Topband: Peru report....and how to make fireworks with an inverted L
jim at audiosystemsgroup.com
Tue Dec 11 03:08:34 EST 2007
On Mon, 10 Dec 2007 17:06:58 -0500, Jeff Maass wrote:
>Where the previously-insulated reflector wire
> was making contact with a limb of a bushy
> tree, the wood was seriously charred.
My wire dipoles are hung up about 120 ft in giant redwoods. For
nearly a year, one end of the 160 dipole was in contact with
branches of the tree that supported it. The wire was #12 THHN. It
worked fine and stayed up. (It was touching the tree because there
was also a 20/15/10 trap dipole in line with it, and there wasn't
quite enough room between the two trees to do it "right.")
Several months ago, I dropped it, found a new home for the
20/15/10 fan so that the 160 dipole wasn't in the tree, and pulled
it back up. I had bare copper at the end in contact with a
thimble, and that 5/16 inch rope of the type sold by DXE and
others went through the thimble. Somehow, 1.5 kW melted that wire
and dropped the antenna to the ground.
I observed that the #12 THHN at the end of the antenna was heavily
charred, and melted through in many places. But it didn't CAUSE a
problem -- in fact, it prevented the rope from melting by
discharging the high voltage at the end of the antenna to the
tree. When I pulled the antenna out of the tree, the high voltage
soon (within a week) melted the rope!
I've since re-rigged all of my antennas with end insulators so
that no bare wire is in contact with rope. One suspects that
moisture in the rope supports enough current to cause the heating.
That might also be a problem at your QTH.
Jim Brown K9YC
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