APPENDIX D: ADVANCED CABLING ISSUES (SKEW)
Optimizing Pairs (General Solution)
Measure pair lengths with a LAN cabling tester (TDR) or view pairs by stripping back a small piece of cable and viewing how tightly pairs are twisted. The most tightly twisted pair is the slowest (longest) and the loosest pair the fastest (shortest). You can also check the relative delays using the test card as described on page 29.
The table below shows the general solution for optimizing CATx cabling for video in order of pair length.
Pins | Pair | Signal |
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7 & 8 | Shortest Pair | Data |
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1 & 2 | 3rd Longest Pair | Blue Video |
4 & 5 | 2nd Longest Pair | Red Video |
3 & 6 | Longest Pair | Green Video |
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Some cables have a ‘3+1’ construction where three pairs closely match. The fourth pair should be used for data and the other pairs sorted as in the above table.
Other cables have a ‘2+2’ construction where there are two sets of dissimilar pairs. Put red and green on one set (tightest) and blue & data on the other.
A suitable
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