noise squelch - for f.m. receivers

Noise is by definition any undesired sound. While an f.m. receiver has less noise on a station than an a.m. receiver, it is noisy between transmissions. In the absence of an incoming signal, a loud hissing sound is heard: this is generated by the noise voltages in the receiver. A received signal is amplitude-modulated by the noise and the amount of modulation is a function of the amplitude of the noise voltage. It is therefore desirable that f.m. receivers have a noise-squelch circuit which mutes the a.f. amplifier when no signal is being received. If your receiver is not fitted with a squelch, the circuit described here may be just what you"ve been waiting for ... noise squelch . . . noise squelch ... elektor may 1984 To keep the circuit simple, our design is based on an old, proven principle: that of controlling the squelch with a carrier- dependent signal. A suitable control voltage is available in virtually all f.m. receivers. In the absence of an incoming carrier, this voltag...