SELECTION OF OPTIMUM LOCATION FOR THE HIGH POWER HF TRANSMITTER-RECEIVER IN A DENSE COMBAT VEHICLE EMI ENVIRONMENT

Abstract

This paper discusses the procedure adapted after carrying out several iterations for selecting the ideal location to introduce a high power HF Transmitter-Receiver in a tactical Combat Vehicle from the Electromagnetic Compatibility point of view. This radio set is generally contributing for very high field strength to neighbouring electronic devices so also to other two VHF Tx-Rx situated in the same vehicular platform. A two pronged approach was followed in deciding the optimum solution to locate the HF Radio set. Emission levels from HF radio set is to be minimised within the vehicle when crew hatches are closed(normal operating condition of the vehicle)to reduce coupling level to neighbouring equipment. Emission from HF antenna was maximised insitu by careful installation of antenna, outside the vehicle environment to ensure optimum radiation of intended signal. Four different configurations experimented are reported in this paper. HF being a congested operating spectrum ,due care was taken in EMI control of HF-VHF radios and other electronic subsystems to have minimal amplitude varying [AM] interfering signals and also to minimise inter modulation EMI effects [IMI]from two VHF- FM radios, thereby ensuring the selection of optimum location. VPL, HF, VHF, AM Modulation, FM, Spectral Congestion, EMI, EMC , IM , VSWR etc. An increase in transmit power extends the range only insignificantly. To achieve double the range one has to increase the transmit power by eight times. For the present case of 100watts at least 35 km range is expected at highest frequency of 30MHz. But at lower frequencies the maximum range of 50 km can be expected. Whenever there is reduction in range it could be due to severe propagation loss/fading or due to interfering signals or both.