Quote:
Originally Posted by Alastair E
I have a case of --something--like this at the moment.
I have an old Bush 405 line set Ive modded to run at the UK's 625 line, and feeding video compo direct into the video-amp stages, via a small gain stage.
--I should point out--the set is a 14" Bush TV62 monochrome set and from 1955-7 vintage, when 405 line and VHF was the only show in town.
Ive potched about with the video amp to remove an overshoot issue--that has also extended its bandwidth probably to over 4 meg according to test-card images
Our chroma sub-carrier is 4.433MHz here....
The effects I get using a Composite Video signal are the herringbone-patterning on parts of the picture of high colour content, but also have an odd vertical strip approx 1/3 picture width that can only be noticed on dark/low contrast scenes, and can be shifted sidewise by use of line-osc setting. It looks exactly like a honeycomb or 'eye pattern' a CD player laser if scoped shows...
Switching the compo video from a PAL 4.43 signal to NTSC 3.38 has the effect of changing the pitch/coarseness of the herringbone and the honeycomb Surprisingly, the set is just as happy to run at 525 line as 625 line, although its not so keen on 60Hz frame-rate, and has somewhat reduced height, and hum on picture becomes an issue. 405 line UK VHF transmissions were frame-frequency locked to 50Hz mains freq so maybe are not as tolerant of hum issues as later 625 line sets ...
Most odd! Really need to try the set out via an S-Video source of just the Luma signal, see if I can banish that darned honeycomb. The herringbone I can live with...
Sure the colour-burst is doing summit odd when it gets in there....
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What is your audio carrier frequency? Someone here pointed out earlier that if you have too much bandwidth (which may be the case if you've modded yours) you can also get that to bleed into the picture - and the result was a herringbone pattern.