System for removing interference distortion in the demodulated signal of

Abstract

A system for removing interference distortion in the demodulated signal of a frequency-modulated signal comprises a demodulator for demodulating an input frequency-modulated signal Ca(t) which has been subjected to interference by another frequency-modulated signal, and thereby obtaining a demodulated signal e.sub.o (t), a first analog multiplier for obtaining a signal in which the input frequency-modulated signal is squared, a low-pass filter supplied with the squared signal and detecting an envelope of the input frequency-modulated signal in square characteristics, and thereby producing as output a squared envelope signal {Env(t)}.sup.2, a second analog multiplier supplied with the demodulated signal e.sub.o (t) from the demodulator and with the squared envelope signal {Env(t)}.sup.2 from the low-pass filter, and thereby producing as output a signal e.sub.oa (t) of the product of both signals, a DC blocking capacitor for suppressing DC component of said squared envelope signal {Env(t)}.sup.2, and thereby obtaining only AC component, a first operation circuit supplied with the product signal e.sub.oa (t), a delay circuit for delaying an output signal of the first operation circuit by a specific delay time, a second operation circuit for adding the output signal of the first operation circuit and the output signal of the second operation circuit, and a third analog multiplier for carrying out multiplication of the AC component signal {Env(t)}.sup.2 and the output signal of the second operation circuit, and thereby supplying the resulting output signal h(t) to the first operation circuit. The first operation circuit substantially carries out subtraction of the signal e.sub.oa (t) and the signal h(t). From the first operation circuit is derived the demodulated signal in which the interference distortion has been substantially cancelled and thus removed.