Automatic Cancellation Method of Multipath Echo Distortion in FM Broadcasting Receivers

Abstract

An automatic canceling method of multipath echo distortion in FM broadcasting receiver is proposed. The cancelling system is composed of two additional parts to the conventional receiver: a programable transversal filter operating at linear IF stage and a microcomputer. The microcomputer calculates echo parameters (relative echo amplitudes, delay times and phase differences between direct wave and echoes at the carrier frequency), from the amplitude-frequency characteristics between sending station and IF stage of the receiver, which is obtained from both outputs of an IF signal envelope detector and FM demodulator. The microcomputer sends control signals to the weighting circuits of the transversal filter. The output signal of the transversal filter is fed back and added to the incoming signal. Tap weighting adjustment is continued until a flat amplitude-frequency characteristics is obtained. The results of computer simulation show this method works well for various echo conditions and the distortion can be completely eliminated.