Intermodulation controller for radio receiver

Claim 1

An intermodulation detector for a radio broadcast receiver comprising: filter means for receiving radio broadcast signals and for filtering said radio broadcast signals to derive a lower adjacent channel passband signal, a desired channel signal, and an upper adjacent channel passband signal, said upper and lower adjacent channel passbands being substantially symmetrical about said desired channel; level detecting means coupled to said filter means for level detecting said filtered signals to produce a lower channel level and an upper channel level; and comparing means for comparing said lower channel level and said upper channel level to determine whether said lower channel level and said upper channel level are substantially equal and are above a predetermined level.

Claim 11

A method for detecting intermodulation distortion in a radio receiver comprising the steps of: receiving transmitted radio-frequency (RF) signals; filtering said radio broadcast signals to derive a lower channel signal, a desired channel signal, and an upper channel signal using upper and lower passbands substantially symmetrical about a desired channel passband; level detecting said filtered signals to produce a lower channel level, a desired channel level, and an upper channel level; and detecting the occurrence of intermodulation distortion when said lower channel level and said upper channel level are substantially equal and are above a predetermined level.

Claim 12

A method for detecting intermodulation distortion in a radio receiver comprising the steps of: receiving transmitted radio-frequency (RF) signals; filtering said radio broadcast signals to derive a lower channel signal, a desired channel signal, and an upper channel signal using upper and lower passbands substantially symmetrical about a desired channel passband; level detecting said filtered signals to produce a lower channel level, a desired channel level, and an upper channel level; and detecting the occurrence of intermodulation distortion when said lower channel level and said upper channel level are substantially equal and are above a predetermined level.

Claim 14

A method for reducing intermodulation distortion in a receiver for receiving transmitted radio-frequency (RF) signals including a desired signal, said method comprising the steps of: filtering said RF signals in a tuned RF filter having a variable RF passband; mixing said filtered RF signals to produce intermediate-frequency (IF) signals; tri-band filtering said IF signals to derive a lower channel signal, a desired channel signal, and an upper channel signal; level detecting said tri-band filtered IF signals to produce a lower channel level, a desired channel level, and an upper channel level; tuning said variable RF passband such that said desired signal is centered in said variable RF passband; shifting the frequency range of said variable RF passband in a first direction while said desired channel level is above a predetermined level and while said lower channel level and said upper channel level are substantially equal but decreasing, and stopping said shifting when either said desired channel level falls below said predetermined level, said lower channel level and said upper channel level are no longer substantially equal, or said lower channel level and said upper channel level fall below a threshold; if said intermodulation distortion is not reduced while shifting in said first direction, then recentering said variable RF passband with said desired signal and repeating said shifting step but shifting said variable RF passband in a second direction opposite said first direction.

Claim 15

A method for reducing intermodulation distortion in a receiver for receiving transmitted radio-frequency (RF) signals including a desired signal, said method comprising the steps of: filtering said RF signals in a tuned RF filter having a variable RF passband; mixing said filtered RF signals to produce intermediate-frequency (IF) signals; tri-band filtering said IF signals to derive a lower channel signal, a desired channel signal, and an upper channel signal; level detecting said tri-band filtered IF signals to produce a lower channel level, a desired channel level, and an upper channel level; tuning said variable RF passband such that said desired signal is centered in said variable RF passband; shifting the frequency range of said variable RF passband in a first direction while said desired channel level is above a predetermined level and while said lower channel level and said upper channel level are substantially equal but decreasing, and stopping said shifting when either said desired channel level falls below said predetermined level, said lower channel level and said upper channel level are no longer substantially equal, or said lower channel level and said upper channel level fall below a threshold; if said intermodulation distortion is not reduced while shifting in said first direction, then recentering said variable RF passband with said desired signal and repeating said shifting step but shifting said variable RF passband in a second direction opposite said first direction.

Claim 16

A method for detecting intermodulation distortion in an FM radio receiver comprising the steps of: receiving transmitted radio-frequency signals; mixing said radio-frequency signals to produce an intermediate frequency (IF) signal with a center frequency f D ; filtering said IF signal in a desired passband filter with a center frequency f D and a bandwidth of about 150 kHz to produce a desired channel signal; filtering said IF signal in a lower passband filter having a passband lower than the passband of said desired passband filter and having a bandwidth between about 5 and 20 kHz to produce a lower passband signal; filtering said IF signal in an upper passband filter with a passband higher than the passband of said desired passband filter and having a bandwidth between about 5 and 20 kHz to produce an upper passband signal; level detecting said lower and upper passband signals to produce a lower passband level and an upper passband level, respectively; and detecting the occurrence of intermodulation distortion when said lower passband level and said upper passband level are substantially equal and are above a predetermined level.

Claim 17

A method for detecting intermodulation distortion in an FM radio receiver comprising the steps of: receiving transmitted radio-frequency signals; mixing said radio-frequency signals to produce an intermediate frequency (IF) signal with a center frequency f D ; filtering said IF signal in a desired passband filter with a center frequency f D and a bandwidth of about 150 kHz to produce a desired channel signal; filtering said IF signal in a lower passband filter having a passband lower than the passband of said desired passband filter and having a bandwidth between about 5 and 20 kHz to produce a lower passband signal; filtering said IF signal in an upper passband filter with a passband higher than the passband of said desired passband filter and having a bandwidth between about 5 and 20 kHz to produce an upper passband signal; level detecting said lower and upper passband signals to produce a lower passband level and an upper passband level, respectively; and detecting the occurrence of intermodulation distortion when said lower passband level and said upper passband level are substantially equal and are above a predetermined level.