How to filter S-video from a DVD player for best picture on vintage color TV

[wa2ise]

This is a fairly simple circuit to build a video prefilter filtering S video to feed to an RF TV modulator. To drive an older or vintage color TV set. Most such color TVs use simple notch filters to separate the chroma and luma signals contained in the video. Which can result in high frequency luma being misrouted to the chroma (color difference) demodulator. Which results in color crawlies on a referee's shirt in a football game. This high frequency luma never gets seen as image detail on these TV sets, so we can throw it away and never miss it.
But if it is removed, we'll get less junk color crawlies. Can't do much to fix this on broadcast or cable stations, but we can prefilter the DVD's S-video output before it becomes composite video. We just filter out the luma info that resides near the chroma subcarrier frequency (3.58 for NTSC, 4.43 PAL) on the luma signal on the S video output jack. I also did some video peaking of the luma at 2MHz to make it look sharper without bringing up the 3.58 frequencies. The chroma signal of the S video jack has a 3.58MHz passband filter before it is added to the filtered luma.

To show the performance improvement, I took screen shots of a notch filter TV showing a "zone plate" test pattern. The improvement can be seen by seeing greatly reduced color fringes on the shot on the right compared to the center shot.

I built this filter inside a DVD player, and also placed inside the DVD player an old TV channel modulator salvaged from a dead VCR. I kept the connecting wires short (like 10cm) so impedance mismatch issues are of little concern. For the audio just merge L and R thru 10K resistors, and feed that to the audio input of the modulator. Adjust the video level feeding the modulator (by adding and adjusting a video termination resistor going from the output of this filter to ground, not shown in diagram) so you don't get buzz on the audio when there is peak white in the video.