[TowerTalk] twisted pair capacitance

[Jim Lux]

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.

Jim, W6RMK