The idea of the Radio Plans decoder is that the video black level was a little bit higher than the start of the signal after the horizontal pulse signal. Becaus

The idea of the Radio Plans decoder is that the video black level was a little bit higher than the start of the signal after the horizontal pulse signal. Because of that, it was possible to detect if the delay was 0 1 or 2... Canal Plus reacted quickly by adding a little bit of noise to the signal after the horizontal pulse.