The issue is that to help with crosstalk, the pairs within a UTP
cable each have a different twist rate, in other words each pair is twisted with a different number of twists per unit
distance. To improve performance in network
applications, CAT5e uses greater variances in twist rates between pairs than does CAT5
while CAT6 uses even greater variances than CAT5e.
The challenge with this for video is that over longer overall cable distances the higher twist rate pairs represent a longer total length of conductor
than the lower twist rate pairs. As a result, you start to get individual components of the video carried on different pairs of the cable traveling different lengths and thus arriving at slightly different times. This is skew
. When you start getting to higher resolutions and scan rates this difference in arrival times can result in things likes the red, green and blue components arriving offset to one another and you may see 'ghost' red and green images to either side of the main image
The solution is to either use 'low skew' or 'skew free' cable or to use receivers that can apply skew compensation, essentially delaying the signals so that they all line
up. If you have to use standard CAT cable for audio and video over UTP
applications then CAT5
is preferred, followed by CAT5e with CAT6 being a less desirable option.
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