Help with VGA extension cable - Page 1
Forum section: electronics / projects

author: alah
author_rank: Contributor
timestamp: March 31, 2020, 10:06:58 pm
content: Hi ALL; I gogled for VGA connections and found some stuff, but I still have doubts and before blowing my very precious portable or Monitor I prefer consulting. I´m attatching a pinout for opinions, it supposed to be the bare minimum connections for it to work; Thanks.

author: Whales
author_rank: Super Contributor
timestamp: March 31, 2020, 10:24:45 pm
content: There are 1000 ways to blow up a device using a cable. You need to tell us what you're doing, otherwise we're just guessing.N.B. the N/C pins are optional, used for things like 'EDID'. The bare minimum is all grounds, HSYNC, VSYNC and at least one colour channel (although some monitors may be picky and need a certain one or all three).

author: Whales
author_rank: Super Contributor
timestamp: March 31, 2020, 11:59:09 pm
content: Doh, it's in the title. Apologies, "extension cable".Some old CRT monitorsmightbe damageable with bad sync pulses, but I think that's about it. You probably want to use coax cable of the right impedence for VGA for each of those signals, otherwise you will get a blurry/bad mess on the other end.I recommend cutting open a shorter VGA cable that you don't care about and having a look inside, see how it's made.If you don't provide the EDID wires (marked as N/C in your diagram): you will have to manually force a resolution/mode on your computer, as it won't be able to auto-detect the monitor.How long of an extension do you want to make? After a certain distance it's really only practical using active (powered) VGA repeaters.

author: bsudbrink
author_rank: Frequent Contributor
timestamp: April 01, 2020, 03:51:14 pm
content: I don't know what your length requirement is or what your budget is, but I've had good luck with these:https://www.ebay.com/itm/VGA-Cat5e-Cat6-Extender-300ft-Video-Repeater-Over-Ethernet-Cable-Up-to-100m/153881643459?hash=item23d40f89c3:m:mKgvrXZBFKzpB_tRnZmpVkQ&var=453930968948

author: richard.cs
author_rank: Super Contributor
timestamp: April 01, 2020, 04:04:25 pm
content: Quote from: bsudbrink on April 01, 2020, 03:51:14 pmI've not tried twisted pair VGA extensions, but I remember reading two key things: 1) It works 2) For long lengths the different twist rates between the pairs appear as differing propagation delays and you get poor horizontal alignment between the colours. I suspect that box has a balun per colour, and then does some clever munging with the fourth pair (and perhaps between pairs) to get the sync and audio in.I'm curious over what length you've tried it and if you saw that effect?

author: magic
author_rank: Super Contributor
timestamp: April 01, 2020, 04:16:44 pm
content: IIRC the correct impedance is 75Ω and all color signals and HSYNC use coax in commercial cables, while the rest runs through normal wires.Pin 9 shouldn't be used and isn't even present on some connectors.Pins 12 and 15 are needed for DDC (autodetection).Wait, wrong. Pin 9 actually is used: it supplies 5V to the monitor. Probably required to power the DDC circuitry. Definitely don't connect it to ground.

author: bsudbrink
author_rank: Frequent Contributor
timestamp: April 01, 2020, 04:28:38 pm
content: I'm using 1600x1200 at 60Hz, about 40M. No visible artifacts (to my eyes anyway). They are Nokia monitors. The signal runs from sender to Cat5 wall socket to closet patch panel to Cat5 wall socket to monitor. One thing to note, these are being used to view "high res" video security cameras, not standard computer displays. I suppose artifacts might show up with window borders, different fonts and that sort of thing.

author: magic
author_rank: Super Contributor
timestamp: April 01, 2020, 04:32:45 pm
content: Magnitude of this effect is of course trivially estimated if one knows the horizontal resolution and refresh rate, cable length and the difference in propagation velocities (probably easy to find on the net).

author: rstofer
author_rank: Super Contributor
timestamp: April 01, 2020, 05:45:23 pm
content: I have never tried VGA over CAT 5 but I would start with these:https://www.amazon.com/StarTech-com-ST121UTPEP-Monitor-Extender-feet/dp/B002KQ6ZD8

author: Miyuki
author_rank: Frequent Contributor
timestamp: April 03, 2020, 09:27:32 am
content: Quote from: bsudbrink on April 01, 2020, 03:51:14 pmThese ones look like send it digital over Ethernet cableAs I look at it there is plenty of chipsets to convert video in any form (VGA, DVI, HDMI), sound and USB to data and send it over Ethernet and convert it back at other side

author: alah
author_rank: Contributor
timestamp: April 08, 2020, 06:57:59 pm
content: Thanks to ALL; I´ll have to wait to wait till quarantine is over to see if I can source the connectors and give it a try with cat5 or 6 cable.I need about 8 meters extension, meanwhile I´ll check another possible solution but that should be another topic; THANKs.

author: Whales
author_rank: Super Contributor
timestamp: April 09, 2020, 12:39:12 am
content: IIRC VGA is unbalanced (coax-style) signalling. CAT5/6 is balanced (twisted-pair) style. You may get poor results unless you use baluns every time you convert from unbal<>bal, ie each end of the CAT cable.

author: magic
author_rank: Super Contributor
timestamp: April 09, 2020, 06:09:15 am
content: Not only that, impedance is wrong too. But there have always been reports on the Internet of people using Ethernet cabling to run VGA with some degree of success.