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Re: [TowerTalk] Mechanical weak link in leg of dipole

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Mechanical weak link in leg of dipole
From: Steve65 <steve65@suddenlink.net>
Date: Sat, 24 Jun 2017 11:36:19 -0400
List-post: <mailto:towertalk@contesting.com>
Hi John,

In my initial posting I forgot to mention the reason for my concern. The north leg of the dipole is supported on the west end of my house at two points. A tree limb falling on the south leg of the dipole would damage those two supports, the areas of the house where the supports are attached, the ridge vent and perhaps shingles. So my goal is not protecting the antenna wire, but, rather, the north supports and roof of the house.

Some web sites I've looked at say the tensile strength of #14AWG stranded copper wire is around 130 pounds. So my thinking is to insert a short length of something much weaker at the south end between the insulator and the support rope.

This is new ground for me, so advice and ideas are appreciated. What should the "something much weaker" be? Rope? Fishing line? Other? What should its breaking point be in order to avoid nuisance breaks but still protect the stuff at the north end of the antenna?

Steve, K8JQ

On 6/24/2017 10:04 AM, john@kk9a.com wrote:
What is your concern? I use the same wire for temporary Beverage antennas
and twice in the last 10 years I had tree branches fall and break the wire.
It is easy to splice the THHN back together.

John KK9A

To:     TowerTalk <towertalk@contesting.com>
Subject:        [TowerTalk] Mechanical weak link in leg of dipole
From:   Steve65 <steve65@suddenlink.net>
Date:   Fri, 23 Jun 2017 15:38:31 -0400
List-post:      <mailto:towertalk@contesting.com>
Hello all,

The south end of my 80-meter dipole runs among trees. The trees are higher
than the antenna wire and have limbs which are above the dipole. Big limbs.
The dipole is made of #14AWG THHN. It is supported at its southern end with
about 40ft of 3/16in rope tied off in a tree.

One of the trees that is near the antenna is a large beech. One of its limbs
broke off a few months ago and narrowly missed the antenna wire. I'm
thinking about installing a mechanical weak link in this leg of the dipole
that would break if one of the heavy limbs falls across the antenna wire.

Good idea? Bad idea?

What material would be a good choice for the weak link?

Thanks.

Steve, K8JQ

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