I have a bunch of Force 12 antennas up in the air, all without any problems
for years. However, that is probably because a good friend of mine bought a
bunch before me, and rather quickly had one of the sections of element tips
simply drop to the ground. The preferred method of construction was to have
three rivets, all on positioned on the bottom of the element and on only one
side of the element. There was enough "play" in the telescoping elements
that the rivets would simply gradually be worked by the play until the
rivets dropped to the ground and the element sections worked out of their
telescoping tubing and drop to the ground also.
MY friend (K5JZ) spent a lot of time talking with Force-12 and they came up
with the process of using 6 rivets per junction, three on one side of the
tubing and opposed by three on the other side of the tubing so they were 180
degrees apart. Placing them on opposing sides removed all the very small
"wiggle" of the elements and held them firmly in position.
On the big elements (40 meter linear loading and 20 meter yagis), George
wrapped each junction with several layers of Scotch 33, then Scotch C-130,
and finally coated the wraps with Scotch liquid electrical tape. He had no
more problems with rivets coming out.
I followed his exact procedure with my identical 340/620 Force 12 yagi and I
have had no problems with either element separation or rivet loosening. My
elements have been up in the air quite a while and no problems.
WE both were close enough to the Gulf of Mexico that we experienced repeated
hurricanes and salt water destruction of joints. The taping procedure adds
to element wind surface but stopped oxidation and corrosion problems with
elements.
Gary W5FI
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Ed Muns
Sent: Wednesday, February 23, 2011 1:37 PM
To: 'Barry Gross'
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Force12 rivets
Barry, N1EU, asked:
> I'm not sure if Force12 still uses riveted construction of
> yagi elements.
> In any event, I just experienced my first rivet failure on
> my C3S (great timing, huh?) and would like to avoid repeating
> this experience. What is the tried and true wisdom on
> preventing rivet failure on these antennas?
N6BT always advised me to put three rivets at each location, 120 degrees
apart around the element. On smaller diameters, only two may be possible
and even they may have to be staggered. What you are trying to prevent is
any wiggle that will, in time, break the rivets.
This has (anecdotally) worked for me for two decades in a high-wind
location.
Ed - W0YK
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