[RFI] Re-wiring station
cbrown at woods.net
Sat Dec 31 06:21:08 EST 2016
There were a number of specs, but for practical purposes
The actual CAT5 specs were almost entirely performance driven.
Std practice to meet the CAT5 performance spec or 155+ACR extended
Per pair twist rate
Insulation type and thickness
pair to pair / pair to outside world orientation over length
Getting into later 5+, pre6 and 6 specs along with multi-cable bundles
things get even more complex.
Things life different insulation materials and thickness per pair within
a cable and similar were fairly common for a while.
But, as I said, specs were almost entirely performance driven, the exact
details of HOW the specs were met was up to the cable maker.
This is a fuzzy memory from 20+ years ago, but IIRC in the early Cat5
days some makers used per pair twist rate to meet crosstalk specs and
some used controlled weave/positioning of pairs initially...But, per
pair twist rates were cheaper and worked better, specially for the
extended spec and quickly became the norm.
On 12/30/16 23:55, Jim Brown wrote:
> On Fri,12/30/2016 8:50 PM, Robert Nobis wrote:
>> As I recall, the CAT5 or CAT6 specifications do not actually
>> specify that each pair have a different number of twists per inch.
>> They do specify that all pairs be less than 38mm per twist and that
>> pair twist lengths shall be chosen to ensure compliance with the
>> transmission requirements of the standard. In practice, I believe
>> manufacturers are using different twists per inch on the wire pairs
>> in order to meet the specifications for cross-talk.
> I haven't read the spec, but since crosstalk depends on the four
> pairs having a different twist ratio, I would bet that those values
> ARE part of the spec. I may be the guy who made hams aware of that
> practice. Some of the big sound systems I was designing used Ethernet
> infrastructure to carry dozens of channels of audio around facilities
> in sync with each other, so I had to learn at least the basics of how
> those systems worked.
> No, the original question wasn't about CAT5 cable, but the principles
> are the same. I thought I answered the original question about twist
> ratio -- more is better, but for our purposes to carry noisy power,
> it's not critical. :) BTW -- twisted pair is also FAR superior to the
> glorified zip cord sold to hi-futility nuts as speaker cable. I've
> solved a lot of RFI issues by replacing zip cord with twisted pair,
> and if big conductors are used (#10 - #12), the twisted pair also
> provides the best possible audio performance from the speakers.
> 73, Jim K9YC
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