OVERLOAD COMPENSATION CIRCUIT FOR ANTENNA TUNING SYSTEM

• US 3,600,684 A
• Filed: 05/15/1969
• Issued: 08/17/1971
• Est. Priority Date: 05/15/1969
• Status: Expired due to Term

• Current Assignee: James R. Cherry
• Original Assignee: James R. Cherry
• Inventors: Cherry, James R.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US04/824,986
• Time in Patent Office: 824 Days
• Field of Search: 325/318,319,362,374,379,383,385,387,404,400,422,454,464,451 334/11,14,15 330/26,29
• US Class Current: 455/193.3
• CPC Class Codes: H03H 2/008 Receiver or amplifier input circuits

Abstract

As the RF signal supplied by an antenna to a varactor-tuned coupling circuit increases in magnitude, the impedance across an inductor in series with the varactor also increases due to the increased conductivity of an AGC-controlled field-effect transistor connected in the circuit of a secondary winding inductively coupled to the inductor. The system also is frequency sensitive, so that as the frequency of the RF signal applied across the inductor increases, the effective impedance also increases to compensate for increases of the reactance of the varactor diode at higher frequencies to maintain the RF signal level across the varactor diode at a level below that at which the diode rectifies the RF signals applied thereacross.

Claims

1. In a wave signal receiving apparatus having an antenna, an RF amplifier stage, and an antenna tuning circuit means electrically coupling the antenna and the RF amplifier stage, the tuning circuit means including voltage-variable reactance means and circuit means connected to the voltage-variable reactance means for applying a variable bias potential thereto to selectively tune the antenna tuning circuit means to a predetermined frequency, an overload compensation circuit for said voltagevariable reactance means including in combination:

frequency and voltage-variable impedance means exhibiting increased impedance with increasing frequencies of signals applied thereacross;

connecting means for connecting said voltage-variable reactance means of said antenna tuning circuit and said variable impedance means in series between said antenna and said RF amplifier stage;

control circuit means responsive to the output of said RF amplifier stage for deriving a control voltage corresponding to the magnitude of the wave signal; and

means for applying the control voltage to said variable impedance means further to vary the impedance thereof in response to variations in the magnitude of the signals obtained from the output of said RF amplifier stage.

2. The combination according to claim 1 further including means for applying the control voltage to said RF amplifier stage to vary the input impedance of said RF amplifier stage in response to variations in the magnitude of the signals obtained from the output of said RF amplifier stage.

3. The combination according to claim 1 wherein said tuning circuit means includes an inductance means connected in series with said voltage-variable reactance means and wherein said frequency-sensitive variable impedance means is formed by inductively coupling a variable impedance to said inductance means.

4. The combination according to claim 3 wherein said voltage-variable reactance means is a voltage-variable capacitor.

5. The combination according to claim 3 further including a winding inductively coupled to said inductance means, wherein said variable impedance includes a transistor having at least a control electrode and another electrode, with said other electrode connected in series with said winding and with the control voltage being applied to the control electrode thereof.

6. The combination according to claim 5 wherein said transistor is a field-effect transistor having a gate and a drain-source path, the drain-source path being connected in series with said winding, and the gate being connected with said means for applying the control voltage.

7. The combination according to claim 6 wherein said control circuit means is an automatic gain control circuit providing an automatic gain control voltage which said applying means applies to the gate of said transistor to increase the conductivity thereof for increased levels of outputs from said RF amplifier stage to reduce the impedance in series with said winding, thereby effectively increasing the impedance of said inductance means in series with said voltage-variable reactance to limit the voltage drop thereacross by causing an increased voltage drop to occur across said inductance means.