Pulsive noise removing apparatus for an fm receiver

Abstract

An apparatus for removing a pulsive noise in an FM stereo signal including a stereo information signal and a stereo pilot signal, said composite signal further including a pulsive noise, said apparatus comprising an FM detector for providing said composite signal, a noise detector for detecting said pulsive noise for providing a control signal of a predetermined pulse width upon occurrence of said noise, a gate circuit to be normally closed for passing therethrough said composite signal and to be opened by the output from the noise detector, an amplifier for amplifying the output from the gate, a frequency band cut off filter coupled to said amplifier to form a negative feedback circuit, said filter being set to the pilot signal frequency and/or the subcarrier signal frequency, an attenuator coupled to the output of said amplifier, and a capacitor coupled to the output of said gate circuit and cooperative with said attenuator for holding, when the gate is opened, the signal level at the output of the gate to the value immediately before the gate is opened, said amplifier, attenuator and the capacitor constituting a closed loop, said closed loop forming a positive feedback circuit with respect to said frequencies of the pilot signal and/or subcarrier signal, which serves as an oscillator when said gate is opened, thereby to provide a pseudo pilot and/or subcarrier signals.