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Re: [TowerTalk] How to support a large loop?

To: towertalk@contesting.com
Subject: Re: [TowerTalk] How to support a large loop?
From: Doug Grant <dougk1dg@gmail.com>
Date: Wed, 22 Sep 2010 16:05:05 +0000
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
> On Tue, 21 Sep 2010 11:01:48 -0600, W4ZW wrote:
>
>>I just received my 1000  spool of flex-weave
>
> My antennas are mostly up 100-120 ft in redwoods, douglas fir,
> and madrones. I have had multiple failures of flex-weave in
> antennas hung in trees and hung from towers. Indeed, virtually
> every antenna I have ever built with flex-weave has failed
> mechanically at points of connection.
>
> ##  and here I thought that flex weave was supposed to be the ultimate wire ?

I used #12 insulated Flex-weave for 80M inverted-Ls in a 4-square a
few years ago. Each wire went up 40-50 feet, then through a
rope-supported pulley, then over to another branch. I left some slack
in the wires, since the location gets a lot of wind, and I wanted the
antennas to ride the wind, not try to fight it. I used Flex-weave
because it seemed that it would run through the pulleys nicely.

After a couple of years, one wire broke at the pulley and came down,
and two of the wires broke inside the insulation...something that I
thought was an old wives' tale until it happened to me. The internal
breaks were at the pulley location. It was an interesting job to
diagnose it...the MFJ meter showed wildly non-resonant impedances at
3.5 MHz, but turning the dial found resonance (35+j0 !) in the 5-6 MHz
range, which told me the wire had broken inside the insulation,even
thought it looked fine from the ground.

When I took the wires down and examined them closely, I noticed a few things...

1. All broke at the point where the wire ran through the pulley

2. The wires were badly corroded

3. There was water inside the wire...when it leaked out, it was rust-colored

My conclusion was that the Flex-weave was significantly stressed going
through a small-diameter pulley (W3LPL agrees with this). The original
pulleys were about 1-inch diameter. I have read that stressed metals
corrode faster and this was probably a contributor. Also, if I had
sealed the "top" end of the wire, the corrosion may have been slowed
down some, but once water gets in, the capillary action of a large
number of small-diameter wires draws it all the way through. And then
the individual strands, which are hair-thin, corrode quickly and break
one by one until that are all gone.

My solution has been to replace the Flex-weave with #13 copper-clad
stranded stuff sold under the name "POLYS-13" from Craig at Radio
Bookstore. I think it is similar to, or the same stuff, sold as
"#531"the Wireman. The Wireman's description reads:

     - Toughcoat 'Silky' 13 AWG, 19 strand 40% copper-clad steel (OD
0.0795") with tough, high density, low-gloss polyethylene (Nominal OD,
0.120" including 0.020" jacket. Designed for through-the-trees, sea
coast, acid rain or other inclement atmospheric conditions. Our most
rugged, longest-lived, stranded antenna wire for any purpose. Jacket
has minimal effect on performance - less than that of a year's
accumulation of oxidation product on bare wire, with less noise.Break
strength 400lbs -

The description of the kind of environment matches where these
antennas are situated (through the trees, seacoast, inclement
atmospheric conditions). This wire is stiffer than the Flexweave, but
easier to work with than solid Copperweld, and does not have that
nasty outer insulation coating that THHN has (which deteriorates in
sunlight and eventually falls off in chunks after hanging off the wire
for a few months).


I also decided to use bigger-diameter pulleys. Stainless/nylon pulleys
are very very expensive ($30-50 each) and I am cheap. I bought
high-strength 3-inch diameter nylon sheaves (the "wheel" part of the
pulley) with stainless bearings for about $5 each, then built my own
pulley frames from aluminum tubing and stainless bolts.

I am two years into these replacement elements and so far, so good.

I kept my leftover unused pieces of Flex-Weave from the spool I bought
originally, and have used it for temporary antennas, because it really
is very nice stuff to work with. But I won't use it for high-stress
permanent antennas at my island location.

Disclaimer - no affiliation with either the Wireman or Radio
Bookstore, but a very satisfied customer of both.

73,

Doug K1DG
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