Ford Motor Company Limited

Robert D Plowdrey

John F Kennedy

Sylvester P Porambo

A frequency modulation (FM) stereo broadcast receiver detects the onset of multipath interference based on phase changes in the received stereo pilot signal. In a preferred embodiment, the phase of the received pilot signal is compared to the phase of a regenerated pilot from a phase-locked loop in a stereo decoder circuit. The severity of a multipath event is determined by the phase shift detected at the onset of the multipath event.

Multipath detector using phase comparison of stereo pilot signal

A frequency-shift keying (FSK) signal detector splits an FSK signal into two paths. In one path, a phase-altering circuit having a variable frequency characteristic between the two encoding frequencies of the FSK signal provides either a phase lead or a phase lag depending upon the instantaneous frequency of the FSK signal. The phase-altered signal is sampled in response to the signal in the second path to decode a digital signal.

High speed frequency-shift keying decoder

A variable frequency RF passband filter is aligned or calibrated to maximize the sensitivity of a radio receiver using reference frequencies obtained using a fixed frequency oscillator present in a different band tuning section of a multiband receiver. The intermediate frequencies of the various band sections of the multiband receiver are selected whereby a fixed frequency source in one band corresponds to an intermediate frequency employed in the band for which the tunable RF filter is being aligned.

RF filter self-alignment for multiband radio receiver

A frequency modulation (FM) stereo broadcast receiver detects the onset of multipath interference and initiates corrective action to minimize the audible effects of multipath. Under an unacceptable multipath interference condition, a multipath detection signal disables the FM RF mixer thereby preventing any further energy in the multipath event from entering succeeding sections of the receiver. This action reduces noise generated by multipath interference and allows the output to return to normal in a shorter time. In another aspect of the invention, a phase-locked loop employed in a stereo decoder circuit is latched during the multipath disturbance in order to avoid rapid changes in the phase of the regenerated pilot employed in the stereo decoder.

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Livonia, MI, United States of America

Robert D Plowdrey