I would add that in my experience THHN (house wire) used as twisted pair
has a "much" better memory than zip cord for twists. The BIG audio
cable with its very thick insulation make getting a reasonable twist
very difficult and much of that will untwist.
73, Roger (K8RI)
On 12/31/2016 3:55 AM, 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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