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Analogdigit, that's funny about the sound-I remember that is all my dad liked about that format. He was convinced the sound quality was much better than VHS. Some selections (about one in every twenty I find) are in stereo. One of the few affordable ways to have stereo video in the early 80s. Stereo programs come in blue caddies, while mono were issued in white.
Arkay, How does it work? Well, CED magic explains it pretty well, but I could try: With an audio record, the needle run through the groove, and variations in the edge wall wiggle the needle, piezoelectrically generating your audio signal. The CED disc has a straight groove. The grooves are much smaller as the needle only keeps track of the video program and that is all. At the bottom of the groove are dash-shaped etchings. This is the video/sound info. The measure of capacitance between these tiny etchings and the needle create a resonant frequency within the player that can be decoded into a picture. The disc is enclosed in a big plastic sleeve, so you never see the actual disc. You stick the whole mess into your player and it spits the plastic shell back out into your hand.
The needle is carried along on a linear tracking arm, a heavy gantry-crane looking unit. A motor provides coarse tracking, bumping forward about every two minutes. The needle itself does the fine tracking, slowly bending inward as it tracks the groove. A pair of coils on either side of the needle measure this bend, and when it gets extreme enough, the coarse motor kicks in and moves the arm down the line a bit more. A potentiometer turns in time with the movement of the arm, which registers on the counter on the face of the machine.
I own the SJT-90, the basic RCA machine. From what I've read, this machine has all of the features of the SJT-100, but those extra buttons are blocked off, punishing those cheap folks that went with the '90.
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