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US3633112A
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US
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Digital audio squelch
Assignee: Collins Radio Co
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Filing: 1970-09-28
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Granted: 1972-01-04
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Expires: 1990-09-28
Abstract
Abstract A digital squelch circuit taking the received audio signal and generating a digital train of pulses representing zero crossing characteristics of the received signal with, for example, if the signal is greater than zero, a logic level one being generated and if it is less than zero, a logic level zero being generated. The processed signal is then repeatedly sampled for predetermined time intervals via a counter (or a charging sample and hold circuit) to determine the time measured apparent zero crossing frequency. The time measured apparent frequency is then used repeatedly to gate and ungate the squelch.
Inventors
- 👤 Dean T Anderson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 01:49
CPC Classifications
H; H03; H03G; H03G3/00; H03G3/20; H03G3/30; H03G3/34; H03G3/342
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
190 words
In a digital audio squelch system: audio signal source connective input means; audio circuit path means extended from said input means for connection to audio signal utilizing equipment; a squelch action controlled switch in said audio circuit path input means; signal-processing means connected to said audio signal input means of the type-sensing signal zero crossing in a received signal and generating a digital train of pulses as an output; gating means connected to receive said digital train of pulses output from said signal processing means; timing means including a clock signal source and having a signal connection to said gating means; signal pulse count responsive means controlled by said timing means for repeated uniform short interval count cycles; upper frequency limit responsive means, and lower frequency limit responsive means with both connected to said signal pulse count responsive means; gating logic means connected to the outputs of both said upper and lower frequency limit responsive means; short interval decision timing signal means connected as an enable input to said gating logic means; and an unsquelch circuit controlling said switch connected to receive activating trigger outputs of said gating logic means.
Claim 2
Dependent Claim
190 words
In a digital audio squelch system: audio signal source connective input means; audio circuit path means extended from said input means for connection to audio signal utilizing equipment; a squelch action controlled switch in said audio circuit path input means; signal-processing means connected to said audio signal input means of the type-sensing signal zero crossing in a received signal and generating a digital train of pulses as an output; gating means connected to receive said digital train of pulses output from said signal processing means; timing means including a clock signal source and having a signal connection to said gating means; signal pulse count responsive means controlled by said timing means for repeated uniform short interval count cycles; upper frequency limit responsive means, and lower frequency limit responsive means with both connected to said signal pulse count responsive means; gating logic means connected to the outputs of both said upper and lower frequency limit responsive means; short interval decision timing signal means connected as an enable input to said gating logic means; and an unsquelch circuit controlling said switch connected to receive activating trigger outputs of said gating logic means.
Claim 3
Dependent Claim
30 words
The digital audio squelch system of claim 1, wherein said timing means also includes reset time signal generating means connected to cycle-terminating means for the repeated short interval count cycles.
Claim 4
Dependent Claim
20 words
The digital audio squelch system of claim 2, wherein said signal pulse count responsive means is a binary counter circuit.
Claim 5
Dependent Claim
20 words
The digital audio squelch system of claim 3, wherein said binary counter circuit includes a series connected chain of flip-flops.
Claim 6
Dependent Claim
28 words
The digital audio squelch system of claim 4, wherein said reset time signal generating means is connected to reset terminals of individual flip-flops of said chain of flip-flops.
Claim 7
Dependent Claim
22 words
The digital audio squelch system of claim 2, wherein said signal pulse count responsive means is a charging sample and hold circuit.
Claim 8
Dependent Claim
41 words
The digital audio squelch system of claim 6, wherein said charging sample and hold circuit includes a charging capacitor that charges to higher and higher voltage levels with each signal pulse applied to the capacitor through each signal pulse count cycle.
Claim 9
Dependent Claim
27 words
The digital audio squelch system of claim 7, wherein said cycle-terminating means includes a transistor completing a circuit discharge path for the capacitor when fired to conduction.
Claim 10
Dependent Claim
27 words
The digitaL audio squelch system of claim 2 wherein said unsquelch circuit controlling said switch includes a signal-activating device; and a time interval activated state hold device.
Claim 11
Dependent Claim
41 words
The digital audio squelch system of claim 9, wherein said time interval activated state hold device is a capacitor; and said signal-activating device is a solid state device connected for completing a discharge path about said capacitor when trigger signal activated.
References Cited (Backward Citations)
US3437937A
Cited
US3564419A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-01-03 | 1975-07-05 | 1976-01-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-01-03 | 1979-07-05 | 1980-01-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-01-03 | 1983-07-05 | 1984-01-04 | $7700.00 | Window Closed / Lapsed |