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CHAPTER 2 SATELLITES AND ANTENNAS LEARNING OBJECTIVES Upon completing this chapter, you should be able to do the following: Identify the theory relating to satellites. Calculate azimuth and elevation, using plotting guides. Identify the types, basic system and fleet broadcast subsystem equipment of communication satellites. Identify the characteristics of antennas and antenna selections. Identify the types of antennas. Explain how the distribution systems interface with antenna assignment and selections. Identify the procedures for setting up antenna couplers, multicouplers, transmitters, and transceivers. Explain how the patch panel is used in conjunction with the equipment. Identify the procedures for raising and lowering antennas. Determine the optimum reception of a directional antenna by rotation, alignment, and tuning. Identify safety precautions that should be observed when working on antennas. Satellite communication (SATCOM) systems SATCOMM ANTENNAS satisfy many military communications requirements The antennas shown in figures 2-1 and 2-2 are used with reliable, high-capacity, secure, and cost-effective telecommunications. Satellites provide a solution to the problem of communicating with highly mobile forces deployed worldwide. Satellites also provide an alternative to large, fixed ground installations. They provide almost instantaneous military communications throughout the world at all but the highest latitudes (above 700). for satellite communications. The OE-82C/WSC-1(V) antenna (figure 2-1) is used with the AN/WSC-3 transceiver and designed primarily for shipboard installation. Depending upon requirements, one or two antennas may be installed to provide a view of the satellites at all times. The antenna is attached to a pedestal. This permits the antenna to rotate so that it is always in view of the satellite. The frequency band for receiving is 248 to 272 MHz; the band for transmitting is 292 to 312 MHz. 2-1

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Page 1: SATELLITES AND ANTENNAS - GlobalSecurity.org · SATELLITES AND ANTENNAS ... (SATCOM) systemsSATCOMM ANTENNAS satisfy many military communications requirementsThe antennas shown in

CHAPTER 2

SATELLITES AND ANTENNAS

LEARNING OBJECTIVES

Upon completing this chapter, you should be able to do the following:

Identify the theory relating to satellites.

Calculate azimuth and elevation, using plotting guides.

Identify the types, basic system and fleet broadcast subsystem equipment ofcommunication satellites.

Identify the characteristics of antennas and antenna selections.

Identify the types of antennas.

Explain how the distribution systems interface with antenna assignment andselections.

Identify the procedures for setting up antenna couplers, multicouplers,transmitters, and transceivers.

Explain how the patch panel is used in conjunction with the equipment.

Identify the procedures for raising and lowering antennas.

Determine the optimum reception of a directional antenna by rotation,alignment, and tuning.

Identify safety precautions that should be observed when working onantennas.

Satellite communication (SATCOM) systems SATCOMM ANTENNAS

satisfy many military communications requirements The antennas shown in figures 2-1 and 2-2 are usedwith reliable, high-capacity, secure, and cost-effectivetelecommunications. Satellites provide a solution to theproblem of communicating with highly mobile forcesdeployed worldwide. Satellites also provide analternative to large, fixed ground installations. Theyprovide almost instantaneous military communicationsthroughout the world at all but the highest latitudes(above 700).

for satellite communications. The OE-82C/WSC-1(V)antenna (figure 2-1) is used with the AN/WSC-3transceiver and designed primarily for shipboardinstallation. Depending upon requirements, one or twoantennas may be installed to provide a view of thesatellites at all times. The antenna is attached to apedestal. This permits the antenna to rotate so that it isalways in view of the satellite. The frequency band forreceiving is 248 to 272 MHz; the band for transmittingis 292 to 312 MHz.

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Figure 2-1.—OE-82C/WSC-1(V) antenna group.

Figure 2-2.—AS-2815/SSR-1 antenna physical configuration.

The AN/SRR-1 receiver system consists of up tofour AS-2815/SSR- 1 antennas (figure 2-2) with anamplifier-converter, AM-6534/SSR-1, for eachantenna. The antennas are used to receive satellite fleetbroadcasts at frequencies of 240 to 315 MHz. Theantenna and converters are mounted above deck so thatat least one antenna is always in view of the satellite.

The newer satellite systems use the SHF band. Oneof the major advantages of these systems is that they usea very small parabolic antenna measuring only 12inches in diameter.

A satellite antenna must be pointed at the satellite tocommunicate. We must first determine the azimuth(AZ) and elevation (EL) angles from a fixed location.Figure 2-3 illustrates how these angles are derived,

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using a pointing guide called the Equatorial SatelliteAntenna Pointing Guide. This guide is normallyavailable through the Navy Supply System.

The antenna pointing guide is a clear plasticoverlay, which slides across a stationary map. Itindicates AZ and EL angles in degrees to the satellite.The values obtained are useful to the operator in settingup the antenna control unit of a satellite system.

To use the guide, follow these procedures:

Center the overlay directly over the desiredsatellite position on the stationary map.

Mark the latitude and longitude of the ship on theplastic antenna pointing guide with a greasepencil.

Determine the approximate azimuth angle fromthe ship to the satellite.

Locate the closest dotted line radiating outwardfrom the center of the graph on the overlay inrelation to the grease dot representing the ship’s

location. This dotted line represents degrees ofazimuth as printed on the end of the line. Someapproximation will be required for ship positionsnot falling on the dotted line.

Determine the degrees of elevation by locatingthe solid concentric line closest to the ship’smarked position. Again, approximation will berequired for positions not falling directly on thesolid elevation line. Degrees of elevation aremarked on each concentric line.

Example: Assume that your ship is located at30° north and 70° west. You want to accessFLTSAT 8 at 23° west. When we apply theprocedures discussed above, we can see theexample indicates an azimuth value of 115° andan elevation angle of 30°.

TYPES OF SATELLITES

Three types of communications satellites are in useby the U.S. Navy today. They are GAPFILLER, FleetSatellite Communication (FLTSATCOM), and Leased

Figure 2-3.—Equatorial Satellite Antenna Pointing Guide.

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Satellite (LEASAT) (figure 2-4). These satellites are ingeosynchronous orbit over the continental UnitedStates and the Atlantic, Pacific, and Indian oceans.Each satellite is described in the following paragraphs.

GAPFILLER

In 1976, three satellites, called MARISAT, wereplaced into orbit over the Atlantic, Pacific, and Indianoceans. Each satellite had three UHF channels formilitary use, one wideband 500-kHz channel, and twonarrowband 25-kHz channels.

The Navy leased the UHF section of each satellitefor communications purposes. To distinguish thespecial management and control functions for

communications on these UHF channels, the Navy gavethe name GAPFILLER to the leased satellite assets.

GAPFILLER was intended to fill the need for acontinuing satellite communications capability insupport of naval tactical operations until the Navyachieved a fully operable Fleet SatelliteCommunications (FLTSATCOM) system.

The GAPFILLER satellite over the Indian Ocean isthe only one still being used by the U.S. Navy. The othertwo GAPFILLER satellites were replaced by LEASAT.The active GAPFILLER satellite will also be replacedby LEASAT as it reaches the end of its operational life.

Within the 500-kHz band, transponders provide 20individual 25-kHz low- and high-data-ratecommunications channels for 75 baud ship-shore

Figure 2-4.—GAPFILLER, FLTSATCOM, and LEASAT satellites.

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communications and for the automated informationexchange systems. The UHF receiver separates thereceive band (302 to 312 MHz) from the transmit band(248 to 258 MHz).

The receiver translates the received carriers tointermediate frequencies (IFs) in the 20-MHz range andseparates them into one of three channels. One charnelhas a 500-kHz bandwidth, and two have a bandwidth of25 kHz each. The signals are filtered, hard limited,amplified to an intermediate level, and up-converted tothe transmit frequency. Each channel is then amplifiedby one of three high-power transmitters.

GAPFILLER also supports the FLTSATCOMsystem secure voice system and the fleet broadcast inthe UHF range. The GAPFILLER communicationssubsystem will eventually be replaced by theFLTSATCOM system.

FLTSATCOM

There are four FLTSATCOM satellites in service.These satellites are positioned at 100° W, 72.5° E, 23°W, and 172° E longitudes. They serve the Third, Sixth,Second, and Seventh fleets and the Indian Ocean battlegroups. These four satellites provide worldwide

coverage between 70° N and 70° S latitudes (figure2-5).

Each FLTSATCOM satellite has a 23-RF-channelcapability. These include 10 25-kHz channels, 12 5-kHz channels, and 1 500-kHz channel. The 500-kHzand the 10 25-kHz channels are reserved for Navy use.Of the 10 25-kHz channels, channel 1 is used for thefleet broadcast. All charnels use SHF for the uplinktransmission. SHF is translated to UHF for thedownlink transmission.

There is a separate UHF downlink transmitter foreach channel. Each of the 23 channels has 3 differentfrequency plans in which the uplink or downlink may betransmitted. This capability precludes interferencewhere satellite coverage overlaps.

LEASAT

The latest generation of Navy communicationssatellites is leased; hence, the program name LEASAT.As we mentioned earlier, these satellites replaced 2 ofthe 3 GAPFILLER satellites and augment theFLTSATCOM satellites.

CONUS LEASAT (L-3) is positioned at 105° Wlongitude, LANT LEASAT (L-1) is positioned at

Figure 2-5.—FLTSATCOM coverage areas,

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15° W longitude, and 10 LEASAT (L-2) is positionedat 72.5° E longitude (figure 2-6).

Each LEASAT provides 13 communicationschannels using 9 transmitters. There are 7 25-kHz UHFdownlink channels, 1 500-kHz wideband channel, and5 5-kHz channels. The 500-kHz channel and the 725-kHz channels are leased by the Navy. One of the 725-kHz UHF downlink channels is the downlink for theFleet Satellite Broadcast.

The broadcast uplink is SHF, with translation toUHF taking place in the satellite. The remaining 625-kHz channels function as direct-relay channels withseveral repeaters. Currently, the LEASAT channelsprovide for the following subsystems:

Channel 1 for Fleet Satellite Broadcasttransmissions;

1 25-kHz channel for SSIXS communications;

1 25-kHz channel for ASWIXS com-munications; and

2 25-kHz channels for subsystems that transmitor receive via DAMA (Demand AssignedM u l t i p l e A c c e s s ) ( f o r e x a m p l e ,CUDIXS/NAVMACS, TACINTEL, and securevoice).

PHASE IV

Operations Desert Shield/Desert Storm reinforcedthe requirement for and greatly accelerated theintroduction of SHF SATCOM capability on aircraftcarriers and amphibious flagships to satisfy minimumtactical command and control (C2), intelligence andwarfighting communications requirements whileimproving Joint and NATO/Allied communicationsinteroperability. To meet the urgent operationalrequirement, the U.S. Navy obtained and modified U.S.Air Force AN/TSC-93B Ground Mobile Forces (GMF)SHF SATCOM vans for installation on aircraft carriersand amphibious flagships deploying to the PersianGulf. The modified vans were coupled with theAN/WSC-6(V) standard U.S. Navy SHF stabilizedantenna system, the SURTASS modem, 2 low speedtime division multiplexer (LSTDMs), and additional

Figure 2-6.—LEASAT coverage areas.

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patch panels. The modified SATCOM terminals weredesignated “QUICKSAT”. The initial introduction ofthese terminals into the fleet officially marked thebeginning of Phase I of the U.S. Navy’s SHF SATCOMfielding plan (with everything prior being referred to asPhase 0) and provided an immediate operationalcapability.

Phase II of the U.S. Navy’s SHF fielding plan,which commenced in FY 94, will replace QUICKSATterminals on aircraft carriers with an AN/WSC-6(V)4terminal. The U.S. Navy will also deploy an SHFDemand Assigned Multiple Access (DAMA) modem.This phase replaces the QUICKSAT terminals onaircraft carriers, and adds SHF SATCOM capabilities tomore ships.

Commencing in FY97, Phase III will deploy thenext AN/WSC-6 variant. The new terminal will be amodem, modular, open architecture terminal capable ofproviding a full spectrum of SHF SATCOM servicesand greatly expand the number of installations.

The system configuration that supports Navy SHFSATCOM consists of an SHF RF terminal andsupporting baseband equipment. The RF terminals forshipboard use are the AN/WSC-6(V) or AN/TSC-93B(MOD) “QUICKSAT” terminal. The terminals processand convert the RF signal transmitted to or receivedfrom the space segment. The transmit frequency rangeis 7.9 to 8.4 GHz, and the receive range is 7.25 to 7.75GHz. The OM-55(V)/USC AJ modems, 1105A/1106time division multiple access (TDMA)/DAMA modem,and the CQM-248A (phase shift keying (PSK)modems) are deployed on shipboard platforms.

The AN/WSC-6(V) and QUICKSAT configuredterminals are compatible with present and future DSCSSHF satellite ground terminals and consist of anantenna group, radio set group and modem group. Theantenna group is configured as either a dual or singleantenna system. The AN/WSC-6(V)1, with the MD-1030A(V) modem, is used on SURTASS shipsequipped with a single antenna. The AN/WSC-6(V)2,with the OM-55(V)/USC, Frequency Division MultipleAccess (FDMA) or TDMA/DAMA modems, is used onboth flag and flag-capable platforms and is configuredwith either a single or dual antenna. The QUICKSATterminal is configured with an FDMA modem, single ordual antenna, and deployed on selected aircraft carriersand amphibious flagships. The AN/WSC-6(V) andQUICKSAT terminals automatically track the selectedsatellite, while simultaneously transmitting andreceiving. An antenna control unit commands theantenna to search for tracking (beacon) signals from the

satellite. Upon satellite acquisition, tracking isaccomplished automatically.

BASIC SATCOM SYSTEM

A satellite communications system relays radiotransmissions between Earth terminals. There are twotypes of communications satellites: active and passive.An active satellite acts as a repeater. It amplifies signalsreceived and then retransmits them back to Earth. Thisincreases the signal strength at the receiving terminalcompared to that available from a passive satellite. Apassive satellite, on the other hand, merely reflects radiosignals back to Earth.

A typical operational link involves an activesatellite and two Earth terminals. One terminaltransmits to the satellite on the uplink frequency. Thesatellite amplifies the signal, translates it to thedownlink frequency, and then transmits it back to Earth,where the signal is picked up by the receiving terminal.Figure 2-7 illustrates the basic concept of satellitecommunications with several different Earth terminals.

The basic design of a satellite communicationssystem depends a great deal on the parameters of thesatellite orbit. Generally, an orbit is either elliptical orcircular. Its inclination is referred to as inclined, polar,or equatorial. A special type of orbit is a synchronousorbit in which the period of the orbit is the same as thatof the Earth’s.

Two basic components make up a satellitecommunications system. The first is an installedcommunications receiver and transmitter. The secondis two Earth terminals equipped to transmit and receivesignals from the satellite. The design of the overallsystem determines the complexity of the componentsand the manner in which the system operates.

The U.S. Navy UHF/SHF/EHF combinedcommunications solution allows each system to provideunique contributions to the overall navalcommunications needs.

The SHF spectrum is a highly desirable SATCOMmedium because it possesses characteristics absent inlower frequency bands: wide operating bandwidth,narrow uplink beamwidth, low susceptibility toscintillation, anti-jam (AJ), and high data rates.Recognizing these characteristics, the U.S. Navydeveloped and installed shipboard SHF terminals.These attributes are discussed in the followingparagraphs.

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Figure 2-7.—Satellite communications systems.

Wide operating bandwidth permits highinformation transfer rates and facilitates spreadspectrum modulation techniques. Spread spectrummodulation is a particularly valuable technique forlessening the effects of enemy jamming. Althoughwide bandwidth permits both high information transferrates and AJ capabilities when using the OM-55(V)/USC modem, it may not permit bothsimultaneously in the presence of jamming. Therefore,high information transfer rates will be significantlyreduced when jamming is encountered, permitting onlycertain predetermined critical circuits to be maintained.

Narrow uplink transmission beamwidth provides alow probability of intercept (LPI) capability. An uplinkLPI capability reduces the threat of detection andsubsequent location, but does not in and of itself denyenemy exploitation of those communications ifdetection is achieved. SHF frequencies are rarelyaffected by naturally occurring scintillation, making

SHF SATCOM a particularly reliable form ofcommunications.

A characteristic of SHF, favorable to flagships, isthe ability to communicate critical C4I for the userinformation in the presence of enemy jamming and withdue regard for enemy detection capabilities. SURTASSMilitary Sealift Command Auxiliary General OceanSurveillance (T-AGOS) ships were initially equippedwith SHF SATCOM, taking advantage of the highinformation transfer rate capability and LPIcharacteristics. Because of larger available bandwidths,inherent jam-resistance, and increasing demands onlimited tactical UHF SATCOM resources, additionalapplications for DSCS SHF SATCOM afloat arecontinually being investigated for the Fleet.

The radio group consists of a high power amplifier(HPA) or medium power amplifier (MPA), low noiseamplifier (LNA), up-converter, down-converter, andfrequency standard. For transmit operations, theup-converter translates the modem’s 70 or 700

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Figure 2-8.—AN/SSR-1 receiver system.

megahertz (MHz) intermediate frequency (IF) to thedesired radio frequency. The signal is then passed to theHPA or MPA and amplified to its authorized powerlevel. During receive operations, the LNA amplifies thereceived RF signal and sends it to the tracking converter

for antenna control and the down-converter fortranslation to 70 or 700 MHz IF. This signal is then sentto the modem for conversion to digital data. Systemfrequency stability is provided by a cesium or rubidiumstandard.

FLEET BROADCAST SUBSYSTEMEQUIPMENT

The SATCOM equipments that the Navy uses forthe fleet broadcast include the SATCOM broadcastreceiver (AN/SSR-1), the FLTSATCOM SHFbroadcast transmitter (AN/FSC-79), the standardshipboard transceiver (AN/WSC-3), the shore stationtransceiver (AN/WSC-5), and the basic airbornetransceiver (AN/ARC-143B). A brief description ofthese equipments is given in the next paragraphs.

The AN/SSR-1 is the Navy’s standard SATCOMbroadcast receiver system. This system consists of up tofour AS-2815/SSR-1 antennas with an AM-6534/SSR-1 Amplifier-Converter for each antenna, an MD-900/SSR-1 Combiner-Demodulator, and a TD-1063/SSR-1Demultiplexer (figure 2-8). The antennas are designedto receive transmissions at 240 to 315 MHz. Theantennas and antenna converters are mounted abovedeck so that at least one antenna is always in view of thesatelli te. The combiner-demodulator anddemultiplexer are mounted below deck.

The AN/FSC-79 Fleet Broadcast Terminal (figure2-9) interfaces the communications subsystems and thesatellite. The terminal provides the SHF uplink for the

Figure 2-9.—AN/FSC-79 Fleet Broadcast Terminal.

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FLTSATCOM system and is used in particular tosupport the Navy Fleet Broadcast system. TheAN/FSC-79 operates in the 7- to 8-GHz band and isdesigned for single-channel operation. TheAN/FSC-79 terminal is installed at the fourCOMMAREA master stations andNAVCOMTELSTA Stockton, Calif.

The AN/WSC-3 Transceiver is the standardUHF SATCOM transceiver for both submarine andsurface ships. The AN/WSC-3 is capable ofoperating in either the satellite or line-of-sight(LOS) mode and can be controlled locally orremotely.

The unit is designed for single-channel, half-duplex operations in the 224- to 400-MHZ UHFband. It operates in 25-kHz increments, and has 20preset channels. In the SATCOM mode, theAN/WSC-3 transmits (uplinks) in the 292.2- to311.6-MHz bandwidth and receives (downlinks) in

the 248.5- to 270.1-MHz band. A separate transceiveris required for each baseband or channel use.

The AN/WSC-5 UHF Transceiver (figure 2-10) isthe common UHF RF satellite terminal installed atNAVCOMTELSTAs for the GAPFILLER subsystem.In FLTSATCOM operations, it is used as the commonRF terminal for all subsystems except the FleetSatellite Broadcast (FSB) and the AntisubmarineWarfare information Exchange Subsystem (ASWIXS).The AN/WSC-5 can be used to back up the AN/FSC-79. The AN/WSC-5 transmits in the 248.5- to 312-MHz range and receives in the 248.5- to 270.1-MHzrange.

The AN/ARC-143 UHF Transceiver (figure 2-11)is used for ASWIXS communications and is installedat VP Antisubmarine Warfare Operation Centers andaboard P-3C aircraft. The unit two parts: a transceiverand a radio set control. The AN/ARC-143

Figure 2-10.—AN/WSC-5 UHF Transceiver.

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Figure 2-11.—AN/ARC-143 UHF Transceiver.

can be used to transmit or receive voice or data in the255.0- to 399.99-MHz frequency range.

The systems discussed are only a few of theSATCOM equipments used by the Navy. Some of thereferences listed in Appendix III of this module areexcellent sources for more information on satelliteequipment and systems.

FLEET SATELLITECOMMUNICATIONS SYSTEM AND

SUBSYSTEMS

The Flee t Sa te l l i te Communica t ions(FLTSATCOM) system and subsystems providecommunications links, via satellite, between shorecommands and mobile units. The system includes RFterminals, subscriber subsystems, training,documentation, and logistic support. Within each

satellite, the RF channels available for use have beendistributed between the Navy and the Air Force.

Equipments in support of the FLTSATCOM systemare on ships, submarines, aircraft, and at shore stations.These equipment installations vary in size andcomplexity. Furthermore, with the exception of voicecommunications, the system applies the technology ofprocessor- (computer-) controlled RF links and uses theassistance of processors in message traffic preparationand handling.

Although any part of the FLTSATCOM system canbe operated as a separate module, system integrationprovides connections for message traffic and voicecommunications to DOD communications networks.

A backup capability that can be used in the event ofan outage or equipment failure is provided for bothshore and afloat commands. All subsystems have someform of backup mode, either from backup equipmentand/or systems, facilities, or RF channels. Thiscapability is built in as part of the system design andmay limit the ability of selected FLTSATCOM systemsto process information.

FLEET SATELLITE BROADCAST (FSB)SUBSYSTEM

The Fleet Satellite Broadcast (FSB) subsystem is anexpansion of fleet broadcast transmissions thathistorically have been the central communicationsmedium for operating naval units. The FSB transmitsmessages, weather information, and intelligence data toships. The shore terminal transmits this data on a directSHF signal to a satellite, where the signal is translated toUHF and downlinked. Figure 2-12 shows a standardFSB subsystem configuration.

Figure 2-12.—Fleet Satellite Broadcast subsystem.

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COMMON USER DIGITAL INFORMATIONEXCHANGE SYSTEM (CUDIXS) ANDNAVAL MODULAR AUTOMATEDCOMMUNICATIONS SYSTEM (NAVMACS)

The CUDIXS/NAVMACS combine to form acommunications network that is used to transmitgeneral service (GENSER) message traffic betweenships and shore installations. NAVMACS serves as anautomated shipboard terminal for interfacing withCUDIXS (shore-based) (figure 2-13) and the FleetBroadcast System.

OTHER SPECIALIZED SUBSYSTEMS

The FLTSATCOM system represents a compositeof information exchange subsystems that use thesatellites as a relay for communications. The followingsubsystems satisfy the unique communicationrequirements for each of the different navalcommunities.

Submarine Satellite Information ExchangeSubsystem (SSIXS)

The SSIXS provides a communications system toexchange message traffic between SSBN and SSNsubmarines and shore stations.

Antisubmarine Warfare InformationExchange Subsystem (ASWIXS)

ASWIXS is designed as a communications link forantisubmarine warfare (ASW) operations betweenshore stations and aircraft.

Tactical Data Information Exchange

Subsystem (TADIXS)

TADIXS is a direct communications link betweencommand centers ashore and afloat. TADIXS providesone-way transmission of data link communications.

Secure Voice Subsystem

Figure 2-13.—NAVMACS (V) communications interface.

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The secure voice subsystem is a narrowband UHFlink that enables secure voice communications betweenships. It also allows, connection with wide-area voicenetworks ashore.

Tactical Intelligence (TACINTEL)Subsystem

TACINTEL is specifically designed for specialintelligence communications.

Control Subsystem

The Control subsystem is a communicationsnetwork that facilitates status reporting andmanagement of FLTSATCOM system assets.

Officer in Tactical Command InformationExchange Subsystem (OTCIXS)

OTCIXS is designed as a communications link forbattle group tactical operations.

Teleprinter Subsystem (ORESTES)

ORESTES is an expansion of the existingteleprinter transmission network.

LEASAT TELEMETRY TRACKING ANDCOMMAND SUBSYSTEM

The LEASAT Telemetry Tracking and Commandsubsystem is a joint operation between the U.S. Navyand contractors for controlling LEASATS. Theinstallation of subsystem baseband equipment and RFterminals aboard ships and aircraft is determined bycommunications traffic levels, types ofcommunications, and operational missions.

Since Fleet Satellite Broadcast message traffic is acommon denominator for naval communications, it isreceived by numerous types of ships. In someinstallations, such as large ships, the fleet broadcastreceiver represents one part of the FLTSATCOMequipment suite. A typical configuration on a large shipwould include fleet broadcast, CUDIXS/NAVMACS,secure voice, OTCIXS, TADIXS, teleprinter, andTACINTEL equipment.

The FLTSATCOM subsystems apply some form ofautomated control to the communications beingtransmitted with the exception of the secure voice andcontrol subsystems. This includes message or data linkprocessing before and after transmittal and control ofthe RF network (link control) in which the messages arebeing transmitted. The automation of these functions ishandled by a processor.

Much of the message processing beforetransmission and after receipt is fully automatic anddoes not require operator intervention. The actualmessage or data link transmission is fully automatedand under the control of a processor. Within thelimitations of equipment capability, each subsystemaddresses the unique requirements of the user and theenvironment in which the user operates.

DEMAND ASSIGNED MULTIPLE ACCESS(DAMA)

DAMA was developed to multiplex severalsubsystems or users on one satellite channel. Thisarrangement allows more satellite circuits to use eachUHF satellite channel.

Multiplexing

The number of communications networks beingused is constantly increasing. As a result, all areas of theRF spectrum have become congested. Multiplexing is amethod of increasing the number of transmissionstaking place in the radio spectrum per unit of time.

Multiplexing involves the simultaneoustransmission of a number of intelligible signals usingonly a single transmitting path. As we mentionedearlier, the Navy uses two multiplexing methods: time-division multiplexing (TDM) and frequency-divisionmultiplexing (FDM). We have already discussed FDMwith the AN/UCC-1. Additional informationconcerning both methods can be found in Radio-Frequency Communication Principles, NEETS,Module 17.

A UHF DAMA subsystem, the TD-1271/UMultiplexer, was developed to provide adequatecapacity for the Navy and other DOD users. Thissubsystem was developed to multiplex (increase) thenumber of subsystems, or users, on 1 25-kHz satellitechannel by a factor of 4.

This factor can be further increased by multiples of4 by patching 2 or more TD-1271s together. Thismethod increases the number of satellite circuits perchannel on the UHF satellite communications system.Without this system, each satellite communicationssubsystem would require a separate satellite channel.

Transmission Rates

The DAMA equipment accepts encrypted datastreams from independent baseband sources andcombines them into one continuous serial output data

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stream. DAMA was designed to interface the NavyUHF SATCOM baseband subsystem and the AN/WSC-5 and AN/WSC-3 transceivers.

The TD-1271/U Multiplexer includes a modemintegral to the transceiver. The baseband equipmentinput or output data rate with DAMA equipment can be75, 300, 600, 1,200, 2,400, 4,800, or 16,000 bits persecond (bps). The DAMA transmission rate on thesatellite link (referred to as “burst rate”) can be 2,400,9,600, 19,200, or 32,000 symbols per second.

Circuit Restoral/Coordination

When a termination is lost in either or bothdirections, communications personnel must observespecial guidelines. During marginal or poor periods ofcommunications, the supervisors should assign adedicated operator to the circuit if possible.

When normal circuit restoration procedures areunsuccessful and/or a complete loss of communicationsexists, an IMMEDIATE precedence COMMSPOTmessage should be transmitted (discussed earlier).Every means available must be used to re-establish thecircuit, including messages, support from other ships orNAVCOMTELSTAs, or coordination via DAMA ifavailable.

The guidelines established in NTP 4, CIBs, andlocal SOPs are not intended to suppress individualinitiative in re-establishing lost communications.Circuit restoral is dependent upon timely action, quickdecisions, and the ability of personnel to use any meansavailable to restore communications in the shortestpossible time.

SPECIAL CIRCUITS

During certain communications operations, youmay be required to activate and operate special circuits.Some of the most common special circuits are discussednext.

UHF AUTOCAT/SATCAT/MIDDLEMANRELAY CIRCUITS

Shipboard HERO conditions and emission control(EMCON) restrictions often prohibit transmission ofRF below 30 MHz.

To provide an uninterrupted flow of essentialcommunications without violating HERO and EMCONrestrictions, AUTOCAT, SATCAT, and MIDDLEMANwere developed. With these techniques, the range of

tactical UHF circuits (voice or teleprinter) can beextended by relay of AM UHF transmissions via HF orsatellite. AUTOCAT accomplishes this using a ship;whereas SATCAT uses an airborne platform forautomatically relaying UHF transmissions.MIDDLEMAN requires an operator to copy themessages with subsequent manual retransmission.

The three techniques just discussed use threedifferent types of circuit for reception and relay of UHFtransmissions. These circuits are as follows:

A voice circuit where some units send andreceive on one frequency, and other units sendand receive on any other frequency;

A voice circuit where all units transmit on onefrequency and receive on another frequency; and

A RATT circuit where all units transmit on onefrequency and receive on another frequency.

FLEET FLASH NET

The Fleet Flash Net (FFN) is composed of senioroperational staffs and other designated subscribers. Thepurpose of the FFN is to distribute high-precedence orhighly sensitive traffic among subscribers. A receipt onthe net constitutes firm delivery, and the message neednot be retransmitted over other circuits to receiptingstations. The FFN is explained in more detail in MissionCommunications, NTP 11.

ANTENNA SYSTEMS

Operation of communication equipment over theentire range of the RF spectrum requires many types ofatennnas. You will need to know the basic type ofantennas available to you operationally, theircharacteristics, and their uses, Very often, you, theoperator, can mean the difference between efficient andinefficient communications. You will have a choice ofmany antennas and must select the one most suitable forthe task at hand. Your operational training will acquaintyou with the knowledge necessary to properly use theantennas at your disposal, However, your operationaltraining WILL NOT acquaint you with the WHY ofantennas, in other words, basic antenna theory. Thefollowing topics are intended to familiarize you withbasic antenna terminology, definitions, andcharacteristics.

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ANTENNA CHARACTERISTICS

As you will learn in this section, all antennas exhibitcommon characteristics. The study of antennasinvolves the following terms with which you mustbecome familiar:

Antenna Reciprocity

The ability of an antenna to both transmit andreceive electromagnetic energy is known as itsreciprocity. Antenna reciprocity is possible becauseantenna characteristics are essentially the same forsending and receiving electromagnetic energy.

Even though an antenna can be used to transmit orreceive, it cannot be used for both functions at the sametime. The antenna must be connected to either atransmitter or a receiver.

Antenna Feed Point

Feed point is the point on an antenna where the RFcable is attached. If the RF transmission line is attachedto the base of an antenna, the antenna is end-fed. If theRF transmission line is connected at the center of anantenna, the antenna is mid-fed or center-fed.

Directivity

The directivity of an antenna refers to the width ofthe radiation beam pattern. A directional antennaconcentrates its radiation in a relatively narrow beam. Ifthe beam is narrow in either the horizontal or verticalplane, the antenna will have a high degree of directivityin that plane. An antenna can be highly directive in oneplane only or in both planes, depending upon its use.

In general, we use three terms to describe the type ofdirectional qualities associated with an antenna:omnidirectional, bidirectional, and unidirectional.Omnidirectional antennas radiate and receive equallywell in all directions, except off the ends. Bidirectionalantennas radiate or receive efficiently in only twodirections. Unidirectional antennas radiate or receiveefficiently in only one direction.

Most antennas used in naval communications areeither omnidirectional or unidirectional. Bidirectionalantennas are rarely used. Omnidirectional antennas areused to transmit fleet broadcasts and are used aboardship for medium-to-high frequencies. A parabolic, ordish, antenna (figure 2-14) is an example of aunidirectional antenna. As you can see in the figure, an

Figure 2-14.—Principle of parabolic reflection.

antenna (normally a half wave) is placed at the “focal”point and radiates the signal back into a large reflectingsurface (the dish). The effect is to transmit a verynarrow beam of energy that is essentially unidirectional.Figure 2-15 shows a large, unidirectional parabolicantenna. Directional antennas are commonly used atshore installations.

Wave Polarization

Polarization of a radio wave is a majorconsideration in the efficient transmission andreception of radio signals. If a single-wire antenna is

Figure 2-15.—Unidirectional parabolic antenna.

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used to extract energy from a passing radio wave,maximum signal pickup results when the antenna isplaced physically in the same direction as the electricfield component. For this reason, a vertical antenna isused to receive vertically polarized waves, and ahorizontal antenna is used to receive horizontallypolarized waves.

At lower frequencies, wave polarization remainsfairly constant as it travels through space. At higherfrequencies, the polarization usually varies, sometimesquite rapidly. This is because the wave front splits intoseveral components, and these components followdifferent propagation paths.

When antennas are close to the ground, verticallypolarized radio waves yield a stronger signal close to theEarth than do those that are horizontally polarized.When the transmitting and receiving antennas are atleast one wavelength above the surface, the two types ofpolarization are approximately the same in fieldintensity near the surface of the Earth. When thetransmitting antenna is several wavelengths above thesurface, horizontally polarized waves result in astronger signal close to the Earth than is possible withvertical polarization.

Most shipboard communication antennas arevertically polarized. This type of polarization allowsthe antenna configuration to be more easilyaccommodated in the limited space allocated toshipboard communications installations. Verticalantenna installations often make use of the topsidestructure to support the antenna elements. In somecases, to obtain the required impedance match betweenthe antenna base terminal and transmission line, thestructure acts as part of the antenna.

VHF and UHF antennas used for ship-to-aircraftcommunications use both vertical and circularpolarization. Because aircraft maneuvers cause cross-polarization effects, circularly polarized shipboardantennas frequently offer considerable signalimprovements over vertically polarized antennas.

Circularly polarized antennas are also used for ship-to-satellite communications because these antenntasoffer the same improvement as VHF/UHF ship-to-aircraft communications operations. Except for thehigher altitudes, satellite antenna problems are similarto those experienced with aircraft antenna operations.

Standing Wave Ratio

Another term used in antenna tuning is standingwave ratio (SWR), also called voltage standing wave

ratio (VSWR). A simple definition could be the“relative degree of resonance” achieved with antennatuning. When tuning an antenna, you must understandthe SWR when expressed numerically.

You will hear SWR expressed numerically in nearlyevery tuning procedure. For example, you will hearsuch terms as “three-to-one,” or “two-to-one.” You willsee them written 3:1 SWR, 2:1 SWR, or 1:1 SWR. Thelower the number ratio is, the better the match betweenthe antenna and the transmitter for transmitting RFsignals. For example, a 2:1 SWR is better than a 3:1SWR.

As you approach resonance, you will notice thatyour SWR figure on the front panel meters will begin todrop to a lower numerical value. A good SWR isconsidered to be 3 or below, such as 3:1 or 2:1.Anything over 3, such as 4:1, 5:1, or 6:1 isunsatisfactory. The SWR becomes increasingly criticalas transmitter output is increased. Where a 3:1 SWR issatisfactory with a 500-watt transmitter, a 2:1 SWR maybe considered satisfactory with a 10-kilowatttransmitter.

Most antenna couplers have front panel meters thatshow a readout of the relative SWR achieved viaantenna tuning. Figure 2-16 shows a multicoupler,

Figure 2-16.—AN/SRA-33 antenna multicoupler.

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consisting of four coupling units, with four SWR metersat the top (one for each coupler).

To achieve a perfect standing wave ratio of 1:1would mean that we have succeeded in tuning out allother impedances and that the antenna is matchedperfectly to the transmitted frequency. With such a lowSWR, the antenna would now offer only itscharacteristic impedance. A 1:1 SWR is rarelyachieved, of course. There will always be some powerloss between the transmitter and the antenna because ofnatural impedances that exist between the two.Nevertheless, the objective is to achieve the lowestSWR possible. In other words, we want only thecharacteristic impedance of the antenna remaining.

Incident Waves

Various factors in the antenna circuit affect theradiation of RF energy. When we energize or feed anantenna with an alternating current (ac) signal, waves ofenergy are created along the length of the antenna.These waves, which travel from a transmitter to the endof the antenna, are the incident waves.

Let’s look at figure 2-17. If we feed an ac signal atpoint A, energy waves will travel along the antennauntil they reach the end (point B). Since the B end isfree, an open circuit exists and the waves cannot travelfarther. This is the point of high impedance. Theenergy waves bounce back (reflect) from this point ofhigh impedance and travel toward the feed point, wherethey are again reflected.

Reflected Waves

We call the energy reflected back to the feed pointthe reflected wave. The resistance of the wiregradually decreases the energy of the waves in thisback-and-forth motion (oscillation). However, eachtime the waves reach the feed point (point A of figure2-17), they are reinforced by enough power to replace

Figure 2-17.—Incident and reflected waves on an antenna.

the lost energy. This results in continuous oscillationsof energy along the wire and a high voltage at point A onthe end of the wire. These oscillations are applied to theantenna at a rate equal to the frequency of the RFvoltage.

In a perfect antenna system, all the energy suppliedto the antenna would be radiated into space. In animperfect system, which we use, some portion of theenergy is reflected back to the source with a resultantdecrease in radiated energy. The more energy reflectedback, the more inefficient the antenna. The condition ofmost antennas can be determined by measuring thepower being supplied to the antenna (forward power)and the power being reflected back to the source(reflected power). These two measurements determinethe voltage standing wave ratio (VSWR), whichindicates antenna performance.

If an antenna is resonant to the frequency suppliedby the transmitter, the reflected waves and the incidentwaves are in phase along the length of the antenna andtend to reinforce each other. It is at this point thatradiation is maximum, and the SWR is best. When theantenna is not resonant at the frequency supplied by thetransmitter, the incident and reflected waves are out ofphase along the length of the antenna and tend to cancelout each other. These cancellations are called powerlosses and occur when the SWR is poor, such as 6:1 or5:1.

Most transmitters have a long productive life andrequire only periodic adjustment and routinemaintenance to provide maximum operating efficiencyand reliable communications. Experience has shownthat many of the problems associated with unreliableradio communication and transmitter failures can beattributed to high antenna VSWR.

Dummy Loads

Under radio silence conditions, placing a carrier onthe air during transmitter tuning would give an enemythe opportunity to take direction-finding bearings anddetermine the location of the ship. Even during normalperiods of operation, transmitters should be tuned bymethods that do not require radiation from the antenna.This precaution minimizes interference with otherstations using the circuit.

A dummy load (also called dummy antenna) can beused to tune a transmitter without causing unwantedradiation. Dummy loads have resistors that dissipatethe RF energy in the form of heat and prevent radiationby the transmitter during the tuning operation. The

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dummy load, instead of the antenna, is conected to theoutput of the transmitter, and the normal transmittertuning procedure is followed.

Most Navy transmitters have a built-in dummyload. This permits you to switch between the dummyload or the actual antenna, using a switch. Fortransmitters that do not have such a switch, thetransmission line at the transmitter is disconnected andconnected to the dummy load (figure 2-18). Whentransmitter tuning is complete, the dummy load isdisconnected and the antenna transmission line is againconnected to the transmitter.

ELECTROMAGNETIC WAVELENGTH

Electromagnetic waves travel through free space at186,000 miles per second. But, because of resistance,the travel rate of these waves along a wire is slightlyslower. An antenna must be an appropriate length sothat a wave will travel from one end to the other andreturn to complete one cycle of the RF voltage. Awavelength is the distance traveled by a radio wave inone cycle. This means that wavelength will vary withfrequency.

If we increase the frequency, the time required tocomplete one cycle of alternating current (at) isnaturally less; therefore, the wavelength is less. If wedecrease the frequency, the time required to completeone cycle of ac is longer; therefore, the wavelength islonger. Another word used to represent wavelength isLAMBDA (designated by the symbol i).

The term “wavelength” also refers to the length ofan antenna. Antennas are often referred to as half wave,quarter wave, or full wave. These terms describe the

Figure 2-18.—DA-91/U dummy load.

relative length of an antenna, whether that length iselectrical or physical.

Earlier, we said that when tuning an antenna, we areelectrically lengthening or shortening the antenna toachieve resonance at that frequency. We are actuallychanging the wavelength of the antenna. The electricallength of an antenna may not be the same as its physicallength.

You know that RF energy travels through space atthe speed of light. However, because of resistance, RFenergy on an antenna travels at slightly less than thespeed of light. Because of this difference in velocity, thephysical length no longer corresponds to the electricallength of an antenna. Therefore, an antenna may be ahalf-wave antenna electrically, but it is physicallysomewhat shorter. For information on how to computewavelengths for different frequencies, consult NEETS,Module 12, Modulation Principles.

BASIC ANTENNAS

Many types and variations of antenna design areused in the fleet to achieve a particular directiveradiation pattern or a certain vertical radiation angle.However, all antennas are derived from two basic types:the half wave and the quarter wave.

HALF-WAVE ANTENNA

An antenna that is one-half wavelength long is theshortest antenna that can be used to radiate radio signalsinto free space. The most widely used antenna is thehalf-wave antenna, commonly called a dipole, or hertz,antenna. This antenna consists of two lengths of wirerod, or tubing, each one-fourth wavelength long at acertain frequency.

Many complex antennas are constructed from thisbasic atenna design. This type of antenna will notfunction efficiently unless its length is one-halfwavelength of the frequency radiated or received.

Figure 2-19 shows a theoretical half-wave antennawith a center feed point. Both sections of the antenna

Figure 2-19.—Half-wave antenna with center feed point.

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are ~/4 (one-fourth wavelength) at the operatingfrequency. Together, of course, the sections make theeffective length of the antenna L/2 (one-halfwavelength) at the operating frequency.

One feature of the dipole antenna is that it does notneed to be connected to the ground like other antennas.Antennas shorter than a half wavelength must use theground to achieve half-wave characteristics. The half-wave antenna is already long enough to radiate thesignal properly.

Because of sophisticated antenna systems andtuning processes, half-wave antennas can beelectrically achieved aboard ship. Thereforewavelength is becoming less and less the criteria fordetermining the types of antennas to be used on ships.Dipole antennas can be mounted horizontally orvertically, depending upon the desired polarization, andcan be fed at the center or at the ends. Because it isungrounded, the dipole antenna can be installed aboveenergy-absorbing structures.

QUARTER-WAVE ANTENNA

A quarter-wave antenna is a grounded antenna thatis one-fourth wavelength of the transmitted or receivedfrequency. You will hear the quarter-wave antennareferred to as a “Marconi antenna.” The quarter-waveantenna is also omnidirectional.

As we mentioned earlier, a half-wave antenna is theshortest practical length that can be effectively used toradiate radio signals into free space. The naturalquestion, then is, “How do we use a quarter-wavelengthantenna if a half-wavelength is the shortest length thatcan be used?” The answer is simple.

Figure 2-20.—Direct and image signal of a quarter-waveantenna.

Figure 2-21.—Current distribution in a real antenna and itsimage.

Two components make up the total radiation froman antenna. One component is that part of the radiatedsignal which leaves the antenna directly. The other is aground reflection that appears to come from anunderground image of the real antenna (figure 2-20).This image is sometimes called the mirror image and isconsidered to be as far below the ground as the realantenna is above it.

Figure 2-21 shows basic current distribution in areal and image antenna. There are certain directions inwhich the direct wave from the real antenna and thereflected wave from the image are exactly equal inamplitude but opposite in phase. Conversely, there areother directions in which the direct and reflected wavesare equal in amplitude and in phase. Therefore,depending on the direction and location of the point atwhich the field strength is measured, the actual fieldstrength may be (1) twice the field strength from the realantenna alone, (2) zero field strength, or (3) someintermediate value between maximum and minimum.It is this “real” and “image” radiated field that forms thebasis for using quarter-wavelength antennas.

This reflected-energy principle is very useful in thelower frequency ranges, although ground reflectionsoccur in the high-frequency range as well.

The antenna does not always need to be placed atthe Earth’s surface to produce an image. Anothermethod of achieving reflected images is through the useof ground planes. This means that a large reflectingmetallic surface is used as a substitute for the ground orEarth. This method is frequently used in the VHF/UHF

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Figure 2-22.—AS-390/SRC UHF antenna with counterpoise,

Figure 2-24.—Wire rope fan antenna.

or ground plane.

frequency ranges. Figure 2-22 shows a commonly usedUHF antenna (AS-390/SRC), which uses this principle.The ground plane is sometimes referred to as a“counterpoise,” as shown in the figure. Together, the rope fans, whips, cages, dipoles, probes, trussedcounterpoise and the radials form the reflecting surface, monopoles, and bow stubs. The selection and use ofwhich provides the reflected image. different types is often governed by the limited space

available.

TYPES OF SHIPBOARD ANTENNAS WIRE ROPE ANTENNASFigure 2-23 shows various shipboard antennas and

their placements. The complex structures of modern Wire rope antennas are installed aboard ship forships and their operational requirements require the use medium- and high-frequency (300 kHz to 30 MHz)of many types of antenna. These types include wire coverage. A wire rope antenna (figure 2-24) consists of

Figure 2-23.—Shipboard antenna systems.

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one or more lengths of flexible wire rigged from two ormore points on the ship’s supurstructure. A wire ropeantenna is strung either vertically or horizontally from ayardarm or mast to outriggers, another mast, or to thesuperstructure. If used for transmitting, the wireantenna is tuned electrically to the desired frequency.

Receiving wire antennas are normally installedforward on the ship, rising nearly vertically from thepilothouse top to brackets on the mast or yardarm.Receiving antennas are located as far as possible fromthe transmitting antennas so that a minimum of energyis picked up from local transmitters.

Because of the characteristics of the frequencyrange in which wire antennas are used, the ship’ssuperstructure and other nearby structures become anelectronically integral part of the antenna. As a result,wire rope antennas are usually designed or adaptedspecifically for a particular ship.

WHIP ANTENNAS

Whip antennas are used for medium- and high-frequency transmitting and receiving systems. For low-frequency systems, whip antennas are used only forreceiving. Essentially self-supporting, whip antennasmay be deck-mounted or mounted on brackets on thestacks or superstructure. The self-supporting feature ofthe whip makes it particularly useful where space islimited and in locations not suitable for other types ofantennas. Whip antennas can be tilted, a design featurethat makes them suited for use along the edges ofaircraft carrier flight decks. Aboard submarines, theycan be retracted into the sail structure.

Whip antennas commonly used aboard ship are 25,28, or 35 feet long and consist of several sections. The35-foot whip is most commonly used. If these antennasare mounted less than 25 feet apart, they are usuallyconnected with a crossbar with the feed point at itscenter. The twin whip antenna (figure 2-25) is notbroadband and is generally equipped with a base tuningunit.

VHF AND UHF ANTENNAS

The physical size of VHF and UHF antennas isrelatively small because of the short wavelengths atthese frequencies. Aboard ship, these antennas areinstalled as high and as much in the clear as possible.

Figure 2-25.—Twin whip antenna with crowbar.

Since VHF and UHF antennas are line-of-sightsystems, they require a clear area at an optimum heighton the ship structure or mast. Unfortunately, this area isalso needed for various radars and UHF direction-finding and navigational aid systems.

VHF and UHF antennas are usually installed onstub masts above the foremast and below the UHFdirection finder. UHF antennas are often located on theoutboard ends of the yardarms and on other structuresthat offer a clear area.

For best results in the VHF and UHF ranges, bothtransmitting and receiving antennas must have the samepolarization. Vertically polarized antennas are used forall ship-to-ship, ship-to-shore, and ground-to-airVHF/UHF communications. Usually, either a verticalhalf-wave dipole or a vertical quarter-wave antennawith ground plane is used. An example of a UHF half-wave (dipole) antenna is the AT-150/SRC, shown in

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Figure 2-26.—AT-150/SRC UHF antenna.

Figure 2-27.—OE-82C/WSC-1(V) antenna group.

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Figure 2-28.—AS-2815/SSR-1 antenna physical configuration.

Figure 2-26. This antenna is normally mountedhorizontally.

BROADBAND ANTENNAS

Broadband antennas for HF and UHF bands havebeen developed for use with antenna multicouplers.Therefore, several circuits may be operated with asingle atenna. Broadband antennas must be able totransmit or receive over a wide frequency band.

HF broadband antennas include the 35-foot twinand trussed whips, half-cone, cage, and a variety of fan-

designed antennas. The AT-150/SRC UHF antenna infigure 2-26 is an example of a broadband antenna.

SATCOMM ANTENNAS

The antennas shown in figures 2-27 and 2-28 areused for satellite communications. The 0E-82C/WSC-1(V) antenna (figure 2-27) is used with the AN/WSC-3transceiver and designed primarily for shipboardinstallation. Depending upon requirements, one or twoantennas may be installed to provide a view of thesatellite at all times. The antenna is attached to apedestal. This permits the antenna to rotate so that it isalways in view of the satellite. The frequency band forreceiving is 248 to 272 MHz and for transmitting is 292to 312 MHz.

The AN/SRR-1 receiver system consists of up tofour AS-2815/SSR-1 antennas (figure 2-28) with anamplifier-converter AM-6534/SSR-1 for each antenna.The antennas are used to receive satellite fleetbroadcasts at frequencies of 240 to 315 MHz. Theantenna and converters are mounted above deck so thatat least one antenna is always in view of the satellite.

The newer satellite systems use the SHF band. Oneof the major advantages of these systems is that they usea very small parabolic antenna measuring only 12inches in diameter.

A satellite antenna must be pointed at the satellite tocommunicate. We must first determine the azimuth(AZ) and elevation (EL) angles from a fixed location.Figure 2-29 illustrates how these angles are derived,

Figure 2-29.—Equatorial Satellite Antenna Pointing Guide.

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using a pointing guide called the Equatorial SatelliteAntenna Pointing Guide. This guide is normallyavailable through the Navy Supply System.

The antenna pointing guide is a clear plasticoverlay, which slides across a stationary map. Itindicates AZ and EL angles in degrees to the satellite.The values obtained are useful to the operator in settingup the antenna control unit of a satellite system.

To use the guide, follow these procedures:

1. Center the overlay directly over the desiredsatellite position on the stationary map.

2. Mark the latitude and longitude of the ship onthe plastic antenna pointing guide with a greasepencil.

3. Determine the approximate azimuth angle fromthe ship to the satellite.

4. Locate the closest dotted line radiating outwardfrom the center of the graph on the overlay inrelation to the grease dot representing the ship’slocation. This dotted line represents degrees ofazimuth as printed on the end of the line. Someapproximation will be required for shippositions not falling on the dotted line.

5. Determine the degrees of elevation by locatingthe solid concentric line closest to the ship’smarked position. Again, approximation will berequired for positions not falling directly on thesolid elevation line. Degrees of elevation aremarked on each concentric line.

Example: Assume that your ship is located at30° north and 70° west. You want to accessFLTSAT 8 at 23° west. When we apply theprocedures above, we can determine an azimuthvalue of 115° and an elevation angle of 30°.

RHOMBIC ANTENNA

The rhombic antenna, usually used at receiver sites,is a unidirectional antenna. This antenna consists offour long wires, positioned in a diamond shape.Horizontal rhombic antennas are the most commonlyused antennas for point-to-point HF navalcommunications. The main disadvantage of thisantenna is that it requires a relatively large area.

MULTIWIRE RHOMBIC

A rhombic antenna improves in performance if eachleg is made up of more than one wire. An improved

antenna, known as a curtain rhombic, uses three wiresspaced 5 to 7 feet apart for each leg and connected to acommon point (figure 2-30).

SLEEVE ANTENNA

The sleeve antenna is used primarily as a receivingantenna. It is a broadband, vertically polarized,omnidirectional antenna. Its primary uses are inbroadcast, ship-to-shore, and ground-to-aircommunications. Although originally developed forshore stations, there is a modified version for shipboarduse. Figure 2-31 shows a sleeve antenna for shorestations.

Sleeve antennas are especially helpful in reducingthe total number of conventional narrowband antennasthat otherwise would be required to meet therequirements of shore stations. With the use ofmulticouplers, one sleeve antenna can serve severalreceivers operating over a wide range of frequencies.This feature also makes the sleeve antenna ideal forsmall antenna sites.

CONICAL MONOPOLE ANTENNA

The conical monopole antenna (figure 2-32) is usedin HF communications. It is a broadband, verticallypolarized, compact omnidirectional antenna. Thisantenna is adaptable to ship-to-shore, broadcast, andground-to-air communications. It is used both ashoreand aboard ship.

When operating at frequencies near the lower limitof the HF band, the conical radiates in much the samemanner as a regular vertical antenna. At the higherfrequencies, the lower cone section radiates, and the top

section pushes the signal out at a low angle as a skywave. This low angle of radiation causes the sky waveto return to the Earth at great distances from the antenna.

Figure 2-30.—Three-wire rhombic antenna.

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Figure 2-31.—Sleeve antenna (shore stations).

Therefore, this antenna is well suited for long-distancecommunications in the HF band.

INVERTED CONE ANTENNA

The inverted cone antenna (figure 2-33) isvertically polarized, omnidirectional, and verybroadbanded. It is used for HF communications in ship-to-shore, broadcast, and ground-to-air applications.The radial ground plane that forms the ground systemfor inverted cones is typical of the requirement forvertically polarized, ground-mounted antennas. Theradial wires are one-quarter-wavelength long at thelowest designed frequency.

Figure 2-32.—Conical monopole antenna.

LOG-PERIODIC ANTENNA

The log-periodic (LP) antenna operates over anextremely wide frequency range in the HF and VHF

Figure 2-33.—Inverted cone antenna.

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mechanisms. This antenna is particularly useful whereantenna area is limited. A rotatable LP antenna, knownas an RLP antenna (figure 2-35), possesses essentiallythe same characteristics as the fixed LP antenna but hasa different physical form. The RLP antenna iscommonly used in ship-shore-ship and in point-to-pointcommunications.

EMERGENCY ANTENNAS

Damage to an antenna from heavy seas, violentwinds, or enemy action can cause serious disruption ofcommunications. Sections of a whip antenna can becarried away, insulators can be damaged, or a wireantenna can snap loose from its moorings or break. Ifloss or damage should happen when all availableequipment is needed, you may have to rig, or assist in

Figure 2-34.—Log-periodic antenna. rigging, an emergency antenna to temporarily restorecommunications until the regular antenna can berepaired.

bands. Figure 2-34 shows a typical LP antenna The simplest emergency antenna consists of adesigned for extremely broadbanded, VHF length of wire rope to which a high-voltage insulator iscommunications. The LP antenna can be mounted on attached to one end and a heavy alligator clip, or lug, issteel towers or utility poles that incorporate rotating soldered to the other. The end with the insulator is

Figure 2-35.—Rotatable log-periodic antenna.

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Figure 2-36.—Antenna multicoupler interconnection diagram.

hoisted to the nearest structure and secured. The endwith the alligator clip (or lug) is attached to theequipment transmission line. To radiate effectively, theantenna must be sufficiently clear of all groundedobjects.

ANTENNA DISTRIBUTIONSYSTEMS

In figure 2-36, we see a distribution system with oneantenna that can be connected (patched) to one ofseveral receivers or transmitters by way of amulticoupler. In this system, you can patch the antennato only one receiver or transmitter at a time. However,some distribution systems are more complex, such asthe one shown in figure 2-37. In this system, you canpatch four antennas to four receivers, or you can patchone antenna to more than one receiver via themulticoupler. In either system, we need a way toconnect the antenna to the receiver or transmitter thatwe want to use. Figure 2-37.—Complex distribution system.

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Figure 2-38.—AN/SRA-12 antenna filter patch panel with receiver antenna patch panel.

Figure 2-38 shows a receiver antenna filter patchpanel, AN/SRA-12, with a receiver patch panel. TheAN/SRA-12 provides seven radio-frequency channelsin the 14-kHz to 32-MHz range. Any or all of thesechannels can be used independently of any otherchannel, or they can operate simultaneously.

On the receiver patch panel, a receiver is hardwiredto each jack. With the use of patchcords, you canconnect a receiver, tuned to a particular frequency, to theantenna by connecting the receiver to the proper jack onthe AN/SRA-12. Figure 2-38 shows how the filterassembly is used in combination with other units to passan RF signal from an antenna to one or more receivers.

NOTE

When patching, YOU MUST ALWAYSINSERT THE END OF THE ANTENNAPATCH CORD TO THE RECEIVERJACK FIRST. THEN, YOU INSERT THEOTHER END OF THE PATCH CORDINTO THE LOWEST USABLE AN/SRA-12 JACK. TO UNPATCH, ALWAYSREMOVE THE PATCH CORD FROMTHE RECEIVER JACK, THEN THEOTHER END FROM THE FREQUENCYFILTER JACK. An easy way to rememberthis is always work the patching from the topdown.

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Transmitting antenna distribution systems performthe same functions as receiving distribution systems.Figure 2-39 shows a transmitter patch panel. These

Figure 2-39.—Transmitter antenna patch panel.

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transmitter patch panels are interlocked with thetransmitter so that no open jack connection can beenergized and no energized patch cord can be removed.This provides safety for both personnel and equipment.

ANTENNA POSITIONING

Raise and lower antennas - raising and loweringphysically of antennas is associated with flight,refueling or PMS operations. Extreme care should betaken that all moving parts are in correct operatingconditions and the Officer of the Deck orCommunications Watch Officers know prior to thephysical movement of the antennas.

USE DIRECTIONAL ANTENNAS

Reception is defined as: when an electromagneticwave passes through a receiver antenna and induces avoltage in that antenna. Further detailed information onantennas, antenna use, wave propagation and wavegeneration can be found in NEETS MODULES 9, 10,and 17.

Rotate For Optimum Reception

This is accomplished by both physical andmechanical means of moving the antenna(s) to properlyalign and tune the antenna.

Align For Optimum Reception

Using the correct antenna location (by rotation) andthe correct equipment for the system, you will bring theantenna into alignment and be ready for the final step,which is tuning.

Tune For Optimum Reception

There are two objectives of antenna tuning: (1) totune out the various impedances and (2) to match thelength of the antenna to the frequency radiated at itscharacteristic impedance.

Impedance: everything exhibits someimpedance, Even a straight piece of copper wire3 inches long will offer some resistance tocurrent flow, however small. The characteristicimpedance of this same piece of copper wire is itsoverall resistance to a signal.

The transmission line between an antenna and atransmitter has a certain amount of characteristicimpedance. The antenna also has a certain amount of

characteristic impedance. This basic mismatch inimpedance between the transmitter and the antennamakes antenna tuning necessary. Naturally, astransmitters, transmission lines, and antennas becomemore complex, antenna tuning becomes more critical.

Antenna length adjustment: When we tune anantenna, we electrically (not physically)lengthen and shorten it. The radiation resistancevaries as we vary the frequency of the transmitterand tune the antenna. The radiation resistance isnever perfectly proportional to antenna lengthbecome of the effects of the antenna height abovethe ground and its location to nearby objects.

You will find that the better the ability of thereceiver to reject unwanted signals, the better itsselectivity, The degree of selection is determinedly thesharpness of resonance to which the frequency-determining circuits have been engineered and tuned.You usually measure selectivity by taking a series ofsensitivity readings. As you take the readings, you stepthe input signal along a band of frequencies above andbelow the circuit resonance of the receiver; forexample, 100 kilohertz below to 100 kilohertz above thetuned frequency. As you approach the tuned frequency,the input level required to maintain a given output levelwill fall. As you pass the tuned frequency, the requiredinput level will rise. Input voltage levels are thencompared with frequency. They can be plotted onpaper, or you may can view them on an oscilloscope.They appear in the form of a response curve. Thesteepness of the response curve at the tuned frequencyindicates the selectivity of the receiver, thus allowingfor the optimum reception.

RF SAFETY PRECAUTIONS

Although electromagnetic radiation fromtransmission lines and antennas is usually ofinsufficient strength to electrocute personnel, it can leadto other accidents and compound injuries. Voltages maybe inducted in ungrounded metal objects, such as wireguys, wire cable (hawser), hand rails, or ladders, If youshould come in contact with these objects, you couldreceive a shock or RF burn. This shock can cause you tojump or fall into nearby mechanical equipment or, whenworking aloft, to fall from an elevated work area. Takecare to ensure that all transmission lines or antennas aredeenergized before working near or on them.

Guys, cables, rails and ladders should be checkedfor RF shock dangers. Working aloft “chits” and safetyharnesses should be used for your safety. Signing a

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“working aloft chit” signifies that all equipment is in anonradiating status (the equipment is not moving). Theperson who signs the chit should ensure that no RFdanger exists in areas where personnel are working.

Nearby ships or parked aircraft are another sourceof RF energy that must be considered when checkingwork areas for safety. Combustible materials can beignited and cause severe fires from arcs or heatgenerated by RF energy. RF radiation can detonateordnance devices by inducing currents in the internalwiring of the device or in the external test equipment, orleads connected to the device.

You should always obey RF radiation warningsigns and keep a safe distance from radiating antennas.The six types of warning signs for RF radiation hazardare shown in figure 2-40.

RF BURNS

Close or direct contact with RF transmission linesor antennas may result in RF burns. These are usuallydeep, penetrating, third-degree burns. To heal properly,these burns must heal from the inside to the skin surface.To prevent infection, you must give proper medicalattention to all RF burns, including the small “pinhole”burns. Petrolatum gauze can be used to cover burnstemporarily before the injured person reports to medicalfacilities for further treatment.

DIELECTRIC HEATING

Dielectric heating is the heating of an insulatingmaterial by placing it in a high frequency electric field.The heat results from internal losses during the rapidreversal of polarization of molecules in the dielectricmaterial.

In the case of a person in an RF field, the body actsas a dielectric, If the power in the RF field exceeds 10milliwatts per centimeter, a person in that field will havenoticeable rise in body temperature. The eyes arehighly susceptible to dielectric heating. For this reason,you should not look directly into devices radiating RFenergy. The vital organs of the body are also susceptibleto dielectric heating. For your own safety, you must notstand directly in the path of RF radiating devices.

PRECAUTIONS WHEN WORKING ALOFT

Prior to going aloft, you must follow all NAVOSHand local requirements such as wearing a harness and ahard hat. You must have a safety observer and meet allother requirements.

When radio or radar antennas are energized bytransmitters, you must not go aloft unless advance testsshow that little or no danger exists. A casualty can occurfrom even a small spark drawn from a charged piece ofmetal or rigging. Although the spark itself may beharmless, the “surprise” may cause you to let go of theantenna involuntarily, and you may fall. There is also ashock hazard if nearby antennas are energized.

Rotating antennas also may cause you to fall whenyour are working aloft. Motor safety switchescontrolling the motion of rotating antennas must betagged and locked opened before you go aloft near suchantennas.

When working near a stack, you should draw andwear the recommended oxygen breathing apparatus.Among other toxic substances, stack gas containscarbon monoxide. Carbon monoxide is too unstable tobuild up to a high concentration in the open, butprolonged exposure to even small quantities isdangerous.

SUMMARY

Naval communications using satellite and variousantennas types must always be ready to shift frompeacetime to wartime requirements. To this end, thediversity of fleet communication operations has giventhe Navy an expanded capability to meet ever-increasing command, control, and supportrequirements by use of satellites and assorted antennas.

Additionally, this variety of communicationstechnology has increased the requirements for greaterproficiency from all operating personnel. As aRadioman, you will be tasked with higher levels ofperformance in an increasingly technical Navy.

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