Automatic fine tuning circuit using capacitance diodes

Claim 1

IN A PIECE OF COMMUNICATION EQUIPMENT HAVING RESONANT CIRCUIT MEANS INCORPORATING CAPACITANCE DIODE MEANS OF THE TYPE WHOSE CAPACITANCE CAN BE VARIED BY THE APPLICATION OF A BIAS VOLTAGE, THE CAPACITANCE CHARACTERISTIC OF SAID DIODE MEANS BEING NON-LINEAR AND THEREFORE HAVING DIFFERENT SLOPES AT VARIOUS POINTS ALONG ITS LENGTH, THE PIECE OF COMMUNICATION EQUIPMENT FURTHER HAVING A FREQUENCY CONTROL CIRCUIT FROM WHICH IS DERIVED A CONTROL VOLTAGE FOR AUTOMATICALLY FINE TUNING SAID DIODE MEANS, A TUNING CIRCUIT FOR VARYING THE CAPACITANCE OF SAID DIODE MEANS AND HENCE THE OPERATING FREQUENCY OF THE PIECE OF COMMUNICATION EQUIPMENT, SAID TUNING CIRCUIT COMPRISING: A VOLTAGE DIVIDER HAVING A TAP CONNECTED TO SAID DIODE MEANS; MEANS FOR PASSING A STABILIZING D.C. THROUGH SAID VOLTAGE DIVIDER; AND MEANS FOR DERIVING A CONTROL D.C. FROM SAID FREQUENCY CONTROL CIRCUIT AND PASSING THE SAME THROUGH SAID VOLTAGE DIVIDER; SAID VOLTAGE DIVIDER, UNDER THE INFLUENCE OF SAID STABILIZING D.C. AND SAID CONTROL D.C., BEING A MEANS FOR DELIVERING AT ITS TAP AND THEREFORE FOR APPLYING TO SAID DIODE MEANS ONLY A SMALL PORTION OF SAID CONTROL VOLTAGE WHEN SAID DIODE MEANS IS BIASED TO OPERATE AT A POINT WHEREAT ITS CAPACITANCE CHARACTERISTIC HAS A STEEP SLOPE AND A LARGE PORTION OF SAID CONTROL VOLTAGE WHEN SAID DIODE MEANS IS BIASED TO OPERATE AT A POINT WHEREAT ITS CAPACITANCE CHARACTERISTIC HAS A SMALL SLOPE, IN CONSEQUENCE OF WHICH THE EFFECT OF THE CONTROL VOLTAGE ON THE CAPACITANCE OF SAID DIODE MEANS, AND HENCE ON THE FREQUENCY OF THE RESONANT CIRCUIT MEANS OF WHICH SAID DIODE MEANS ARE A PART, REMAINS SUBSTANTIALLY CONSTANT THROUGHOUT THE FREQUENCY BAND OVER WHICH THE PIECE OF COMMUNICATION EQUIPMENT IS TUNED BY THE VARYING OF THE CAPACITANCE OF SAID DIODE MEANS.