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Interference cancellation system having noise reduction features and method

  • US 5,117,505 A
  • Filed: 02/22/1990
  • Issued: 05/26/1992
  • Est. Priority Date: 02/22/1990
  • Status: Expired due to Term
First Claim
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1. An interference cancellation system for connection to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line electrically coupling the receiver antenna to the receiver, the interference cancellation system comprising:

  • an auxiliary antenna for receiving an interfering signal, the auxiliary antenna providing a reference signal corresponding to the interfering signal received by the auxiliary antenna;

    a first directional coupler, the reference signal being provided to the first directional coupler, the first directional coupler having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

    a second directional coupler, the second directional coupler being electrically coupled to the receiver transmission line, the second directional coupler having an output and providing thereon a sample signal corresponding to an interfering signal and desired signal received by the receiver antenna;

    a third directional coupler, the third directional coupler being electrically coupled to the first directional coupler and having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

    a first detector, the first detector being electrically coupled to the third directional coupler and providing a first detected output signal in response to the first output signal of the third directional coupler;

    a synchronous detector, the synchronous detector having at least two inputs respectively electrically coupled to the third and second directional couplers and being responsive to the second output signal of the third coupler and the sample signal of the second coupler, the synchronous detector comparing the third coupler second output signal and the sample signal and providing at least one synchronous detector output signal in response thereto;

    a signal controller, the signal controller having a first input electrically coupled to the first directional coupler and being responsive to the first output signal of the first coupler, and at least a second input electrically coupled to the synchronous detector, the signal controller having an output and providing thereon a cancellation signal in response to the synchronous detector output signal;

    a subtractor, the subtractor being electrically coupled to the receiver transmission line and being further electrically coupled to the signal controller, the subtractor having an input on which is provided the cancellation signal, the subtractor effectively injecting the cancellation signal onto the receiver transmission line carrying the received interfering and desired signals, the cancellation signal injected into the receiver transmission line being equal in amplitude and opposite in phase to the interfering signal received by the receiver antenna and carried by the receiver transmission line so as to cancel the interfering signal on the receiver line;

    a comparator, the comparator being provided with the first detected output signal of the first detector and with a predetermined threshold signal, the comparator comparing the first detected output signal and the predetermined threshold signal and providing an output signal in response thereto; and

    switch means for coupling and decoupling at least a portion of the interference cancellation system from the radio receiver system, the switch means being electrically coupled to the comparator and being responsive to the output signal therefrom, the switch means including a first switch circuit, the first switch circuit being electrically coupled to the signal controller and to the subtractor and providing an electrical path between the signal controller and the subtractor in response to the output signal from the comparator.

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