eyewitness info birth of cable tv

[ChrisW6ATV]

Originally Posted by DavGoodlin

IIRC, there was a 15 khz sinewave added to the video, synchronized to invert the sync pulse as Mr Squirrel says.
Also thanks for the missing piece of this puzzle by pointing out this early application of MTS, jogging my memory.
In order to de-scramble, you had to "extract" this pulse from the sound subcarrier, invert it and add it back to the video.
The decoder box looked very homebrew IIRC

Ah yes, sinewave scrambling. You filtered out the 15.734 kHz sinewave from the video itself, inverted it, and combined it with the original video to get a watchable picture. The sound was on a 15 kHz subcarrier on the audio channel, but I don't think you needed that subcarrier for the video (well, you did not with OnTV descramblers, anyway, if I remember right). An LM565 chip and a few other components demodulated the sound for you.