Issues with connecting a VGA cable to a computer monitor

[GreensandsParticipant @greensands]

Can someone please explain the significance of the integral filter unit found incorporated in some vga cables used for connecting a PC to a display monitor? The reason for asking the is that I have an old PC system running W98 which gives a perfectly good display when connected using a plain 1.5m vga cable but when replaced with a 2m cable incorporating a filter unit the display rapidily becomes unstable.

I need to buy a replacement cable of 3m length for the new set up but should this new cable be a plain cable as before or are there other factors to be considered?

[GreensandsParticipant @greensands]

[densleighParticipant @densleigh]

Hi,

You canb get VGA cables from CPC in various lengths, looking on their web site 28 came up. I have used various cables, some linked together in a daisy chain with no noticable signal degradation.

No connection to CPC just a satisfied user.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Greensands on 02/07/2022 21:19:26:

Can someone please explain the significance of the integral filter unit found incorporated in some vga cables used for connecting a PC to a display monitor? […]

.

This chap does a pretty good job of it: **LINK** https://youtu.be/LuMlM8zWQFk

… Shame some of his solutions are so hideous though 

 

MichaelG.

Edited By Michael Gilligan on 02/07/2022 22:29:15

[not done it yetParticipant @notdoneityet]

Ask the supplier? If they cannot give you a good reason, find another supplier.

[Michael GilliganParticipant @michaelgilligan61133]

The first answer here: **LINK**

https://electronics.stackexchange.com/questions/344627/why-do-some-computer-power-cables-not-have-ferrite-beads-what-type-is-usually-u

… is quite succinct.

MichaelG.

[Clive Brown 1Participant @clivebrown1]

As said, it's a ferrite bead for EMI suppression. VGA is analogue technology, obsolescent in computer terms. AFAIK, it's signal won't be enhanced by the bead, and may possibly be degraded. I'd go for a cable without one if available.

[SillyOldDufferModerator @sillyoldduffer]

The filter (see Michael's link) is just a ferrite ring around the outside of the cable; it's purpose is to stop the cable radiating and/or picking up external interference. Good practice rather than essential, and unlikely to be the reason the longer cable doesn't work.

VGA cables are short-range. The wires inside have considerable self-capacitance and self-inductance that distort fast-changing signals such as video. They're 'good enough' to link a monitor to a nearby computer, but not for long runs. The absolute maximum length of a high-end VGA cable sending low resolution video in perfect conditions is about 30 metres, and they can't send ultra-high video at all.

Reasons a longer cable might not work include:

• The computer's transmitter is weak or distorts the signal. Old electronics perform less well than modern electronics especially at the budget end.
• The monitor's electronics don't do a good job of recovering mangled signals.
• The cable isn't well-made; skimping on copper, screening, and the connectors increases distortion, as does sub-optimal layout of the wires relative to each other. (A cheap cable might have no screening at all.)
• Something nearby is generating interference,

Not unlikely that all four factors occur together. Fixing this type of problem varies case by case.

If several long cables are available, try them all. One might perform better than the others. Or try coughing up for the best VGA cable on the market, cross-fingers, sacrifice a virgin, and hope for the best! It might not work.

But all is not lost, this isn't an unusual problem! Search ebay, amazon and the other Usual Suspects for 'VGA Extender', which are available in various forms. This example on ebay might do. A CAT5 patch cable is needed as well, so a 'VGA Booster' like this example on Amazon might be easier. (Out of stock at the moment.)

VGA has been superseded by faster more reliable technologies like HDMI; they're also short-range!

Dave

Edited By SillyOldDuffer on 03/07/2022 09:26:02

[Clive SteerParticipant @clivesteer55943]

Greensands

The ferrite bead found on some computer cables are there to prevent the lead becoming an aerial for radio interference produced in the computer. The bead should not significantly affect the signals in the cable, which would normally be screened, but seems to in your case although other factors in the new cable may be the cause. However you can remove the bead with a nut cracker eg a large hammer, after removing the heat shrink sleeve that normally holds it in place. On some cables however this may be more difficult as the bead could be moulded in.

CS

[David JuppParticipant @davidjupp51506]

My money would be on the 2m cable just being made with lower specification wires, or having been damaged or degraded. Or one of the green (I think synch is on green signal) connector pins having pushed back into the connector (I've seen that before).

I doubt that the ferrite is of any significance.

[Author]

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