Shipboard HF interference: problems and mitigation

Cosite HF interference on shipboard is becoming more acute because of emerging requirements that call for simultaneous transmissions with antijam and frequency-hopping formats. The authors quantify several interferers and suggest ways to improve transmission. They include self-steering, low-level filters, linearized transmitters, intermod cancellation, improved transmitter-antenna coupling, time-disciplined data transmission and the exploitation of other new HF hardware developments. The poor frequency agility found in present shipboard HF systems can be improved by employing low-level, self-steering filters and the dedication of a power amplifier to each of three antennas. Reduction of radiated IM (intermodulation) can be accomplished by predistortion techniques. Shipboard IM into receivers from local transmitters can be reduced by partial cancellation. New hardware offers adaptive modems and dual diversity for improved performance