Abstract: In an amplifier, which amplifies high-frequency communication signals, there develops odd-order intermodulation products which, because of the identical frequency spacing of the channels, fall into directly adjacent useful channels. In order to keep these intermodulation products below an admissible level, the input of the main amplifier is preceded by an attenuator of adjustable attenuation. The output of the main amplifier is connected to the input of an auxiliary amplifier which has a broader pass band than the main amplifier and amplifies also second-order intermodulation products. The auxiliary amplifier is followed by a low-pass filter which allows those intermodulation products to pass but shuts off other frequency ranges. The second-order intermodulation products which were allowed to pass are rectified in a detector and are amplified in a control circuit the output of which determines the attenuation of the attenuator.