Switched diversity method and apparatus for FM receivers
First Claim
1. In an FM diversity receiver system having at least two antennas, antenna switching means for switching the receiver system from one antenna to the other, sensing means for producing a fade control signal related to the amplitude of the received FM signal, multipath disturbances in the received signal such as frequency selective fading and non-multipath disturbances such as received electrical noise impulses, including ignition noise signals, being manifested in said fade control signal, decision and control means responsive to the fade control signal from said sensing means for producing an antenna switching signal for control of said switching means, the improvement wherein said decision and control means comprises,means for establishing a threshold voltage, andmeans for comparing the threshold voltage to the magnitude of disturbances manifested in the fade control signal and for momentarily disabling antenna switching operation for a time period when the disturbances manifested in the fade control signal initially exceeds the threshold voltage to prevent antenna switching in response to short duration disturbances produced by electrical noise impulses, including ignition noise signals.
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Abstract
An FM diversity receiver system and method are disclosed which include two antennas and a switch for switching the receiver from one antenna to the other. A fade control signal is produced which is related to the received FM signal, in which fade control signal both multipath and non-multipath disturbances are manifested. Disturbances in the fade control signal are compared with a threshold voltage and, when the disturbance exceeds the threshold voltage, antenna switching is momentarily prevented to prevent antenna switching in response to electrical noise impulses, such as ignition noise, which are shorter than the period during which antenna switching is momentarily prevented. If the fade control signal disturbance continues to exceed the threshold voltage after the momentary period of disablement, the threshold voltage is reset to a level related to the maximum level of the fade control signal disturbance, after which antenna switching takes place. Antenna switching then is again momentarily prevented; this time to prevent antenna switching in response to switching transients produced during the antenna switching operation.
64 Citations
37 Claims
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1. In an FM diversity receiver system having at least two antennas, antenna switching means for switching the receiver system from one antenna to the other, sensing means for producing a fade control signal related to the amplitude of the received FM signal, multipath disturbances in the received signal such as frequency selective fading and non-multipath disturbances such as received electrical noise impulses, including ignition noise signals, being manifested in said fade control signal, decision and control means responsive to the fade control signal from said sensing means for producing an antenna switching signal for control of said switching means, the improvement wherein said decision and control means comprises,
means for establishing a threshold voltage, and means for comparing the threshold voltage to the magnitude of disturbances manifested in the fade control signal and for momentarily disabling antenna switching operation for a time period when the disturbances manifested in the fade control signal initially exceeds the threshold voltage to prevent antenna switching in response to short duration disturbances produced by electrical noise impulses, including ignition noise signals.
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12. In an FM diversity receiver system having at least two antennas, antenna switching means for switching the receiver system from one antenna to the other, sensing means for producing a fade control signal related to the received FM signal, multipath disturbances, including frequency selective fading, in the received signal and non-multipath disturbances such as received electrical noise impulses, including ignition noise signals, being manifested in said fade control signal, and decision and control means responsive to the fade control signal from said sensing means for producing an antenna switching signal for control of said switching means, the improvement wherein said decision and control means comprises,
means for establishing a threshold voltage, means for comparing the threshold voltage, immediately prior to said antenna switching operation, to the disturbance level manifested in the fade control signal and for producing an antenna switching operation when the disturbance level exceeds the threshold voltage, means for resetting the threshold voltage to a level related to the disturbance level manifested in the fade control signal immediately prior to said antenna switching operation, the reset threshold voltage slowly returning toward the level provided by said means for establishing a threshold voltage, and means for momentarily disabling further antenna switching operation for a time period upon occurrence of an antenna switching operation without disturbing the reset threshold voltage to prevent antenna switching in response to switching transients produced during said antenna switching operation.
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15. In an FM diversity receiver system having at least two antennas, antenna switching means for switching the receiver system from one antenna to the other, sensing means for producing a fade control signal related to the received FM signal, multipath disturbances, including frequency selective fading, in the received signal and non-multipath disturbances such as received electrical noise impulses, including ignition noise signals, being manifested in said fade control signal, and decision and control means responsive to the fade control signal from said sensing means for producing an antenna switching signal for control of said switching means, the improvement wherein said decision and control means comprises,
means for establishing a threshold voltage, means for comparing the threshold voltage to the disturbance level manifested in the fade control signal and for producing an antenna switching operation when the disturbance level exceeds the threshold voltage, means for resetting the threshold voltage level, immediately prior to said antenna switching operation to a level established by the disturbance level manifested in the fade control signal immediately prior to said antenna switching operation whereby the fade control signal produced by said sensing means immediately following said antenna switching operation is compared to the reset threshold level established immediately prior to said antenna switching operation, the threshold voltage decreasing to a lower threshold level over a period of time following operation of said resetting means, and means for momentarily disabling further antenna switching operation for a time period upon occurrence of an antenna switching operation to prevent antenna switching in response to switching transients produced during said antenna switching operation.
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16. In an FM diversity receiver system having at least two antennas, antenna switching means for switching the receiver system from one antenna to the other, sensing means for producing a fade control signal related to the received FM signal, multipath disturbances, including frequency selective fading, in the received signal and non-multipath disturbances such as received electrical noise impulses, including ignition noise signals, being manifested in said fade control signal, and decision and control means responsive to the fade control signal from said sensing means for producing an antenna switching signal for control of said switching means, the improvement wherein said decision and control means comprises,
means for establishing a threshold voltage, means for comparing the threshold voltage to the disturbance level manifested in the fade control signal and for producing an antenna switching operation when the disturbance level exceeds the threshold voltage, means for momentarily disabling further antenna switching operation for a time period upon occurrence of an antenna switching operation to prevent antenna switching in response to switching transients produced during said antenna switching operation, said receiver system including means for producing meter and mute control signals, and said decision and control means including means for combining said meter and mute control signals to provide said fade control signal in the presence of a mute control signal from said receiver system.
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18. In an FM diversity receiver system having at least two antennas, antenna switching means for switching the receiver system from one antenna to the other, sensing means for producing a fade control signal related to the amplitude of the received FM signal, and decision and control means responsive to the fade control signal from said sensing means for producing an antenna switching signal for control of said switching means, the improvement wherein said decision and control means comprises,
means for establishing a threshold voltage, means for comparing the threshold voltage to the fade control signal and for producing an antenna switching operation when the fade control signal exceeds the threshold voltage, and means for resetting the threshold voltage level, immediately prior to said antenna switching operation, to a level established by the fade control signal immediately prior to said antenna switching operation whereby the fade control signal produced by the sensing means immediately following the antenna switching operation is compared with the reset threshold level established immediately prior to said antenna switching operation, the threshold voltage decreasing to a lower level over a period of time following operation of said resetting means.
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20. In an FM diversity receiver system having at least two antennas and antenna switching means for switching the receiver system from one antenna to another, the method comprising,
in response to a received signal, generating a fade control signal which is related to the received signal and in which both multipath disturbances, such as frequency selective fading disturbances, and non-multipath disturbances, such as electrical noise impulses and switching transients produced during antenna switching operation, are manifested, comparing the magnitude of disturbances manifested in the fade control signal with a threshold voltage and producing an antenna switching operation when the manifested disturbance magnitude exceeds the threshold voltage, and momentarily preventing switching from one antenna to another when the manifested disturbance magnitude initially exceeds the threshold voltage to prevent antenna switching is response to electrical noise impulses which terminate while antenna switching is momentarily prevented.
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25. In an FM diversity receiver system having at least two antennas and means for switching the receiver system from one antenna to another, the method comprising,
in response to a received signal, generating a fade control signal which is related to the received signal and in which fade control signal both multipath and non-multipath disturbances are manifested, including frequency selective fading, electrical noise impulses and switching transients produced during antenna switching operation, comparing the fade control signal with a threshold voltage and momentarily disabling antenna switching operation when the level of disturbances manifested in the fade control signal exceeds the threshold voltage, if the level of disturbances manifested in the fade control signal exceeds the threshold voltage level immediately after said momentary disablement of antenna switching operation, then resetting the threshold voltage to a level related to the level of disturbances manifested in the fade control signal, otherwise continuing operation without resetting the reference threshold voltage, said threshold voltage slowly returning to a nominal level after resetting thereof, and producing an antenna switching operation after resetting of the threshold voltage.
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27. In an FM diversity receiver system for processing transmitted FM signals comprising an FM receiver and at least two antennas,
antenna switching means for switching the receiver from one antenna to the other, means for generating a fade control signal in response to disturbances in the FM receiver signal which fade control signal manifests both multipath and non-multipath disturbances in the receiver signal, and decision and control means responsive to the output from the fade control signal generating means for controlling said antenna switching means, said decision and control means including time gating means responsive to fade control signals for gating out manifested disturbances of short time duration from the fade control signal to prevent operation of said antenna switching means in response to disturbances of short duration, such as electrical noise impulses produced by ignition noise, manifested in said fade control signal.
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31. In a method for switching between a plurality of antennas to select an antenna that has a satisfactory signal thereon, the steps of
sensing the received signal while the received signal has amplitude fluctuations as a result of multipath disturbances to obtain a fade control signal in which said amplitude fluctuations are manifested, establishing a threshold voltage, comparing the threshold voltage to the magnitude of disturbances manifested in the fade control signal, when the magnitude of disturbances manifested in the fade control signal exceeds the threshold voltage for a time period, then momentarily resetting the level of the threshold voltage to a value related to the magnitude of the disturbance manifested in the fade control signal, and switching to another antenna following said momentary resetting of the threshold voltage level.
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33. In a diversity receiver system having at least two antennas,
antenna switching means for switching the receiver system from one antenna to the other, sensing means for producing a fade control signal related to the amplitude of the received signal, multipath disturbances in the received signal being manifested in said control signal, means for establishing a first threshold voltage level, means responsive to the fade control signal and threshold voltage for rapidly resetting the first threshold voltage level to a level related to the fade control signal when the fade control signal exceeds the threshold voltage level, the reset threshold voltage remaining only momentarily at said reset level and then decaying slowly toward the first level provided by said means for establishing a first threshold voltage level, and means for activating said switching means after resetting of the first threshold voltage level by said threshold voltage level resetting means.
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36. In a diversity receiver system having at least two antennas,
antenna switching means for switching the receiver system from one antenna to another, sensing means for producing a fade control signal related to the amplitude of the received signal, multipath and non-multipath disturbances such as received electrical noise impulses including ignition noise signals being manifested in said fade control signal, means for establishing a threshold voltage, means responsive to the fade control signal and threshold voltage for momentarily disabling operation of said antenna switching means when the level of disturbances manifested in the fade control signal initially exceeds the threshold voltage, means operable after operation of said momentary disabling means for resetting the threshold voltage to an increased level related to the magnitude of the disturbances manifested in the fade control signal if the level of such disturbances immediately after operation of said momentary disabling means exceeds the threshold voltage level, said threshold voltage slowly returning toward a level established by said means for establishing a threshold voltage after resetting thereof, and means for actuating said antenna switching means immediately after resetting of the threshold voltage by said threshold voltage resetting means.
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37. In a diversity receiver system having at least two antennas,
antenna switching means for switching the receiver from one antenna to the other, means for producing meter and mute control signals, means for combining said meter and mute control signals to provide a fade control signal, means for establishing a threshold voltage, and means responsive to the threshold voltage and fade control signal for actuating the antenna switching means.
Specification