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I’ve been asked to install a new monitor in an EMS (Ambulance) station. The monitor is by the garage doors, and needs to mirror another monitor connected to a computer on the other side of the garage. This is a volunteer EMS group, so the budget is limited. I’d rather not buy a new graphics card, but it’s not out of the question.

We’ve measured the cable run at roughly 55ft (17m).

The monitor we need to mirror is connected by DVI.

There’s a second monitor also connected via VGA.

The computer has no third monitor port; it has just 1 VGA port and 1 DVI-D port. It’s a cheapish old Dell. The sole use for the computer is showing currently active calls, and the people who’ve paged in to take them.

What’s the best solution to setup display mirroring on the new monitor? No kb/mouse is required at that distance. This is view only. To be clear, the monitor is already mounted. Just need to know the best way to get the signal to it, given the constraints I have.

I’ve taken a look at kits: I can get either DVI or VGA splitters, and 20M cables for both.

Are these options decent, or would I need a powered splitter? Bear in mind, that’s $10 vs $150 it seems.

Which is preferable over longer lengths? VGA or DVI?

  • What resolution is the monitor you'll be connecting? – Downgoat Dec 14 '15 at 6:04
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    Unsure, but it's pretty low - the software is an old-school CICS style screen. Probably 1024x768 would be fine. – Alex Dec 14 '15 at 6:55
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Use an active-splitter with VGA cables. With a long length on one end, you will need active electronics.

VGA is analog. The quality of your picture is going to depend on the quality of the cable you use and the electronics on your video card and monitor. With a decent quality cable of 20 meters, I would expect a good quality picture at 1024*768 resolution and 60 Hz.

Use a splitter similar to this model and a cable similar to this Monoprice 75-foot product. The reviews on these products suggest this is feasible.

  • The sources in Downgoat's answer are very poor on a technical level. Try necdisplay.com/Documents/WhitePapers/… for an improvement. Without additional equipment, I would still recommend VGA for a length over 15 meters. – davidmneedham Dec 14 '15 at 6:15
  • Also, please note that the positive reviews for the products linked in Downgoat's answer are for shorter-length products. Tripp says "Note: Most applications will require a B120-000-SL signal booster to perform optimally". – davidmneedham Dec 14 '15 at 6:27
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    DVI-D requires clock recovery on the TMDS pairs to display an image at all. I don't see positive references that this is possible with unamplified consumer equipment and normal cables. High-quality VGA cables are composed of individual 75-ohm coaxes, which are well-suited for long-distance transmission of video. With a VGA cable that is too long, you will get a smeary image. With a DVI-D cable that is too long, you won't get any image at all. – davidmneedham Dec 14 '15 at 6:58
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    A reference for VGA being more reliable than HDMI (similar to DVI) over this length: bluejeanscable.com/articles/how-long-can-hdmi-run.htm?hdmiinfo . Note also that the clock frequency of the digital signals for a given display size is much higher than that of the VGA signals. – pjc50 Dec 14 '15 at 12:26
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DVI

If your budget isn't too tight (< $40) then I would recommend DVI.

As for all cables, signal quality is dependent on the length of the cable. VGA cables are much more susceptible to degradation due to distance1 so I would highly recommend against VGA.

While cable quality may play a role, VGA is very old-school and DVI is better than it in almost every way. Your result is also dependent on your resolution. At your range you're probably going to be able to run a 1,280 × 1,024 display, and you may need a booster the longer you go.

I would definitely note that 55ft would require a rather very long cable. (~75ft). This means that cables can get expensive quickly, especially the higher you go in terms of quality

If you choose to get an extender (link to one such extender), you'll be able to use really any cable and get flawless video. If you're running CICS, then I wouldn't see any benefit to an extender.

A Few Links

These were found from a quick google search. You might want to look at more options and reviews for other cables. Shorter cables would be preferable but 75ft is the most common option above 50ft

All of these seem to perform to the required resolution.


There many more, doing a google search for 65ft or 55ft DVI cable yells quite a few results

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HDMI extender

The kind when you have 2 small boxes to be connected with pair of Ethernet-style cables. I'm using Unitek Y-5115 (I've paid about $30-$40), but this one looks promising. I think this simple devices work by having an analog amplifier pump the signal into cheap cable and then normalize it at the other end - it doesn't really understand the protocol so it works with pretty much anything that can be crammed into HDMI cable. I've tested mine with pair of 25m patchcords and it worked flawlessly up to 1080p and also with DVI. In your case you can connect it via DVI-splitter to the DVI monitor.

UPDATE: I've tried mine at 4k, but it only managed to work on 20cm patch cords. Anything longer and there was no signal. But still - I was amazed that the extender itself did worked at 4k even though it's specced up to FullHD.

The biggest advantage of this system is that all the expensive parts (the converters themselves) are concentrated in 2 small locations and can be put out of harm's way. The long cable is cheap and can be easily trimmed or replaced should a need arise. Also the transmission is fully digital (although I suspect analog amplification) so you get perfect quality.

I'd recommend against long VGA, DVI or HDMI cable - simply because they are quite expensive and when they get damaged you have to replace entire length of it. The picture quality degradation of VGA cable is less of an issue, as I've witnessed surprisingly good quality out of about 15-20m cables used at conference rooms - although judging by the thickness they were probably quite expensive.

As with all experiments, I advise you make the purchases as a consumer (that is, not as company or organization) so you can return it if you're not satisfied with results.

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Another option, for even longer distances, is a KVM over CAT5 extender. Startech has many options, among other vendors. I'd search on Amazon as the prices are generally better than buying directly from Startech.

For example, the SV565UTP (they are sold in pairs):

enter image description here

You take one and put it next to the computer and connect it to the machine's keyboard, mouse, and monitor outputs. You take the other one and plug a keyboard, mouse, and monitor into it. Then you run a CAT5 cable between them and you get up to 500 feet.

They make longer distance ones; there's a 650 ft VGA/USB extender, there's a whopping 1500 ft DVI/USB extender, and so on.

These are overkill for your 55 ft in terms of cost, but if you need even longer runs, or you have the budget, they're a good option. It's a lot easier to run CAT5 through walls and such than VGA / DVI, too, and cheaper to replace failed cables (or re-terminated failed connectors). If the building already has CAT5 wiring for ethernet you may be able to repurpose one of the existing runs. If you already have a network closet with a patch bay for wall jacks around the building, it also makes moving your console around in the future pretty trivial.

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