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Re: [TowerTalk] Conduit for cables to the tower?

To: "'Jim Brown'" <>,"'Tower Talk List'" <>
Subject: Re: [TowerTalk] Conduit for cables to the tower?
From: "Daron J. Wilson" <>
Date: Thu, 14 Sep 2006 16:19:12 -0700
List-post: <>
> First, use TWISTED PAIR for all control cables and for power. This
> minimizes crosstalk/noise to control lines. Don't bother with
> shielded cable -- cable shields provide NO magnetic shielding, and
> virtually all coupling below 1 MHz or so is magnetically coupled.
> Twisted pairs also reduces the coupling at RF.

Twisted pair is a wonderful technology for balanced circuits, but, doesn't
do the same for unbalanced circuits.  Try running your coax (unbalanced)
twisted around another coax, you don't get the same results.  Many circuits
for control are unbalanced, while you may gain something by putting a
control signal (DC) on one wire of a pair and it's respective ground on the
other wire, simply taking 12 control wires that do different things and
putting them on twisted pairs doesn't necessarily benefit you.

As far as shielded cable, I strongly disagree.  We run literally miles of
shielded twisted pair for current loop controls.  There is a reason they
make it, there is a reason they sell miles of it, and that is basically for
the improved isolation from other signals by having a (grounded) shield.  Be
sure to ground the shield at least at the station end, it may be
advantageous to not ground it at the distant end depending on what you have
on it and how it works.

Having wired a few AM studios where the transmitter is in the building, we
exclusively used shielded twisted pair wire and even then it was a challenge
to keep the RF out.

Your mileage may vary.


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