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

[Hans Hammarquist]

If you chose a fishing line you have a nice indication of the strength of the line, right?

Hans - N2JFS


-----Original Message-----
From: Steve65 <steve65 at suddenlink.net>
To: towertalk <towertalk at contesting.com>
Sent: Sat, Jun 24, 2017 11:38 am
Subject: Re: [TowerTalk] Mechanical weak link in leg of dipole


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