A few years later I came across a "SelecTV" box (a competing over-the-air scrambled subscription TV service). Their box was more advanced. It had the same bas

A few years later I came across a "SelecTV" box (a competing over-the-air scrambled subscription TV service). Their box was more advanced. It had the same basic sine-wave/SCA scrambling, but they had added an additional scrambling feature that would periodically invert, or not invert the video. It also had a set of four hex thumbwheel encoders on the front panel. (Subscribers would be given their unique enable code each month after they had paid.) By this time I had my own oscilloscope and lots of computer components. I built a circuit that would decode the (22-bit) data stream (coded in the same place that now includes Closed Caption data), and fed a magnitude comparator circuit fed with 3-position toggle switches (one/zero/don't care). I could hone in on the needed enable code for the invert/normal video signal in just a few minutes. SelecTV stayed in business for a few years beyond after ON TV went bankrupt.