Topband: Inv-L wire in contact with tree branches
jim at audiosystemsgroup.com
Fri Sep 28 13:08:49 EDT 2012
On 9/28/2012 8:45 AM, Gary Smith wrote:
> All that to say; since I have no choice
> but to run the wire over the tree tops,
> what would be a better wire?
I'm near the Pacific coast, and also get some pretty good winds. K2RD
showed me a really nice method of dealing with your problem. It takes
more work to get it done, but it stays up. First, launch fairly small
diameter line or rope over your high branch, then use it to pull up some
of the nice support rope that DXE and others sell. I use the 5/16-in
diameter size. My neighbor, W6GJB, an aeronautical engineer who works in
the space program, recommends Vectran rope, which you can buy from
sailing supply stores. It's pretty pricey, but quite strong. Use enough
of that rope to make a continuous loop, secure a pulley (a marine
pulley) to it, put your antenna wire through it, and pull the pulley up
to the top. Put an insulator at the far end and tie down at a suitable
point. Somewhere in that system, use a weight to control the tension on
the wire so that it can move in the wind. Now, when the trees move,
the motion is at the pulley, and there's relatively little rub on the
rope going over the branch.
In my 160M Tee vertical, I have a "mechanical fuse" at the base in the
form of mating banana plug and jack. There's a bottom insulator tied
down with a length rope that is slack under normal conditions, but which
secures the wire when the wind opens the fuse.
BTW -- my current favorite wire for high antennas that see a lot of
stress is #10 THHN. It will stretch with a lot of tension on it, but
that's easy to deal with if it's up with pulleys. Every few years I
lower my 80/40 fan and trim the 80M elements.
73, Jim K9YC
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