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Old 08-12-2012, 02:42 AM
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ChrisW6ATV ChrisW6ATV is offline
Another CT-100 lives!
 
Join Date: Feb 2007
Location: Hayward, Cal. USA
Posts: 3,464
Jeff, Bryan mentioned that he was at a house where they were subscribing to the service; that is how/why they could hear the audio.

Apparently many cities had similar services around the same time period (roughly 1979 to 1985). In Chicago, it was on channel 44 and called OnTV (plus their later partner Sportsvision on channel 60). A competitor, Spectravision, was on channel 66 with a different scrambling scheme.

In that time period, I, umm, did some "bad behavior". In fact, for a while I had the circuit to decode the OnTV audio (swear words and all!) memorized down to every component. It used an LM565 PLL chip, a transistor, and a few other capacitors and resistors to decode the audio from a 31 kHz or 60 kHz subcarrier. You had to tap the TV's audio detector before any de-emphasis components eliminated the subcarrier from the baseband audio. A cheap-and-dirty but useable way of decoding the video was to put a J.W. Miller 6333 coil in series with the video detector and tune it to eliminate the 15.75 kHz sine wave that scrambled the video. A DPDT switch completed the modification to the TV (to select normal or scrambled).
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Quote from another forum: "(Antique TV collecting) always seemed to me to be a fringe hobby that only weirdos did."
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