in performance compared to conventional detectors attempts have been made to implement zero crossing detection of the complex valued base band signal instead of zero crossing detection of a real valued received signal at an appropriately chosen intermediate frequency if however despite many advantages such base band demodulators require a considerable amount of analog circuitry in contrast if detectors including the if detectors of this invention are predominantly digital hardware rather than analog circuitry and consequently benefit enormously from the continuing advances in digital microelectronics in order to suppress out of band noise and adjacent channel interference the deployment of analog bandpass filters at the input of the zero crossing detector is mandatory usually symmetrical bandpass filters with time bandwidth products in the order of unity are used such filters lead to distortions of the received signal and therefore must be considered in the receiver design fortunately since the received perturbation is narrow band at the bandpass filter output and the modulation index h is smaller than one frequency modulation fm click noise is negligible in a preferred embodiment of the present invention a linear digital filter developed by setting out from a least squares ls approach as detailed below applied to the output of the digital zero crossing detector yields a favorable bit error ratio ber performance the improved zero crossing detector of this invention is sometimes termed a zero crossing decorrelation detector zxdd.