LEARNING EVENT 5: ANTIJAMMING AND ECCM TECHNIQUES
1. Physical damage and hostile electromagnetic jamming threaten all communications including satellite. This
system presently does not offer any antijamming protection to the TACSAT terminal. Mobile TACSAT
terminals offset the need for providing protected multiple ground relay sites. In addition, it reduces exposure
time to hostile actions. The protection of these terminals by terrain, such as valleys, further reduces the
possibility of detection. Where ordinary means of communications are subject to varying degrees of radio
direction finding (RDF), the satellite system can be used to deter enemy RDF success. The short transmission
times of burst mode present less attractive jamming targets than the longer continuous communications of
regular nets. The only options available to tactical UHF satellite terminals are data burst, alternate frequency
selection, mobility, and reducing the on-air time of each transmission.
2. 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 bp/s. It provides the operator with the
ability to transmit in a few seconds what would normally take minutes in a standard continuous mode (CW)
mode. The DMDG microprocessor unit features a 32-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 bp/s using American standard code for information interchange (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.
SS0031
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