Diversity receiver for FM stereo utilizing a pilot tone multiple for phase alignment of received signals

A multiple antenna FM stereo receiving system comprising:

• a plurality N of antennas for receiving respective RF signals having a common frequency but potentially different phases, where N is a whole number greater than 1,
• an FM receiver having a detector output and a pilot output on which a pilot tone is present,
• means for summing said signals and inputting the summed signals into said receiver,
• frequency generating means for deriving N-1 perturbation frequency signals from the pilot tone, the perturbation frequency signals each having a perturbation frequency that is a different whole number multiple greater than 1 of the frequency of the pilot tone,
• N - 1 amplitude modulator means coupled to the frequency generating means for receiving respective perturbation frequency signals and connected respectively between N - 1 of said antennas and said summing means for amplitude modulating the N - 1 RF signals on said N - 1 antennas at respective perturbation frequencies with the respective perturbation frequency signals provided by the frequency generating means,
• said FM receiver producing N -1 phase signals on the phase detector output having frequencies equal respectively to said perturbation frequencies and magnitudes corresponding to the respective phase errors between the RF signals on said N - 1 antennas and the RF signal on said antenna not associated with an amplitude modulator means, and
• N - 1 controllable phase shifter means connected respectively between said N - 1 antennas and said summing means and responsive to respective said N - 1 phase signals for shifting the phase errors between said N - 1 RF signals and the RF signal not associated with an amplitude modulator means.

In an FM stereo receiving system having a plurality N of antennas receiving respective N RF signals of a common frequency but potentially different phases, where N is a whole number greater than 1, and an FM receiver operating at a pilot tone of a given frequency, a method of aligning the phases of all of said RF signals comprising;

• deriving N-1 modulation frequency signals from the pilot tone, each modulation frequency signal having a different modulation frequency that is a positive whole number multiple greater than 1 of the pilot frequency,
• amplitude modulating N - 1 of the RF signals at respective N - 1 different modulating frequencies with the respective N-1 different modulation frequency signals,
• summing the modulated signals and the one non-modulated signal and inputting the summed signals into the FM receiver,
• generating N - 1 phase signals having frequencies equal respectively to the perturbation frequencies and magnitudes corresponding to the respective phase errors between the N - 1 RF signals and the one unmodulated RF signal, and
• shifting the phases of the N - 1 RF signals by amounts corresponding to the magnitudes of the respective phase signals to thereby eliminate the phase errors between all of said RF signals.

An FM stereo receiving system comprising:

• two antennas for receiving respective RF signals having a common frequency but potentially different phases,
• an FM receiver having a detector output and a pilot output on which a pilot tone is present, the pilot tone having a frequency of substantially 19 kHZ,
• means for summing said signals and inputting the summed signals into said receiver,
• an amplitude modulator means connected between one of said antennas and said summing means for amplitude modulating the RF signal carried by said one antenna at a perturbation frequency that is a whole number multiple of the pilot tone frequency, the whole number being greater than 1 and less than 4,
• said FM receiver producing on the detector output a phase signal having a frequency equal to the perturbation frequency and a magnitude corresponding to the phase error between the RF signals, and
• a controllable phase shifter means connected between said one antenna and said summing means and responsive to the phase detector output signal for shifting the phase of the signal received by said one antenna by an amount sufficient to eliminate the phase error between the two RF signals.