Amplifier with narrow band, IF filter - picks up harmonic heterodyne wave adjacent to required signal

The amplifier has an upper IF filter (6) which picks up the upper side of a heterodyne wave, adjacent a desired signal. The upper filter operates with mean frequency, offset by a preset frequency w.r.t. the upper side of the desired signal. A lower, narrow band IF filter (5) picks up a lower heterodyne wave, adjacent to the desired signal from the received signal. The lower filter has a mean frequency offset by a preset frequency to the desired signal lower side. The output signals of the IF filters are treated by rectifiers (9,10), whose output signals are processed by a differential amplifier (11). A further IF filter (12) displaces its mean frequency to those, at which less heterodyne waves appear. USE/ADVANTAGE - For FM radio and TV receivers. Reduced heterodyne waves for improved audio quality.