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English Manual
6. Configuring and using the skew compensator
6.1 What is the skew compensator and why is it needed?
The skew compensator corrects the video colour split that is sometimes introduced when a video picture is
transmitted over twisted pair cables. Twisted pair cables are typically constructed using four pairs of twisted wires.
Each of the pairs of wires are normally twisted at slightly different rates to reduce the crosstalk between the pairs.
This is highly advantageous for digital data transmission but can sometimes cause a problem when the cables are
used to carry video signals. The reason for this is that three different pairs are used to carry the red, green and blue
colour components of the video picture. If the length of cable used is long enough and the twist rates differences
between the twisted pairs are large enough then there will be a significant length difference between the wires that
carry the different video colour signals. This means that the colour signals will arrive at the C5 KVM remote
receiver at different times and the colours on the video picture will appear to split causing the picture clarity to be
reduced. A typical characteristic of this colour split effect is a red, green or blue shadow around bright white
objects. The skew compensator removes this colour split by deliberately delaying some of the colour signals so that
all the signals arrive at the remote receiver at the same time.
6.2 Can I predict if a skew compensator will be needed?
It is remarkably difficult to predict if a skew compensator will be needed because twisted pair cables from different
manufacturers have substantially different characteristics. Although Category 5e and Category 6 cables typically
have larger twist rate differences than Category 5 cables there are several types of Category 5e and Category 6
cables with low twist rate differences. With similar specification cables, the colour split introduced by one cable may
be four times the colour split introduced by another apparently similar cable. What's more, colour split effects
become more noticeable at higher screen resolutions. The reason for this is that the pixel time on higher resolution
screens is shorter and so a given colour delay represents more pixels.
As a general rule, colour signal skew is more of a problem with higher specification cables (i.e. Cat 6 / Cat 5e),
longer cable lengths and higher screen resolutions. For example, an installation running a screen resolution of
1024 x 768 over 50 metres of Cat 5 cable will probably exhibit minimal colour split whereas an installation running a
screen resolution of 1600 x 1200 over 100 metres of Cat 6 cable will probably exhibit some noticeable colour split.
6.3 Correcting the colour split
If you have a noticeable problem with colour split then you have several choices. You could use a shorter length of
twisted pair cable or a different type of twisted pair cable. Alternatively you could reduce the screen resolution that
you are using. If none of these are possible then the colour split may be corrected using the C5-Series skew
compensator. The skew compensation unit is inserted into the twisted pair cable connection between the local
transmitter and remote receiver as shown in figure 11.
34
LINDY KVM Extender C5-Series
Installation and Use
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