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Re: Topband: Pulleys for antennas in trees

To: topband@contesting.com, towertalk reflector <towertalk@contesting.com>
Subject: Re: Topband: Pulleys for antennas in trees
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 27 Jan 2015 10:32:00 -0800
List-post: <topband@contesting.com">mailto:topband@contesting.com>
On Tue,1/27/2015 9:50 AM, Mel Crichton wrote:
So if using a pulley, please be sure the supporting branch is stout.... I had to replace the windshield of my truck to prove this point to me. I find it best to install inverted vee type (center supported) dipoles or very light inverted L's to minimize the sideways stress on the branch (sideways stress intensifies when the wind blows hard). And yes I have pulleys high in trees.

Hi Mel,

I can't dispute your mechanical engineering and rigging thoughts, but I strongly prefer flat dipoles if I can rig them. So does N6BT, the excellent antenna engineer behind the original Force 12 antennas, who observes that the performance of the antenna will be dependent on its average height.

Quite a few years ago, I saw a piece in QST stating that a lag screw going horizontally into the trunk of tree was one of the least invasive ways to rig an antenna. That means, of course, that someone has to climb the tree. My wire antennas are mostly rigged that way.

Since the subject line is about pulleys, I'll link to the pulley I use. It's a really neat pulley, and is sold out here by stores who cater to arborists and tree climbers.

http://www.cmi-gear.com/collections/frontpage-2-service-line-pulleys/products/rp115

Here's a photo of the pulley and the lag screw.

k9yc.com/Pulley.JPG

I use the 5/16-in rope distributed by Synthetic Textiles. DX Engineering and HRO also sell it. I use the 5/16-in size because it's big enough to be able to grab it hard enough to put a lot of tension on it. It's a double-braid polyester rope with a black outer sheath that provides UV protection.

 http://www.synthetictextilesinc.com/supportham.html

My wires are up 130 ft in redwoods, so they need pretty robust rigging hardware. Not everyone needs stuff this robust. :) Another important rigging element for any wire in a tree is a weight below a pulley terminating one end of the antenna to provide some "give" for tree sway. There are many ways to skin this cat, including old window weights and cement in a bucket. I use big water jugs that I fill with dry sand. I'm typically using 70-90 pounds of tension.

73, Jim K9YC

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