Method of scrambling and descrambling a television signal, and descrambling apparatus therefor

摘要

1. Process for scrambling and descrambling a television signal including an image signal occupying a first frequency band about an image subcarrier (fi ) and a sound signal occupying a second frequency band about a sound subcarrier (fs ), these two frequency bands being separated, a process in which there is superimposed, on transmission, a scrambling signal (f1 , f2 , f3 ) on the television signal, the said scrambling signal occupying a third frequency band, separated from the first and second frequency bands, the said process being characterised in that, on the one hand, the relative difference between the frequency of the scrambling signal and the frequency of one of the two image or sound subcarriers (fi or fs ) is less than 5% and, on the other hand, the descrambling consists in isolating the scrambling signal from the scrambled television signal by filtering (14), in equalizing the amplitude and the phase (18, 22) of the scrambling signal and of the scrambled television signal, and in subtracting (26) the said scrambling signal from the said scrambled television signal.