig. 10). Abovethis point the direct and reflected waves inter-fere with each other and result in maximumand minimum Fresnel patterns. The first maxi-mum occurs when the difference in path lengthbetween the direct and reflected wave is one-half wave length because the reflected signalundergoes a 180' phase reversal at the reflectingpoint. The succeeding maximums are odd multi-ples of one-half wave lengths. The magnitudesof the maximum and minimum fields depend onthe amount of reflection by the surface. If thetransmission path is clear-that is, without inter-vening obstacles-an increase of 6 db in receivedsignal strength will be obtained by doubling theheight of one antenna, or 12 db if both antennaheights are doubled. This phenomenon holds trueonly for a distance of about 40 miles, or withinthe limits of the radio horizon.

19. Propagation in Vhf Bonda. Over Smooth Earth or Water.

(1) Under the ideal condition of smoothearth, the intensity of the transmitted

TAGO 1284C 27

IST 20DMAXIMUM MAXIMUMI

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Figure 10. Results of wave propagation phenomena.

signal beyond the first mile or so de-creases with distance. Similar resultsare obtained over water because thesurface is smooth enough to approachthe ideal.

(2) Figure 11 shows the theoretical rela-tionship between transmission loss indecibels (db) and distance over smoothland. The frequencies used in this caseare 50 and 300 mc, with antenna heightsof 45 feet. The field intensities obtainedin practice will be less than those shown,because of irregularities in terrain, thepresence of trees, and other factors thatcause the actual conditions to differ fromthe theoretical. With allowance forthese factors, it is possible to calculatethe distance range to be expected.

28 TAGO 1284C

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Figure 11. Graph of db loss versus distance oversmooth earth.

b. Over Irregular Terrain.

(1) Propagation characteristics over irreguzlar terrain are quite different from thosefrom smooth earth or sea water. Inthis case, the variation of db loss withdistance depends largely on the profileof the terrain between transmitting andreceiving antennas. An increase in dis-tance may result in either decreased orincreased db loss, depending on the

TAGO 12940 29

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topography involved. Substantialchanges in db loss may result from re-locating stations, even without anychange in the distance between them.

(2) A profile for an assumed transmissionpath over hills with typical values of dbloss likely to be encountered at variouspoints along the path is shown in figure12. Two facts with regard to trans-

30 TAGO 1284C

mission in hilly country are emphasized:first, the choice of antenna site is veryimportant; and, second, there is no satis-factory basis for calculating generaldistance ranges. Instead, the db lossmay be estimated for a given site in-volving a path of known profile, andthus the selection of antenna sites maybe based on the db loss estimated forvarious available locations.

c. Over Very High Obstacles. Recent experi-ments have indicated considerable gains in re-ceived signal strength above that obtained oversmooth earth may be expected from diffractionover an obstacle located in the transmission path.In quite a number of instances, transmissionpaths containing a very high obstacle have beenspanned with excellent results for distances over150 miles. Experiments also have shown thatfor the best use of this diffraction phenomenon,the obstacle should be equivalent to a knife edge,and be situated in the approximate center ofthe transmission path. To prevent excessive at-tenuation radio repeater or terminal sets shouldbe placed as far from the obstacle as possible.

Section III. SITING TECHNIQUES

20. GeneralSiting is the practical application of radio relay

theory. Many factors must be taken into accountin order to lay out a radio relay system. It is

TAGO 12840 31

possible to set up a radio relay system by in-stalling radio repeater sets on hills selected atrandom, without regard to any of the factorsmentioned in section IV. Such a system mightoperate, but the chances of satisfactory and ef-ficient operation would be very small. This sec-tion covers some of the general considerations in-volved in siting, and a more detailed study isgiven in section IV.

a. In addition to other considerations, physicalsecurity must also be considered as a factor inthe selection of a radio repeater site-this is par-ticularly true in isolated areas. A guide fororganizing a perimeter defense is given in ap-pendix III.

b. In engineering a radio relay system, espe-cially where continuous operation is essential,considerable attention must be given to the loca-tion of radio repeater station, particularly inrolling terrain, or in areas where scatter or re-flection may introduce problems.

c. Radio repeater sites usually follow a zigzagcourse. One reason for this pattern is that theterrain seldom lends itself to a straight line ofradio repeaters without having some of the hopsunnecessarily short and others too long for satis-factory reception. Also, hills rarely are spacedso that the repeaters are in a straight line, andstill have adequate elevations. However, thereare exceptions to every rule and zigzagging is notalways necessary. It is possible and practical tosite the repeaters in a straight line and still havereliable reception. Alternate polarization of

32 TAGO 12840

antennas, and/or alternate frequencies may beused to give satisfactory reception.

d. Siting may be done by a number of methodsor by a combination of separate methods. Con-tour maps, aerial photographs, and surveys maybe used satisfactorily. Usually, sites are chosententatively from contour maps, and a field tripor aerial survey made to verify the choice.

21. Remote OperationTerminal stations usually are located fairly

near the headquarters they serve. However, ifsuch headquarters are located in a valley, or be-hind a terrain obstacle, remote operation of theradio terminal may be required. In such in-stances, a wire link to the radio station is in-stalled.

22. Field Inspectiona. The initial contour map reconnaissance to

select terminal and repeater sites should provideseveral alternate locations for each proposed in-stallation. Some of the alternate sites will be dis-carded on the basis of profiling, and the balancemust be checked by actual on-the-ground inspec-tion.

b. A field trip should be made for the purposeof locating accessible roads; determining whetherthe ground is suitable for vehicles and the erec-tion of antennas; and determining the amount ofclearing needed to prepare the site. Under idealconditions, where portable beam-antenna equip-ment and sufficient time are available, a further

TAGO 1284C 33

check on signal attenuation may be made betweenadjacent sites.

23. Siting by Radio Altimetera. In areas where accurate contour maps are

not available, the altimeters on Army airplanesand helicopters may be utilized to profile a pro-posed vhf hop. Either the aneroid (pressure) orthe radio altimeter may be utilized for this pur-pose. Initial readings should be taken at each endof the hop; subsequent readings taken at signifi-cant terrain features in a straight path betweenthe two ends of the hop then may be plotted on 4/3earth radius paper (DA Forms 11-47 and 11-48).In using these data, just as with profiles developedfrom contour maps, the curvature of the earth andthe average refraction may be computed. Theearth's curvature, plus atmospheric refraction willeffectively elevate an obstruction several hundredfeet higher than it actually appears on flat earth,or on a rectangular coordinate profile. This isespecially true where a long hop is involved.

b. Aerial photographs are useful in determin-ing locations of roads, power lines, or other de-tails which may affect the site choice. In the finalanalysis, however, an on-the-spot inspection ofthe site is most desirable, since this will revealproblems which would not otherwise be apparent.

24. Accessibility of Sitesa. One of the most important considerations in

selecting radio repeater sites is accessibility.Where no road exists to a proposed site, a fieldtrip will be required to determine the amount of

34 TAGO 1284C

work necessary to establish accessibility. Forrolling terrain, road construction may not be toodifficult, whereas in rocky, hilly terrain moreserious problems will be met. Often it may bemore advantageous to select another site, less de-sirable from a radio standpoint, rather than at-tempt to establish accessibility at the best site.Such problems, however, involve both tactical andlogistical considerations. In hilly country, land-slides and washouts hamper operations and pro-vide a hazard for operating and maintenance per-sonnel. The quality of the access road will dependprimarily on the amount of use it will receive-equipment powered by engine generators requiresfrequent trips with fuel.

b. Emergency and routine supply by helicopteris worthy of consideration in cases where tacticalrequirements justify sites located in otherwiseinaccessible locations. The two significant ques-tions are: Can a helicopter land? If not, can itapproach the site close enough to drop supplies?

25. Power ConsiderationsThe reliability of the radio repeater-and

therefore of the entire system-is dependent uponthe source of power. Maintenance and operatingprocedures as outlined in SOP's and equipmentmanuals should be rigidly adhered to for re-liability of operation. If a power line is availableat a proposed site, it should be carefully appraisedto determine whether the line is capable of carry-ing the additional load of the radio repeater. Thepower should be regulated, both in frequency and

rAGO 1284C 35

voltage, and the wires should be large enoughto carry the added load without excessive voltagedrop. In any case, standby engine generatorsmust be available and in operating condition, andmust be regarded as the primary source of power.

26. Polarization of Antennasa. General. For practical purposes, radio

waves in the vhf range transmitted from a ver-tical antenna usually are regarded as being ver-tically polarized, while those from a horizontalantenna normally are regarded as being hori-zontally polarized. Either type of polarizationmay be used for vhf transmission, but the per-formance of each will vary with different con-ditions. For best results, the orientation of thereceiving antenna ordinarily should be the sameas that of the transmitting antenna.

b. Advantages of Vertical Polarization.(1) Simple vertical dipole or whip antennas

are nondirectional in a horizontal plane.This feature is advantageous when goodcommunication is desired in several di-rections from a radio set.

(2) Where antenna elevations do not exceed10 feet, vertical polarization in the 50-to 100-me band results in a strongersignal than can be obtained from hori-zontal polarization using antennas ofthe same height. However, this differ-ence is negligible when using frequen-cies higher than 100 mc.

(3) For transmission over sea water, verti-

36 TAGO 1284C

cal polarization is better than horizontalpolarization when antennas are below acertain elevation. This elevation isabout 50 feet at 85 mc and lower at thehigher frequencies. This means thatwith ordinary antenna mast heights of45 feet, vertical polarization is betterat frequencies lower than 100 mc. Athigher frequencies, there is little differ-ence.

(4) From limited observations, it appearsthat vertical polarization is less subjectto variations in received field intensitysuch as those caused by reflections fromaircraft flying over the transmissionpath. In locations where aircraft trafficis heavy, this becomes an important con-sideration.

c. Advantages of Horizontal Polarization.(1) A simple horizontal antenna pointed

east and west, for example, transmitsand receives best in north and southdirections and performs poorly by com-parison in east and west directions. Thisinherent directivity is sometimes of ad-vantage as a means of minimizing inter-ference.

(2) Horizontal antennas are less apt to pickup man-made interference, which ordi-narily is vertically polarized.

(3) Indications are, that when antennas arelocated in fairly dense forests, horizon-tally polarized waves usually suffer

TAGO 1284C 37

lower losses than vertically polarizedwaves; this is especially true in thehigher portion of the vhf range. Forany small change of antenna location inmoderately wooded areas, the standingwave effects of vertically polarized an-tennas will cause relatively large changesin field intensity; under the same condi-tions, these adverse effects are not sopronounced on antennas horizontallypolarized. In very dense jungles, per-formance generally is poor for bothtypes of polarization.

Section IV. COMPUTING RADIO RELAY PATHS

27. ProcedureThe procedure to be followed in planning a

single-route radio relay system is outlined in bthrough g below. When planning a system of in-terconnecting or parallel routes, follow the pro-cedure for each route in the system. Also bearin mind the considerations mentioned in sectionIII.

a. Determine specific locations of the terminalpoints of the radio relay system. These pointswill be based on tactical and geographic con-siderations and by the location of the equipmentsconnected to the radio terminals.

b. For each radio relay system, draw a sketchon paper as shown in figure 13. Label the radioterminal at the higher headquarters A and theother point B. Assuming a 30-mile radius as a

38 TAGO 1284C

2

M~~~~~~

TAGO 12840 39

TAGO 1284C 39:a

yardstick for propagation distances, use A as theapex and draw an are of that radius about ter-minal A and in the general direction of terminalB. Use of an air chart permits rapid visualidentification of possible line-of-sight paths sincethe color contours are easily evaluated.

c. Choose a site with high elevation, on or nearthe 30-mile radius are drawn about terminal A.Label this site relay point 1 and draw a profilegraph of the ground between terminal point Aand relay point 1 (par. 28).

d. Use the procedure outlined in paragraphs29 and 30 to determine if a line-of-sight pathexists between terminal A and the first repeaterstation. If the site chosen does not give a line-of-sight path, discard the site and select another.Label the site selected relay point 1.

e. If it is impossible to obtain a line-of-sightpath between terminal A and any proposed relaypoint 1, shorten the hop distance by selecting asuitable closer site.

f. When a site has been provisionally selectedfor a radio repeater, determine by power-balancecalculations (par. 31) whether the site selectedis adequate. If the calculations indicate that thesite is not adequate, discard it and select a newsite; repeat the procedure. If very high obstaclesare located in the path, refer to paragraph 32.

g. Use the procedure outlined above to deter-mine the sites for all radio relays in the systemuntil the distant terminal is reached. The maxi-mum allowable number of relay points will bedetermined by the equipment used. Such in-

40 TAGO 1284C

formation is contained in the equipment manual.

28. Plotting Profiles on Nonlinear Graph Papera. To determine that a line-of-sight path exists

when choosing a site, draw a profile map (fig. 14)of the terrain between the two proposed sites.Nonlinear graph paper, such as DA Forms 11-47and 11-48, may be used for plotting profiles fromterrain maps. When using graph paper, followthe procedure in b through i below.

b. Determine from the terrain map the scalesused for the distances involved.

c. Draw a line between the two proposed sites(E or H, fig. 14). Measure the length of thisline and convert it to the distance between twopoints.

d. Determine the elevation of each site as indi-cated by the contour lines. Add the height ofthe antenna mast to this elevation to determinethe total elevation. For example, station N atpath D (H, fig. 14) is 1,350 feet high. Assumingan antenna height of 50 feet, the total elevation is1,400 feet. This point is marked off on the ver-tical scale of the graph above the zero-mile point(J, fig. 14). Station 0 has an indicated elevationof 1,400 feet. This height plus an antenna heightof 50 feet gives a total elevation of 1,450 feet.This point is plotted on the vertical scale (J, fig.14) above the 27-mile point, because 27 miles isthe distance between the two proposed sites.

e. Draw a straight line between these twopoints on the profile chart. Check this line andnote its lowest point.

TAGO 1284C 41

f. Draw a complete profile of the terrain be-tween the two sites. Follow the line drawn onthe terrain map and pick up high and low points.Plot these points on the graph paper and jointhem. All points that are above the straight lineon the graph (I, fig. 14) represent interveningobstructing terrain.

g. If intervening hills exist between the twoproposed sites, as in path C (I, fig. 14), or if thesite line is below the curvature of the earth, as inpart B (G, fig. 14), poor communication will re-sult. If possible, therefore, use paths such as D(J, fig. 14) where intervening obstructing hills,do not exist, and good communication probablywill be obtained.

h. A quicker method of determining line ofsight sometimes may be used. After the straightline has been drawn on the profile chart, scan theline and determine the elevation of the lowestpoint on the line. Next, scan the correspondingline on the contour map and determine whetherany point is at a higher elevation than that ofthe lowest point of the profile-chart line. Ifthere is none, as on path D, a line-of-sight pathexists between the end points of the line, and itis not necessary to plot the profile of the inter-vening terrain. If there are elevations above thepoint of lowest elevation, as on path C, draw acomplete profile to determine whether these highpoints represent obstructions. For example, thepoint of lowest elevation on the profile-chart linefor path A (F, fig. 14) is 10 feet. On the ter-rain map, note that path A passes over a portion

42 TAGO 1284C

of terrain that exceeds 10 feet in elevation.Therefore, it is necessary to plot the profile chartbefore deciding that path A will provide a line-of-sight path.

i. If the proposed site is intended for a radiorepeater station, the transmission path to suchsite, and also from the site to the next radio re-peater or terminal station must be considered.It usually is necessary that line-of-sight pathsexist in both directions.

29. Plotting Profiles on Linear Graph PaperIf profile graph paper is not available, a profile

may be plotted on linear graph paper and thencorrected for the curvature of the earth. Use thefollowing chart; then proceed as indicated in athrough e below.

Conversion of Sea-level Eelevations to Line-of-sight Elevations

Elevation ElevationD (miles from correction (ft) D (miles from correction (ft)

reference Doint) (k = 1) reference point) (k = 1)

2 3 20 2664 11 22 3236 24 24 3848 43 26 450

10 67 28 52212 96 30 60014 130 32 68216 170 34 77118 217 36 865

Note. The corrected elevation in feet equalsD'k1.5

where k is the ratio of the effective radius of the earth to the trueradius of the earth and D is the distance in miles from the referencepoint. Using I for k in this formula does not correct for the effectof refraction of the radio wave.

TAGO 1284C 43

E"pm

# *0

. 1 ..... . . .. -.

133S NI NOILA353

44 TAGO 12840

a. Determine from the terrain map the scalesused for distances and elevations. Draw a lineon the terrain map between the two proposedsites.

b. Pick out high and low points along the lineand plot these to scale on the linear graph paper.A sample profile is plotted as a broken line curveon this type of graph paper (fig. 15).

c. Draw a line on the graph paper betweenterminal points A and B.

d. Correction must be made for the curvatureof the earth to obtain a true picture of the line-of-sight path. A high or low point is selected asnear as possible to the halfway point betweenthe terminals, in this case R. Next, by means ofthe figures shown in the conversion chart above,the heights of all prominent points in both direc-tions from this central point must be corrected(shown as a solid-line curve). For example, pointP shown in figure 15 is 6 miles from referencepoint R. After correction, P becomes P', 24 feetlower than the original point.

e. Some profile maps will indicate a line-of-sight path with the drawing uncorrected. Withcorrection, however, intervening objects may be-come apparent.

30. Determining Line-of-Sight Profile GraphAfter drawing the profile graph for a particu-

lar path and correcting for the earth's curvature(if linear graph paper is used), check the graphcarefully to see that a true line-of-sight pathexists. The path should not be obstructed in any

TAGO 1284C 45

way nor should it come closer than 200 feet toany intervening obstructions. If the path is ob-structed, discard the site and choose a new one,if possible. If it is still impossible to achieve aline-of-sight path, determine the adequacy of apath from the power-balance calculations (par.31).

31. Power-Balance Calculations

a. Power-balance calculations are made whenplanning a system to determine if the estimatedloss over a particular path does not exceed theallowable loss for the path. If the estimated pathloss is greater than the allowable path loss, eitherthe path should be changed, the hop length shouldbe shortened, or an intermediate radio repeatershould be used. If it is not possible to do any ofthese things, the hop may be established eventhough calculations indicate that there will beexcessive loss. However, in a system where oneor more hops have a greater estimated loss thanallowable loss, these hops will limit the operatingeffectiveness of the radio system. Every effortshould be made to reduce path attenuation whileplanning before the actual establishment of theradio relay system.

b. Power-balance calculations performed whileplanning a radio relay system give only an ap-proximate indication of the system performance.The only way to finally determine system per-formance is to actually set up the system and testit. If the loss of any particular hop is difficult

46 TAGO 1284C

to determine from power-balance calculations, theequipment may be installed and tested.

c. Technical circuit criteria for trunking lossesare available in TM 11-486-3; path loss informa-tion may be obtained in TM 11-486-6.

32. Use of Obstacles to Obtoin Long TransmissionPaths

Successful vhf communications have been re-ported over extremely long paths across moun-tainous terrain, where there was a knife-edgeobstacle near the center of the transmission path.In mountainous terrain where such obstacles areencountered, the following procedure may be fol-lowed:

a. Place antennas on each side of the obstacle,at equal distances and not too close to the ob-stacle-signal attenuation increases as antennasare moved closer to the obstacle.

b. Set up the two radio sets, one at each endof the hop, and test the quality of transmission.Vary the height and position of one antenna untila position and height is found where the signal ofmaximum intensity is received.

c. Use figure 16 to obtain an approximate indi-cation of the path loss due to a very high ob-stacle. For path lengths of 50 and 150 miles, thechart shows the free-space transmission loss andthe smooth earth transmission loss when usingthe principle of diffraction over high obstacles.The antenna heights are given as 100 feet abovethe surface. Also shown is the path loss at 50and 150 miles plotted against the obstacle height.

TAGO 1284C 47

TANITTIINO &*N AEC¢IVINO A.I#EI#A #lO"tS?: EACH 100 fElI ArlOV Tt SURFCE

o Mo Sl L I '-I I I \ | | | I| | \ _

.' r4 l ro SLE0 ?- tU

B., HE%0WT OF OBSTAtLE ABOVE SEA LEVEL IN FEET

Figure 16. Theoretical obstacle gains at 100 mc.

Section V. SYSTEM RELIABILITY

33. Estimate of Reliabilitya. There are many factors other than the possi-

bility of equipment failures to be considered inestimating the reliability of a radio relay system.Transmitter output, distances between stations,

48 TAGO 1284C

and receiver sensitivity are some of the charac-teristics that will affect reliability of a system.Other factors, such as reflected or refracted sig-nals, fading due to ionospheric storms, and evenseasonal changes in the terrain, can affect thesignal strength, and hence affect the reliability.Maniy of these variables may be eliminated or con-trolled, however, by careful choice of sites, use ofproper equipment, and allowance for fading.

b. One way of obtaining higher reliability is todecrease distance between radio repeaters. Re-peater spacing of 30 to 50 miles generally will besatisfactory for frequencies below 10,000 me, pro-vided good path clearance is available.

c. A signal will be affected by the receiver an-tenna gain and the transmission line loss betweenthe antenna and the receiver. In order for thesignal to be intelligible it must be stronger thanthe receiver noise level. Manufacturers of thereceiving equipment determine a signal level fortheir equipment which depends on the type ofmodulation used and the receiver design. Thislevel is called the threshold level, and representsthe lowest signal level that will be intelligible.Although a received signal may be only barelyabove this level, satisfactory transmission results,provided there is no fading. Since fading lowersthe signal strength at the receiver, it is necessaryto have a much stronger signal arrive under nor-mal conditions, in order that an intelligible signalmay be received under expected fade conditions.The difference between the field strength of thelevel normally received and the threshold level

TAGO 12840 49

is called the fade margin. The field strength tobe expected for any radio site can be calculatedwithin +5 db by using information from theequipment manual and data taken on the indi-vidual hops of a radio relay system.

34. Acceptable Reliabilitya. Reliability is determined by the percent of

the time that the signal strength at the receiveris above a predetermined level. This level is thesignal strength to be expected 90 percent of thetime and is independent of the receiver character-istics and fade conditions expected in the areawhere the radio relay system is to be installed.Should the signal strength be equal to the thresh-old level of the receiver, the outage time would be10 percent, and obviously not acceptable. Noradio relay system should be planned to operate atthe receiver threshold level since a fade of anymagnitude would immediately result in circuitoutage.

b. By planning the hops so that the signal ishigher than the threshold level of the receiver,higher reliability is obtained. This acts as acushion to absorb fading. For example, if thereceived field strength at the receiver is -10decibels referenced to 1 milliwatt of power(dbm), and the receiver threshold level is -50dbm, the difference, 40 db, is the fade marginfor that hop. On the basis of previous experi-ence, it has been found that a 40-db fade maybe expected not over .01 percent of the time, sothat the 40-db fade margin gives a reliability of

50o TAGO 1284C

99.99 percent. The relationship between relia-bility and fade margin usually is given in applica-ble technical manuals, so that the radio relaysystem can be engineered for whatever reliabilityis desired. In most instances, path attenuationwill be the greatest source of attenuation, so thatwhere a lower reliability is acceptable, the re-peater stations may be spaced farther apart.

c. In calculating the reliability to be expectedfrom a radio relay system, the simplest and safestmethod is to assume that outages in the varioushops will not occur simultaneously. For example,if a radio system has 10 hops, with an efficiencyof 99 percent for each hop, it is safe to estimatethat each will be out 1 percent of the time. How-ever, since outages are assumed to occur at differ-ent times, the total outage time for the entire10-hop system then would be 10 percent, so thatthe system as a whole would have a reliability of90 percent. As the number of hops increase,however, the likelihood of the outages occurringsimultaneously also will increase.

35. Factors Increasing Range or ReliabilityThere is no method of simply evaluating the

effect on a vhf system of such factors as changesin weather or terrain conditions. However, theeffect of many other important factors can beevaluated. When installation of radio relay sta-tions beyond the radio line of sight is necessary,the following factors tend to improve perform-ance on either the normal or the obstructedcircuits:

TAGO 1284C 51

a. Proper Siting. Careful selection of stationsites and particularly the selection of good an-tenna sites is probably the most important singlefactor to insure successful radio relay operation.Hilltop installations and well elevated antennasusually provide the best results. Since experienceindicates that significant variations in signalstrength exist within relatively small areas, itoften is profitable to test antennas in other loca-tions in the same general vicinity for maximumsignal strength. Similarly, antennas should betried at several different mast heights in thevarious locations. Thus, if a specific site provesunsuitable, other acceptable sites may be foundin the same vicinity which will prove satisfactory.Locations near hilltops on the hillside facing theother terminal or radio repeater usually are best.Trial and error is an accepted technique in mak-ing the final antenna installation. This is espe-cially true for very rough terrain or when onlyrelatively low elevation sites are available. Everyeffort should be made to locate the antenna abovefoliage.

b. Proper Antenna Orientation. Terrain inthe vicinity of either the transmitting or receivingantenna can distort the antenna pattern; there-fore, antennas should be experimentally rotated(ch 8) to arrive at the best orientation. Suchrotation frequently will reduce the effects of in-direct (reflected) signals caused by rough ter-rain features, such as river valleys or near-byhigh mountains. Conversely, however, sharpterrain features may be capitalized upon to pro-

52 TAGO 1284C

vide usable indirect radio paths when both trans-mitting and receiving antennas are properlyoriented. Normally, propagation by indirectpaths is inferior to that of direct paths, but insome instances circuits can be established throughuse of such indirect paths where no circuit nor-mally can be realized.

c. Radiation of Strong Signals.(1) After the site is selected and the proper

antenna orientation determined, the sig-nal level at the receiver will depend onthe strength of the radio signal directedtoward the receiver location. Vhf sys-tems should be established with the mini-mum amount of power required for goodreception, while at the same time allow-ing sufficient power to overcome fadingdue to atmospheric disturbances. Thisprocedure also will minimize adjacentand co-channel interference, reduce theamount of interference between adjacentor interconnected vhf systems, and lessenthe possibility of enemy interception.

(2) If a high-gain antenna, such as a vhfrhombic is used, more of the lower pow-ered signal will be directed toward thereceiving site and the effect will be thesame as if transmitter power were in-creased.

(3) Losses between the transmitter and theantenna may be minimized by using ahigh quality transmission line as short

TAGO 1284C 53

as possible and properly matched at bothends.

(4) When a circuit is subjected to enemyjamming, the change from multichannelto single-channel operation allows moreof the transmitter power to be concen-trated in the single channel, and therebyimproves the signal strength of thechannel. (This procedure should beused only under emergency conditions.)

(5) On marginal circuits, it may be neces-sary to use an rf amplifier to increasethe transmitted power.

d. Use of Lower Level Signals at Receiver.(1) The ability of the receiver to operate on

a weak signal is directly dependent onthe ability of the receiving antenna tocapture as much of the signal as possiblewithout picking up excessive noise in-terference. High gain antennas, prop-erly oriented toward the signal sourceand situated away from noise sources,will provide better reception thansimpler antenna types. The amount ofnoise picked up by any antenna will in-crease unless local sources of inter-ference, such as high-voltage transmis-sion lines, ignition systems, or otherelectrical equipment, are eliminated. Inmany installations, nearby communica-tion equipment may generate spurioussignals which merge into a high back-ground noise level. In some installa-

54 TAGO 12840

tions, adjacent channel or co-channelinterference will determine the lowestuseful signal at the receiving site.

(2) In addition to external noise, the re-ceived signal must compete with noisegenerated within the receiving set itself.High quality receivers located in an areafree from interference and connected toa high gain antenna by a short highquality transmission line will providethe best signals.

TAGO 1284C 55

CHAPTER 4

FREQUENCY SELECTION

Section I. GENERAL

36. Assignment of Frequenciesa. Problems encountered in planning radio

relay systems (ch 3) are similar. The assign-ment of frequencies, however, imposes a particu-lar problem especially when a large number ofradio relay systems are concentrated in one area.As a consequence, the selection and assignmentof noninterfering frequencies become proportion-ately more difficult. Scarcity of available fre-quencies may even require changes in choices ofstation locations to help reduce interference.

b. Some of the factors to consider in choosingfrequencies for a single vhf radio relay system areas follows:

(1) Separation between transmitter and re-ceiver frequencies at a given station.

(2) Separation between receiving frequen-cies at the station.

(3) Re-use of frequencies.

(4) The type of equipment used.

56 TAGO 1284C

(5) Generation of harmonics by equipment.(6) The nature of the traffic to be sustained.

(At certain frequencies, high-gradetransmission is difficult.)

(7) Relationship of frequencies used by anadjacent system or systems in a givenarea.

37. Frequency CharacteristicsFrequencies above 30 mc usually do not have

long-range propagational characteristics andtherefore may be used simultaneously by manyunits throughout a theater with a minimum ofinterference. When there is some freedom ofchoice, frequencies that are best propagatedshould be selected: Higher frequencies should beselected for short hops and for hops over smoothterrain; lower frequencies should be used forlonger hops or for obstructed paths.

38. Minimum Frequency Separation Between Ad-jacent Transmitters and Receivers

a. At vhf, the transmitting frequencies forradio relay equipment which does not requirethe use of interference charts (AN/TRC-3 and-4; and AN/GRC-39 and -40) must be well-separated from the receiving frequencies by aguard band to minimize transmitter-to-receiverinterference. However, guard bands alone are noabsolute guarantee of interference-free systemsemploying these vhf sets. The transmitter fre-quencies are kept on one side of the guard bandand the receiving frequencies on the other side.

TAGO 1284C 57

b. The receiving frequencies at a station mustbe well separated from each other to prevent re-ceiver-to-receiver interference. Usually this isdone by operating the receivers so that at leastone unused frequency channel separates the op-erating frequencies between any two receivers.

39. Frequency Plan Flexibilitya. Frequency plans should be flexible so that

the system layout may be changed on short notice,and so that the frequencies of the stations thatare moved will be compatible with the frequen-cies in use at the new locations. Flexibility inthe plans is increased by the following:

(1) Providing ample frequencies.(2) Avoiding frequencies that presuppose

particular physical arrangements.b. Factors that may affect the assignment of

frequencies are-(1) Terrain obstacles between higher and

lower headquarters. Circuits originallyinstalled over a direct path may requireradio repeaters if such headquarters dis-place to new locations. Such repeaterfrequencies must be compatible with as-sociated terminal frequencies.

(2) Lack of alternate means of communica-tion may require that all trunk circuitsbe provided by radio relay systems.This situation may necessitate manychanges in radio relay system arrange-ments. A flexible frequency plan makessuch rearrangements easier.

ss TAGO 1284C

40. Methods of Frequency SelectionThe method of frequency selection depends

primarily on the kind of equipment used and thephysical make-up of the radio relay network.The methods for each equipment is described inthe technical manual covering the equipment.An example of such a method is given in para-graphs 41 through 43. For a more complexcommunication network having parallel and inter-connecting or crossing systems, the method offrequency selection described in paragraphs 44through 55 is used.

Section II. DIVISION AND CORPS LEVEL

41. Selection of Receiving FrequenciesObserve the following rules when selecting the

frequencies of receivers that are to be operatedat the same location as the transmitters. Be-cause these frequencies will be transmitting fre-quencies at some other location, the rules fortransmitting frequencies also may apply (par.42), depending on the location of the transmit-ters to which the receivers will be tuned.

a. Do not use frequencies for any two receiversat the same location unless the frequencies areseparated by the minimum spread recommendedin the equipment manual. Minimum frequencyseparation may be reduced through use of cross-polarization, separation of antennas by greaterdistances, and reorientation of antennas.

b. Do not use a frequency for a receiver unless

TAGO 1284C 59

·{ 8~E Ns e t ' EXEN md

EI og2 dh·E

Ct·t

co E04

{cE!mC2 ¢l Vo ¢~

1 r Coi N go~

N e _ Cs >'eO

._ S.DDD>O

60 TAG0 1284C

it is separated by the minimum allowable amountfrom a transmitting frequency at the same loca-tion.

c. Especially for equipments that do not con-tain rf filters as a built-in feature, try to keepthird-order interference at a minimum. For ex-ample, assume three transmitting frequencies, A,B, and C, at one location. Select one of the trans-mitting frequencies and multiply it by 2. Fromthe result, subtract one of the other transmittingfrequencies and record the difference. In turn,subtract the other transmitting frequencies fromthe result and record the difference. Repeat thisprocedure for the remaining transmitting fre-quencies; multiply each by 2 and, in turn, sub-tract the other transmitting frequencies from theresult. If possible, do not use any of the finalanswers for receiving frequencies at the samesite where the transmitting frequencies are to beused. A detailed procedure for this type of cal-culation is shown in the chart below: transmitterA operates at 65.6 me, transmitter B at 66.1 me,and transmitter C at 66.5 mc.

42. Selection of Transmitting Frequenciesa. Use frequencies separated by at least the

minimum amount recommended in the equipmentmanual.

b. Whenever possible, use only the operatingfrequencies recommended-do not use borderlinefrequencies (par. 43b).

c. When selecting frequencies to be used at onelocation, divide the assigned frequencies into two

TAGO 1284C 61

blocks; let one block contain the higher frequen-cies (transmitter), the other block the lower fre-quencies (receiver).

d. If possible, do not repeat a transmittingfrequency in any one complete relay circuit. Ifscarcity of available frequencies dictates suchrepetition, a minimum of 3 hops separation shouldbe maintained.

43. Mutual Interference Chart

a. For those equipments which necessitate theuse of interference charts, transmitter versus re-ceiver frequencies must be checked, using a chartto determine their compatibility. Figure 17 isan example of a mutual interference chart. Trans-mitting frequencies are shown along the scale atthe bottom edge of the figure; receiving frequen-cies are shown along the vertical edge.

b. When two or more transmitters are locatedin the same area, the paper strip method shouldbe applied to the mutual interference chart. Toemploy this method-

(1) Prepare a strip of paper about 1 inchwide and long enough to touch the verti-cal edges of the chart.

(2) Place the paper strip on the chart, withits lower edge alined with the bottomof the chart.

(3) Make a mark on the paper strip at eachselected transmitting frequency.

(4) Slowly slide the paper strip upward onthe chart. Keep it straight by alining

62 TAGO 1284C

one end with one vertical edge of thechart.

(5) As each horizontal row of squares ispassed, note the type of square that isshowing at each of the transmittingfrequency marks. If any of the marksrests on a black square, continue tomove the paper strip upward until allmarks rest on white squares. Squarescontaining an X indicate a borderlinecondition. Frequencies indicated by anX may give satisfactory results; how-ever, they are doubtful and recommendedfor use only in cases of necessity.

TAGO 1284C 63

A START FII-

Figure 17. Use of mutual interference ch art.

6 D TAGO 12840

64.-

64 ~~~~~~~~~~TAGO 1284C

10 l0

oCE E

0~ I 280 FT

LOWEST ALTITUDE- LOWEST ALTITUDECURVATURE BELOW CURVATURE 51,280 FT

OF THE EARTH ITUE OF THE EARTH

0'o~~~ J

fl.-

55.*

550

540

Figure 17-Continued.

TAGO 1284C 65

5".9

50'5

g7JI 11 I a 3I

66 TACO 18 1

,5,- xn I- --~ril~rTT I DC

C GOOD FM 1111-9 -9

66 TAGO 1284G

4.0 I I

TACO 12840 67

SI- I I I I cl0 r r I I

Section III. ARMY LEVEL

44. GeneralThe manner of selecting frequencies for equip-

ments that do not require the use of interferencecharts necessitates a more detailed procedurethan the method described in section II. A dis-cussion of the problems encountered in parallel,and interconnecting or crossing systems is givenin paragraphs 46 through 48. Specific plans forthe solution of intricate systems are:Plan PararlrphAbm ...............................-- --- - ------....- 49-53Double-abm .............--- ------ ------- ------..................... 54Xy _ _ 5-5...... ................... 65

45. Two-Block Method of Avoiding Interferencea. The following method of choosing frequen-

cies will give the greatest freedom of tacticalaction for an isolated route. (An isolated routeis one that does not cross or connect with otherradio relay routes.) Divide the frequency chan-nels available for use into two blocks that con-tain equal numbers of frequencies. The blocksshould be separated by a frequency interval thatmust be at least as great as the separation re-quired between transmitter and receiver frequen-cies at any one site. This interval is the wideguard band (A, fig. 18). Frequency separationrequired will be found in the appropriate equip-ment manual. At each station, assign all trans-mitter frequencies to one block and all receiverfrequencies to the remaining block. The op-

68 TAGO 1284C

* 0

o E

- 0*

C -·

,,~' a d

tI -

I'' I 9

La 0

"~~~~~~~ 0,

'ait~~" "

TAGO~~ it8P I

positely directed arrows indicate that in any hop,frequencies in block A are oppositely directed tofrequencies in block B. The block diagram in Billustrates the application of the equipment andassignment of frequencies by the 2-block method.Alternate (frog) the blocks as shown in C of theillustration. This is called a 2-block method withwide guard band.

b. The following is an example of the 2-blockmethod with wide guard band. Assume an iso-lated route consisting of three hops. The totalnumber of vhf channels needed is 3 x 2 = 6.The signal planning officer should request sixnonadjacent frequencies, divided into two blocksof three frequencies each. Each frequency mustbe separated by at least the minimum prescribedin the equipment manual (channel width varieswith equipment). Assume that the followingfrequencies (in me) are assigned-

lower block (A) Upper block (B)

226.5 290.5229.5 294.5237.5 300.5

c. For each hop, the planning officer may pickany pair of the frequencies in the manner men-tioned in a above. No duplicate use of frequencychannels should be made in the same general area.If the planning officer is assigned two closelyseparated blocks, cross-polarization (par. 26) maybe used to prevent interference.

46. Parallel SystemsThe usual troubles found in parallel systems are

similar to those encountered at multiterminal and

70 TAGO 1284C

radio repeater points. To minimize interferencein parallel systems, use the procedure outlined ina through e below:

a. Determine the number of vhf channelsneeded for each system on the route by using the2-block method (par. 45). Allow for expectedtraffic growth on the route.

b. Work out a tentative frequency plan accord-ing to the principles given in the equipmentmanual.

c. Request the necessary vhf channels from theassignment authority. (The channels assignedmay differ from those requested so that it willbe necessary to work out a frequency plan withthose assigned.) If these plans lead to difficul-ties, use applicable expedients as outlined in para-graph 53. If difficulties continue, try to obtainfrequency assignment changes from the assign-ment authority.

d. As soon as the added (parallel) radio systemis set up, operate the equipments to see whetherthey are free of interference.

e. Try the added system with the existing sys-tems in full operation to determine whether thereis any mutual interference.

47. Interconnecting or Crossing SystemsWhen planning a large number of radio sys-

tems that interconnect or cross at various points,the 2-block method may be used. However, thegeneral difficulty that occurs when using thismethod for interconnecting or crossing systemsis that both the transmitting and receiving fre-

TAGO 1284C 71

2 ? 3

?TM 607-73

Figure 19. Triangle situation.

quencies planned for a site fall into the sameblock. This may result in transmitter-to-receiverinterference at the site. If the frequency chan-nels on one of the routes are reassigned, the diffi-culty frequently clears up at one station, but itmay reappear at another station. Expedientscan sometimes be worked out, but when additionalsystems are added the difficulty is likely to re-appear, forcing another set of frequency changesand another set of expedients. Three differentsituations are encountered with interconnectingor crossing systems. These are referred to asthe triangle, odd-and-even, and re-entrancy situa-tions. They are described as follows:

a. Triangle Situation. Figure 19 shows threeradio stations interconnected by a single-hopradio system. Assume that only two blocks offrequencies, A and B, are available. If, at sta-tion 1, all the transmitting frequencies are as-

72 TAGO 1284C

4 80~~9 10 ~TM 687-74

Figure 20. Odd-and-c en situation.

signed to block A and all the receiving frequen-cies are assigned to block B, then:

(1) At stations 2 and 3, transmitting fre-quencies are in block B, and receivingfrequencies are in block A.

(2) With only blocks A and B available,there is no simple way of planning in-terference-free radio communication be-tween stations 2 and 3.

(3) Trial and error planning may be usedwith first one selection of frequenciesand then another, but this is time-consuming and may fail in the end.

b. Odd-and-Even Situation. The odd-and-evensituation is similar to the triangle situation. Fig-ure 20 shows alternate routes between radio sta-tions 4 and 8. One of the routes contains an oddnumber of hops and the other an even number.Obviously, a difficulty similar to that in the tri-angle situation exists. Stations 4 and 8 neednot be terminals and there need be no through-circuits from station 4 to station 8 to have thisdifficulty occur.

c. Re-entrancy Situation. The re-entrancy situ-ation occurs when at a given station the same

TAGO 124lC 73

block of frequencies is used for transmitting onone route and receiving on another. At this sta-tion, the communication network is re-entrant.Re-entrancy can be avoided by replacing a radiosystem by wire on the route or routes that causethe re-entrancy, so that the group of frequencieswhich are re-entrant are used only for transmit-ting, or only for receiving at the station. An-other solution is the assignment of supplementfrequencies, if they are available.

48. Plans for Solving Interconnecting or CrossingRadio Systems

Three plans to solve difficulties with intercon-necting or crossing radio systems are the 6-blockabm, double-abm, and xy plans discussed in para-graphs 52 through 55. The type plan for an areashould be chosen before making channel assign-ments to a particular route in the area.

49. Advantages of Six-Block Abm PlanThis plan is based on a method for dividing a

broad frequency region (all or a large part of anallotted band) into six frequency blocks of suit-able widths. Vhf channels obtained are dividedapproximately equally among the blocks. Thebasic planning is then done in terms of theseblocks. This results in the following advantages:

a. Planning is simplified.b. Any station can be connected with nearly

any other station with a minimum effect on therest of the network.

c. Quick changes are accomplished with mini-mum effort.

74 TAGO 1284C

d. Guard blocks at one station are used forfrequency assignments at some other station, sothat none of the frequency space allotted isbarred from use.

e. It is not necessary to use vhf channels scat-tered over the whole band.

50. Description of Abm Plana. Block Widths. For simplicity, consider first

the case where the six frequency blocks (fig. 21)are contiguous (touching), so that there is no fre-quency space between them. The width of eachblock must then be at least as great as the requiredtransmitter-to-receiver frequency separation forantennas on separate masts. Furthermore, therequired separation between receiver and trans-mitter on the same mast will dictate the totalspread of two blocks; that is, the difference be-tween the highest frequency in block I and thelowest frequency in block IV should be at leastequal to, or greater than the separation requiredon the same mast. If any block is not used at aparticular station, it will serve as a wide guardband sufficient to prevent transmitter-to-receiverinterference at that station. The frequencies inthis wide guard band block will be used at otherstations in the abm plan.

b. Abm Blocks. At the top of figure 21 areshown the six frequency blocks (I through VI).At the left of the figure are shown three waysof use for these blocks, namely: a, b, and m. Theuse of the symbols a, b, and m, is helpful in plan-ning. One symbol is assigned to each radio sta-

TAGO 1284C 75

FREQUENCYBLOCKS:

WAYS OFUSE

a | T | | R |

b| R | | T

TM 687-75

Figure 21. Abrn plan.

tion. The symbols identify a block (or blocks)of frequencies that may be used to transmitand/or receive at a station. For example, whenway a is used at a particular station, the frequen-cies in either block I or II can be used for trans-mitting; and those in block IV or V can be usedfor receiving. When way b is used at a radiostation one hop away, frequencies in block II orIII may be used for receiving frequencies andthose in block V or VI for transmitting. Thus,in a single hop between stations a and b, frequen-cies in block II may be used to transmit from a tob, and those in block V from b to a. Similarly,if the symbol m is assigned to a third station,that is one hop from a on another route, frequen-cies in block I may be used to transmit from ato m, and those in block IV from m to a.

51. Applications of Six-Block Abm Plana. Triangle Situation. The abm solutions to

the triangle situation is shown in figure 22. To

76 TAGO 1284C

b irr m

mTM 687-76

Figure 22. Abrm solution of triangle situation.

solve it, draw a triangle and assign the letters a,b, and m, at the three stations. Any availablevhf channels in blocks I through VI may be as-signed as shown without transmitter-to-receiverinterference occurring. The particular vhf chan-nels assigned must be chosen so that the rules forseparation between receiving frequencies at a sta-tion are observed. Thus, the abm plan solves thetransmitter-to-receiver interference problem auto-matically.

b. Assignment of Specific Vhf Channels. Thefollowing is an example of specific channels as-signed according to the abm plan. Suppose thatin the triangle situation two parallel radio sys-tems are required on each hop. Use the symbolsshown in figure 22, and request two channelsproperly separated in each of blocks I to VI. Sup-pose the following channels and their correspond-ing frequencies are assigned:

TAGO 12840 77

a.

b 210,213 hI

90,96

TM 687-7T

Figure 23. Sample channels for triangle situation.

Channel No. Frequenncy (me)3 101.25

12 105.7545 122.2548 123.7590 144.7596 147.75

132 165.75165 182.25168 183.75204 201.75210 204.75213 206.25

c. Arrangement of Channels. Figure 23 illus-trates how these channels may be arranged. Theycan be paired in the two circuits in any mannerdesired. Again, suppose that interference fromsome unknown source, not traceable, appears inchannel 3, so that a substitute channel is needed.Any other available channel in block I, exceptchannels 10, 11, 13, and 14 (which are too close

78 TAGO 1284C

b m o.

b Tn nb m 0f

0. o.

TM 667-76

Figure 24. Abm solution of odd-and-even situation.

to channel 12), may be substituted without affect-ing the rest of the network.

d. Use of Adjacent Channels. Channels 45 and48 are separated by only 1.5 me as are channels165 and 168. Assume that these pairs are underthe minimum required separation (2 mc). Theymay, however, be used by cross-polarizing the an-tennas (par. 26). Thus the transmitter operatingon channel 45 may have a vertically polarizedantenna while the one on channel 48 a horizon-tally polarized antenna. Channels 165 and 168may be operated in a similar manner.

52. Other Applications of Six-Block Abm Plan

a. Odd-and-Even Situation. Two differentmethods of assigning abm symbols to solve theodd-and-even situation are shown in figure 24.When using the abm plan for the odd-and-evensituation, write out the frequency block layouts

TAGO 1284C 79

LO0

b-- X 11- \ .

NOTES:I O INDICATES RADIO RELAY STATION (INTERMEDIATE OR TERMINALI

2 CO INDICATES A HOP WITH ITS TWO STATIONS

S EAC SYMBOL, , D,1 OF THE BLOCK, APPLIES TO THE STATIOnNEXT TO IT

4. SYMBOLS AT LEFT IHOICATE MILITARY KEAOOUARTERS. EACHSUCH SYMBOL APPLIES TO ALL STATIONS ON ITS LEVELACROSS THE PAGE. FIJI-S-IO

Figure 25. Sample abm solution of large network.

corresponding to each of ways a, b, and m. Alsodetermine at least one other method of assigningabm symbols to solve the odd-and-even situation.The frequency blocks are automatically arrangedto avoid difficulty in choosing vhf channels forany cross-links that may be desired between tworadio systems.

b. Large Layout. As a further example, alarge layout is shown in figure 25. Only one ofmany possible methods of assigning abm symbolsis shown. In practice, some of the hops would be

so80 TAGO 1284C

wire instead of radio, or wire paralleled by aradio system. Also, radio sets using differentfrequency bands would be used in various places;and additional hops would probably exist, suchas those connecting supply points or other head-quarters.

c. Noncontiguous Blocks. The edges of succes-sive frequency blocks need not touch each other.The difference between the top frequency used inany block and the bottom frequency used in theblock (which is two blocks above it and separatedby one other block) should be at least as great asthe required transmitter-to-receiver frequencyseparation. This method assures the requiredguard band.

d. Multiples of Six Blocks. If adjacent broadbands of frequencies are divided into six blockseach to use in the abm plan in the applicablebroad band of frequencies, the arrangement forthe first six blocks should be repeated in the nextsix (block VII would be like block I, and so on).This is done to avoid transmitter-to-receiver in-terference at the common edge of the two broadbands of frequencies.

e. Different Types of Radio Relay Sets. If thefrequency widths of the blocks are properlychosen, different types of radio relay sets canshare the blocks.

53. Methods of Decreasing Necessary B oa c kWidths

In the 6-block abm plan (for general applica-tion in an area), expedients to decrease the block

TAGO 1284C 81

width are more difficult to attain than they are ina simple application to a particular route. Manyof the expedients decrease flexibility, and the ob-ject of the 6-block abm plan is flexibility. Theexpedients that can be used to decrease the neces-sary block width are given in a through c below.

a. Pairing. Pairing of transmitter and re-ceiver rf channels can be used for either the abm,double abm (par. 54), or the xy plan (par. 55).The procedure used is to assign the frequencies inpairs: the lowest frequency in the transmittingblock at a station is paired with the lowest fre-quency in a receiving block. This is called pair1 and is assigned to one radio set at a station.The next lowest frequency in a transmitting blockis paired with the next lowest frequency in the re-ceiving block and called pair 2. This pair is as-signed to another radio set at the same station.The same method is used for all the frequenciesin the transmitting and receiving blocks at a sta-tion. By the use of paired frequencies, the sepa-ration of transmitting and receiving frequenciesof a hop is greater than that of the block servingas the wide guard band. Thus, the width of theblocks may be reduced.

b. Cross-Polarization. If the frequency widthof a particular block is to be reduced by use ofcross-polarization (par. 26), the frequencies inthe block immediately below it should be polarizedoppositely to those in the block immediately aboveit. The following chart uses this method to re-duce the frequency width of all the blocks in twoadjacent 6-block units.

82 TAGO 1284C

Cross-Polarization Chart

Six-block unit

Block I II III IV V VIPolarization H H V V H H

Adjacent 6-block unit

Block I II ' IV' V' VI'Polarization V V HI H V V

c. Separation of Antennas. Physical separa-tion of antennas should be used only when neces-sary to reduce block width in last-minute plan-ning, or in field rearrangement, when interfer-ence is experienced.

54. Double-Abm Plan

a. Explanation. If the traffic load on a par-ticular route is so great that, with the channelsavailable, use of the abm plan becomes difficult,the double-abm plan should be used.

(1) The double-abm plan uses the same sixfrequency blocks as the single-abm plan.The double-abm plan uses ways a, b, andm of employing these blocks, and alsothree more ways, a' b' and m'. Figure26 shows all six ways of use. Also itshows that a station labeled a can com-municate with a station one hop awaylabeled a'. Four of the six frequencyblocks can be used for communicationbetween a and a' (two blocks in each di-rection). Thus, a heavy traffic routecould be made up of radio stations

TAGO 12840 B3

FREOUENCYBLOCKS: I | 3 m I

WAYSOF

USE{ Ir T R

b | I T |

b. I T |b' [R T r

z z z I i R ]

i- | T | | R | | T |TM 667-79

Figure 26. Double-abm plon.

labeled a, a', a, a', etc. Similarly, b andb', or m and m', could be used.

(2) Suppose that symbol a is assigned to astation S. Then, on a heavy trafficroute, the station one hop away from Scould be assigned a'. On a lighter traf-

84 TAGO 1284C

FREQUENCY I n m | n8LOCKS:

WAYSOF

USE

_ | ' I R J8 I . | | r I

TM 687-81

Figure 27. Xy plan.

ice route, the station one hop away fromS could be assigned b or m.

(3) The series of symbols with prime andnonprime letters (a, a' b, b' or m, m')need not be used for heavy traffic routesonly. However, the single-abm seriesor the single a', b', m' series is better forthe lighter traffic routes because it per-mits a greater number of interconnec-tions.

(4) A route can be made up partly of oneseries of symbols and partly of another,such as a', a, b' m'. Symbol shifts ofthis kind help in making interconnec-tions.

b. Example. As an example of the double-abmplan, consider the case previously worked out infigure 25. If the route from X to Y in this figurewere required to carry more traffic than could behandled with available abm frequencies, thedouble-abm plan could be used on this routemerely by changing b to m' at stations Z and W.

TACO 1284C 85

55. Xy PlanThe xy plan is used when planning a very heavy

traffic route. This plan is not as flexible as theprevious plans (abm and double abm) and forflexibility, it relies on interconnection with them.Interconnection between the xy plan and the abmor double-abm plan can be worked out by theplanning officer.

a. The xy plan uses the same six frequencyblocks as the abm and double-abm plans (fig. 27).Stations labeled x and y can communicate witheach other (without mutual interference) byusing vhf channels in four frequency blocks (twoin each direction).

b. If adjacent broad bands of frequencies aredivided into six blocks each, it is necessary toavoid transmitter-to-receiver interference be-tween blocks VI and VII (VII is block I of theadjacent group). A station using way x in oneof the broad bands of frequencies should useway y in the adjacent broad band, and vice versa.This would practically eliminate interconnectionpossibilities with abm plans, if both xy and abmplans were used in both broad bands of frequen-cies. However, interconnections can be made byplacing a guard band between the two broadbands of frequencies and by using way x at thesame stations in both bands, or by using the xyplan in only one of the two broad bands of fre-quencies.

86 TAGO 1284C

CHAPTER 5

SYSTEM OPERATING TECHNIQUES

Section I. GENERAL

56. Operating PracticesUniform operating practices must be estab-

lished throughout the communication system toassure efficient use of signal personnel and facili-ties. SOP's must be distributed to all points inthe system where personnel operate and main-tain communications.

57. Control Stationsa. A circuit control station must be designated

for each system to simplify circuit managementproblems and to insure orderly control of opera-tions. The terminal serving the higher, or larger,headquarters usually is designated as the controlstation. The control station is responsible forsupervision of initial and overall tests, coordina-tion of maintenance effort for trouble location andclearance, and temporary circuit reassignment tomeet emergency conditions.

b. The control station must maintain a log toshow which circuits are out of service, the reasonfor such outage, and the prospects for restoral.

TAOO 1284C 87

The log also must show when permission has beengranted radio repeater stations to remove thecircuit for routine tests, to patch in spares, or toperform any operation affecting circuit perform-ance. Copies of all circuit orders must be sentpromptly to the control station to insure thatcontrol station personnel have accurate informa-tion on the condition of assigned circuits.

58. Use of Order Wiresa. To carry out necessary testing functions,

order wires usually are required between controland subordinate stations. Normal trunk circuitsmust be made available for maintenance opera-tions between main terminals; this is especiallytrue where large centers of signal communica-tion facilities are involved. Order-wire circuitsmay be an integral part of the communicationequipment, or be a voice channel of the system.

b. Order-wire circuits are required as a com-munication means during the system lineup.Therefore, it is important to complete lineup ofthe order-wire circuit before attempting thelineup of the other channels.

Section II. SYSTEM LINEUP

59. GeneralThe overall system must be lined up by adjust-

ing transmission levels at all points in the system,where such adjustments are possible, in accord-ance with instructions contained in the appro-

88 TAGO 1284C

priate equipment manual. The overall systemlineup consists of the radio-system lineup, whichis accomplished first, and the carrier-systemlineup, which is accomplished after the radio-system lineup is completed. Procedures for lineupof both equipments are detailed in the equipmentmanuals.

60. Control of Lineupa. All lineups are supervised by the control

station, designated Terminal A; the remainingterminal in the system being designated TerminalB. Where carrier equipment is physically sepa-rated from the radio-terminal equipment, the car-rier attendants at Terminal A will supervise theoverall system lineup.

b. During system lineup, intermediate repeaterstations (radio or carrier) report all readings tothe control station.

c. Permission to make lineup adjustments mustbe obtained from the control station. If tele-photo, facsimile, or other transmissions that re-quire critical signal levels are being transmittedover the system, the control station must insurethat no more than a 2-db change will result inthe system as a result of any one lineup.

61. Radio-System Lineupa. The radio-system lineup is given in b and c

below. This lineup is performed only after thestarting procedure, as outlined in the appropriateequipment manual, has been performed for eachradio set of the radio system. The lineup in-

TAGO 1284C 89

sures that the radio system is operating at maxi-mum efficiency prior to superimposing the lineup.If connections to the carrier system have beenmade, the control carrier terminal must be in-formed when the radio-system lineup is com-pleted so the overall system lineup may be accom-plished.

b. The radio lineup procedure is accomplishedfirst in the A-B direction, and then in the B-Adirection. When performing the lineup, the con-trols of the transmitter at radio Terminal A areadjusted first. When this has been accomplished,the control radio-terminal attendant directs theattendant at the next receiver in the A-B direc-tion to adjust his receiver control appropriately.When this has been accomplished, radio TerminalA then directs that the next transmitter in theA-B direction be adjusted. Each successive re-ceiver and transmitter in the A-B direction islined up in sequence until the receiver at Ter-minal B is lined up. At this point, radio TerminalB assumes temporary control, and directs thelineup in the B-A directions.

c. After all stations have reported readinessfor overall system lineup, the control carrier sta-tion is notified.

62. Overall System Lineupa. The overall system lineup is performed for

both the carrier system and the radio system.This lineup is controlled by the carrier terminaldesignated as the control station. As in the caseof the radio system lineup, the carrier system

90 TAGO 1284C

lineup is accomplished first in the A-B directionand then in the B-A direction. The procedurefollowed is the same at both terminal and re-peater stations.

b. The carrier-system lineup adjustments aremade in accordance with the procedure outlinedin the equipment manual or SOP's. The step-by-step process for lining up the carrier system issimilar to that for the radio-system lineup (par.61).

63. Monitoring and Operating ChecksMonitoring and operating checks must be per-

formed at periodic intervals. These checks nor-mally are performed while the system is operatingand should not interrupt the normal use of theradio and carrier equipment. Equipment man-uals and SOP's provide a list of checks to be per-formed.

64. Circuit Order Testsa. Overall circuit order tests are required after

installation tests have been completed and beforethe systems, trunks, and circuits are placed inservice. These tests are made on trunks thatare a part of new installations, are additions toan exciting system, or which have been reroutedby wiring changes or by patching. They aremade on an overall system basis, from switch-board to switchboard (or, if available, from test-board to testboard).

b. All circuit order tests are under the direc-tions of the control station. The tests include

TAGO 1284C 91

overall signaling and talking, with supervisorychecks being made to assure efficient operation.Adjustrment and alinement checks also are madeto determine whether facilities meet establishedperformance requirements. Noise measurementsare made on long distance networks. If the over-all performance requirements are met, the trunksare released for use in the communication net-work; if not, they are subjected to sectionalizingtests to bring the system up to acceptable stand-ards.

Section III. NOISE AND INTERFERENCE

65. GeneralThe range of radio relay equipment is inversely

related to the amount of noise or interference atthe receiver location; the more noise or inter-ference present, the shorter the distance that canbe spanned satisfactorily. The most objectionableresult of high noise level is reduced intelligibilityin telephone circuits, and errors in carrier tele-typewriter circuits. Unshielded electrical equip-ment, power lines, motor vehicle ignition systems,certain hospital equipment, and power units aresources of radio noise. Normally, all receivingequipment is set up away from heavy motor traf-fic routes, and vehicles are not permitted within200 yards of receiver antennas. Harmonic radia-tion from other transmitters also may cause con-siderable interference. The prime requirement

92 TAGO 1284C

for good communication is a high signal-to-noiseratio.

66. Mutual Interferencea. Spurious radiation refers to signals radi-

ated from the transmitter on many frequenciesother than the fundamental or carrier frequency.While these spurious radiations are weaker thanthe fundamental or carrier frequency, they maybe strong enough to cause interference (noise) innear-by receivers. Noise is strongest when thereceiver is tuned to a frequency corresponding toone of the spurious transmitter radiations.

b. If these other signals above and below thefrequency to which the receiver is tuned arestrong enough, they may be amplified to the pointwhere they will render the desired signal un-intelligible. It is possible for the local oscillatorin a superheterodyne-type receiver to radiate asignal which can cause interference. This isknown as receiver radiation.

c. Various ways in which mutual interferencecan occur are-

(1) Transmitter fundamental radiation toreceiver fundamental response.

(2) Transmitter spurious radiation to re-ceiver fundamental response.

(3) Transmitter fundamental radiation toreceiver spurious response.

(4) Transmitter spurious radiation to re-ceiver spurious response.

(5) Receiver radiation to receiver funda-mental response.

TAGO 1284C 93

d. When receivers are situated close to trans-mitters, the frequency separation must be greaterthan normal.

e. Interference caused by spurious radiations ofthe transmitter being picked up by the spuriousresponses of the receiver need be considered onlywhen a large number of transmitters and re-ceivers are operated at one site and the receiveddesired signal is weak. No interference of thistype will be encountered in a communication sys-tem where transmitters and receivers are op-erated with antennas separated by at least 60feet and with the receivers operating on strongsignals.

67. Operation With High System Noisea. Occasionally, traffic channel noise is exces-

sive. This may be caused by a higher noise levelat one or more radio hops than at others. A hopmay have relatively high path attenuation due toa long transmission path or line-of-sight obstruc-tions. A high noise level also may be caused byexternal sources such as ignition or radio in-terference.

b. Under such conditions, it frequently will bepossible to improve the overall system signal-to-noise ratio. Better reception may be obtained byincreasing the signal output of the transmitterand reducing the gain of the receiver where thehigh noise level occurs.

c. There are limits to signal-to-noise improve-ment, however. Changing 4-channel output to1-channel output (or 12- - 4-) will increase the

94 TAGO 1284C

relative signal-to-noise level. This assumes thatall of the transmitter power that was used in thehigher number of channels is applied to the lowernumber.

d. When a particular hop is operating with ex-cessive noise, follow the procedure outlined in theequipment manual.

TAGO 1284C 95

CHAPTER 6

MAINTENANCE CONSIDERATIONS

Section I. GENERAL

68. Maintenance Plana. A properly organized and coordinated main-

tenance plan is one of the most valuable aids toinsure maximum system operating efficiency andminimum expenditure of manpower and materiel.

b. The maintenance goal is to minimize circuitoutage and, when such interruptions occur, tocorrect them and restore service as rapidly aspossible.

c. Maintenance forces should be organized,equipped, and trained to isolate and correct equip-ment failures in a minimum of time. Preventivemaintenance detects and eliminates potentialtroubles before they can cause service failures(par. 71). Corrective maintenance locates re-

ported troubles and restores the equipment tosatisfactory working conditions (par. 72).

69. Factors Affecting Overall Operation a n dMaintenance

a. Reliability. To insure reliable operation,signal equipments are tested and inspected at the

96 TAGO 12840

source of supply. Accurate records on equipmentperformance and the prompt submission of re-ports covering unsatisfactory equipment per-formance furnish a guide for future equipmentimprovement.

b. Installation. Before the equipment is placedin service, proper installation and performancetesting procedures must receive careful attention.This is particularly important when the com-munication channels consist of widely dispersedequipments operated together to make up a circuitor system.

70. Basic Requirements for Maintenance PlanThe essential factors for a well-functioning

maintenance plan may be summarized as follows:a. A well-trained group of radio relay at-

tendants and carrier maintenance personnel arerequired.

b. Standing operating procedures coveringmaintenance instructions and testing and repairprocedure must be formulated.

c. Tool equipments, test equipments, and spareparts must be provided in adequate quantities andat the right places.

Section II. PREVENTIVE AND CORRECTIVEMAINTENANCE

71. Preventive Maintenancea. Preventive maintenance is a responsibility

of all echelons of operation and maintenance. Itspurpose is to disclose and correct incipient

TAGO 32840 97

troubles, and it consists of performing thosemaintenance operations that will prolong the lifeof signal equipment.

b. The basic principle of maintenance is thatthe repair will be performed at the lowest echelonwhen the necessary tools, test equipment, parts,skills, and time are available. Equipment supplymanuals SIG 7 & 8's are guides for determiningthe limits of each echelon of maintenance. Theemphasis at user level is prevention rather thancure.

c. Preventive maintenance may be subdividedbroadly into three categories as follows:

(1) Operations directed toward preventingdamage to equipment-avoidance ofrough handling, proper storage, protec-tion from exposure to the elements, andproper operation.

(2) Routine operations directed toward pro-longing the life of the equipment-lubri-cating, cleaning, adjusting, and inspect-ing.

(3) Periodic performance tests directedtoward disclosing incipient troubles; per-formance tests of telephone trunks, car-rier equipments, and radio sets are typi-cal examples. Procedures for these testsare found in the technical manuals cov-ering the specific equipment. Whensuch tests are made, they must be per-formed under the supervision of the con-trol station, since the tests may involveremoving the equipment from service or

98 TAGO 1284C

otherwise interfering with circuits inuse.

d. The functions outlined in c above are per-formed by the operators. Defective equipmentfound should be replaced with spare equipment,and the defective equipment sent to unit main-tenance personnel for repair.

e. Preventive maintenance must be performedon a scheduled basis and should cover a list ofwork items to be checked daily, weekly, andmonthly. DA Forms 11-238 and 11-239 shouldbe used as guides. Keeping comprehensive rec-ords of troubles and classifying them by typeswill aid the signal officer to evaluate the conditionof his equipment.

f. When new equipment is received in defectivecondition or when equipment does not performsatisfactorily, the following will be used for re-porting such unsatisfactory condition:

(1) DD Form 6 (Report of Damaged or Im-proper Shipment) will be filled out andforwarded as prescribed in AR 700-58(Army).

(2) DA Form 468 (Unsatisfactory Equip-ment Report) will be filled out and for-warded to Commanding Officer, UnitedStates Army Signal Equipment SupportAgency, Fort Monmouth, N. J., as pre-scribed in AR 700-38.

72. Corrective MaintenanceCorrective maintenance is the work done to lo-

cate and correct troubles which have affected the

TAGO 1284C 99

operation of circuits or equipment. Usually, cor-rective maintenance is more time consuming thanpreventive maintenance, and generally requiresthat equipment be removed from service. Todiagnose and clear troubles efficiently, the re-pairman must be thoroughly acquainted with theequipment and its components, the functioning ofthe equipment, and the possible symptoms for thedifferent troubles that may occur. Correctivemaintenance procedures are found in the techni-cal manuals associated with the equipment.

Section III. OVERALL AND SECTIONALIZINGTESTS FOR TROUBLE CLEARANCE

73. Multichannel SystemsA standard multichannel radio relay system

basically consists of the following:Radio-terminal sets.Radio-repeater sets.Telephone carriers.Telegraph carriers.Ringing equipments.

a. The radio relay portion of the system isshown in figure 1. A simplified block diagram ofthe carrier portion of the system is shown infigure 28.

b. All operators in a system must be in com-munication with each other by an order-wirechannel (voice channel reserved for operationaluse). If any of the channels on the 2-wire lineside of the telephone carrier are used for voice

100 TAGO 1284C

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101

transmissions, they must be passed through ring-ing equipment to provide ringing facilities. Tele-phone channels normally are connected to aswitchboard, usually less than 5 miles from thecarrier. Channels used for facsimile or telegraphmust be strapped around ringing equipment, orconnected directly to their respective terminalson the voice-frequency (vf) equipment. Channelsused for telegraph transmissions are terminatedin a telegraph carrier terminal, from where theymay be brought out to a telephone switchboard(used for teletypewriter switching) as shown infigure 28. For simplicity, the telephone circuitson figure 28 have not been terminated in a switch-board.

c. Trouble in the system can be localized bytesting the following:

(1) The radio circuit between terminal sta-tions in both directions.

(2) The spiral-four circuit between the ter-minal radio stations and terminal car-rier stations at each end of the system.

d. A step-by-step procedure for sectionalizingtroubles in c(1) and (2) above is shown in figure29. This is further described in paragraphs 75through 77.

74. Long Distance NetworkA long distance network comprises the long

distance trunk or radio link with its associatedcentral office equipment. The local network com-prises the user's equipment and the associatedcentral office equipment and local loops. Overall

102 TAGO 1284C

tests are used to verify the transmission andsignaling features of communication trunks as-sociated with new installations, with additions tothe existing plant, and with reassignment of cir-cuits.

75. Overall Testsa. The overall talking, signaling, transmission,

and other tests should be made from switchboardto switchboard under the supervision of the con-trol station. If trouble is encountered, the faultytrunks should be removed from the switchboard,and further tests continued from testboard totestboard.

b. Once a trouble is suspected or reported,overall tests should be conducted to verify thetrouble condition. Sectionalizing and localizingtests then should be made to identify and locatethe failure point.

76. Station Operation and MaintenanceOverall tests of communication channels in-

clude initial and periodic tests to assure service-ability. Adequate testing equipment is requiredat terminals and intermediate points to performoverall and sectionalizing tests. The facilityunder test should be removed from service atboth terminating switchboards before proceedingwith the tests. Under the supervision of the con-trol station, overall signaling, talking, and trans-mission tests from terminal to terminal shouldbe made first. These are followed by sectionaliz-ing tests between control stations and, finallybetween relay stations.

TAGO 1284C 103

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104 TAGO 1284C

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TiAG I i 105

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TAGO 12840 105

77. Test on Trunks of Radio Relay Systemsa. Standing operating procedures must be set

up to insure orderly control of maintenance andother work for those long distance circuits whichpass through several test or carrier and radio re-peater stations in different administrative areas.

b. Overall and sectionalizing tests on trunks ofa radio relay system are shown in figure 29.Order-wire circuits often are a built-in featureof military radio relay equipment, as indicated inthe figure. The order wires may be extended toorder wires of connected systems in the circuitlayout.

c. Maintenance personnel are required at allstations in a system to permit coordination oftesting activities on long distance trunks andtransmission systems. Control and subordinatestation procedures must provide for orderlyanalysis of troubles, and should designate re-sponsibility for placing and maintaining circuitsin service. Once a trouble is located, correctivemaintenance procedures must be carried out.

d. The areas of responsibility for the activitiescomprising an integrated radio relay and wirecommunication system are shown in figure 29.In addition, the procedure and sequence of opera-tions for testing and troubleshooting is outlinedin steps 1 through 8 (fig. 29). SOP's must beformulated for forward, intermediate, and reararea radio relay communication systems so thatspecific responsibilities are assigned to the sepa-rate activities of the system. By this means,

106 TAGO 1284C

troubleshooting and testing procedures may beestablished and preventive and corrective mainte-nance performed in a minimum of time and effort.

TAGO 1284C 107

CHAPTER 7

ANTIJAMMING

Section I. CHARACTERISTICS OFJAMMING OPERATIONS

78. GeneralEnemy jamming is the transmission of disturb-

ing radio signals to interfere with the receptionof the desired signal. The effects sought by theenemy are to disrupt our system and deny its useto our forces. Techniques employed to minimizethe effects of enemy jamming are called anti-jamming. The term electronic counter-counter-measures (eccm) encompasses antijamming.

79. Vulnerability to Jamminga. All radio relay equipments are vulnerable

to jamming activity, and it must be assumed thatjamming operations will be conducted by theenemy whenever it is to his advantage.

b. Prior to jamming, the enemy searches thefrequency spectrum to locate radiated signals.After identifying a transmission, the enemytunes a transmitter to the same frequency andtransmits a jamming signal. In so doing, thejammer attempts to prevent the effective recep-tion of desired signals on that frequency.

108 TAGO 1284C

80. Defense Against JammingIn most instances, antijamming measures will

go beyond the efforts of operators. Most presentday radio relay equipment has been designedwith built-in antijamming features. Special fre-quency assignments, frequency changes, the useof alternate communication routes, operationaladjustments, and the location and destruction ofthe jamming station are techniques that may beused to overcome enemy jamming. Additionalpreventive measures include proper siting, useof alternate frequency assignments, code words,and a frequency change system.

Section II. ANTIJAMMING INSTRUCTIONS

81. GeneralOperator skill and confidence are essential for

maintaining communications during enemy jam-ming. These can be developed by individual,team, and unit training in which simulated enemyjamming is used to approximate actual field con-ditions. The operator must be familiar withantijamming instructions in the equipment man-ual and he should refer to FM 11-151, DefenseAgainst Electronic Jamming, for additional in-formation.

82. Instructions for Commanders and Staff Offi-cers

a. If possible, study and plan all operations inadvance; use brevity codes to direct plans.

TAGO 1284C 109

b. Keep messages as short as possible.c. Stress radio discipline and security.d. Destroy enemy jamming stations if possible.e. Always inform next higher headquarters of

enemy jamming activities.

83. Instructions for Signal and Communication Of-ficers

a. Initial siting is probably the most importantand effective antijamming measure that can betaken-it becomes more important the closerradio relay is brought to the enemy location.Where possible, forward area terminals and re-lays should be chosen with a well-defined land-mass shielding stations from possible enemy in-terception and jamming. In addition to terrainmass, foliage and man-made structures can beused in achieving this protection.

b. When directional antennas are employed,they can be rotated to minimize the strength ofthe jamming signal in relation to the strength ofthe desired signal.

c. Mobile facilities should be relocated to siteswhere the jamming signal is received at minimumstrength.

d. Polarization of antennas may be changedfor maximum signal strength (par. 26).

e. Antenna heights may be changed.f. Where possible, alternate frequencies should

be available, and by using spare equipment, thecircuit should be re-established on the new fre-quency, with the original equipment continuing tooperate on the original frequency.

110 TAGO 12S4C

g. Circuits should be established on minimumpower requirements consistent with circuit qual-ity; high power should be used during jammingto attempt to override the interference. If thereare many radio sets in a given area, the SOIshould specify, on priority basis, the circuitswhich will switch to higher power.

h. Generally, forward area radio relay circuitsshould not be installed in a line perpendicular tothe line-of-contact with the enemy. This may beprevented by installing radio repeaters to permitapproach to a forward area at an angle. Suchequipment utilization must be weighted againstall other requirements.

i. Filters should be used, if available, to mini-mize unwanted signals.

84. Instructions for Operatorsa. Site the station and antenna to minimize

enemy jamming.b. Learn to recognize enemy jamming; report

all details to the officer-in-charge.c. Learn to readjust the set to minimize the

effects of jamming.d. Operate with minimum power until jammed

-then increase the power.e. Shift to alternate frequencies and call signs

as directed.f. Authenticate all transmissions over the order

wire.g. Keep the order wire transmissions as short

as possible.h. When jammed, keep calm, keep trying, keep

TAGO 1284C 111

operating-the enemy may not realize the suc-cess of his jamming action and he may shift toanother frequency.

112 TAGO 1284C

CHAPTER 8

FIELD EXPEDIENTS

Section I. GENERAL

85. Definitiona. A field expedient is a positive action that

can be taken by personnel to maintain, facilitate,or expedite communications under unusual con-ditions. These conditions may originate as a re-sult of normal wear or use of equipment, acci-dental damage, or enemy action. Employment offield expedients requires the application of com-mon sense and ingenuity on the part of personnelimmediately concerned.

b. Because of the many possibilities of equip-ment failure, complete and comprehensive solu-tions cannot be formulated; however, certain ofthe commoner field expedients are presented inthis chapter.

86. Use of Printed Materiala. Certain former expedients which have

proved themselves during field operations and areadopted as official operating procedures are de-scribed in Department of the Army publications.Examples of this type literature are TB SIG's.

TAGO 1284C 113

These bulletins are published to acquaint SignalCorps personnel with difficulties encountered withequipment in the field and to suggest methods ofovercoming such difficulties. Usually, they areinterim measures and describe corrective actionfor equipments prior to final publication ofMWO's, which are designed to permanently im-prove the equipment. Such MWO's are officialDepartment of the Army publications which di-rect, and describe in detail, physical alterationsto be made to Army equipment.

b. Published TB SIG's and MWO's are listedin DA Pam 310-4. Communication personnelshould familiarize themselves with these publica-tions and take the necessary action.

Section II. CONNECTIONS AND ANTENNAS

87. Coaxial Cablea. Coaxial cable should be kept off the ground,

preferably on fabricated supports; however, in atactical situation it may be laid directly on theground to expedite communications. Coaxialcable deteriorates by exposure to the elements,however, and such deterioration results in ex-cessive cable losses. Normally, the proper lengthcable, as specified in the equipment manual,should be used. During emergencies, longerlengths may be used. Spiral-four cable and fieldwire may be tried as a substitute for coaxial cablebut should be used only when the proper cable isbadly damaged or not available. Use of spiral-

114 TAGO 1284C

four or field wire as a substitute generally re-sults in excessive line losses.

b. Cable connections and fittings on equipmentmust always be kept clean and dry.

88. Vehicular Expedient for Coaxial Cablea. Normally, coaxial cable is run from the an-

tenna directly to the equipment inside the vehiclethrough apertures in the siding. This methodresults in an unwieldy arrangement of cable andalso decreases the dustproof and heat-retainingfeatures of the truck. To correct the situation, amake-shift terminal strip, consisting of a boardon which antenna couplings are fastened, may bemounted on the exterior of the truck and thecables connected to the mounted couplings. Ashort length of appropriate cable may be per-manently installed in the interior of the truck,thus connecting the cable to the equipment.

b. For ease in running the cable from the ve-hicle to the antenna, an appropriate reel unitmay be mounted on the rear of the vehicle trailer,using a ground rod as an axle. By this method,the desired length of cable may be payed out, andthe coupling taped and connected with ease. Thisfacilitates installation and also helps to preventknotting and kinking of the coaxial cable-kinkedcoaxial cable has extremely high rf loss.

89. Effective Protection for Coaxial Couplingsa. Frequently, use of coaxial couplings in field

operations has been limited by impairment dueto climatic conditions. To eliminate trouble from

TAGO 1284C 115

this source, use of nonadhesive, polyethylenerubber-and-rosin composition tape, %-inch wide,has proved effective. Use of ordinary frictiontape generally is unsatisfactory; however, thisspecial rubber tape overcomes coupling troubleseffectively.

b. Coaxial couplings protected by this tape canbe submerged in water or subjected alternately tofreezing and thawing temperatures without ad-versely affecting transmission qualities.

90. AntennasSome expedients that may be used for antennas

are:a. Antennas may be installed on a tree, build-

ing, house, or similar structure in an emergency.b. Field wire, rope, or any similar material may

be used in place of lost or damaged guy wires.c. Where the site is located at high elevations,

a shorter than normal mast may be used. Thisfacilitates maintenance and orientation, and alsoany alteration in antenna settings which may berequired by change of operating frequency.

d. A standard dipole antenna may be used, ifcut to proper length; however, gain and direc-tivity are reduced by the absence of reflector anddirector elements.

91. Storage for Antenna GuysAntenna guys may be wound and stored on a

1- by 6- by 24-inch board by making semicircularcuts at each end for winding the guys lengthwisearound the board. The guy lengths may be indi-

116 TAGO 1284C

cated on the board and several guys may be woundon each board. These boards may be made to fitthe appropriate antenna parts case. This methodeliminates fumbling and groping for antennaguys, and facilities locating guys of appropriatelength.

92. Use of Double-Head Most for Radio RelayEquipment

Fifty percent of the time required for assem-bly and disassembly of antennas of the type usedwith Radio Terminal Set AN/TRC-3 can besaved by the application of a relatively simpleexpedient. This requires construction of adouble-head mast section, as shown in A, figure30. Normally, two single masts (one for receiv-ing and one for transmitting) each with a sepa-rate antenna head, are required for a terminal.With the use of the double-head expedient, onlya single mast is required. Details showing theconstruction of the double-head mast section areshown in B, figure 30. Field tests indicate noappreciable deterioration of signal qualitythrough use of this type antenna. Where highwinds and accumulations of ice and snow prevail,loading considerations must be taken into ac-count.

93. Expedient for Rapid Antenna InstallationIf concurrence is obtained from the local ord-

nance officer, angle-iron may be welded to thefront of the standard 21/ 2-ton general-purposetruck. If two or three straps are riveted to thisangle-iron, it will be able to support a vhf an-

TAGO 1284C 117

at| a m + \L~~ SLOTS MUST BE ALIGNEO

MAST MAST SECTION CUT AND WELDED AS SHOWN

PART OF ANTENNA SUPPORT AB-33

FMI-S-1is

Figure 30. Use and construction of double-headmast section.

tenna that may be quickly fastened by two men.This support will eliminate the use of guy wiresunder normal conditions when using short an-tenna supports. Similarly, straps may be fastenedto the rack sides of 11/2 trailers to permit thesame type of antenna mast fastenings withoutantenna guy wires.

118 TAGO 1284C

Section III. POWER SOURCE EXPEDIENTS

94. Method of Reducing Unit Noise at Forward-Area Sites

The procedure outlined below is designed toreduce power unit noise approximately 90 per-cent.

a. Construct a dugout with adequate clearancealong the sides and top to provide sufficient spacefor maintenance and ventilation.

b. Locate the dugout preferably on a slightrise or hill so that accumulations of water andrain will be drained off. Construct drainageditches from the low side of the dugout.

c. Reinforce the sides of the shelter with sand-bags, or a wooden or steel framework, to providesupport and to prevent cave-ins.

d. Mount the power unit on a platform to pro-tect it from the moisture of the bare earth floorof the dugout.

e. Erect a roof of available material to provideprotection from the weather. Allow space for aventilator shaft to carry exhaust fumes away.(An exhaust system may be improvised by usingflexible metal pipes or carrying cases from 155millimeter shells.)

f. Drape empty sacks or canvas along the roofoverhang to muffle generator noise.

g. Camouflage the dugout with available ma-terial that matches surrounding terrain.

95. Other Expedients for Power Sourcesa. Usually power units that are recommended

for specific equipments are best. However, in

T'AGO 1284C 119

emergency situations any power unit of appro-priate output-voltage, current, wattage, and fre-quency, may be used. Sometimes spare equip-ments are available to provide additional outputpower; in such cases, it is recommended that onlyas many units be used as are required to carrythe load.

b. In case of emergency, turn off all equipmentand lights except those actually required to keepthe circuits in operation.

Section IV. OPERATIONAL EXPEDIENTS

96. Proper Antenna Orientation for Improvementof Marginal Circuits

Terrain in the vicinity of either the trans-mitting or receiving antenna can seriously dis-tort the antenna pattern so that a weak insteadof a strong signal will be received (A, fig. 31).Often the strong signal can be obtained only bytrial and error methods. During experimentalorientation, advantage often may be taken ofindirect radio paths utilizing adjacent obstaclessuch as river valleys or high mountains. In B,figure 31, antennas are oriented for a direct pathand a weak signal is obtained because of inter-vening hills. In addition, part of the signal isreflected by the adjacent obstacle, canceling thedirect signal. In C, figure 31, the transmittingand receiving antennas are oriented for the in-direct path which results in a relatively strongersignal than that obtained by the direct path.

120 TAGO 1284C

THEORETICAL I ACTUALPATTERN - I PATTERN

A

XMTRANT

ADJACENTOBSTACLE

j WEAK DIRECT

WEAK INDIRECTSIGNAL RCVR

ANT B

XMTRANT.

ADJACENTOBSTACLE

ST \E WEAK DIRECT-TR GE PSIGNALSTRONGER ./

INDIRECT RCVRSIGNAL " ANT C

FMII -8-17Figure 31. Orientation of transmitting ana' receiving

antennas for indirect signal paths.

'rAGO 1284C 121

97. Improvement of Marginal CircuitsNormally, operating sites should be selected as

outlined in chapter 3 of this manual. Under cer-tain situations however, it may not be feasible tolocate them within line-of-sight distances. Mar-ginal circuits may result from operation beyondline-of-sight distances. To increase the sensi-tivity of marginal circuits follow the procedureoutlined below.

a. Check and tighten cable couplings and con-nections.

b. Retune all transmitters and receivers in thecircuit.

c. Check to see that antennas are adjusted forproper operating frequency.

d. Try changing the heights of antennas.e. Try changing locations of antennas.f. Separate transmitters from receiving equip-

ment, if feasible.

98. Transmission and Reception of Strong Signalsa. After an adequate site has been selected, and

the proper antenna orientation obtained, the sig-nal level at the receiver will be proportional tothe strength of the transmitted signal. The useof an amplifier at the transmitter provides astronger signal.

b. Excessive signal strength may result in ad-jacent and co-channel interference; therefore, theuse of an amplifier usually is not recommended.If a high gain antenna, such as a rhombic, is used,a stronger signal can be obtained; thus eliminat-ing the need for an amplifier. Losses between the

122 TAGO 1284C

antenna and the equipment can be reduced byusing a high quality transmission line, as shortas possible and properly matched at both ends.When traffic conditions permit, the change frommultichannel to single-channel operation willallow more of the transmitter power to be con-centrated in the single channel. This will rela-tively increase the strength of the signal.

99. Mounting of Radio Relay Equipments in Ve-hicles

Some older type radio relay equipments arenot issued with standardized vehicle installationkits. For tactical purposes, it frequently is de-sirable to mount these equipments in vehicles.Vehicular mounting has both inherent advantagesand disadvantages:

a. Advantages.(1) Less time and fewer personnel are re-

quired for station setup and tear downoperations, and station movement.

(2) Tactical mobility is increased.(3) Equipment maintenance time is reduced.

b. Disadvantages.(1) General purpose vehicles are converted

to a special use.(2) Vehicle maintenance becomes a critical

factor since the equipments are semi-permanently mounted.

Note. Refer to SB 11-131 for a list ofavailable mounting kits.

100. Operation in Extremely Mountainous TerrainThe following subparagraphs outline useful in-

TAGO 1284C 123

formation based on operational experiences inmountainous terrain:

a. It is recommended that skid chains be usedon vehicles operating on unpaved roads, regard-less of the weather conditions.

b. Personnel should be well trained in the useof ropes and pulleys.

c. In hauling and lowering, equipment must bewell packaged to prevent damage.

d. At times, radio relay equipment can be op-erated through masking hills.

e. As a general rule, for every man at the topof a mountain, three will be required for hislogistical support.

101. Extension of Order-Wire Circuitsa. It is expedient at times to install an extra

physical circuit between the switchboard and theradio carrier terminal. This circuit may be usedto extend the carrier order-wire channel to theswitchboard to provide telephone service duringan emergency when wire communications or otherradio telephone channels are out. If this pro-cedure is used, the Signal SOP must specify thatonly personnel designated by the Signal Officermay authorize the use of these circuits for mes-sage traffic.

b. In addition, this circuit may be used bysupervisory personnel for control and coordina-tion of the radio relay system from any telephoneconnected to the terminating switchboards.

c. Some disadvantages to this method of op-eration are as follows:

124 TAGO 1284C

(1) Switchboard operators could disruptsystem lineup procedures if the order-wire circuit was used for traffic withoutgetting prior approval.

(2) While the order-wire circuit is beingused for traffic, there is no channel forcoordination and control of the radiorelay system.

(3) Additional ringing converters to pro-vide signaling must be installed onorder-wire circuits.

TAGO 1284C 125

APPENDIX I

REFERENCES

1. GeneralThis appendix is a selected list of publications

and training films pertinent to field radio relay.For availability of publications and training filmson additional subjects, refer to DA Pamphlets108-1, 310-1, 310-3, and 310-4.

2. Army and Special Regulations

AR 105-15 Field Signal Communica-tions.

AR 220-50 General Provisions.SR 320-5-1 Dictionary of United States

Army Terms.AR 320-50 Authorized Abbreviations.

3. Field Manuals

FM 11-151 Defense Against ElectronicJamming.

FM 21-5 Military Training.FM 21-6 Techniques of Military

Instruction.FM 21-30 Military Symbols.

126 TACO 12840

FM 24-5 Signal Communications.FM 24-18 Field Radio Techniques.

4. Technical BulletinTB SIG 66 Winter Maintenance of Sig-

nal Equipment.TB SIG 69 Lubrication of Ground Sig-

nal Equipment.TB SIG 75 Desert Maintenance of

Ground Signal Equipment.TB SIG 237 Microwave Radio Relay

Siting.

5. Technical Manuals

TM 11-221 Radio Sets AN/TRC-42 andAN/TRC-47.

TM 11-222-B Radio Repeater Set AN/FRC-34 and Radio SetAN/FRC-35.

TM 11-486-6 Radio.*TM 11-614 Radio Set AN/GRC-10,

Radio Terminal Set AN/GRC-39, Radio RepeaterSet AN/GRC-40.

TM 11-618 Radio Set AN/TRC-8(XC-3); Radio TerminalSet AN/TRC-11 (XC-3);Radio Relay Set AN/TRC-12 (XC-3).

*Radin manual of Electrical Communicatons Systems Engineeringgroup of manuals. This manual contains siting, propagation, andantenna design data.

TAGO 1284C 127

TM 11-618A Radio Sets AN/TRC-8, -8Aand -8B; Radio TerminalSets AN/TRC-11, -11A,and -11B; Radio RelaySets AN/TRC-12, -12A,and -12B; and Amplifier-Power Supply Group AN/TRA-19.

TM 11-666 Antennas and Radio Propa-gation.

TM 11-687 R adi o Set AN/TRC-24,Radio Terminal SET AN/TRC-35, and Radio RelaySet AN/TRC-36.

TM 11-689 Radio Set AN/TRC-29 andRadio Repeater Set AN/TRC-39.

TM 11-2139 Telephone-TerminalAN/TCC-7.

TM 11-2141 Multiplier Set AN/TCC-13,Multiplier Group AN/TCA-1, and Pulse FormRestorer Group AN/TRA-10.

TM 11-2239 Telegraph-TelephoneTerminal AN/TCC-14.

TM 11-2242 Telegraph Terminal AN/TCC-4 a n d TelegraphTerminal AN/TCC-20.

128 TAGO 12840C

TM 11-2601 Radio Sets AN/TRC-1, -1A,-1B, -IC, -ID, -1E, -1G,and -1H; Radio TerminalS e t s AN/TRC-3, -3A,-3B, -3C, -3D, -3E, -3G,and -311; Radio RelaySets AN/TRC-4, -4A,4B, -4C, -4D, -4E, -4G,

and -4H; and AmplifierEquipment AN/TRA-1,-1A, -lB, -1C, and -1D.

TM 11-2501A Radio Terminal Set AN/TRC-3H, Radio Relay SetAN/TRC-4H.

6. Training FilmsTF 11-1632 The Effects of Ionosphere on

Radio Wave Propagation.TF 11-1779 AN/TRG-The Radio Relay

Systems of Communica-tions.

TAGO 1284G 129

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APPENDIX III

PHYSICAL SECURITY

1. Security FactorsRadio relay repeater stations in isolated areas

must have adequate security to insure continuousoperation. This security can best be attained byestablishing a perimeter defense. Security fac-tors to be considered are outlined in a through cbelow.

a. Terrain. Defense against enemy attack maybe improved by taking advantage of natural ter-rain features.

b. Vulnerability. The location of the site withrelation to its proximity to enemy forces will in-fluence the extent of the defensive measures re-quired.

c. Tactical and Logistic Requirements. Tacti-cal requirements, such as the availability of per-sonnel and materials must be considered whenplanning perimeter defenses. If the site cannotbe reached by vehicle then air drops may be re-quired.

2. Preparations for Defensea. Immediately after occupying a site, person-

nel not engaged in establishing communications

TAGO 1284C 139

should start the preparations for perimeter de-fense. A reconnaissance of the area must bemade to determine the best location for theperimeter defense line. Some of the factors thataffect this location are-

(1) Critical terrain features around or nearthe site.

(2) Locations for good observation andfields of fire.

(3) Locations that offer the best camouflageand concealment for personnel andequipment.

(4) Advantageous locations for obstacles.(5) Protection against the best avenues of

enemy approach.b. Obstacles that may be used in the perimeter

defense are-(1) Tactical barbed wire (double-apron and

concertina).(2) Trip firing devices attached to grenades,

flares, or dynamite.(3) Antipersonnel and antitank mines.(4) Barricades and other applicable field

fortifications.c. Augmentation of the defense personnel by

Infantry (or other available troops) may benecessary. Such an augmentation would permitradio relay operation personnel to devote fulltime to primary duties.

3. Example of Typical Radio Repeater SiteAssume that a team of six men are assigned to

operate a radio repeater site only a few miles from

140 TAGO 1284C

enemy territory. The site is subject to raids fromguerilla or enemy patrols and is situated at thetop of a high ridge, where there are many ave-nues of approach for enemy attack. This ar-rangement is depicted in figure 32. Defense posi-tions are located so that personnel may be ro-tated to defend the sector under attack. A rov-ing sentinel is assigned to alert the remainderof the crew in event of attack. Note that em-placements are located so that guns and person-nel may take up positions to defend any sector.Through the proper arrangement of obstaclesand deployment of personnel, the 6-man crew maybe capable of resisting enemy attack from anydirection for a limited time. The use of bunkersfor protection against grenades and mortar fire,mines and booby traps well out in front of posi-tions, and pits and holes cleverly concealed affordmaximum physical security.

4. Camouflage, Cover, and ConcealmentStrict compliance with the principles estab-

Iished in FM 5-20, Basic Principles of Camou-flage, is mandatory. In certain cases completecamouflage is impossible; for example, camou-flage material may seriously attenuate antennasignal strength. Antenna masts and guys, maybe camouflaged with no adverse effects.

5. Defense Against Air AttackGround defense against air attack includes

both active and passive measures.a. Active measures against air attack consist

TAGO 1284C 141

LEGEND

i UNOCCUPIEO POSITION > RADIO STATION

OCCUPIED POSITION "* ROVING SENTINEL

CREW POSITION( NOT UNDER ATTACK) SOt 50 CAL MACHINE GUN

-MMMINEFIELD W ANTIPERSONNEL MINES

CJW CONCERTINA WIRE OPERATIONAL VEHICLE

F11l-S-13

Figure 32. Physical security for radio repeater sites.

of concentrated fire from small arms and ma-chine guns. Since attacking aircraft are a targetfor only a few seconds, all available weapons mustbe brought into action promptly.

142 TACO 1284C

b. Passive measures against air attack in-clude-

(1) Dispersal of facilities within an area.(2) Camouflage of vehicles and equipment

by concealment or deception.(3) Use of terrain features to provide con-

cealment.(4) Rigid blackout discipline.(5) Control of the use of fire to avoid dis-

closing positions by smoke or flames.

6. Destruction Plansa. In a retrograde movement equipment facili-

ties and supplies that cannot be evacuated aredestroyed to prevent possible use or study by theenemy. Destruction of facilities and supplies isauthorized only by the commander and is doneaccording to an approved destruction plan.

b. A well prepared destruction plan is detailedand comprehensive. It contains instructions thatare easy to perform, and is consistent with pro-cedures prescribed in equipment technical man-uals.

c. Destruction must be performed as rapidlyand be as thorough as time permits.

TAGO 1284C 143

APPENDIX IV

GLOSSARY OF TERMS

Absorption-The loss of radiated energy due todissipation in a conducting medium.

Amplification-The process of increasing the elec-trical strength of a signal.

Antenna-An electrical conductor or a system ofconductors used to radiate or receive radiowaves.

Array (antenna)--An arrangement of antennaelements, usually dipoles, to achieve desira-ble directional characteristics.

Attenuation-The reduction in strength of a sig-nal.

Authentication-A security measure designed toprotect a communication system againstfradulent messages and other transmissionsoriginated by the enemy.

Axis-of-communication-The line or route onwhich lie the starting position and probablefuture locations of the command post or aunit during a troop movement. The mainroute along which messages are relayed orsent to and from combat units in the field.

Band of frequencies-The range of frequenciesbetween two specified limits.

144 TAGO 1284C

Carrier frequency-The frequency of the wavewhich is modulated by the intelligence wave.

Channel-A band of frequencies used for com-munication.

Circuit-A communication link between two ormore points, capable of providing one ormore communication channels.

Coaxial cable-A transmission line consisting ofone conductor, usually a small copper tube orwire, within and insulated from anotherconductor of larger diameter, usually coppertubing or copper braid. Radiation from thistype of line is practically zero. Coaxial cableis also called concentric line.

Command post (CP)-The establishment set upby the forward echelon of a headquartersduring combat, from which tactical controlnormally is exercised and to which tacticalinformation is sent by subordinate units.

Communication center (comcenter)-A communi-cation agency charged with the responsi-bility for receipt, transmission, and deliveryof messages. It normally includes a messagecenter, cryptocenter, and transmitting andreceiving facilities.

Conductivity-The relative ability of a materialto allow the flow or passage of an electricalcurrent.

Critical frequency-The limiting frequency belowwhich a radio wave is reflected by, and abovewhich it penetrates, an ionospheric layer.

Cross-modulation-Modulation of a desired sig-nal by an undesired signal.

TAGO 1284C 145

Decibel (db)-The standard unit of comparisonbetween two quantities (ratios) of electricalor acoustical power.

Demodulation-The process of recovering theaudio component (audible signal) from amodulated rf carrier wave.

Dielectric-An insulating material between theplates of a capacitor.

Dipole antenna-Two metallic elements placedend to end, each approximately one-fourthwave length long.

Distortion-Distortion exists when the outputwave form is not a true reproduction of theinput wave form. Distortion may exist be-cause of transmission or amplification irregu-larities in amplitude, frequency, or phase.

Duplex operation-The operation of radio equip-ment in conjunction with equipment at an-other location in which the process of trans-mission and reception are concurrent.

Electromagnetic field-The magnetic field that anelectric current produces around the conduc-tor through which it flows.

Facsimile-A system for the transmission of stillpictures or printed matter by means of elec-trical impulses that are controlled by a photo-electric cell and reproduced at the receiverby a mechanical device.

Fading-Variations in the strength of a receivedradio signal caused by changes in the charac-teristics of the propagation or transmissionmedium.

146 TAGO 1284C

Frequency-The number of complete cycles persecond existing in any form of electrical orsound wave motions.

Frequency distortion-Distortion that occurs asa result of failure to amplify or attenuateequally all frequencies present in a complexwave.

Frequency modulation-The process of varyingthe frequency of an rf carrier wave in ac-cordance with the amplitude and frequencyof an audio signal.

Ground-A reference value for a voltage or po-tential; usually the earth or a conductor thatis common to other circuits.

Ground wave-That portion of a transmittedradio wave that travels near the surface ofthe earth.

Interference-Any electrical disturbance from adifferent source which causes undesirable re-sponses in electronic equipment.

Ionosphere-Highly ionized layers of atmosphere(between the altitudes of approximately 35and 250 miles) that affect the propagationof radio waves.

Jamming-Deliberate blocking or impairing ofradio reception by means of interfering elec-trical radiation.

Means of signal communication-A medium bywhich intelligence is conveyed from oneperson or place to another.

Mega-A prefix meaning one million.Micro-A prefix indicating one-millionth.

TAGO 1284C 147

Modulated carrier-An rf carrier whose ampli-tude or frequency has been varied in accord-ance with the intelligence to be conveyed.

Modulation-The process of. varying the ampli-tude or the frequency of a carrier wave inaccordance with other signals to convey in-telligence. The modulating signal may bean audio signal, a video signal (as in tele-vision), or electrical pulses or tones.

Network-A'designated system, consisting of twoor more stations, able to communicate witheach other.

Point-to-point circuit-A nonswitched circuit per-manently connected between two telephonesets or other terminal equipments.

Radiate-To send out energy into space; as in thecase of rf waves.

Radio frequency (rf)-Any frequency of electro-magnetic and electrostatic fields capable ofenergy propagation into space. Radio fre-quencies are usually higher than those asso-ciated with sound waves.

Radio repeater set-Radio set designed to give2-way service as a receiving and retrans-mitting unit between two terminals (or aterminal and another radio repeater set).

Radio terminal set-Radio set designed to give2-way service as a receiving and transmit-ting terminal (to or with a radio repeateror other terminal). It may contain neces-sary wide-band modulation or associated car-rier multiplexing equipment.

148 TAGO 1284C

Rear echelon-A rear installation of a head-quarters usually consists of those staff agen-cies having administrative or supply dutiesthat are not located at the main commandpost (main CP).

Reflection-The turning back of a radio wavefrom a metallic object, the surface of theearth, or the ionosphere with the angles ofincidence and reflection equal and lying inthe same plane.

Refraction-A phenomenon which causes a wavethat enters another medium obliquely toundergo an abrupt change in velocity in themedium and also in direction. Also, thebending of radio waves in the troposphereor around an object.

Relay-A process of retransmitting intelligencethrough an intermediate station.

Repeater-A combination of apparatus for thereception and retransmission of signals thatare either amplified or reshaped, or both.

Skip distance-The distances on the earth's sur-face between the points where a radio waveis successively reflected between the earthand the ionosphere.

Simplex operation-A method of operation inwhich communication between two stationstakes place in one direction at a time.

Siting-Properly locate an antenna (or radioset) to obtain optimum performance.

Transmission line-Any conductor or system ofconductors used to carry electrical energyfrom its source to its load.

TAGO 1284C 149

Tuning-The process of adjusting a radio circuitto resonance with the desired frequency.

Wave length-The distance in meters traveled bya wave during the time interval of one com-plete cycle. It is equal to the velocity dividedby the frequency.

150 TAGO 1284C

INDEX

Paragraph Pave

Abm plan, description.... 50 75Acceptable reliability .........- 34 50Accessibility of sites.......... 4 4Air attack, defense ......... App III, 5 141Antenna guys, storage .........- 91 116Antenna orientation .......... . 35b 52Antennas, polarization ............. 26 36Antijamming ..................... 78 108Antijamming instructions:

Commanders and staff officers 82 109General -..........---... 81 109Operators ...................... 84 111Signal and communication

officers ......................- 83 110

Baseband connections ........... 15c 21Block width, decreasing ............. 53 82

Camouflage .......................-- ... App III, 4 141Carrier and multiplex, separation ... 16 21Chart:

Conversion, sea-level to line-of-sight ....- --.............. ... . 29 43

Mutual interference ............. 43 62Circuit order tests .................... 64 91Coaxial cable ................----- ............----- ------------- 87 114Coaxial cable, vehicular expedient._- 88 115Coaxial couplings, protection......... 89 115Computing radio relay paths........ 27 38Connections, multiplexing ........ 15 21Control station ...................... 57 87

TAGO 1284C 151

Paragraph PageCorrective maintenance .... _........ 72 99Cover and concealment ---............ App III, 4 141Cross-polarization ........... ......- 53b 82

Defense preparations ................-- . App III, 2 139Destruction plans ..--................ App III, 6 143Diffraction .............--.....-.. . 18d 26Double-head mast ................... 92 117Double-abm plan .................... 54 83

Estimate of reliability ................ 33 48Expedient:

Antenna ..................-....... 90, 93 116, 117Mast .............................. 92 117Operational ....................._ 96 120Power unit ...................... 94, 95 119

Factors increasing range orreliability .....--................ 35 51

Field expedient, defined .........--- 85 113Field inspection ....._................... 22 33Frequencies:

Army level ..............-............... 41 59Division and corps level ....... 44 68Receiving, selection ........ 41 59Transmitting, selection ........ 42 61

Frequency:Characteristics .....----........... 37 57Selection .__...... _ ..... --- 36 56Separation ....... _ _.. 3----------- 8 57

Frequency plan:Abm ........... _...._._. .... ._... 49-53 74Double-abm ........... _....5... 64 83Flexibility ...........--......... 39 58Xy ...... ---.................. . 55 86

Frequency selection:Interconnecting or crossing

systems ................--- ....- 47 71Methods .....................-... 40 59Parallel systems ......--.....-- 46 71

152 TAGO 1284C

Paragraph PaelGuard band ............ ....-. 38 57Half-duplex operation ........... 11 18High system noise, operation.......... 67 94Horizontal polarization .............. -- 26c 37

Interconnecting or crossingsystems ...-...... . ...--- ........... 48 74

Jamming:Defense against ......... .._ 80 109Vulnerability ....._... .. ._ 79 108

Line-of-sight, from profile graph _ 30 45Lineup, control ---........................... 60 89Long distance network ................. 74 102

Maintenance:Basic requirements ........-. 70 97Corrective .................. _..... 72 99General ................. ..... 68 96Preventive .---......---.... ----...........------ 71 97

Marginal circuits, improvement 97 122Methods of operation -...._....._ 11 18Monitoring and operating checks 63 91Multichannel systems .........------ 73 100Multiplexing equipment connections 15 21Mutual interference ...................- _ 66 93Mutual interfence chart....-----....... 43 62MWO ........... _............... 86 113

Noise and interference...... .. _....._ 65 92

Obstacles, use to obtain long trans-mission paths .................... .. _ - 32 47

Odd-and-even situation .....---..._ 47b 70Operation:

In mountainous terrain........ 100 123Methods -.......... _............. 11 18

Operation and maintenance:Factors ..- --..................... 69 96Station ....---...... _ _.....-.--- 76 103

TAGO 12S4C 153

Paragraph Page

Order-wire circuits, extension ......... 101 124Order wires, use ...................._ 58 88Orientation, antenna .............- 35b 52Overall system lineup .............. _ 62 90Overall tests ......- ... _... 75 103

Pairing ..................--- ----......--- ----------- 53a 82Physical security .......................- App IV 144Plans, destruction _.--......... _ App III, 6 143Plotting profiles:

Linear graph paper ....... _ 29 43Nonlinear graph paper .......... 28 41

Polarization of antennas ....... 26 36Power-balance calculations ... --...... 31 46Power considerations ...... _............ 25 35Power unit noise, reducing ....... 94 119Preventive maintenance ............- 71 97Printed material, use ................. 86 113Propagation, radio wave............... 17, 18 23, 24Propagation, vhf band .............. 19 27

Radiation, strong signal ............. 35c 53Radio relay equipment:

Characteristics ............ - --- App II 130Vehicular mounting .......... 99 123

Radio relay paths, computing....... 27 38Radio relay systems:

Administrative, field-army ------.... 10 16Advantages - -........._...... .__.... . 4b 6Considerations ....--......... 6, 14 8, 20Corps-type ..............- - .........------- 10 16Disadvantages ._ ............ _.... 4e 7Division-type ... ........... _ ....- 10 16Planning ..... ---................. 6 8Tactical employment ......-..... 7b, 9 10, 14Tests on trunks ................- 77 106Use -.........---................ 4 4

Radio repeater site, example........ App III,.3 140Radio terminal separation ......... 16 21

154 WrAGO 1284C

Paragraph PageRe-entrancy situation .........- - ..... 47c 73References .................................. App I 126Reflection..... 18c 25Refraction ....................................... 18b 24Reliability:

Acceptable 34 50Estimate 33 48

Remote operation .........-........... 21 33

Security factors .................................. App III, 1 139Signal plan - -............ 5 8Simplex operation ............................ 11 18Siting .......................- 20, 23, 35a 31, 34, 52Six-block abm plan:

Advantages .... 49 74Applications.... 51, 52 76, 79

Strong signals ............................-....... 98 122System:

Flexibility ........... 8 12Lineup ......................................._ 59 88Planning ...... 13 19Procedures .................................... 7 10

Tactical applications ......................-. 10 16TB SIG 86 113Terminal connections .......................... 15a 21Through-connections ...................-..... 15b 21Triangle situation 47a 72Troposphere ................................. 18 24Two-block method __ 45 68

Vertical polarization ....................... 26b 36Vulnerability to jamming 79 108

Wave propagation phenomena 18 24

Xy plan .....-.................................. 55 86

TAGO 1284C 155

[AG 353 (10 Apr 57)]

By Order of Wilber M. Brucker, Secretary of the Army:

MAXWELL D. TAYLOR,General, United States Army,

Official: Chief of Staff.HERBERT M. JONES,

Major General, United States Army,The Adjutant General.

Distribution:

Active Army:

ASA USA Elct PGDCSOPS USA Sig Engr LabsTechnical Stf, DA Mil MisUSA Sig Bd MAAGUSCONARC ARMAOS Maj Comd Mil DistArmies Units org under fol TOE:MDW 11-16, Sig Bn, Corps orCorps Abn CorpsDiv 11-22, Hq&Hq Det, Sig GpBrig 11-95, Sig Opr BnSvc Colleges 11-116, Hq&Hq Det, SigBr Svc Sch Spt BnUSA Sig Tng Cen 11-117, Sig Spt Co

NG: State AG.

USAR: None.

For explanation of abbreviations used, see AR 320-50.

1U*. S. GOVERNMENT PRINTING OFFICE: 1958 O -440499 (5S5IC)

156 TAGO 12840