Coding and decoding circuits for TV diffusion network - requires magnetically coded key to operate decoder allowing separation and demodulation of received signals

摘要

The vision signal from a coder is applied to a separation and filtering circuit to separate out the three signal components. A frequency demodulator obtains the luminance signal on which a clamp circuit operates to align the signal with the black level. The output passes to a chopping circuit controlled from a logic unit at the input to reconstitute the luminance signal for a mixer stage. A balanced ring modulator uses a local oscillator to reform the lower sideband to obtain the chrominance signal via a low pass filter. This signal is applied to the mixer to produce the combined chrominance and luminance signal. The sound output is derived from a demodulator followed by a deaccentuation filter.