High speed squelch circuit

DETAILED DESCRIPTION It is, accordingly, the principle object of this invention to provide a novel and improved squelch circuit wherein the effective time constant under strong signal conditions is short enough to completely eliminate the noise burst in the audio at the end of the received transmission.
Another object of the invention is to provide a variable time constant, which allows a long time constant under weak signal condition and varies the time constant proportional to the RF signal strength such that under strong signal conditions the audible noise burst is completely eliminated.
Briefly, in accordance with one embodiment of the invention, a filter circuit is adapted to receive detected noise voltage from a receiver and is responsive to high frequency noise above the audio frequency range (preferably frequencies from 40 kHz to 100 kHz).
The filter circuit filters the detected noise voltage to develop a filtered noise voltage which is composed of a wide bandwidth of noise frequencies above the audio frequency range.
This filtered noise voltage is coupled to a squelch control circuit whic develops a squelch control voltage in response to the filtered noise voltage.
According to another feature of the invention, circuitry is provided to amplify the filtered noise voltage and to limit the amplified noise voltage from the filter circuit.
This amplified, limited and filtered noise signal is then coupled to the squelch control circuit.
According to yet another feature of the invention, the squelch control circuit utilizes a relatively long time to respond to the noise voltage under weak signal conditions and varies the time to respond proportional to the RF signal strength under strong signal conditions.
The invention as herein described provides the overall muting speeds necessary to achieve total squelch tail elimination.
In addition, the circuit can achieve these speeds without serious degradation of the squelch circuit chatter, clamping and lock-up performance by sampling a wide band of high frequency noise