Squelch circuits for stereophonic receivers

Claim 1

IN A RECEIVER FOR SINGLE CHANNEL COMPATIBLE STEREOPHONIC SIGNALS WHICH INCLUDES A REFERENCE OSCILLATOR AND A SOURCE OF A FIRST SIGNAL COMPRISING TWO PROGRAM SIGNALS MULTIPLEXED ON AN INTERMEDIATE FREQUENCY CARRIER WAVE, MEANS FOR GENERATING A SQUELCH SIGNAL COMPRISING SYNCHRONOUS DETECTOR MEANS RESPONSIVAE JOINTLY TO SAID FIRST SIGNAL AND THE OUTPUT SIGNAL OF SAID REFERENCE OSCILLATOR FOR PRODUCING A FIRST DETECTED SIGNAL INCLUDING SELECTED PROGRAM SIGNAL COMPONENTS, SECOND DETECTION MEANS RESPONSIVE TO SAID FIRST SIGNAL FOR PRODUCING A SECOND DETECTED SIGNAL INCLUDING PROGRAM SIGNAL COMPONENTS CORRESPONDING TO SAID SELECTED PROGRAM SIGNAL COMPONENTS OF SAID FIRST DETECTED SIGNAL, SIGNAL ADDER MEANS FOR COMBINING SAID FIRST DETECTED SIGNAL AND SAID SECOND DETECTED SIGNAL TO EFFECT MUTUAL CANCELLATION OF SUBSTANTIALLY ALL OF THE SIGNAL COMPONENTS OF SAID FIRST AND SECOND DETECTED SIGNALS WHICH ARE REPRESENTATIVE OF SAID TWO PROGRAM SIGNALS, AND SIGNAL AMPLITUDE DETECTOR MEANS FOR DETECTING THE RESIDUAL OUTPUT SIGNAL, IF ANY, OF SAID SIGNAL ADDER MEANS.