Notch filter for digital transmission system

In a receiver for receiving an information signal including digital information samples which are contaminated with an interference component having known frequency characteristics, a filter is provided having a signal generator responsive to at least a portion of the received signal for generating an output signal having the frequency characteristics of the interference component and an amplitude and phase controlled by the portion of the received signal. A combiner combines the generator output signal with the received signal for generating a filtered output signal having the interference component substantially removed therefrom, which is then applied to an interpolator. In response to the identification of incorrect digital information samples in the received signal, control of the generator by that portion of the received digital information signal which contains the samples identified as incorrect is disabled. In this manner the generator "free-runs" during the receipt of incorrect samples, thereby allowing it to continue to provide samples representative of the known characteristics of the interference component until correct samples are again received.