SPEECH-NOISE DISCRIMINATING CONSTANT PULSE WIDTH SQUELCH

• US 3,603,884 A
• Filed: 06/04/1969
• Issued: 09/07/1971
• Est. Priority Date: 06/04/1969
• Status: Expired due to Term

• Current Assignee: Gary A. Cannalte, George C. Hawkins, Paul J. Jr. Zaura
• Original Assignee: Gary A. Cannalte, George C. Hawkins, Paul J. Jr. Zaura
• Inventors: Zaura, Paul J. Jr., Cannalte, Gary A., Hawkins, George C.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US04/830,350
• Time in Patent Office: 825 Days
• Field of Search: 179/1SW,1VC,1P,1SA,1VL 325/348,478,480 340/148
• US Class Current: 455/222
• CPC Class Codes: H03G 3/342 Muting when some special characteristic of the signal is sensed which distinguishes it from noise, e.g. using speech detector H03G3/344, H03G3/345 take precedence

Abstract

A squelch circuit for a receiver wherein the detected signals at the discriminator are amplified and converted to pulses of constant period or width. The pulses are detected and used to develop a control voltage to actuate an audio or transmitter switch. A decrease in the noise signal due to the presence of a proper radio frequency signal will decrease the pulse rate, increase the control voltage and actuate the switches allowing the audio signal to pass through the audio stages of the receiver and activating an associated transmitter.

Claims

1. A squelch circuit responsive to detected noise and modulation signals from a receiver discriminator for actuating a switch which responds to a control signal of a predetermined amplitude, and wherein said detected noise signals extend in a frequency range above said modulation signals, said squelch circuit including in combination, first circuit means coupled to said discriminator and adapted to receive the detected noise and modulation signals and responsive to said signals to develop pulses in response thereto having a predetermined constant duration, the number of said pulses varying in accordance with the frequency of said noise and modulation signals coupled thereto, detector means coupled to said first circuit means and responsive to said pulses to develop a control signal having a an amplitude which varies with the repetition rate of said pulses, and means couplinG said detector to the switch and applying thereto said control signal to actuate said switch when said control signal exceeds said predetermined amplitude.

2. The squelch circuit of claim 1 wherein said first circuit means includes, input means for receiving the detected noise and modulation signals, second circuit means coupled to said input means and responsive to said signals to develop first pulses therefrom, said second circuit means being operative to produce a number of first pulses varying in accordance with the frequency of said noise and modulation signals coupled thereto, a multivibrator means coupled to said second circuit means and responsive to each of said first pulses to develop a second pulse having a predetermined duration.

3. The squelch circuit of claim 1 wherein said first circuit includes, input means for receiving the detected noise and modulation signals, amplifier limiter means coupled to said input means and responsive to the detected noise and modulation signals to amplify and limit said detected noise and modulation signals, switch means coupled to said amplifier limiter means and responsive to said amplified and limited signals to switch from a first to a second state, differentiation means coupled to said switch means and responsive to said changes in state to produce pulses of short time duration, and second circuit means coupled to said differentiation means and responsive to each pulse to produce a pulse having a predetermined duration.

4. The squelch circuit of claim 3 wherein said second circuit means is a monostable multivibrator.

5. The squelch circuit of claim 4 wherein said detector means includes, semiconductor means coupled to said monostable multivibrator, and capacitor means coupled to said semiconductor means, said semiconductor means being operative in response to said constant duration pulses to control the signal developed across said capacitor means to provide said control signal.

6. The squelch circuit of claim 1 wherein said detect of means includes, semiconductor means coupled to said first circuit means, capacitor means coupled in said semiconductor means, said semiconductor means being operative in response to said constant period pulses to control the signal developed across said capacitor means to provide said control signal.