Apparatus for the decoding coded frequency modulated signals

Abstract

A circuit for decoding coded frequency modulated signals eliminates perturbing effects of noise pulse signals by coupling the signal to be detected through a filter having a transfer function that is related to the conjugated transfer function of the frequency modulation deemphasis filter, the spectrum of the noise pulse, the spectral power density of the signal to be demodulated, and the spectral power density of the noise. A comparison circuit provides the signal at the output of the filter when the output signal exceeds a threshold level. A decision circuit, which provides signals representative of the temporal position and polarity of the noise pulses to the correction circuit, is coupled between the comparison circuit and a circuit for generating noise correction pulses. The noise correction pulses are coupled to the decoder with the output signal of the detector to eliminate the effects of the noise pulse.