You made no mention of how you measured the skew in the cable. If you =
used a TDR technique, then was the risetime the same amongst the pairs? =
It may be that the bandwidth of the different pairs is not the same and =
you may be seeing the effects of limited bandwidth. This may be a case =
where a network analyzer would be more useful.
Chuck Hill, consultant
From: Muzahid Huda
Sent: Monday, March 23, 1998 7:40 PM
Subject: [SI-LIST] : Cable skew
I have just finished measuring the intra-pair skew in seven samples of a
6-foot twin-ax cable. This cable consists of 4 twisted pairs (ie. 8
lines) and an individual shield for each pair (ie. 4 shields). The =
bundle is enclosed by an outer shield.
In all seven samples, the measured intra-pair skew in three of the pairs
was within 50ps. The fourth pair consistently exhibits at least
150ps-200ps of skew. In these samples, it is always the <underline>same
pair</underline> that consistently measures this variation.
I have checked my measurement technique and equipment to eliminate any
systematic errors. I have also cut open a cable to check for physical
length differences, etc. The cable assembly has a molded ferrite choke
on one end; I have even removed this choke and remeasured the skew.
Nothing seems to make a difference.
Any suggestions/ideas/theories will be greatly appreciated.
Silicon Image, Inc.
Tel: (408)873-3111 X132