FM demodulation click analysis and improved detection techniques



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The clicks resulting from F14 demodulation below threshold are analysed bouh theoretically and experimentally, and methods are proposed for reducing the effects of these clicks. First, the interaction of signal and noise is described in terms of cochannel interference. Using this technique, an independent derivation of the area of a click is derived which agrees with the classic model developed by Rice in 1963. Second, an active receiver is proposed and it employs the properties of the clicks to add a level of complexity to secure communications to all receivers which are not set up with the receiver code. Third, a modified integrate-and-dump system is described which detects and then nullifies the effects of clicks in the integrator circuit by injecting a pulse of 2w radian volt-seconds in opposition to the already detected clicks. Finally, a Hilbert Transform click eliminator is proposed which gives an amplitude spike of shape similar to that of the phase spike and thereby allows a system of spike cancellation in the FM receiver. In conclusion, experimental data are presented which verify the number of clicks predicted by Rice as well as the heuristic arguments given by Schwartz.