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Re: [TowerTalk] LMR400

Subject: Re: [TowerTalk] LMR400
From: W0UN -- John Brosnahan <>
Date: Thu, 27 Sep 2007 12:43:48 -0500
List-post: <>
At 12:20 27-09-07, you wrote:
>LMR400 has a minimum bend radius during use of 4
>This tells me that it is ok to us it on a rotatable
>antenna as long as the minimum bend radius is 4 inches
>or more - that is, the loops around the mast have a
>minimum diameter of 8 inches.
>Is this ok?
>Thanks in advance.
>Jeff, W3KL


There is a big difference between a one-time (or limited number of
bends) bending radius and repetitive flexing. I would use something
like Ultra-Flex for repetitive bending applications around a rotator.

But if you must use something like LMR400 I would make the bend
larger and make the percentage of flexing limited to a small amount.

I tend to wrap MULTIPLE coils of cable in a flat plan around
the mast at the top bearing point.  As the rotator goes through
360 degrees the increase and decrease of the coil diameter is
small since it is distributed among a number of turns.   (And
the coil also acts as an additional RF choke for currents
flowing on the outside of the shield.)

So I would wind, say, 4 or 5 turns of coax around the mast with
a 12 inch (minimum) diameter and then as the rotator turns
this coil will expand or contract slightly, with no gross bending
in any small region.

Of course the details of your installation may limit your options.

--John  W0UN


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