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fuzzy VDU with extension cable

Posted on 2000-02-21
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Last Modified: 2012-08-13
I wanted to position my VDU further away from my Windows NT 4
box and so bought a High Density DB 15 extension cable.  It all fits
ok, but the text is now a bit out of focus?  Any ideas.  
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Question by:s_wiseman
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oldgreyguy earned 300 total points
ID: 2543829
you can buy good video cables and not so good ones, sounds like you got the latter. A good shielded cable would probable run around 45-75 bucks. Take a look at:

www.cablestogo.com


bill
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Expert Comment

by:EDStech
ID: 2544558
Recently i was buying a video cable.  The sales gent said that the "Normal" cable you buy is a VGA only.  They make (But are hard to find) SVGA cables nowdays.  They happened to have one so i got that instead.  I recently found a spare vga cable and figured what the hey.. so i plugged it in and DARNED if the SVGA doesn't make a difference.  I figured the salesguy was BS'ing me, but it really does matter.

In summary, buy a better cable.
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Expert Comment

by:RoadWarrior
ID: 2544783
Well SVGA cables would be designed to handle higher frequencies better. Compare the quality of the picture at say 1024x768 at 75hz with 800x600 or 640x480 at 60hz.

There are several variables here in determining what happens when you extend a video cable.

* The quality of the extension cable, one of the prime factors.
* The output from the graphics card, the current it can source etc.
* The quality of the line termination at the monitor.
* The ability of the monitor to sync when the syncs are faint
* The ability of a digital monitor to preprocess the signal.
* The quality of the grounding in both the monitor and the PC, they should have a common ground, no 2 wire power cables please.

Sometimes a different graphics card (even two cards of the same chipset from different manufacturers) can make a difference. So if you have spare it is worth a try, probably not worth buying one to try though.

The cable you have probably does not have individually shielded signal pairs, therefore there is crosstalk between the rg&b analogue signals and the syncs, resulting in a loss of sharpness in the peaks of the signals which in turn translates to a loss of sharpness on the monitor.

A good cable would have a shielded pair of each signal and return, maybe they just grounded all the returns too, which can be done, and may be done on some graphics cards, but isn't the way to get good signal propogation.

regards,

Road Warrior


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Author Comment

by:s_wiseman
ID: 2545288
I looked again at both the original cable and the
extension.  The original has 15 pins, while the
extension only has 14 (pin 9 is missing).  Does this
make a difference?  I bought a SVGA one.  Do I
need an "Enhanced SVGA" at double the price?
Road Warrior - your comments noted, thanks.
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Expert Comment

by:oldgreyguy
ID: 2546396
the pins may or may not be missing, depending on the specific manufacturer. All 15 pins in the connector are not used. I think that if you want to see clearly, you will have to bite the bullet and get a better extension

bill
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Expert Comment

by:EDStech
ID: 2547070
Its normal to be "Missing" up to four pins.  We work with extensions all the time and i've seen as many as four missing with no problems.  Some of the pins are used for the two-way communication in PnP monitors.  I'm not sure what the rest are used for...
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Expert Comment

by:jhance
ID: 2547225
The problem is the QUALITY of the cable.  High-res video is a HIGH BANDWIDTH signal and low quality cables have high loss, poor shielding, and poor impedance matching.  The results are dim images, ghosts to the right of vertical lines, and color interference (which looks like your out of focus problem).

Get a good cable.  I've had the best luck with ones from Black Box.  They are expensive but it's the only way to go.  
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Author Comment

by:s_wiseman
ID: 2547261
I guess oldgreyguy was first to highlight
the cable quality issue and so he gets the points.
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