An improved HF squelch technique

The HF band is subject to noise, interference, multipath, and fading. These degradations make the implementation of robust squelch algorithms difficult. HF squelch methods generally exhibit an unacceptable decrease in reliability as channel conditions degrade. However, it is under channel conditions degraded by noise and interference where a reliable squelch function is most desirable to reduce operator fatigue. This paper discusses the design, performance and applications of an HF squelch technique based on a burst serial tone waveform that operates in low signal to noise ratio and high interference environments. A discussion of existing HF squelch techniques as well as a description of the presented technique is provided. Performance data, in the form of probability of unsquelch versus channel conditions for a specified mean time between false unsquelch are presented. In addition, the results of a performance comparison with an example of a passive squelch technique are given