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SubjectRe: linux as a minicomputer ?
J. A. Magallon writes:
>
> On 2002.04.13 Richard Gooch wrote:
> >H. Peter Anvin writes:
> >> Richard Gooch wrote:
> >> >
> >> > Actually, there is some impedance matching. I've seen monitors with
> >> > hi/lo impedance switches. And I've used 15 m long high-quality VGA
> >> > cables. The result has been pretty good.
> >> >
> >>
> >> The best I've seen is to use Sun D-sub coax or plain coax inputs on
> >> the monitors that have them. Those are impedance matched and can be
> >> extended without problem.
> >
> >Sure, coax inputs are the best. But there are still problems. Even
> >expensive coax has higher attenuation at higher frequencies, so the
> >longer the cable, the more fuzziness you get. Also, there are
> >differential delay effects between the R, G and B components. You
> >don't want the pixel components to arrive at different times. So
> >there's a length limitation there as well.
> >
> >But even though coax is better, VGA isn't that bad. 15 m gets you
> >quite a lot of terminals in a web kiosk (or undergrad computer lab).
> >
> >BTW: I agree that X terminals suck. Even worse are SunRays. Ug!
> >
>
> We have built a 'pseudo-CAVE' for presentations, and have six vgas
> feeding sony projectors with cabling between 15 and 20m, running
> at 1024x768@32. Quality is ok.
>
> The problem is finding good PCI vga cards, even finding any,
> good or bad. Now they are TNT-M64. I'm also aware that SiS has some,
> but nothing special. But, to use it as terminals, they could be ok.
>
> And coax is not so good. Even with expensive cable, the bounces of
> the signal made me see double like drunk. Video did not worked right
> until we got _golden_ connectors and soldered with silver. Believe
> me you could even put more mony on the cables that on the box.

Are you sure your monitors had properly matched terminators?

Regards,

Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca
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