Enhanced selectivity signal receiver

Abstract

In a reception system which includes a receiver having a plurality of inter-connected stages and a demodulator, and where there appears at an input of the receiver a desired signal which occupies substantially a predetermined bandwidth, and at least one undesired signal which occupies a bandwidth different from, though partially overlapping the predetermined bandwidth, the improvement includes a signal selector coupled to receiver terminals upstream of the receiver demodulator for normally continuously selecting one of the signals appearing across the receiver terminals, a gain-controlled feedback stage connected with one input thereof to an output of the signal selector for negatively feeding back to the receiver terminals one of the signals substantially 180.degree. out of phase with the spectrum characteristic of the undesired signal when the one of the signals is the undesired signal, a frequency-dependent selection device connected to the receiver terminals for selecting the undesired signal, so as to substantially isolate it from any other signals, and a comparator for comparing the output thereat of the undesired signal at least with a reference level, and for generating at least one error control signal, which feeds another input of the gain-controlled feedback device. The reference level is set so as to force any remnants of the undesired signal which still appears at the input of the demodulator of the receiver to assume, through the error control signal, a level below a level of the desired signal thereat, which differs from the level of the desired signal by at least such a level difference between the desired and undesired signals, which permits the demodulator to demodulate the desired signal at an acceptable signal-to-noise ratio, so that demodulation of the undesired signal is prevented.