Balancing arrangement for min. cross=talk in stereo decoder - synchronises phase of local oscillator using pilot tone filtered from auxiliary carrier of stereo multiplex signal

摘要

From the input stereo multiplex signal (MPX) a 19 kHz pilot tone is extracted (2) and phase-shifted (8) for comparison (3) with outptut of the local oscillator (4) and two-stage frequency divider (5, 6). In one possible phase comparison control scheme a calibration signal is switched (13, 14) simultaneously to inputs of the pilot filter (2) and local oscillator (4). Alternatively a stereo multiplex calibration signal may be injected into the input, and crosstalk attentuation balanced to max., or mid-band filter frequency balanced to local min. USE/ADVANTAGE - Esp. for high precision stero measuring decoder. Channels are balanced automatically by phase setting of pilot tone filter branch.