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Originally Posted by Chip Chester
(Hopefully you have a line-select scope.)
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Sorry, I'm using a basic old (1980s) analog scope. I don't understand everything in that captioning article, but I did notice that caption coding may be different for HD. On our cable system, channels below 100 are all non-HD and some low channels have their HD versions 100 channels higher (for instance, channel 5 non-HD is repeated as channel 105 HD). I had hoped that I could avoid this problem by always selecting the HD channels, but unfortunately, if the interference is present on the non-HD channel, it's also present on the HD (channel+100) version. I still don't understand why the coding is totally absent on the higher channels (about 150 and above), which includes all of the premium content and both HD and non-HD programming.
Quote:
Originally Posted by old_tv_nut
The regularity of variation and going to greater than 100 IRE definitely mean it's a deliberate copy protection. Not accidental, no doubt whatsoever. The same techniques as used for stabilization of other sources will work, but the timing has to be modified to eliminate the pulses on these particular scan lines.
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Whether it's copy protection or caption encoding, I'm getting the idea that I can't fix the problem by phoning the cable company (i.e., the signal is intentionally present, not some malfunction or glitch on their side).
Retroactively adding blanking circuits to all of my restored TVs (a couple of dozen) ain't gonna happen, particularly considering that the rudimentary circuit I added to my Philco 49-1240 did not help with this interference.
My video stabilizer is a cheap item, bought several years ago from a company that no longer exists. No chance of getting a schematic for it, and I don't have the skills or equipment to dive in and hotrod this sort of thing bareback. Here is a peek at the board for those who are curious.
Possibly there is some other stabilizer or signal cleaner out there that could eliminate the interference. The question is how to find it?
Phil Nelson