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Originally Posted by wa2ise
We do have "closed caption" which is similar to teletext. That is, a bit stream in the vertical interval. Also, some channels do have data transmissions (stolen credit card numbers and such) using teletext methods in the vertical interval. All these can create trash in the picture if the set doesn't suppress the vertical interval well.
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I have seen these data retrace lines on screenshots of vintage tv sets here in the Audiokarma forum too, when the photos in the threads still were available. But I did not know that these data lines were used for other purposes.
Here I have some more screenshots with teletext retrace lines and with teletext retrace lines suppressed.
With teletext retrace lines:
http://bs.cyty.com/menschen/e-etzold...7_ohneUVB1.JPG
http://bs.cyty.com/menschen/e-etzold...47_ohneUVB.JPG
And with teletext retrace lines suppressed:
http://bs.cyty.com/menschen/e-etzold.../MC47_UVB3.JPG
http://bs.cyty.com/menschen/e-etzold...g/MC47_UVB.JPG
http://bs.cyty.com/menschen/e-etzold.../MC47_UVB2.JPG
The UVB board for suppressing retrace lines is easy to assemble. Ask Darius (oldeurope) for kits, he sells them for a small amount of money. I am happy that I need not to change the vintage circuits for getting no retrace lines. If you have questions please ask us.