Circuitry for multiplex transmission of fm stereo signals with pilot signal

Claim 1

A CIRCUIT FOR PRODUCING A COMPOSITE SIGNAL, COMPRISING TERMINALS FOR INPUT OF TWO SIGNALS, EACH OF SAID SIGNALS LYING IN A GIVEN FREQUENCY BAND AND RESPECTIVELY COMPRISING A SUM COMBINATION OF TWO AUDIO FREQUENCY SIGNALS AND A DIFFERENT COMBINATION OF SAID TWO AUDIO FREQUENCY SIGNALS, SAID TWO AUDIO FREQUENCY SIGNALS BEING STEREOPHONICALLY RELATED, MEANS FOR PRODUCING A CARRIER WAVE AT A FREQUENCY SUFFICIENTLY HIGH SO THAT WHEN AMPLITUDE MODULATED BY SAID DIFFERENCE COMBINATION OF SIGNALS THERE WILL BE A FREQUENCY GAP BETWEEN THE LOWER SIDEBAND OF THE MODULATED CARRIER WAVE AND THE BAND OF SAID SUM COMBINATION OF SIGNALS, SAID FREQUENCY GAP INCLUDING A FREQUENCY THAT IS ONE-HALF THAT OF SAID CARRIER WAVE, MEANS FOR AMPLITUDE MODULATING SAID CARRIER WAVE WITH SAID DIFFERENCE COMBINATION OF SIGNALS THEREBY PROVIDING SAID FREQUENCY GAP, MEANS FOR PRODUCING A PILOT SIGNAL AT A FREQUENCY EQUAL TO ONE-HALF THAT OF SAID CARRIER WAVE AND LYING IN SAID FREQUENCY GAP, SAID FREQUENCY OF THE PILOT SIGNAL BEING SPACED FROM SAID SIDEBAND AND SAID BAND OF THE SUM COMBINATION OF SIGNALS SO AS TO PERMIT THE PILOT SIGNAL TO BE SEPARATED FROM SIGNALS OF SAID SIDEBAND AND SAID BAND OF THE SUM COMBINATION OF SIGNALS BY FREQUENCY SELECTIVE MEANS IN A RECEIVER, MEANS FOR SUPPRESSING SAID CARRIER WAVE, AND MEANS FOR COMBINING SAID SUM COMBINATION OF SIGNALS, SAID PILOT SIGNAL, AND THE DIFFERENCE COMBINATION OF SIGNALS AS MODULATED ON THE SUPPRESSED CARRIER, TO PROVIDE THE AFORESAID COMPOSITE SIGNAL.