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FM 24-18: Tactical Single-Channel Radio Communications Techniques


L-1. Need and Employment

Most of the satellite communications in today's military environment are multichannel. It is, in fact, more economical to process many voice channels over a single wideband satellite channel than to restrict the satellite to single-channel usage. However, there still exists a strategical need for single-channel operation in which satellite communications offer the best means of mission accomplishment.

Whereas ordinary means of communications are subject to varying degrees of radio direction finding (RDF), the satellite system can be used in such a manner as to deter enemy RDF success. The short transmission times of burst communications present less attractive jamming targets than do longer, continuous communications of regular nets.

Special forces and other users find that satellite communications fill their special needs more effectively than other means of communications. Therefore, the Army has developed a single-channel, ultra high frequency (UHF) manpack system to fill these needs. Figure L-1 illustrates a basic manpack system concept of operations.

Figure L-1. Manpack system concept of operation.

The special forces and engineers concept is to deploy the manpacks with selected teams with net control at the forward operation bases of both the engineers and special forces groups. The rangers concept of operation is for the deployment of manpacks at the company headquarters/combat patrol bases with net control at the ranger battalion headquarters. (See fig L-2 and L-3 for concepts of employment.) The system can be used with the AN/PRC-70, AN/PRC-77, SINCGARS, and the AN/VRC-12 series radio sets for retransmission capabilities.

Figure L-2. Manpack system typical employments.

Figure L-3. Special Forces BCS concept of operation.

L-2. System Description

The manpack system is designed for low-echelon, highly mobile unit communications where units operate in either friendly or enemy territory at great distances from the home unit. The equipment can operate in the on-the-move/line-of-sight (LOS) mode using 2 watts output power or in the at-halt/satellite (SAT) mode using 35 watts output power. It can transmit and receive in either voice or data format in either mode. The system complements the older tactical radios which operate in the high frequency (HF) spectrum and which are highly susceptible to enemy RDF and jamming as well as requiring relay-switching in order to operate over long distances. Furthermore, the manpack system requires less personnel training than does the older HF equipment and it requires no additional personnel at unit or support levels.

L-3. Equipment Description

Radio Set, AN/PSC-3( ) (fig L-4(a) and (b)) is a battery-operated, portable communications terminal employing an RT-1402( )/G receiver/transmitter (RT) unit (fig L-5) which provides two-way communications in the frequency range of 225 MHz to 400 MHz in both SAT and LOS modes of operation.

Figure L-4a. AN/PSC-3( ) with OA-8990( )/P DMDG.

Figure L-4b. Radio Set AN/PSC-3( ) components.

Figure L-5. Receiver/Transmitter RT-1402( )/G.

The terminal uses a low-gain omnidirectional whip antenna for LOS operation while in motion. This antenna also enables reception of a satellite alert ringing signal while in LOS mode (fig L-4b). The set uses an AS-3567( )/PSC-3 medium-gain antenna (fig L-7) for at-halt satellite communications. The terminal provides half duplex communications at 300 BPS and 1200 BPS biphase shift keying (BPSK), 2400 BPS synchronous BPSK, 16 KBPS frequency modulation (FM) and frequency shift.

Figure L-6. Hi- and low-gain (whip) antennas.

Figure L-7. Medium-gain antenna AS-3567( )/PSC-3.

The vehicular net control station (NCS) AN/VSC-7 uses the basic AN/PSC-3RT unit installed in a C-11119( )/VSC-7 control converter which is shock-mounted into a communications shelter or a military ground vehicle. Power to the NCS is derived from the vehicle's electrical system. It may also be used with a S-280 communications shelter mounted on an M-832 mobilizer. The power amplifier module in the control converter is blower-cooled to allow continuous key-down operation at temperatures up to 86 C (155 F). The NCS can serve up to 15 AN/PSC-3( ) terminals in a communications net with the selection of conference or individual call-codes available at the control converter front-panel. The NCS uses a high-gain (9 dB) AS-3568( )/VSC-7 antenna and a low-gain whip antenna (fig L-6). The low-gain AS-3566( )/G whip antenna is used for LOS operation and for CALL reception. The AS-3567( )/PSC-3 medium-gain antenna, used for satellite relay operation, provides 6 dB gain in the frequency range of 240-318 MHz and 5.5 dB gain in the frequency range 318-400 MHz. Terminal characteristics include all features of the AN/PSC-3( ) and additionally provide--

  • Operation from vehicle electrical system

  • Transmission of selective or conference call signals

  • Input-power conditioning

  • Automatic transmission/reception mode changeover

  • Electromagnetic interference protection against colocated transmitter(s)

  • Continuous key-down operation

  • High-gain (9 dB) antenna

The Digital Message Device Group (DMDG) OA-8990( )/P is the major "used with" component of the AN/PSC-3 and AN/VSC-7 in the burst communications system (BCS). This hand-held device provides digital input to the radio for burst transmissions at data rates of 300 and 1200 BPS. It provides the operator with the ability to transmit in a few seconds what would normally take minutes in a standard CW mode. The DMDG microprocessor unit features a 32-key keyboard, a 16-character light emitting diode (LED) display, an HF modem, and a 1,020-character memory. Power is supplied by rechargeable Nicad batteries. Data rates are 300 or 1200 BPS using ASCII 6-bit code. Selection of bit rate for compatibility with the satellite is accomplished by an internal switch. The maximum DMDG weight will be 3.9 kilograms (8.0 lbs); maximum volume will be 3.7 cubic centimeters (225 cu in). Interface equipment used with but not part of the manpack system, such as TSEC/KY-57 and KY-65 secure voice applique devices, are current Army inventory assets and may be issued as dictated by mission requirement.

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