At 11:56 AM 6/11/2007, Jim Jarvis wrote:
>Tom's right. What you were thinking of is telco cable,
>where the pairs are twisted for a distance, then twisted
>in the REVERSE direction for an equal distance. the result
>is that at audio frequencies, the net capacitance is reduced.
Or, actually, that cross talk to adjacent pairs is reduced, and that
the parasitic C from conductor to shield/ground is balanced. I don't
think it would reduce C, and because it's very stretched out, it
doesn't reduce inductance either.
You can also see this on 3 phase power lines, where the positions of
the phases on the supports are periodically rotated, so that the C to
ground is balanced.
And, if they still exist, on wayside telephone lines next to train
tracks, where every few dozen poles, one of the pairs gets swapped around.
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