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Patent US3626294A successfully refreshed from Google Patents.
US3626294A
Expired / Lapsed
US
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Carrier-plus-noise to noise-operated am squelch circuit
Assignee: GTE Sylvania Inc
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Filing: 1970-07-13
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Granted: 1971-12-07
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Expires: 1990-07-13
Abstract
Abstract In an AM radio receiver including a mixer, IF amplifier, detector and audio output section, a squelch circuit which operates on the basis of a synchronously averaged carrier-plusnoise to noise ratio sensing of the received signal. The squelch circuit comprises a signal amplitude limiter and a discriminator for processing the IF output signal to derive noise power inversely related to received carrier power. An amplitude modulator is provided at the input, output or bias source of the discriminator for synchronously modulating the derived noise power in response to the demodulated signal output of the detector. This modulated noise power is then processed through a noise filter, a dual time constant rectifier and a threshold sensor for providing a gate control signal for muting the audio output in response to excessive noise.
Inventors
- 👤 Charles H Dancy
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 23:26
CPC Classifications
H; H03; H03G; H03G3/00; H03G3/20; H03G3/30; H03G3/34; H03G3/344
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
141 words
In a radio receiver for receiving an amplitude modulated carrier signal and having a detector for demodulating said received signal and means for reproducing an audio signal from the demodulated signal output of said detector, a squelch circuit comprising, in combination, means for processing said received amplitude modulated carrier signal to derive noise power inversely related to received carrier power, means for synchronously modulating said derived noise power in response to the demodulated signal output of said detector, means for filtering said modulated derived noise power to pass noise power in a selected range of frequencies above the modulating frequencies of said received signal, means for rectifying said filtered noise power to provide a direct current signal of representative amplitude, and means controlled by said direct current signal for muting said audio signal reproducing means in the preseNce of excessive noise.
Claim 2
Dependent Claim
141 words
In a radio receiver for receiving an amplitude modulated carrier signal and having a detector for demodulating said received signal and means for reproducing an audio signal from the demodulated signal output of said detector, a squelch circuit comprising, in combination, means for processing said received amplitude modulated carrier signal to derive noise power inversely related to received carrier power, means for synchronously modulating said derived noise power in response to the demodulated signal output of said detector, means for filtering said modulated derived noise power to pass noise power in a selected range of frequencies above the modulating frequencies of said received signal, means for rectifying said filtered noise power to provide a direct current signal of representative amplitude, and means controlled by said direct current signal for muting said audio signal reproducing means in the preseNce of excessive noise.
Claim 3
Dependent Claim
45 words
The combination of claim 1 wherein said means for processing the received signal to derive noise power comprises a signal amplitude limiter, means coupling said received amplitude modulated carrier signal to said limiter, and a discriminator circuit coupled between said limiter and said filtering means.
Claim 4
Dependent Claim
44 words
The combination of claim 2 wherein said modulating means comprises an amplitude modulator having a first input connected to the output of said limiter, a second input coupled to the output of said detector, and an output connected to the input of said discriminator.
Claim 5
Dependent Claim
30 words
The combination of claim 3 wherein said modulating means further includes a low pass filter coupled between the output of said detector and the second input of said amplitude modulator.
Claim 6
Dependent Claim
79 words
The combination of claim 2 wherein said discriminator circuit has a source of bias voltage, and said modulating means comprises a low pass filter having an input connected to the output of said detector, and means connecting the output of said low pass filter to said source of bias voltage in a manner operative to amplitude modulate the bias voltage for said discriminator in response to the signal output of said detector as coupled via said low pass filter.
Claim 7
Dependent Claim
42 words
The combination of claim 2 wherein said modulating means comprises an amplitude modulator having a first input connected to the output of said discriminator, a second input coupled to the output of said detector, and an output connected to said filtering means.
Claim 8
Dependent Claim
30 words
The combination of claim 6 wherein said modulating means further includes a low pass filter coupled between the output of said detector and the second input of said amplitude modulator.
Claim 9
Dependent Claim
35 words
The combination of claim 1 wherein said muting means comprises a gate connected between said detector and said audio signal reproducing means and having a control terminal coupled to the output of said rectifying means.
Claim 10
Dependent Claim
59 words
The combination of claim 8 wherein said muting means further includes threshold sensing means coupled between the output of said rectifying means and the control terminal of said gate, whereby said threshold sensing means is operative to actuate said gate in response to a direct current signal from said rectifying means having an amplitude exceeding a preselected threshold level.
Claim 11
Dependent Claim
25 words
The combination of claim 1 wherein said rectifying means includes a filter network having a short charging time constant and a long discharge time constant.
Claim 12
Dependent Claim
18 words
The combination of claim 10 further including an amplifier connected between said filtering means and said rectifying means.
Claim 13
Dependent Claim
34 words
The combination of claim 10 wherein said filtering means is operative to pass noise power in a frequency range having a minimum approximately an octave above the highest modulating frequency expected for said receiver.
References Cited (Backward Citations)
US2468030A
Cited
US3056087A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-12-06 | 1975-06-07 | 1975-12-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-12-06 | 1979-06-07 | 1979-12-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-12-06 | 1983-06-07 | 1983-12-07 | $7700.00 | Window Closed / Lapsed |