Channel evaluation from predicted zero crossing analysis

This paper presents an investigation into real-time channel evaluation (RTCE) from predicted zero crossing analysis of; (i) a pilot-tone, and, (ii) frequency shift keying (FSK) modem tones within a HF (high frequency) radio system. This work extends the initial investigations from the early 1970s which used an analogue implementation analysing phase perturbation by time-differential phase comparisons of a low-level pilot-tone inserted in-band. The results presented compare the theoretical analysis and measured results in Gaussian and flat fading conditions, and hence identify the close relationship between the phase threshold, zero crossing error rate and SNR (signal to noise ratio). This type of non-parametric system measurement technique is widely applicable for other constant envelope modulation types, e.g. MFSK, and as such is suitable for incorporation into frequency management systems for various different radio systems operating in the HF, VHF and UHF bands