An FM Detector for Low S/N

Conventional frequency-modulation (FM) detectors show a marked decrease in output below an input of 5 to 10 dB. This threshold effect is caused by "clicks" or phase slips of multiples of π. This effect is related to a normalization (clipping) which is very beneficial at high . A detector is described which has no normalization and is superior to the ideal detector below zero to 10 dB input . The noise at the output of the detector is additive for all input ratios and in this sense is comparable to synchronous detection of AM. Plots of output noise spectrum and output with and without sine-wave modulation are given. Another detector is also proposed that is asymptotic to the ideal detector at high and the aforementioned detector at low . Comparison is made with conventional detectors. The results indicate that this detector may be especially useful in the detection of frequency-shift keying and phase-shift keying in telemetry systems.