Cw interference canceller (cwic)

Claim 2

In an AFC loop tracking system in the presence of interference signals, the combination comprising: a. input terminal means, b. mixer circuit means coupled to said input terminal means producing output doppler signal, c. filter circuit means coupled to said mixer circuit means for passing signals within a predetermined frequency range, d. a switch having a first position for coupling the output of said filter circuit means to an output terminal and to the feedback loop controlling said mixer circuit means and having a second position, e. interference signal detecting circuit means coupled to said filter circuit means and being responsive to the presence of a false target doppler signal to switch said switch to said second position and to generate a near replica of the true target doppler signal.

Claim 3

The system of claim 1 wherein said interference signal detecting circuit means comprises: a. envelope detector means coupled to said filter circuit means for producing an output signal proportional to the envelope of signal received from said filter circuit means, b. highpass filter means for filtering the dc from the output of said envelope detector means, c. hard limiter means coupled to said filter circuit means for removing the amplitude modulation from the signal passed by said filter circuit means, d. a first balanced modulator coupled to said highpass filter and to said hard limiter for producing an output signal that is a product of the two input signals, e. a second balanced modulator having a first input coupled to said highpass filter through a wideband 90° phase shifter and a second input coupled to said hard limiter through a 90° phase-shifter for producing an output signal that is a product of its two inputs, f. combining network means coupled to said first and second balanced modulators for producing an output signal which is the near replica of the target doppler signal.