an unwanted portion of a radio frequency signal spectrum appearing on a signal line is adaptively canceled by first sampling the unwanted portion of the spectrum , and thereafter filtering the sample , typically at an intermediate frequency , to reduce signal losses . the first sample is then processed to yield a cancellation signal , having a variable phase . the cancellation signal is then injected into the signal spectrum after which time , the spectrum is again sampled . the second sample is correlated with the cancellation signal and the resultant correlation is employed to adjust the phase of the cancellation signal to maximize the cancellation of the unwanted portion of the spectrum .