Receivers of stereophonic programs from a single multiplex transmitting station

Claim 1

IN A CIRCUIT FOR RECEIVING A SIGNAL WHICH MAY BE EITHER STEREOPHONIC OR MONOPHONIC, WHERE THE STEREOPHONIC SIGNAL IS DERIVED FROM A TRANSMITTED COMPOSITE OF A CONTROL FREQUENCY AND A HIGH FREQUENCY MODULATED BY SIGNALS FROM A PAIR OF DISTINCTLY DIFFERENT AUDIO SOURCES, AND WHERE THE MONOPHONIC SIGNAL CONTAINS ERRANT HISS AND NOISE FREQUENCIES, THE CONTROL FREQUENCY BEING A PART OF THE TRANSMITTED COMPOSITE ONLY WHEN THE COMPOSITE IS A STEREOPHONIC SIGNAL, FM CIRCUIT MEANS FOR SEPARATING AN AUDIO FREQUENCY FROM THE RECEIVED MODULATED HIGH FREQUENCY, THE FM CIRCUIT MEANS BEING OPERATIVE TO PRODUCE AN AUDIO FREQUENCY FROM THE RECEIVED HIGH FREQUENCY WHETHER THE RECEIVED HIGH FREQUENCY IS STEREOPHONIC OR MONOPHONIC, MEANS FOR SEPARATING THE TRANSMITTED CONTROL FREQUENCY, IF PRESENT, FROM THE HIGH FREQUENCY OF THE RECEIVED SIGNAL, MEANS FOR UTILIZING THE CONTROL FREQUENCY AFTER SEPARATION FROM THE HIGH FREQUENCY TO PRODUCE SEPARATE AND DISTINCT AUDIO SIGNALS FROM THE SEPARATED AUDIO FREQUENCY IN ACCORDANCE WITH THE DISTINCT MODULATION OF THE HIGH FREQUENCY BY THE SEPARATE AUDIO SOURCES, MEANS ENERGIZED ONLY BY THE CONTROL FREQUENCY WHEN THE CONTROL FREQUENCY IS PRESENT IN THE TRANSMITTED COMPOSITE FOR DISCLOSING THAT THE RECEIVED SIGNAL IS A STEREOPHONIC SIGNAL, AND MEANS FOR UTILIZING A PORTION OF THE ERRANT FREQUENCIES TO BLOCK THE CONTROL FREQUENCY SEPARATING MEANS TO PREVENT ACTUATION OF THE SIGNAL DISCLOSING MEANS BY THE ERRANT FREQUENCIES.