Monaural to stereo automatic switching system for an fm multiplex stereo radio receiver

Claim 1

A MONAURAL TO STEREO AUTOMATIC SWITCHING SYSTEM FOR AN FM MULTIPLEX STEREO RADIO RECEIVER HAVING A B+ POWER SOURCE WHEN ENERGIZED AND HAVING FIRST AND SECOND SIDE BAND DETECTOR DIODES CONNECTED IN OPPOSITE DIRECTIONS BETWEEN A STEREO CARRIER FREQUENCY INPUT JUNCTION AND LEFT AND RIGHT SIGNAL OUTPUT LINES RESPECTIVELY, COMPRISING: A HIGH RESISTANCE HAVING ONE END CONNECTED TO SAID B+ POWER SOURCE AND ITS OTHER END CONNECTED TO SAID DIODES TO PROVIDE A FORWARD BIAS ON SAID DIODES OF SUFFICIENT MAGNITUDE THAT THE SAME ELECTRICALLY APPEAR AS SUBSTANTIALLY SHORT CIRCUITS IN THE ABSENCE OF A STEREO CARRIER FREQUENCY AT SAID INPUT JUNCTION WHEREBY SAID DIODES ARE EFFECTIVELY NO LONGER PART OF THE FM MULTIPLEX STEREO DETECTOR CIRCUIT UNTIL SUCH TIME AS A STEREO CARRIER FREQUENCY SIGNAL APPEARS AT SAID JUNCTION, SAID CARRIER FREQUENCY SIGNAL OVERCOMING SAID FORWARD BIAS TO CAUSE SAID DIODES TO PERFORM THEIR DEMODULATING FUNCTION IN A NORMAL MANNER TO PROVIDE STEREO SIGNALS TO SAID LEFT AND RIGHT OUTPUT LINES; AND A RECTIFIER MEANS HAVING ITS INPUT CONNECTED TO RECEIVE SAID CARRIER FREQUENCY SIGNAL AND ITS OUTPUT CONNECTED TO SAID DIODES TO PROVIDE A D.C. REVERSE BIAS DERIVED FROM AND IN RESPONSE TO SAID CARRIER FREQUENCY SIGNAL ON SAID DIODES OF SUFFICIENT MAGNITUDE TO INSURE, IN COMBINATION WITH SAID CARRIER FREQUENCY SIGNAL AT SAID JUNCTION, POSITIVE CANCELLING OUT OF THE FORWARD BIAS ON SAID DIODES SO THAT SAID DIODES PERFORM THEIR DEMODULATING FUNCTION IN A NORMAL MANNER WHEN SAID CARRIER SIGNAL IS PRESENT EVEN IN FRINGE AREAS.