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.

Thanks for that, too kool.

Once broadcast goes digital will a similar circuit be possible? Obviously it would be quite a bit more complex, but I mean could it have a similar output?

Anthony

[wa2ise]

Thanks.

Once broadcast goes digital will a similar circuit be possible? Obviously it would be quite a bit more complex, but I mean could it have a similar output?

Most likely yes.

Digital TV systems all use 3 signals, luma (B&W) and two color difference signals (U and V, or Cr and Cb, or Pr and Pb). The luma gets sent thru a DAC chip to the "Y" pins of an S video connector. The U and V can be either sent thru a pair of DAC chips to feed "component" output jacks on the back of the DTV decoder/receiver, or converted/modulated onto a chroma subcarrier and then sent to the "Ch" pins of an S video connector, or then merged with the luma to make composite video (yellow core RCA connector). All DTV boxes will likely have S video avaliable, and there we can do the above filtering trick. If the DTV designers are smart, they could do this filtering internally (make it a selectable menu option).

Wasn't Zenith instrumental in developing the North American standards for HDTV?

Anthony

[Chad Hauris]

It almost seems like Zenith devolped an advanced definition TV system that was somehow actually better that the current HDTV, maybe it was compatible with regular analog TV or something, but it seems like the Zenith plan might have lost out in favor of another HDTV system which was then accepted as standard.

[wa2ise]

Back in the early days of HDTV development a number of analog based schemes were developed and proposed as a standard, but then someone figured out how to do digital video compression (MPEG) and then the FCC said that they wanted an all digital system for HDTV. I had actually worked on a 2 channel analog HD system, one channel the normal NTSC signal (for backwards compatability) and another channel with extra picture resolution, side panels and digital sound. It worked fairly well, but there would have been reception issues (differences of noise in one of the channels vs the other, likely one VHF and the extra info in UHF, alias problems from the progressive to interlace conversion to get the NTSC image for the first channel, and such).

Another backward compatable analog scheme was to try to make use of what was called the "Fukanuki hole" (Dr Fukanuki was a Japanese research enginner working for one of the big japanese TV makers, and determined that there was a set of spectral holes similar to that with luma and chroma (comb filter sort of thing). And that side panel information was to be modulated onto a "Fukanuki" subcarrier and merged into the composite video, but 12 dB down. The side panels were to be image info to make the 4:3 image into a 5:3 image, side panels stitched on both sides of the NTSC 4:3 image. Being 12 dB down was an attempt to be less visible in the 4:3 image, but the signal to noise would be that much worse for the side panel portion of the 5:3 image. Also, you would still see random crap swimming thru the 4:3 part of the picture. In NTSC, the chroma subcarrier is in the luma, but we get away with it because the colored parts of the picture and the chroma subcarrier patterns track each other when things move about in the image. This system didn't work and was forgotten quickly.

As for today's HDTV, there's 18 different resolution settings possible, but they all use MPEG-2 compression and decoding. And then there is another set of standards addressing the packetization of the digital bits and another on how to modulate an RF carrier to transmit it on a TV channel. Along the way, there is variable length encoding, where common bytes get shorter digital codes. If the TV channel picks a lower resolution setting, they can broadcast two independent programs at the same time. IIRC, use the lowest setting and they can do 6 programs.

Most HDTV receivers are not "multiscan" (like VGA monitors) but scan convert to whatever rate the display is built for. Some of the 18 flavors are done at 24 progressive frames a second (movies) but you can't display that at that rate on a CRT (too much flicker). The receiver up converts it to a faster display rate.

Just something more to get confused by when you're at the local "Crazy Eddie" electronics shop trying to select a good HD set....

(Crazy Eddie was a big chain around NYC, but has since folded. Something about stockholder fraud or such...).

Thanks for all the info, my brains are leaking out of my ears now!

Crazy Eddie was a modern day Madman Muntz in terms of marketing. The funny thing is that the on screen spokesman was NOT Eddie but a buddy of his (IIRC) that he hired to do the spiel.

Eddie went public with the company and disappeared to Israel before everyone found out he had either oversold the stock or had falsified the books. I believe he came back to the US and did some time and is now free. Since then someone has tried to restart the company or at least use the name. There was an online site but they seem to be now gone. Here's some history on them.....there are tons of sites out there.

http://pocketcalculatorshow.com/crazyeddie/
http://www.tvacres.com/admascots_crazy_eddie.htm

Anthony