On Wed, 22 Sep 2010 16:05:05 +0000, Doug Grant wrote:
>When I took the wires down and examined them closely, I noticed a few
things...
>1. All broke at the point where the wire ran through the pulley
>2. The wires were badly corroded
>3. There was water inside the wire...when it leaked out, it was rust-
colored
>My conclusion was that the Flex-weave was significantly stressed going
>through a small-diameter pulley (W3LPL agrees with this).
All of this is consistent with my experience, although I wasn't observant
enough to notice the water issue, or to notice there was any steel
content. I used flex weave to build several fan dipoles, using 1/2-inch
PVC conduit as spacers, with the wire running through holes drilled in
the spacers. Two of these wires broke at a spacer, and there was
significant wear at multiple spacers.
>My solution has been to replace the Flex-weave with #13 copper-clad
>stranded stuff sold under the name "POLYS-13" from Craig at Radio
>Bookstore.
Sounds very interesting.
>nasty outer insulation coating that THHN has (which deteriorates in
>sunlight and eventually falls off in chunks after hanging off the wire
>for a few months).
Aside from the visual aspect of that coating falling off, I haven't seen
any electrical or mechanical issues on my antennas. BTW -- if I'm not
mistaken, that outer coating is a protective nylon. The underlying PVC
insulation remains intact. It could, of course, be an issues if the wire
were moving through a pulley, but I wouldn't do that -- I think that the
flexing of the wire would eventually cause failure unless the wire was
especially designed to be flexed.
Rather, I run ROPES through pulleys, trying to use rope and pulleys that
are mechanically suited to each other and to the environment. What I
would GREATLY appreciate is for guys like Frank, who have detailed
knowledge of pulleys and ropes to write up some specific advice on the
subject, including part numbers and sources of both pulleys and ropes.
I found the CMI RP115 at a shop here in Santa Cruz that specializes in
hardware and equipment used by tree climbers. The website lists MANY
distributors. This is only one of MANY pulleys that CMI makes.
http://www.cmi-gear.com/catalog/pulleys/2insvc.asp
Although it isn't clear from the photo, the two halves of the red sheave
rotate to expose the barrel, so that the middle of a rope can be looped
over the pulley rather than needing to be threaded through it from one
end of the rope. This can be VERY helpful in rigging. I use these with
the 5/16-inch antenna rope that is sold by several good ham vendors,
including DXE, the Wireman, and Ham Radio Outlet.
73, Jim K9YC
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