VGA over CAT5e

Al

Well I was going to say different cable for different uses, but then I found this site:

author says they've achieved 15 metres. For the cost of the cable and solder time, worth trying.

If that doesn't work you can get gadgets that convert from VGA to RJ45 and back again:

Best Paul.

generates 257,000 hits.

generates 140, 000 hits.

Here's a few that look promising:

You would need the skills of a micro-surgeon and a very fine solder tip.

I am liking the ethernet idea. I found these mounts I could use which have sealed end caps for when not in use:

This way it has a fighting chance of surviving in the marine enviroment!

-Al

How about cutting the connector from one cable end, pulling the cable and then soldering a new one to the end. Or building entirely new VGA cable the length you want by soldering the connectors yourself to both ends. The soldering the cable consisting of several mini coax condictors and many other conductor DB15 VGA connector is not the easiest job, but doable if you are good at building cables. I have done that kind of soldering myself when I have needed some custon VGA cables for some applications.

Runnign VGA over CAT5e is possible. There are commercial active adapters that do the conversion "right" and work even for some longer distances. Those cost money but work quite well. Then in Internet there are some simple plans to run VGA over CAT5e cables. When you use a shielded CAT5e cable and not too long distances, those hacks can work quite well but might not give perfect "crystal clear" picture like a real VGA cable or commercial converter would give. Running VGA signal on unshielded CAT5e cable with simple DIY passive adapters is not a vry good idea: the image quality will get worse and your cable will radiate out considerable RF interference which could interfere for example with boat radios.

I just gave you several ideas.

Yes. I have done this several times.

You have lots of replies to this already, but just curious as to whether you've considered instead putting a small laptop in your "bridge" and using remote desktop or vnc to control your "Nav Station" (assuming its a standard pc). You could even go wireless and avoid the need for cable runs all together.

The impedance is different enough that you will get visible reflection at anywhere close to VGA frequencies. I believe VGA, like most analog video signals, is 75 ohm coax (unbalanced). Matching that to 100 ohm balanced line is not easy with passive parts. Using active circuitry you can generate the balanced signal needed, and convert it back at the other end. That takes a number of very fast amplifiers (I think three video, plus two sync, but I am not so sure about sync signals for VGA.)

I believe the boxes are commercially available, because it is sometimes the best way to send video long distance. (The cheaper cable makes up for the added cost of conversion.)

If you find the connectors with separate pins that you solder and then install it isn't too hard. You still want the appropriate multiple coax cable, though.

Finding ready made cables has been easy enough, and finding the required cable in bulk hard enough, that I haven't tried.

-- glen

VGA cable is shielded and CAT5 is not, so you would get some horrible ghosting.

BTW, there may still be some ghosting even with VGA cable

If you are handy with a soldering iron there is no problem. You may have to buy a new plug/socket though as the one you cut off may be potted.

I used to make up VGA cables for control room applications. 15M using individual screened conductors was about the recommended limit

STP CAT5e or CAT 6 would do the trick, and at these lengths the cost difference isn't an issue.

-John O

It might be worthwhile to think-out a bit beyond the size of the hole though which you want to pass this signal. Stuff like "what will hold-up best when I'm at the bridge, in a storm, near a rocky shore and I really need to know where I am?" I say that only half in jest.

rick jones

You can use a transformer, but wired as a *balun* (coils in series with the lines instead of across them); this provides the required impedance transformation while still passing DC.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

There might be a minimum amount that they will sell, but the real problem isn't shielding but impedance and balanced/unbalanced line.

If you transition from a balanced line (UTP) to an unbalanced line (coax), unless exactly impedance matched, it won't work right. UTP cable depends on the voltage and currents on the two wires being exactly opposite to cancel out and not radiate the signal. Coax depends on the voltage on the shield being zero. To couple between them you either need a transformer (if there is no DC component), or active circuitry such as differential amplifiers. VGA has a DC component so you can't use transformers.

-- glen

Rich Seifert wrote: (snip)

So that is how they do it.

TV baluns, from 300 ohm balanced to 75 ohm coax, don't do that.

Does that restrict which impedance transformation you can make?

-- glen

I have worked with commercial solutions using this technology. Was about 5 or 6 years ago.

I forget the name of the product.

One serious problem was that by *design* (as I understand it) the various different pairs in the cat5 cable have different twist rates. This results in different cable lengths and produces different delays for each of the RGB and Sync. The solution overcame this by having user adjustable delays controlled by DIP switches at the remote end.

(or is sync on one of the RGB?) doesn't matter - is still broken.

NIGHTMARE - in the event of any moves or changes.

Not sure of your proposed length would run into this or not. I suspect it would since the frequency required to drive a display is rather high.

In the case I observed the differential delay issue was *very* significant over two floors of a narrow buillding.

There of course may be commercial solutions available now that avoid the problems entirely. Perhaps by combining the signals into one pair.

Composite Video?

The most common solution now is to use an ethernet KVM (keyboard, video and mouse) switch. All signals get packetized.

Length in this case 4m absolute MAX!

-Al

Thethe wrong cable impedance and lack of shileding between RGB signals will not cause ghosting. Most ghosting will be caused by the impedance mismatches.

The lack of shield in cable will cause that that cable will pick up more easily external interference and will radiate out more RF interference and properly shielded VGA cable.

True. The VGA cables vary in quality. The good ones are good but there are also bad ones. One thing to keep in mind in VGA connections is that it is a good idea to keep the number of VGA connectors along the link minimum (ideally only at source and destination), because the VGA connector impedance is not exactly 75 ohms as the system is designed for, and having many such wrong impedance connectors on the way will cause impedanc mismatches that cause reflections. For VGA cables is best to use a correct length cable in the beginning, and avoid using orignal cable + extension cable combinations.

The impedance transformation is determined by the winding ratio, regardless of whether the coils are in series or parallel with the lines.

Putting the balun in series provides better low-frequency response (down to DC), but of course this configuration does not provide any electrical isolation. It functions very much like a common-mode choke, with an impedance change.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com