Video telephone extension system has series binary data - coded uses two positive and two negative half-waves representing two logical levels

摘要

The video telephone extension system has its binary signals coded so that the logical 'L' is represented by a half wave of period T consisting of two sequential positive, sinusoidal half waves each of period T/2 and the logical 'O' represented by a half wave also of period T but consisting of two sequential, negative, sinusoidal half waves each of period T/2. The coding process is reversed at the decoder. The waves are produced by a sinewave generator coupled over a square wave pulse shaping circuit and frequency divider to a parallel/series converter. The converter output data is passed to a control circuit synchronised to the generator and feeding gate which gates the generators output after the latter has been rectified.