Automatically adjustable fm receiver squelch

Claim 2

An automatically adjustable squelch circuit responsive to detected noise and modulation signals from a receiver discriminator to actuate a switch, said squelch including in combination; control means responsive to receipt of a command signal to initialize sequential development of control signals, variable attenuation means coupled to said discriminator and to said control means, said attenuator means being responsive to each of said control signals in said sequence to attenuate signals coupled therethrough from said discriminator by a predetermined amount, detector means coupled to said attenuator means for receiving said attenuated signals, said detector means being responsive to said signals exceeding a predetermined level to develop a detection signal, means coupling said detector means to said switch means, said switch being operative in response to said detection signal to actuate, said control means further being responsive to Receipt of said detection signal to terminate said sequence and maintain said last developed control signal in said sequence.

Claim 3

The squelch circuit of claim 1 wherein said control means includes timing means for developing a timing signal at predetermined intervals, and circuit means coupled to said timing means and operative in response to each one of said timing signals to develop one of said control signals in said sequence.

Claim 4

The squelch circuit of claim 2 wherein said attenuator means includes a plurality of attenuator circuits coupled to said circuit means, each of said attenuator circuits being responsive to one of said control signals to change the attenuation through said attenuator means by said predetermined amount.

Claim 5

The squelch circuit of claim 3 wherein said circuit means includes bistable means, said control signals are binary signals and said timing means is a clock.

Claim 6

The squelch circuit of claim 4 wherein said control means is further operative in response to said command signal to develop a discharge signal, said detector means being coupled to said control means and operative in response to said discharge signal to initialize said detector means.

Claim 7

The squelch circuit of claim 5 wherein said detector means includes detection circuitry responsive to the presence of said signals to develop a first signal varying in accordance with the amplitude of said signals, comparison means coupled to said detection circuitry and operative in response to said first signals exceeding a predetermined amplitude to develop said detection signal.

Claim 8

The squelch circuit of claim 6 wherein said means coupling said detector means to said switch includes a switching circuit operative in response to said detection signal to develop a second signal, said switch being operative in response to said second signal to actuate.

Claim 9

The squelch circuit of claim 7 wherein said control means is coupled to said comparator means, said control means being operative in response to said detection signal to terminate said sequence and maintain said last developed control signal in said sequence.

Claim 10

The squelch circuit of claim 8 wherein said control means is further operative in response to said command signal to develop an inhibit signal, said switching circuit being coupled to said control means and operative in response to said inhibit signal to develop said second signal.

Claim 11

In a frequency modulation receiver including means for receiving a modulated wave and for converting the same to an intermediate frequency wave, and including low frequency amplifying means for the derived modulating signal the combination including, discriminator means for deriving from the intermediate frequency wave the modulating signal and noise signals extending in a frequency range substantially greater than the modulating signal which noise signals increase substantially in amplitude in the absence of the modulating signal, control means responsive to receipt of a command signal to initialize sequential development of control signals, variable attenuation means coupled to said discriminator means and to said control means, said attenuator means being operative in response to each of said control signals in said sequence to attenuate said noise signals coupled therethrough from said discriminator by a predetermined amount, detector means coupled to said attenuator means, said detector means being operative in response to said noise signals exceeding a predetermined level to develop a detection signal, and second circuit means coupling said detector means to the low frequency amplifying means of the receiver for squelching the low frequency amplifying means in response to said detection signal, said control means further being operative in response to receipt of said detection signal to terminate said sequence of control signals and maintain said last developed control signal in said sequence.

Claim 12

In a frequency modulation receiver including means for receiving a modulated wave and for converting the same to an intermediate frequency wave, and including low frequency amplifying means for the derived modulating signal the combination including, discriminator means for deriving from the intermediate frequency wave the modulating signal and noise signals extending in a frequency range substantially greater than the modulating signal which noise signals increase substantially in amplitude in the absence of the modulating signal, control means responsive to receipt of a command signal to initialize sequential development of control signals, variable attenuation means coupled to said discriminator means and to said control means, said attenuator means being operative in response to each of said control signals in said sequence to attenuate said noise signals coupled therethrough from said discriminator by a predetermined amount, detector means coupled to said attenuator means, said detector means being operative in response to said noise signals exceeding a predetermined level to develop a detection signal, and second circuit means coupling said detector means to the low frequency amplifying means of the receiver for squelching the low frequency amplifying means in response to said detection signal, said control means further being operative in response to receipt of said detection signal to terminate said sequence of control signals and maintain said last developed control signal in said sequence.

Claim 13

The squelch circuit of claim 10 wherein said second circuit means inclUdes first switch means coupled to said detector means and operative in response to said detection signal to develop a first signal, and second switch means coupled to said first switch means and said low frequency amplifying means and operative in response to said first signal to squelch the low frequence amplifying means.

Claim 14

The squelch circuit of claim 11 wherein said detector means includes detection circuitry responsive to the presence of said noise signal to develop a second signal varying in accordance with the amplitude of said noise signals, and comparison means coupled to said detection circuitry and operative in response to said second signal exceeding a predetermined amplitude to develop said detection signal.

Claim 15

The squelch circuit of claim 12 wherein said control means is further operative in response to said command signal to develop a discharge signal, said detection circuitry being coupled to said control means and operative in response to said discharge signal to reduce said second signal to zero.

Claim 16

The squelch circuit of claim 13 wherein said control means is further operative in response to said command signal to develop an inhibit signal, said first switching circuit being coupled to said control means and is operative in response to said inhibit signal to develop said first signal.

Claim 17

The squelch circuit of claim 14 wherein said control means includes timing means for developing a timing signal at predetermined intervals, and third circuit means operative in response to each one of said timing signals to develop one of said control signals in said sequence.

Claim 18

The squelch circuit of claim 15 wherein said attenuator means includes a plurality of attenuator circuits coupled to said circuit means, each of said attenuator circuits being operative in response to one of said control signals to change the attenuation through said attenuator means by said predetermined amount.