Demodulator of sampled data fm signals from sets of four successive

Abstract

An FM signal is demodulated by the technique of sequentially sampling the signal and combining the samples to approximate the standard formula for the instantaneous frequency deviation ##EQU1## where the dots indicate the first derivative of the samples. The FM signal is assynchronously sampled at approximately four times the carrier frequency rate. Alternate samples are substantially equivalent to orthogonal components x and y of the FM signal. At least four successive samples are successsively stored so that at least four of the lastmost samples are always available for processing. Particular x samples are summed to create averaged samples x.sub.n and differenced to create approximations of derivatives x.sub.n of the x signal components and particular y samples are similarly summed and differenced to create averaged values y.sub.n and derivatives y.sub.n. These values are used in the equation for F.sub.n. In terms of successive samples, S, the equation for F.sub.n becomes