Abstract: Co-channel interference in baseband digital samples of an FM communications (e.g. AMPS) signal is cancelled by a complex signal limiter and non-linear filter (CLNF), to which the samples are supplied, and a time-varying null filter unit, to which the output samples from the CLNF are supplied, for separating the desired signal from residual interference. The output samples from the CLNF are also supplied via a selective narrow band filter bank to a non-linear transform unit for producing an energy based demodulation signal from which time-varying coefficients for the null filter are obtained. The units can be used individually or in different arrangements and combinations, and the transform unit can be augmented and used to replace a conventional FM demodulator.