Method for noise reduction in the reception of RF FM signals
First Claim
Patent Images
1. A method for noise reduction during FM reception comprising:
- attenuating a detected FM audiosignal having a momentary frequency and FM carrier frequency;
deriving a field strength indicative muting control signal from an IF signal;
controlling an attenuation of the audiosignal using the muting control signal, when the field strength decreases below a certain threshold level, wherein the mute control signal has a time constant which is increased with an increasing deviation of the momentary frequency of the received FM signal from the FM carrier frequency; and
detecting a baseband FM modulation signal, wherein the time constant in the mute control signal is controlled with a time constant control signal derived from rectifying the detected baseband FM modulation signal.
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Abstract
A method for noise reduction during FM reception and a receiver executing the method. A detected audiosignal is being attenuated. A field strength indicative muting control signal is derived from an IF signal which is used to control an attenuation of the audiosignal, when the field strength decreases below a certain threshold level. To prevent false mute responses from distorting the audiosignal, a time constant in the mute control signal is increased with an increasing deviation of the momentary frequency of the received FM signal from the FM carrier frequency and vice versa.
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Citations
8 Claims
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1. A method for noise reduction during FM reception comprising:
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attenuating a detected FM audiosignal having a momentary frequency and FM carrier frequency;
deriving a field strength indicative muting control signal from an IF signal;
controlling an attenuation of the audiosignal using the muting control signal, when the field strength decreases below a certain threshold level, wherein the mute control signal has a time constant which is increased with an increasing deviation of the momentary frequency of the received FM signal from the FM carrier frequency; and
detecting a baseband FM modulation signal, wherein the time constant in the mute control signal is controlled with a time constant control signal derived from rectifying the detected baseband FM modulation signal. - View Dependent Claims (2)
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3. A receiver for noise reduction during FM reception comprising:
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an RF front end coupled to a selective IF amplifier;
an FM detector which detects a baseband FM modulation signal having an audio signal;
a muting circuit which attenuates the audio signal, the muting circuit having a mute control terminal which supplies the mute control signal, the IF amplifier being coupled through an IF level detector and a lowpass filter to the mute control terminal of the muting circuit; and
a baseband FM modulation signal level detector being coupled between an output of the FM detector and a time constant control terminal of the lowpass filter which varies the time constant of the lowpass filter depending on the level of the baseband FM modulation signal. - View Dependent Claims (4, 5, 6)
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7. A method for noise reduction during FM reception comprising:
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attenuating a detected FM audiosignal having a momentary frequency and FM carrier frequency;
deriving a field strength indicative muting control signal from an IF signal;
controlling an attenuation of the audiosignal using the muting control signal, when the field strength decreases below a certain threshold level, wherein the mute control signal has a time constant which is increased with an increasing deviation of the momentary frequency of the received FM signal from the FM carrier frequency; and
detecting a baseband FM modulation signal, wherein the time constant in the mute control signal is controlled with a time constant control signal derived from rectifying the detected baseband FM modulation signal.
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8. A method for noise reduction during FM reception comprising:
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attenuating a detected FM audiosignal having a momentary frequency and FM carrier frequency;
deriving a field strength indicative muting control signal from an IF signal;
controlling an attenuation of the audiosignal using the muting control signal, when the field strength decreases below a certain threshold level, wherein the mute control signal has a time constant which is increased with an increasing deviation of the momentary frequency of the received FM signal from the FM carrier frequency; and
wherein the derivation of the time constant control signal from the audio signal is non-linearly amplified.
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Specification