UTP Cable and Colour drift

UTP cable is often used with video or KVM extenders to extend the reach of a video signal. It's popular for this application because it's lightweight, easy to handle, and inexpensive. But when you transmit video over long stretches of twisted-pair cable, you sometimes run into a phenomenon called colour drift or colour split.

UTP cable consists of four twisted pairs or wire. Because each pair is twisted at a different rate, different pairs of wires may actually have different lengths.

Colour drift shows up as that annoying coloured shadow you occasionally see around objects on a video screen. It sometimes happens with UTP cable because the pairs of wire in the cable are twisted a slightly different rates to reduce crosstalk between pairs. Because of these differences between wire pairs, video signals for different colours often travel different distances before they reach the remote receiver. When one colour signal arrives behind the others because its wire is longer, you get a red, blue, or green shadow around the objects on your video screen.

UTP cable varies widely by manufacturer, so before installing video extenders it's difficult to determine whether or not you're going to have a colour drift problem. You're more likely to experience colour drift whith higher grades of cable (CAT5e or CAT6), on longer cable runs, and on high-resolution screens.

If you experience colour drift, there are several possible solutions. You can use a shorter length of cable, switch from CAT5e or CAT6 cable to CAT5 cable, use a lower sreen resolution, or use a video skew compensator.

A video skew compensator removes colour drift by delaying some colour signals to compensate for differences in wire pairs.