Method and device for modulating television signals, in particular of the D2-MAC/Packet type

摘要

Method of frequency modulation on the basis of a modulating video signal with time-division multiplexing of an analogue part and a digital part for each line, with transmission of the continuous component of the modulating signal, characterised in that: a) with each line, from the modulating signal are extracted a time window (COM) demarcating the digital part of the signal and a clamping window demarcating the clamping period provided with each line outside of line 625 of the frame blanking; b) the modulating signal is base band processed in order to clamp it during the said clamping window and carry out an energy spreading with predetermined period, and possibly a pre-emphasising of the signal; c) the processed signal is applied to the input of a voltage-control oscillator which provides the modulated signal on an output; d) a fraction of modulated signal is sampled for the duration of the time window (COM) and is subjected to discrimination and filtering to obtain an error signal from which automatic frequency control of the oscillator is carried out. The circuit is in particular usable to modulate a signal of the D2-MAC/PACKET type. <IMAGE>