Coding and receiving circuits for compatible stereophonic broadcast systems

Claim 1

IN A CIRCUIT ARRANGEMENT FOR RECEIVING COMPATIBLE BROADCAST MULTIPLEXED STEREOPHONIC SIGNALS, IN WHICH THE MAIN CARRIER IS MODULATED WITH (1) A SUM SIGNAL, (2) AN INTERMEDIATE CARRIER FREQUENCY ON WHICH THE LOW FREQUENCY DIFFERENCE SIGNAL IS AMPLITUDE MODULATED WITH CARRIER SUPPRESSION, AND (3) A PILOT FREQUENCY EQUAL TO HALF THE INTERMEDIATE CARRIER FREQUENCY, ALL OF WHICH COMPRISE THE WHOLE STEREOPHONIC SIGNAL, SAID CIRCUIT ARRANGEMENT COMPRISING, IN COMBINATION: (A) AN INPUT FOR PROVIDING THE WHOLE STEREOPHONIC SIGNAL; (B) FREQUENCY DOUBLING MEANS CONNECTED TO SAID INPUT FOR DERIVING FROM THE WHOLE STEREOPHONIC SIGNAL AN INTERMEDIATE CARRIER SIGNAL OF TWICE THE PILOT FREQUENCY AND IN PHASE THEREWITH; (C) AN ELECTRONIC SWITCH, INCLUDING (1) FIRST AND SECOND SWITCHING TRANSISTORS EACH HAVING INPUT, OUTPUT AND CONTROL TERMINALS, (2) CIRCUIT MEANS FOR FEEDING THE WHOLE STEREOPHONIC SIGNAL FROM THE INPUT TO THE INPUT TERMINALS OF EACH OF THE SWITCHING TRANSISTORS, AND (3) FURTHER CIRCUIT MEANS FEEDING THE OUTPUT OF THE FREQUENCY DOUBLING MEANS TO THE CONTROL TERMINALS OF THE SWITCHING TRANSISTOR FOR ALTERNATELY TURNING THE SWITCHING TRANSISTORS ON AND OFF, IN PHASE OPPOSITION TO EACH OTHER, AT A RATE EQUAL TO THE INTERMEDIATE CARRIER FREQUENCY; (D) LEFT AND RIGHT AUDIO OUTPUT CHANNELS CONNECTED TO RECEIVE SIGNALS RESPECTIVELY FROM THE FIRST AND SECOND SWITCHING TRANSISTOR OUTPUT TERMINALS; AND (E) MEANS CONNECTED TO THE INPUT FOR FEEDING A PORTION OF THE SUM SIGNAL TO EACH AUDIO OUTPUT CHANNEL TO EQUALIZE THE AMPLITUDE OF THE SUM AND DIFFERENCE SIGNALS.