Dark vertical stripes between color bars?
 

Here's something I hadn't been curious about until I viewed things on an oscilloscope: dark vertical stripes between bands in NTSC color bars.

http://antiqueradio.org/art/RCACT-100July19Bars.jpg

In this scope pic, the lower trace shows the video output from my pattern generator. The top trace shows the messy signal at the input of my 1st video amplifier tube. Presumably the dark stripes are those "stalacites" dripping down between color bands, arising somewhere in the front end.

http://antiqueradio.org/art/RCACT-100VideoAmpInput.jpg

I hooked up a 1980s Panasonic and saw that it has stripes, too, although not so pronounced.

http://antiqueradio.org/art/RCACT-100PanasonicBars.jpg

I'm not going to lose sleep over the stripes if they can occur in an OK-looking 1984 TV. Just curious about what causes them.

Phil Nelson

These are two different phenomena. The dark edges in the 1984 set are the result of video processing to improve sharpness, and are deliberate.

The effects in the earlier set indicate some sort of problem, like improper fine tuning or IF misalignment, or maybe AGC adjustment. Note that the dark edges are combined with greatly increased chroma level, which would indicate the chroma transients are also being enhanced. I think this indicates the set is tuned too high in frequency (or the IF is tilted) putting the video carrier at too low an amplitude.

The stripes do change intensity or move from here to there as you change the fine tuning. I don't think there's any setting where they're totally absent and the picture's otherwise acceptable, though.

Phil

Do you have a DVD with an Indian head and/or a video sweep? Would be interesting to see what they look like.

My pattern generator has the usual crosshatch, cross, dots, etc. Nothing like the Indian head, although years ago I pointed a camcorder at a printout and got a caveman version that way. Not sure what a video sweep is.

Phil

video sweep - sine waves with frequency increasing left to right:
http://www.horita.com/sweep.htm

Hey! My pattern generator does that! Cool.

So, how do you imagine my old TV would display this pattern?

Phil

Test signal is called multi burst.

Phil

Your Sencore VA-62 has this pattern.

Phil,
On several occasions, I've seen "ringyness" in the video caused by the last IF tube. You might try subbing it just as a shot in the dark. Have you checked the IF tubes for shorts/gas? Bill(oc)

Strictly speaking, multiburst has groups (bursts) of vertical stripes, each burst having a particular constant frequency of stripes, while "sweep" changes frequency continuosly left to right - but they have similar use, testing the frequency response of the video.

I wasn't sure if an IF tube could cause this - thanks for the info.

Oh no, you said the name that must not be spoken in this house :)

I got disgusted with my VA62A and put it away quite a while ago. Last I remembered, it made colorless color bars on new and old TVs. I hauled it out today and it hasn't reformed. Plus, it makes a wicked, slowly rolling horizontal fold on my tube TVs.

http://antiqueradio.org/art/temp/VA62ABarsPanasonic.jpg

http://antiqueradio.org/art/temp/VA62ABarsCTC-11.jpg

The same CTC-11 shows OK color bars with no fold when I hook up my humble Leader pattern generator.

http://antiqueradio.org/art/temp/VA6...C-11Leader.jpg

VA62A makes the same rolling fold on the older TV.

http://antiqueradio.org/art/temp/VA6...atchCT-100.jpg

http://antiqueradio.org/art/temp/VA6...urstCT-100.jpg

It's a poor workman who blames the tool. Perhaps I'm doing something stupid with the VA62A, but I simply got tired of horsing around with it. Meanwhile, the Leader generator makes useful patterns without any fuss.

Phil

P.S. The final photo shows the pattern that VA62A calls "multiburst bar sweep."

looks like bad power supply ripple in that VA62A