Squelch systems—New designs for high performance

This paper describes a new approach to a noise operated squelch utilizing a desensitizing loop to sustain operation over short fades. This feature also provides a sharp demarkation between the operate and non-operate condition and minimizes "squelch tail". Another factor contributing to high performance is the use of an audio frequency desensitization input which prevents audio talk down during conditions of high modulation. The circuit is additionally stabilized to operate over the temperature range of -30°C to +80°C. In addition to the above, the paper describes one approach made to secure a squelch circuit capable of operation at high levels of quieting. Such operation is desirable for installations employing more than one base station receiver and using some means of selecting the receiver with the highest signal-to-noise ratio or where the range of operation is deliberately reduced for the sake of improved transmission quality at the fringes.