Figure 2-7.—Satellite communications systems.
Wide operating bandwidth permits high
information transfer rates and facilitates spread
spectrum modulation techniques. Spread spectrum
modulation is a particularly valuable technique for
lessening the effects of enemy jamming. Although
wide bandwidth permits both high information transfer
rates and AJ capabilities when using the OM-
55(V)/USC modem, it may not permit both
simultaneously in the presence of jamming. Therefore,
high information transfer rates will be significantly
reduced when jamming is encountered, permitting only
certain predetermined critical circuits to be maintained.
Narrow uplink transmission beamwidth provides a
low probability of intercept (LPI) capability. An uplink
LPI capability reduces the threat of detection and
subsequent location, but does not in and of itself deny
enemy exploitation of those communications if
detection is achieved. SHF frequencies are rarely
affected by naturally occurring scintillation, making
SHF SATCOM a particularly reliable form of
communications.
A characteristic of SHF, favorable to flagships, is
the ability to communicate critical C4I for the user
information in the presence of enemy jamming and with
due regard for enemy detection capabilities. SURTASS
Military Sealift Command Auxiliary General Ocean
Surveillance (T-AGOS) ships were initially equipped
with SHF SATCOM, taking advantage of the high
information transfer rate capability and LPI
characteristics. Because of larger available bandwidths,
inherent jam-resistance, and increasing demands on
limited tactical UHF SATCOM resources, additional
applications for DSCS SHF SATCOM afloat are
continually being investigated for the Fleet.
The radio group consists of a high power amplifier
(HPA) or medium power amplifier (MPA), low noise
amplifier (LNA), up-converter, down-converter, and
frequency standard. For transmit operations, the
up-converter translates the modem’s 70 or 700
2-8
