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, makingSHF 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 7002-8
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