APPENDIX D: ADVANCED CABLING ISSUES (SKEW)
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Appendix D: Advanced Cabling Issues (Skew) The suggestions made in this Appendix should only be investigated if you cannot obtain
satisfactory image quality after configuring the Remote unit (as described in Section 4). The
techniques described here are usually only necessary when you are operating at the highest
screen resolution (1600x1200) with long Interconnect cables.
Dealing with Severe Skew
The CATx KVM extender provides a maximum skew compensation of 42nS. This is more
than adequate for most cables. However, it may not be enough if a particularly long cable is
used that exhibits severe delay skew. In this case, some of the procedures described below
should be considered. In extreme cases, you should consider using an additional external
delay line (Model: ACUDLY) or an alternative CATx cable as recommended by Technical
Support.
Green Delay
Introducing delays in the video signals inevitably may cause some distortion. For example, it
may result in pixels being sampled twice on TFT screens.
The human eye is extremely sensitive to green distortion. To obtain optimal video
performance it is best to ensure that no green delay is required. You can visually check the
relative pair delays by viewing the test card (without any delays applied). The two color bars
on the left require delaying, but the color bar on the right requires zero delay (slowest) and is
the reference. Ideally, green should be the reference signal.
If your system requires a large delay on the green signal, try using a
crossover patch cable at each end of the link (instead of straight patch cables
to connect to wall outlets). In many cases, the crossover should transfer the
delay requirement to the blue signal rather than green. The human eye is
much less sensitive to blue distortion and so video quality can be improved.
Check the result using the test card and adjust the delays accordingly. The
main cable should be wired according to EIA-568B as shown below.