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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