US3904969A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Audio periodicity squelch system
Assignee: Motorola Solutions Inc
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Filing: 1974-03-07
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Granted: 1975-09-09
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Expires: 1994-03-07
Abstract
Abstract Squelch circuit responsive to the periodicity of a voice signal for controlling the output of a radio receiver to provide transmission of speech and reject noise. The audio signal from the receiver is amplitude limited and the transitions in the limited wave control a bistable multivibrator having first and second out-of-phase outputs. The outputs are used to activate circuits which produce voltage samples proportional to the time period between zero crossings, with the alternate periods producing voltages across two capacitors. The difference between the successive voltage samples is derived and compared with a reference voltage to provide a control voltage. The control voltage, which is produced as long as the difference between the samples is less than the reference, is applied to a gate circuit which controls the charging of a squelch control capacitor. A control voltage which continues through a plurality of samples causes the voltage across the squelch control capacitor to raise to a level which operates a squelch switch to allow transmission of the audio signal.
Inventors
- 👤 Bruce C Eastmond
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 04:56
CPC Classifications
H; H03; H03G; H03G3/00; H03G3/20; H03G3/30; H03G3/34; H03G3/342
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
232 words
A squelch system for controlling the passage of audio signals including periodic signals received in the presence of noise, which system responds to the periodicity of the signals, including in combination: pulse producing means for receiving an audio signal having first and second outputs providing pulses of opposite polarities, said pulses extending between zero crossings of the audio signal, first and second capacitor means for storing voltages thereon, first control means coupled to said first and second outputs of said pulse producing means and to said first capacitor means for charging said first capacitor means to a voltage which depends upon the duration of each pulse of one polarity at said first output, second control means coupled to said first and second outputs of said pulse producing means and to said second capacitor means for charging said second capacitor means to a voltage which depends upon the duration of each pulse of said one polarity at said second output, comparator means coupled to said first and second capacitor means and responsive to the voltage stored thereon for producing an output signal when the difference between the voltages on said first and second capacitor means is less than a given value; and control circuit means including a squelch switch connected to receive the output signal from said comparator means and said audio signal to control the transmission of audio signals in response thereto.
Claim 2
Dependent Claim
232 words
A squelch system for controlling the passage of audio signals including periodic signals received in the presence of noise, which system responds to the periodicity of the signals, including in combination: pulse producing means for receiving an audio signal having first and second outputs providing pulses of opposite polarities, said pulses extending between zero crossings of the audio signal, first and second capacitor means for storing voltages thereon, first control means coupled to said first and second outputs of said pulse producing means and to said first capacitor means for charging said first capacitor means to a voltage which depends upon the duration of each pulse of one polarity at said first output, second control means coupled to said first and second outputs of said pulse producing means and to said second capacitor means for charging said second capacitor means to a voltage which depends upon the duration of each pulse of said one polarity at said second output, comparator means coupled to said first and second capacitor means and responsive to the voltage stored thereon for producing an output signal when the difference between the voltages on said first and second capacitor means is less than a given value; and control circuit means including a squelch switch connected to receive the output signal from said comparator means and said audio signal to control the transmission of audio signals in response thereto.
Claim 3
Dependent Claim
65 words
A squelch system in accordance with claim 1 wherein said pulse producing means includes limiter means for limiting the amplitude of the audio signal, and bistable multivibrator means coupled to said limiter means and triggered by the output thereof each time such output makes a transition from one output to the other, said multivibrator having first and second outputs providing said pulses of opposite polarities.
Claim 4
Dependent Claim
128 words
A squelch system in accordance with claim 1 wherein said first control means includes a third capacitor means, first switch means coupled to said first output and to said third capacitor means for discharging said capacitor at the beginning of each pulse of said one polarity at said first output, second switch means coupled to said first output and to said third capacitor means for charging said first capacitor at a substantially constant rate for the duration of said pulse of said one polarity, and third switch means coupled to said second output and coupling said third capacitor means to said third capacitor means during said pulse of said one polarity at said second output for transferring the voltage on said first capacitor to said third capacitor means.
Claim 5
Dependent Claim
73 words
A squelch system in accordance with claim 1 wherein said comparator means includes combining means connected to said first and second capacitor means for producing a resultant voltage corresponding to the difference between the voltages stored on said first and second capacitor means, and means coupled to said combining means and responsive to a reference voltage for producing a control voltage when said resultant voltage has a value less than said reference voltage.
Claim 6
Dependent Claim
108 words
A squelch system in accordance with claim 4 wherein said control circuit means includes a control capacitor, means for charging said control capacitor including switch means for controlling the time said control capacitor is charged, gate means coupled to said switch means and to said comparator means for rendering said switch means operative to charge said control capacitor in response to said control voltage, and further comparator means coupled to said control capacitor and responsive to a further reference voltage for producing a squelch control voltage when the voltage across said control capacitor exceeds said further reference voltage and supplying said squelch control voltage to said squelch swtich.
Claim 7
Dependent Claim
103 words
A squelch system in accordance with claim 5 wherein said switch means includes first and second switches, said first switch being connected across said control capacitor to discharge the same and said second switch being connected to apply current to said control capacitor to charge the same, and wherein said gate means includes first and second gates with said first gate being coupled to said first switch for operating the same to discharge said control capacitor in the absence of said control voltage, and said second gate being coupled to said second switch for operating the same in response to said control voltagE.
Claim 8
Dependent Claim
55 words
A squelch system in accordance with claim 6 wherein said pulse producing means includes limiter means for limiting the audio signal, and means coupling said limiter means to said first and second gates for enabling said gates each time the output of said limiter means makes a transition from one polarity to the opposite polarity.
Claim 9
Dependent Claim
42 words
A squelch system in accordance with claim 7 further including a monostable multivibrator coupled to said second gate for operating said second switch, said monostable multivibrator rendering said second switch operative for a predetermined time period each time said second gate operates.
Claim 10
Dependent Claim
37 words
A squelch system in accordance with claim 5 wherein said control circuit means further includes circuitry coupling said further comparator means to said squelch switch for operating said squelch switch in response to said squelch control voltage.
Claim 11
Dependent Claim
23 words
A squelch system in accordance with claim 9 wherein said circuitry includes timer means for controlling the time said squelch switch is operated.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-09-08 | 1979-03-10 | 1979-09-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-09-08 | 1983-03-10 | 1983-09-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-09-08 | 1987-03-10 | 1987-09-09 | $7700.00 | Window Closed / Lapsed |