Hi Phil!

Their are a couple of reasons for twisting:

-mechanically, the bundle handles better, like a single wire.
-interference cancellation.  This is the most often thought about, but
you may end up with too few twists if you ignore the mechanical reasons.
The idea is that magnetically coupled interference will cancel because
in successive twists the induced current will be in opposite directions.
Theoretically you end up with a bit left over if you have an odd number
of twists.  The wires between each set of crosses behaves like a loop
antenna.  The amount of energy coupled into each of these antennas
depends on the distance between twists and the enclosed area of each
twist.  Since the twisting forces the wires tighter together, that helps
a lot too.  In order for the energy coupled into each of these loops to
cancel properly, the magnetic fields need to be relatively constant.
This consistency depends on a whole bunch of factors, but the wavelength
of the interfering signal is the major one.  The higher the suspected
interferer, the more twists you want.  Ten twists per wavelength of the
highest frequency you are trying to carry with the twisted pair is
probably not too bad a place to be in, but most people do far more for
the mechanical considerations--as noted above, keeping the "loops"
closed up tight.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Tuesday, December 11, 2007 10:06 AM
To: [log in to unmask]
Subject: [TN] twists per inch

Is there any standard on the number of twists per inch for twisted pair
wire?

Thanks in advance.

Phil Nutting

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