Multipath detector using phase comparison of stereo pilot signal

Claim 2

Apparatus for detecting multipath in a received radio signal comprising: stereo pilot means for isolating a stereo pilot signal from said received radio signal; phase-locked loop means coupled to said stereo pilot means for producing a regenerated pilot signal in quadrature with said stereo pilot signal; window means for determining first and second phase windows each having a duration fixed by transitions in said stereo pilot signal and said regenerated pilot signal; and multipath means for generating a multipath signal when one of said first or second phase windows has a duration outside a predetermined range of duration.

Claim 3

The apparatus of claim 1 wherein said multipath means generates said multipath signal if one of said first or second phase window durations is greater than a predetermined duration.

Claim 4

The apparatus of claim 2 wherein said multipath means comprises: first counting means for counting at a predetermined frequency during said first phase window to derive a first count; second counting means for counting at said predetermined frequency during said second-phase window to derive a second count; and comparison means for indicating whether either of said first or second counts is greater than a predetermined count.

Claim 5

The apparatus of claim 1 further comprising: phase intensity means for indicating a severity of a multipath event in proportion to the duration of the longer of said first and second phase windows.

Claim 6

A radio receiver with reduced multipath distortion comprising: RF mixer means for generating an intermediate frequency (IF) signal; switchable power means for selectably providing power to said RF mixer means; stereo pilot means for isolating a stereo pilot signal from said IF signal; phase-locked loop means coupled to said stereo pilot means for producing a regenerated pilot signal in quadrature with said stereo pilot signal; window means for determining first and second phase windows each having a duration fixed by transitions in said stereo pilot signal and said regenerated pilot signal; multipath means for generating a multipath signal when one of said first or second phase windows has a duration outside a predetermined range of duration; and control means for momentarily causing said switchable power means to remove power from said RF mixer means in response to said multipath signal.

Claim 7

A radio receiver with reduced multipath distortion comprising: RF mixer means for generating an intermediate frequency (IF) signal; switchable power means for selectably providing power to said RF mixer means; stereo pilot means for isolating a stereo pilot signal from said IF signal; phase-locked loop means coupled to said stereo pilot means for producing a regenerated pilot signal in quadrature with said stereo pilot signal; window means for determining first and second phase windows each having a duration fixed by transitions in said stereo pilot signal and said regenerated pilot signal; multipath means for generating a multipath signal when one of said first or second phase windows has a duration outside a predetermined range of duration; and control means for momentarily causing said switchable power means to remove power from said RF mixer means in response to said multipath signal.

Claim 8

The receiver of claim 5 further comprising phase intensity means for indicating a severity of a multipath event in proportion to the duration of the longer of said first and second phase windows, and wherein said control means removes power from said RF mixer means for a time period corresponding to said indicated severity.

Claim 9

A radio receiver with reduced multipath distortion comprising: RF mixer means for generating an intermediate frequency (IF) signal; stereo pilot means for isolating a stereo pilot signal from said IF signal; phase-locked loop means coupled to said stereo pilot means for producing a regenerated pilot signal in quadrature with said stereo pilot signal, said phase-locked loop means having a switchable time constant so that said phase-locked loop means is latched with a long time constant in response to a multipath signal; window means for determining first and second phase windows each having a duration fixed by transitions in said stereo pilot signal and said regenerated pilot signal; and multipath means for generating said multipath signal when one of said first or second phase windows has a duration outside a predetermined range of duration.

Claim 10

A radio receiver with reduced multipath distortion comprising: RF mixer means for generating an intermediate frequency (IF) signal; stereo pilot means for isolating a stereo pilot signal from said IF signal; phase-locked loop means coupled to said stereo pilot means for producing a regenerated pilot signal in quadrature with said stereo pilot signal, said phase-locked loop means having a switchable time constant so that said phase-locked loop means is latched with a long time constant in response to a multipath signal; window means for determining first and second phase windows each having a duration fixed by transitions in said stereo pilot signal and said regenerated pilot signal; and multipath means for generating said multipath signal when one of said first or second phase windows has a duration outside a predetermined range of duration.

Claim 11

The receiver of claim 7 further comprising phase intensity means for indicating the severity of a multipath event in proportion to the duration of the longer of said first and second phase windows, and wherein said multipath signal has a time period corresponding to said indicated severity.