Signal separation networks

Abstract

A bridged-T network is provided which functions as both a trap circuit for the intercarrier sound signal in the video signal path, and a take-off network for the sound processing circuitry in a television receiver. A bandpass filter, tuned to the intercarrier sound signal frequency, has an input, and an output coupled to the input of the sound processing circuitry. A detector is provided for producing detected video frequency and intercarrier sound signals. First and second signal paths are coupled between the output of the detector and the input of video processing circuitry, the second signal path including a first reactive impedance element of one sign. A third signal path is coupled between the second signal path and the input of the bandpass filter and includes a second reactive impedance element of an opposite sign. A fourth signal path is coupled between the junction of the third signal path and the input of the bandpass filter and a point of reference potential, and has an impedance which is significantly less than the impedance of the third signal path at the intercarrier sound signal frequency. The four signal paths comprise a tuned circuit which attenuates the intercarrier sound signal at the input of the video processing circuitry. The combined sound trap and take-off network is tuned by varying a single adjustable inductor in the shunt leg of the network.