Hi Bob,
As you may know, the original Telrex designs used a double wall tip to
dampen the low rate oscillations caused by the wind or other (and many used
the corona tear drop too). The double walls on the element tips of my
20M436 were in the neighborhood of 4' - 6'. Put in backwards the element
tips broke off in just a few months. Double wall toward the boom and none
failed, ever. And it never rattled in the wind either. Element wig-wag
became my next foe...
73's Mike K9MK
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Robert Chudek - K0RC
Sent: Wednesday, September 07, 2011 6:16 PM
To: TowerTalk@contesting.com
Subject: Re: [TowerTalk] Aluminum tubing slip joints seized - my final
answer
The issue was a little more "complex" than I first thought.
I discovered there wasn't a simple 4" to 6" of overlap, but about 48"
instead. It's apparent this antenna was not assembled to manufactures
specifications. The extra tubing did not add to the mechanical strength.
It only added unnecessary weight. The excess tubing was at the tip end
of the tube, not the tower end.
What did work to some extent was inserting another (long) tube from the
opposite direction and driving the inside tube toward the tip. This was
only partially successful and I had to resort to the hacksaw. Actually,
I used a tubing cutter for a clean cut. Then I drove the remaining
inside piece back toward the tower end. I had to use this method on both
halves.
Pulling a few pieces from my aluminum pile I was able to reassemble the
antenna. At the same time I added stiffening to the junctions by adding
internal sleeves where needed.
The remaining task is to model this (again) and see how to make a 62.5
foot element resonate at 7.1 MHz. I'm thinking capacity hats somewhere
out near the ends, like the Cushcraft 2 element 40m yagi.
73 de Bob - K0RC in MN
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