Gadgets and Gizmos
Adapters for VGA Video over Cat5 Cable
Yes, these adapters support VGA video over a Cat5 cable. Use one adapter on the computer, one on the monitor, and a good patch cable between them. These adapters are great for those difficult installations with long distances or small conduits for the video signal.
To purchase, call in your order with a credit card.
The item numbers are:
- VM45 Adapter, VGA Male to RJ45 Female - $20.00 each
- VF45 Adapter, VGA Female to RJ45 Female - $20.00 each
The design was developed by Doug Burbidge and he has graciously given his permission for us to share his work.
It's possible to send a VGA "video" signal down an ordinary Cat-5 ethernet cable. This is possible for two reasons: firstly, although VGA connectors have 15 (or 13) pins, only about 8 wires are actually necessary to send the VGA signal; and secondly, ethernet cable is twisted pair, and we can use the magic of twisted pair to push the analog VGA signal further than it is supposed to be able to go (by specifications).
We have used these adapters over Cat-5 for distances of about 15 metres (50 feet) in the real world and about 200 feet in a lab environment. At this range, the 800x600 screen looked fine when it was displaying a coloured background; although when it was displaying black, a lighter gray region was visible, probably due to interference from the synch signals. Your mileage will vary depending on screen res and refresh rate (lower settings will go further), contrast and brightness in the image (high contrast and brightness will go further), and interference from other sources (running the cable in its own metal conduit is best; if you're not in conduit, running parallel to other cables is bad).
This trick will work equally well with Cat-5e and higher.
In some installations we have noticed a "ghost" image on the screen, where a second image is offset horizontally by a few mm from the main image. This occurs where we have used a regular VGA cable in series with these adapters and Cat5 cable; such as a monitor with a permanently attached VGA cable. Apparently, the ghost is a result of a reflected signal caused by the transition from Cat5 to VGA. You can change the amount of horizontal offset in the ghost image by changing the relative lengths of VGA and Cat5 cable, which sorta confirms the reflected signal theory. We get the best results by attaching the adapters directly to the PC and Monitor and using a patch cable with no splices or other connectors between Computer and Monitor.