IHSE USA R434-91 Series SDLink Rackmount Hubs User Manual
Page 55
Appendix D: Advanced Cabling Issues (Skew)
53
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 24.
The table below shows the general solution for optimizing CATx cabling for
video in order of pair length.
Pins Pair
Signal
7 & 8
Shortest Pair
Data
1 & 2
3
rd
Longest Pair
Blue Video
4 & 5
2
nd
Longest Pair
Red Video
3 & 6
Longest Pair
Green Video
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 pair-swapping scheme is easily made using custom wired patch
cables at each end.