Peter TB Brett wrote:
On Thursday 15 March 2007 02:30:06 sinkam wrote:
On Thu, 22 Feb 2007 13:41:39 +0500, Peter TB Brett <[EMAIL PROTECTED]>
wrote:
Once again, your idea is impractical.
From: Carlo Salinari <[EMAIL PROTECTED]>
Subject: [Open-graphics] Slashdot | HDMI-Enabled Graphics Cards Debut
http://hardware.slashdot.org/article.pl?sid=07/03/13/126250
There are 10s comments in the discussion, people want to buy long HDMI
cable
<snip>
And they are ready to spend $150 for that. Peter, say them 'your demand is
impractical' :-)
Then clearly someone should design a standard for VGA over a bundle of, say,
four optical fibres. And design it so that Joe Bloggs can install it without
breaking it. And make it affordable.
There are good electrical reasons why there are problems with 100 ft cables
for transmitting HD video. At the sorts of frequencies required to be able
to transfer data at the rate required, the impedance of a long cable is very
significant,
Capacitance actually. There should be a simple solution to this. To
start with, the driver must be capable of driving that long a cable.
Drivers have a maximum output current and, therefore, too long a cable =
too much capacitance = insufficient slew rate.
resulting in considerable attenuation of the signal (probably
resulting in a fractional S/N ratio by the time you get to about 100 ft).
This is in addition to the problems generated by cross-talk between the
several conductors you'll need.
With VGA, the solution is simple, you need a breakout box on each end
with 5 BNC connectors and connect them together with 5 RG6 Coax cables.
The maximum distance with RG6 is going to depend on the maximum
drive current of the video output amps. If these don't provide
sufficient current then the break out box on the transmitter end needs
to have high current video buffers in it.
Large diameter (= low capacitance) coax can be used to transmit video
signals for miles with a suitable buffer driving it. So, a few hundred
feet should be no problem. But, it is going to require much larger
cable than is in the typical VGA cable.
--
JRT
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