FM Tactical Communications Under Intentional Interference

This study is undertaken to determine whether it is possible to develop a realistic computerized mathematical model for FM tactical radios operating under the influence of enemy jamming. A simplified model of the single channel communication system with interference is developed. The various parameters of this model which affect the quality of communications are then discussed. Specifically, performance data for the VRC-12 radio for various signal-to-interference ratios is introduced and a message quality indicator is developed for various received friendly and jamming signal strengths. Next, mathematical relationships for signal propagation over various terrain are introduced. The specific communication links considered were those for air-to-ground, line-of-sight (LOS), and single and multiple obstacle paths. Consideration was also given to the moisture content of the soil as this is an important consideration at the frequencies involved in the analysis. A comparison is then made between the path losses predicted by the various mathematical relationships and actual field tests. It is shown that the developed expressions produce realistic results. These tested signal propagation relationships are then integrated with the VRC-12 radio's performance under interference to produce the final computerized model. In addition to the terrain between friendly transmitter and receiver and enemy jammer and receiver, several other variables are incorporated in the model.