Jack, for the past 10-12 years, our club has used a simple device for our 80M
vee over a 20M quad for Field Day. We found a sealed automotive bearing whose
O.D. was just right for slipping into the mast we use to hold the Vee above the
quad (you'll have to do the math to figure out how high it needs to be to clear
the A3WS). Slot the mast so the bearing can be FIRMLY clamped into the mast at
the top. Find a 1/4-20 galvanized eyebolt about 10" long, and bend the threaded
end, with heat, at 90 degrees to the 'eye-end'. Bend just enough of the
threaded part to be passed through the I.D. of the bearing and be clamped in
place by washers with nuts on top & bottom. We used the washers that are found
at the top of automotive front shock absorber mounts (the ones that squeeze the
rubber mounting washers). The nice thing about these washers (the metal ones)
is that they are dished a bit and will self-center in or around the bearing
I.D. while clearing the outer race. With the bent end
in place in the center of the bearing, clamp the bearing O.D. in the mast
using a S.S. hose clamp. Now you have a pivoting hanger that's offset from the
mast by the unbent length of the eyebolt. It might be a good idea to use some
cold galvanizing at the spot that was heated.
When you choose the anchor points for the inverted vee ends, make sure they are
not directly in line with the mast. There needs to be a little side-load on the
eyebolt to keep it always on one side as the mast rotates under it. You'll have
to adjust the antenna tension by watching the position of the pivot; pull one
end or the other until the pivot is straight out from the mast and roughly 90
degrees to the plane of the vee. A loose wrap or two of coax around the mast
will be sufficient. We use two 10' sections of cheap TV mast, but that's a
Field Day approach and, besides, you might need more height to clear the yagi.
We've always wondered about whether the threaded part in the bearing would
remain lined up with the mast axis, but it has survived a LOT of Southern
Summer thunderstorms and is still perfect. One weekend per year doesn't amount
to a definitive test, even after quite a few years; but there's no evidence of
degradation so far. I wouldn't hesitate to use it for a
permanent installation, but your mileage may vary!
Good Luck!
Chuck, N4NM
----- Original Message -----
From: Jack White
To: towertalk@contesting.com
Sent: Wednesday, August 17, 2011 2:31 PM
Subject: [TowerTalk] Inverted vee mounted above HF Yagi
Hi Guys
I have a standard 60ft Versatower with a Yaesu G-1000 and bearing mounted at
the top, and just above this I have a Cushcraft A3WS (pic on QRZ). I want to
extend the stub mast about 20ft above the A3WS to support the centre of a
160/80/40 trapped inverted vee. I'm looking for some type of mount that will
allow me to mount the centre of the inverted vee at the top of the stub mast
and remain fixed whilst the stub mast rotates. Ideas/advice would be great.
73, Jack G8DX
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