US4489431A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Signal interference protection circuit for AM stereo receiver
Assignee: Motorola Solutions Inc
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Filing: 1982-06-08
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Granted: 1984-12-18
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Expires: 2002-06-08
Abstract
Abstract In the field of AM stereo detection, co-channel or adjacent channel interference may cause some distortion and side-to-side movement of a stereo signal source as well as false "stereo detect" signals in AM stereo receivers having phase locked loop (PLL) systems. The invention provides a filter receiving the incoming signal and passing only the frequencies resulting from said interference; a sensor measures the output of the filters and if this signal is above a given level, the monophonic mode is enabled, i.e., the pilot detector, the stereo presence indicator and the stereo mode switch are disenabled for a timed interval. A higher given level of interference is required for stereo disenablement when stereo transmission with pilot tone is already being received.
Inventors
- 👤 Lawrence M. Ecklund
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 20:08
CPC Classifications
H; H04; H04H; H04H20/00; H04H20/44; H04H20/46; H04H20/47; H04H20/49
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
153 words
A protection circuit for an AM stereo receiver having input means for receiving a signal which may contain a predetermined infrasonic tone and which may also contain interfering signals; the protection circuit comprising: filter means coupled to the input means and having a pass band for passing only the range of possible frequencies of said interfering signals; level sensing means coupled to the filter means output for providing an output signal in response to filtered signals having at least a predetermined amplitude; detector means coupled to the input means for detecting the presence of said predetermined infrasonic tone and controlling at least one portion of said receiver in response thereto; first control means coupled to the detector means input for resetting the detector means; and timing control means coupled to the level sensing means output and to the detector means input for cooperating in the control of the at least one receiver portion.
Claim 2
Dependent Claim
153 words
A protection circuit for an AM stereo receiver having input means for receiving a signal which may contain a predetermined infrasonic tone and which may also contain interfering signals; the protection circuit comprising: filter means coupled to the input means and having a pass band for passing only the range of possible frequencies of said interfering signals; level sensing means coupled to the filter means output for providing an output signal in response to filtered signals having at least a predetermined amplitude; detector means coupled to the input means for detecting the presence of said predetermined infrasonic tone and controlling at least one portion of said receiver in response thereto; first control means coupled to the detector means input for resetting the detector means; and timing control means coupled to the level sensing means output and to the detector means input for cooperating in the control of the at least one receiver portion.
Claim 3
Dependent Claim
35 words
A protection circuit for an AM stereo receiver in accordance with claim 1 and wherein the interfering signals are the result of an unwanted broadcasting station at essentially the same frequency as the desired station.
Claim 4
Dependent Claim
38 words
A protection circuit for an AM stereo receiver in accordance with claim 1 and wherein the interfering signals are the result of an unwanted broadcasting station on a broadcast channel adjacent to the channel of the desired station.
Claim 5
Dependent Claim
28 words
A protection circuit for an AM stereo receiver in accordance with claim 1 and wherein the at least one portion of the receiver is a stereo tone indicator.
Claim 6
Dependent Claim
29 words
A protection circuit for an AM stereo receiver in accordance with claim 1 and wherein the at least one portion of the receiver is a stereo/mono mode control circuit.
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) | 1987-12-18 | 1988-06-18 | 1988-12-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-12-18 | 1992-06-18 | 1992-12-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-12-18 | 1996-06-18 | 1996-12-18 | $7700.00 | Window Closed / Lapsed |