On Fri,6/24/2016 8:16 AM, jimlux wrote:
or that matter, that's why cat 5 has twisted pairs with different
twist rates.
Actually, the reason is to minimize crosstalk between pairs by the
mechanism that Neil Muncy (W3WJE, SK) called "shield-current-induced
noise." He was describing it on shielded twisted pair where the shield
was foil plus drain, with the drain twisted at the same rate (lay) as
the signal pair, but much closer to one of the pair conductors than the
other. That caused shield current to inductively couple more strongly to
that conductor than the other, creating a differential voltage in the
signal pair. The different twist rates of CAT5 eliminates that by
randomizing the coupling.
His paper documenting both this mechanism and The Pin One Problem were
presented in Oct 1994, and published in the Journal of the Audio
Engineering Society in June 1995. That same issue also includes Bill
Whitlock's definitive work on the balanced interface, which caused IEC
to later rewrite its Standard on measuring balance in circuits. JAES is
in most engineering libraries, and articles can be downloaded from
aes.org (but not for free).
73, Jim K9YC
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