Adaptive heterodyne filters (AHF) for detection and attenuation of narrow band signals

A fixed filter may be converted into an adaptive filter with a single adaptation parameter through the use of a new adaptive heterodyne filter (AHF) concept in which the frequency of the heterodyne signal is adjusted thereby translating the entire filter transfer function in frequency. If the fixed filter is selected to be a very narrow-band band-pass filter, the new AHF concept can be used very effectively in the elimination of narrow band interference in wide-band communications or control systems. A specific example of the removal of a slow-moving time-varying mechanical resonance from the control signal for a flight control system demonstrates the power of the new AHF concept