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Pastimes : Dream Machine ( Build your own PC ) -- Ignore unavailable to you. Want to Upgrade?

To: Jon Tara who wrote (14574)	5/8/2004 3:25:17 AM
From: Jon Tara	Respond to of 14778

DVI long-cable WORK-AROUND! I finally solved my problem with getting 20 foot DVI cables to work on my Xentera GT-4 AGP. This is a work-around that may work for others with similar problems using this or other cards. I tried analog cables (25 foot) BTW, without success. These were good quality cables, that the vendor claims will work to 100 feet at 1600x1200, but no such luck for me. Though the reflections weren't fierce, they were there (look at vertical lines in particular, then look for a reflection to the right of the line.) The analog cables go back to the vendor on Monday. I got desperate, and started playing with pixel timing using PowerStrip. Success! I bought PowerStrip so that I can match colors on my 4 LCDs using a different color ramp for each LCD. I hadn't thought that it would help me solve my long cable problem. The solution was to drop the horizontal scan rate from 75 kHz to 70.625 kHz. This dropped the pixel clock from 126 mHz to 118.6 mHz. This was enough, in combination with hand-selecting cables and monitors to go on the troublesome channel 3 and 4 outputs, to get a perfect picture. No more purple sparklies, and no more sync problems. I still think there is a problem with the card - channels 1 and 2 work perfectly with any combination of cables and monitors. Not sure what, if any, side-effects there are to lowering the horizontal scan rate. I will talk to the engineering manager at Colorgraphic on Monday and see what his thoughts are. I may be able to lower the pixel clock without dropping the scan rate, by fiddling with sync width, front porch, etc. (Dropping some non-active pixels from each line.) Obviously, the cable was right on the edge. So, I could probably also go ahead and get a higher-quality cable, but I hate to pay the outrageous prices. $50 is already plenty for a 20-foot cable, especially when you are buying 4 of them! The "super" cables run $100, $150, and higher for a 20-foot cable. The cheapest extender box I have been able to find goes for $200. Fibre extenders are $2000 and up. The real answer is dual-link. Unfortunately, this is currently supported only by a handful of monitors that have higher resolutions. (That is, higher than 1600x1200). I don't know of any 1600x1200 or lower monitors that support dual-link. DVI single-link uses 4 wires. 1/4 of the bandwidth goes on each wire. Dual-link uses 8 wires. 1/8 of the bandwidth goes on each wire. The maximum resolution with single-link is 1600x1200 or (for TVs) 1920x1024. DVI's dirty little secret is that it is awfully difficult and expensive to go further than 6 feet at these resolutions. Dual-link would solve the length problem completly at these resolutions. The standard sure was poorly thought-out - especially given it's orientation toward HDTV applications. The 6-foot length is terribly limiting. I see that some of Sharp's LCD TVs use a remote connector box, with a proprietary (not DVI) cable that can run to 100 feet. You would, of course, have to locate the remote box within 6 feet of your DVI source.