Cochannel FM interference suppression using adaptive notch filters

In this paper, a method of reducing cochannel FM interference with adaptive tracking notch filters, first proposed by E. Baghdady (1959), is refined and extended. Analytical descriptions and computer simulations of a novel adaptive notch filter are presented. The new form of adaptive notch filter is useful for suppressing strong cochannel FM and CW signals and allows simple, practical realizations of very high and adaptive notch filters in either analog or digital technologies. The analysis demonstrates that when the instantaneous frequency of the stronger interfering FM carrier signal is known precisely, the stronger signal can be completely eliminated. In some cases, placing an additional adaptive notch filter in front of the stronger signal demodulator to suppress the weaker desired cochannel signal improves the estimate of the stronger signal. >