Long run of VGA

[FunnyFellow]

Would any of you on here happen to know the longest run of VGA I can get without any signal loss?

[00AVD]

Signal loss will occur at any length. How much is dependent on the length and quality of the cable. Whether you'll notice it is also dependent on the resolution - you'll get away with longer distances with lower resolutions.

All that said, I've used 50+ metres of good quality cable with SVGA from PC to projector and had no issues. Also bear in mind that not all PC outputs (I find some laptops bad) will be happy driving a long cable, instead requiring the use of a booster at the PC end.

[NickJones]

It all depends on the type of cable and the resolution. If you run one at a resolution like 800x600, it will go longer than running at 1200x800. If you go with the cheapest, it will be very different to the most expensive.

There are alternatives though.

You can use boosters, but they can be expensive, it is possible to turn VGA into a signal that will go niceley along standard Cat5 cabling, this is often cheaper on longer runs, although Cat5 will not stand up to as much abuse.

Another option is to "Scan Convert" your signal into a single RCA or S-Vhs cable, this will make your signal quality a lot lower but it will be cheaper and easier to get it where it needs to go, and this is normally fine in terms of a movie, but on a big screen, or showing a power point or something with words it becomes noticeable.

Hope I helped,
Nick

[museav]

Would any of you on here happen to know the longest run of VGA I can get without any signal loss?

0', beyond that there will be some loss. Seriously, I agree that the loss incurred depends on the actual cable used and the signal bandwidth. You can also find wide variations in how much loss any application can accept.

[Chris15]

If you need to get a long run, then to retain acceptable performance you are going to needer better and likely thicker coax. 5 single coaxes will work fine given appropriate adapters each end.

I echo the comments about laptops in particular. As part of the quest for better battery life etc., designers have reduced the drivers omph. Hence go past a metre or two and the signal starts noticeably falling off.

A splitter can usually be used as an amplifier...

[ruinexplorer]

In addition to the quality of the cable, the power of the signal (adding one more agreement to laptop sentiment), and resolution (I don't agree that you have less signal loss at lower resolution, I say that you just notice it less), but you want to incur the fewest number of connections possible. If you have a 100' cable, you will have less loss than four 25' cables with turn-around connectors.

How far are you looking to run a signal?

[FunnyFellow]

Thank you for all this information. The run will be 50 feet and the wire is even shielded. The resolution will be 1024x768.

[00AVD]

What sort of cable are you talking about exactly?

[FunnyFellow]

I cant be sure. The cable doesn't have any labels on it or anything. It is an off the shelf model so I didn't make it myself.

[00AVD]

Ah, I see. So it's a standard off the shelf VGA cable? Just be wary of the really thin ones. They are often woeful quality and are usually missing the ferrite core at each end.

[NickJones]

If I were you I would seriously look at getting a Balun to run VGA over Cat5 if you intend to do this on a regular basis.
Nick

[museav]

If I were you I would seriously look at getting a Balun to run VGA over Cat5 if you intend to do this on a regular basis.

Which also points out the importance of establishing factors such as whether the application is portable or a permanent install.

1024x768 with a 50' run should not be a problem with good cable. With a generic cable of unknown quality and construction you might be on the edge of whether it will work acceptably. If you already have the cable and projector it would typically be pretty easy to just try it and see what you get.

[00AVD]

A decent quality pre-made VGA lead will work just fine for 1024 x 768 over 30m (100') or so. Even if you need to use a booster (due to crappy laptop output), it's still way cheaper than an active (powered) CAT5 solution.

[ruinexplorer]

I agree that a balun is completely unnecessary for this purpose. Depending on the quality of cable, I have used laptops to drive XGA without noticing any signal degredation. If you are driving your signal with a desktop or a DA, you should have no problems with a 50' run.

[FunnyFellow]

Ah, I see. So it's a standard off the shelf VGA cable? Just be wary of the really thin ones. They are often woeful quality and are usually missing the ferrite core at each end.

It is reasonably thick (about the thickness of a mains power cable) and does have ferrite cores at both ends.

[00AVD]

Sounds like you're good to go then!

[Chris15]

I don't agree that you have less signal loss at lower resolution, I say that you just notice it less

To approach this from an engineering point of view, a higher resolution signal means that to maintain the same refresh rate, the scan rates must increase. This creates a higher demand for bandwidth. Bandwidth is length dependant on all media (including fibre), so for a given cable having a fixed bandwidth per unit length, you will get more loss at a higher resolution...

[ruinexplorer]

To approach this from an engineering point of view, a higher resolution signal means that to maintain the same refresh rate, the scan rates must increase. This creates a higher demand for bandwidth. Bandwidth is length dependant on all media (including fibre), so for a given cable having a fixed bandwidth per unit length, you will get more loss at a higher resolution...

Ok, so, yeah, I guess I hadn't had my coffee when I wrote that. Currently wiping mud from my face.

Thanks for clarifying.

[firewater88]

It is reasonably thick (about the thickness of a mains power cable) and does have ferrite cores at both ends.

you will be fine. I have run many different setups, but the last one was about 60' of extensions run from stage to an ancient A/B vga box at FOH to switch my Mac and stage inputs. It then goes from A/B box via 100' of older VGA cable to a powered DA a the projectors (I twin stack mine). All running 1024x768 with no problems. In fact the presenter showed up with a little netbook with his presentation on it and it ran just fine. My extensions are 10'ers and seem to resemble the ones you are using.

[Clarissa]

Here's one of my favorite solutions:

For only $83.70 each when QTY 50+ purchased - VGA Extender PLUS upto 180 Meter | Video Extender

They provide a local monitor output AND the ability to run several hundred feet of CAT5 without major quality loss. For $90. Flexible, versatile, and use it nearly anywhere - sometimes you get so lucky as to not even need to pull cables (extra CAT5 runs for future use are often conveniently floating around)

[museav]

you will be fine. I have run many different setups, but the last one was about 60' of extensions run from stage to an ancient A/B vga box at FOH to switch my Mac and stage inputs. It then goes from A/B box via 100' of older VGA cable to a powered DA a the projectors (I twin stack mine). All running 1024x768 with no problems. In fact the presenter showed up with a little netbook with his presentation on it and it ran just fine. My extensions are 10'ers and seem to resemble the ones you are using.

I'm glad it works for you but I would be careful about declaring that it will work in general. I have had some similar experiences but I have also had experiences where less than 50' of generic VGA cable caused problems. And that is the problem, there is a difference between something that you know should work and something that may work and dealing with unknowns such as the specifics of the cable that virtually forces any situation into the latter category.

[rwhealey]

We had a group come in with a cheap VGA cable (50 or so feet) and every time somebody talked into a wireless mic, the picture quality would go to hell.

They came back the next time with bulans + Cat5, and it worked perfectly, and was an easier to handle cable

[FMEng]

What makes good VGA cable is that each of the signals in carried inside a miniature, impedance matched, coaxial cable inside the over-all jacket. Each signal has its own tiny coax, and there are five of them inside the jacket. The impedance matching and shielding of the coaxial contruction reduces signal loss and high frequency roll-off, and prevents standing wave reflections that would cause ghosting in the image.

There seems to be an un-written rule about VGA cables. The ones with smooth jackets are not impedance matched, and may not use coaxial construction at all. I wouldn't trust smooth cable more than 6 feet. The ones with fine ribs running along the jacket of the cable generally are impedance matched and should work reasonably well over longer distances. There may be exceptions to ribbed/smooth, but I haven't encountered it yet. As others have said, 50 feet is a good rule of thumb. Farther if you can live with a little degredation.

Also, keep in mind that VGA cables are inherently fragile. Kinks, crushes, and mechanical wear and tear can ruin the constant impedance of the individual coaxes, and will reduce performance. That's why most of these cable are designed to be rather stiff to prevent damage. Roll and un-roll it gently, limit the amount of handling, and protect it from abuse.

If you have the space for a really fat bundle of cables, you can go much farther without significant loss by using VGA to BNC adapters and then running five, RG-59 or RG-6 (75 ohm) coax cables. The reason is that the bigger the diameter of the coax, the less loss and roll-off it has. The individual coaxes need to be kept exactly the same length, or the pixel colors won't line up (more on skew in a moment). Where space allows for this bundle of cables, it is probably the best long distance solution. For places where space is limited, such as small conduits, then conversion to Cat-5 is the next best.

Baluns and Cat-5 cable is often a decent solution, especially when the cable has to be small. But, you have to watch out for skew. Skew is mis-alignment of the three colors that make up the image. Skew is caused by the different length of each of the pairs in the cable, due to different twist rates of the pairs. Skew becomes a factor as the cable becomes longer. Skew is worse for Cat-6 cable. Belden and Mohawk make video-specifc, low skew cable, and there are converter boxes that allow for skew correction on standard cables. Again, mechanical damage and wear is a big factor with Cat-5 cables. At least they are cheap enough to replace frequently.