An improvement in co-location performance of 100 W transceivers by means of low level filtering

In many instances two or more HF 100 W single sideband radio installations are required to operate independently into separate communication networks from one vehicular platform. For mechanical reasons whip antennas are often the antenna of choice, although from a communication viewpoint they may be non-ideal. This means whip antennas have to be co-located at a proximity of typically 1.5 metres. It has been found that the isolation between 5 metre whip antennas matched with pi-couplers to 50 Omega feeder cable on a vehicle can be as little as 15 dB at 1.5 metres with 10% frequency spacing between transmission and receiving frequencies. In these situations deleterious effects will occur should large amplitude signals from a transmitting radio impinge on a receiving antenna causing blocking and cross-modulation due to limiting effects in the receiver's front end.<>