Consumer Electronics

DEMODULATING THE (L–R) SIGNAL

The carrier with which the sidebands are combined at the receiver must have the desired 38 kHz frequency within very close limits and remain synchronised to prevent distortion when these sidebands are demodulated. The desired synchronisation is provided by the 19 kHz pilot carrier added to the modulation signal. This steady 19 kHz unmodulated signal is demodulated from the main carrier at the receiver and passed through a frequency doubler, whose output at 38 kHz is combined with the (L–R) signal. The output from the double R may be used directly for combining with the sideband, or as in some designs, this output can be used to synchronise a 38 kHz oscillator whose output is in turn used to combine with the sidebands. ...