An FM Detector for Low S/N
暂无分享,去创建一个
Conventional frequency-modulation (FM) detectors show a marked decrease in output S/N below an input S/N 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 S/N . A detector is described which has no normalization and is superior to the ideal detector below zero to 10 dB input S/N . The noise at the output of the detector is additive for all input S/N ratios and in this sense is comparable to synchronous detection of AM. Plots of output noise spectrum and output S/N with and without sine-wave modulation are given. Another detector is also proposed that is asymptotic to the ideal detector at high S/N and the aforementioned detector at low S/N . 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.
[1] Nelson M. Blachman. The Demodulation of an F‐M Carrier and Random Noise by a Limiter and Discriminator , 1949 .
[2] F.L.H.M. Stumpers,et al. Theory of Frequency-Modulation Noise , 1948, Proceedings of the IRE.
[3] D. Middleton. On Theoretical Signal‐to‐Noise Ratios in F‐M Receivers: A Comparison with Amplitude Modulation , 1949 .
[4] L. Enloe. Decreasing the Threshold in FM by Frequency Feedback , 1962, Proceedings of the IRE.