F. m. stereophonic receiver having noise prevention means in the pilot circuit

Claim 1

IN A RADIO RECEIVING SYSTEM FOR RECEIVING MONOPHONIC AND STEREOPHONIC SOUND, AND WHEREIN THE RECEIVED CARRIER WAVE FOR STEREOPHONIC RECEPTION IS FREQUENCY MODULATED BY A COMPOSITE SIGNAL INCLUDING A STEREO SUM SIGNAL, A SUPPRESSED CARRIER WAVE AMPLITUDE MODULATED BY A STEREO DIFFERENCE SIGNAL, AND A PILOT SIGNAL HAVING A FREQUENCY ONE HALF THAT OF THE SUPPRESSED CARRIER WAVE, AND WHEREIN NOISE HAVING COMPONENTS OF THE FREQUENCY OF THE PILOT SIGNAL MAY BE PRESENT IN THE ABSENCE OF THE COMPOSITE SIGNAL, THE COMBINATION INCLUDING, A FREQUENCY SELECTIVE SYSTEM FOR DERIVING THE PILOT SIGNAL FROM THE COMPOSITE WAVE, A FREQUENCY DOUBLER CIRCUIT RESPONSIVE TO THE PILOT SIGNAL FOR PRODUCING A WAVE HAVING TWICE THE FREQUENCY OF THE PILOT SIGNAL, SAID FREQUENCY BOUBLING CIRCUIT INCLUDING AN ELECTRON DEVICE BIASED TO BE NORMALLY NONCONDUCTING, RECTIFIER MEANS COUPLED TO SAID SELECTIVE SYSTEM AND RESPONSIVE TO THE PILOT SIGNAL FOR SELECTIVELY RENDERING SAID ELECTRON DEVICE CONDUCTING, SAID RECTIFIER MEANS INCLUDING A FIRST RECTIFIER ELEMENT AND LOAD MEANS ACROSS WHICH THE RECTIFIED PILOT SIGNAL AND NOISE COMPONENTS ARE DEVELOPED, A CAPACITOR, A SECOND RECTIFIER ELEMENT CONNECTING SAID CAPACITOR TO SAID LOAD MEANS FOR CHARGING SAID CAPACITOR THEREFROM, SAID SECOND RECTIFIER ELEMENT BEING CONSTRUCTED AND POLED TO HAVE A HIGH IMPEDANCE TO CURRENT FLOW FOR CHARGING SAID CAPACITOR FROM SAID LOAD MEANS TO THAT THE VOLTAGE ACROSS SAID CAPACITOR RISES SLOWLY TO APPROACH THE VOLTAGE ACROSS SAID LOAD MEANS, SAID SECOND RECTIFIER ELEMENT HAVING A LOW IMPEDANCE TO CURRENT FLOW FOR DISCHARGING SAID CAPACITOR SO THAT SAID CAPACITOR DISCHARGES RAPIDLY TO THE VOLTAGE ACROSS SAID LOAD, AND MEANS COUPLING SAID CAPACITOR TO SAID ELECTRON DEVICE FOR APPLYING THE VOLTAGE ACROSS SAID CAPACITOR THERETO TO CONTROL THE CONDUCTIVITY OF SAID ELECTRON DEVICE.