Hi Pete,
I have am identical setup.
AB-577
C3S Force 12 tribander
6M5X M2 6m yagi just above the C3S but only about 3ft above.
10 ft aluminum mast
G-1000 rotor
I originally had the 6m yagi mounted about 8ft up.
As it turned out, we had to lower the tower for a minor rotor problem.
While doing that it was decided the load of placing the 6m near the top (around
7-8ft above the C3S) was too high.
A local ham did the calculation and the difference was frightening.
We put the 6m yagi only 3ft above the C3S, absolutely no ill effects.
Low SWR on the 6m yagi, and low normal SWRs on the C3S (all favoring CW, but
typically under about 1.6:1 upper band edges 15 and 20.
You probably wouldn't have any trouble with the 6m higher up but why risk it?
I don't think 3 or 4 ft higher will give you much extra performance.
I put the AB-577 up last Oct. It's made it through the winter, only a couple
big storms, but one storm had 60mph winds and the yagis didn't even flex a bit
in the wind. Something to be said for trapless design!
73 and all the best,
Darrell AB2E
________________________________
From: TowerTalk <towertalk-bounces@contesting.com> on behalf of Pete Smith N4ZR
<pete.n4zr@gmail.com>
Sent: Sunday, June 4, 2023 9:40 PM
To: TowerTalk <TowerTalk@contesting.com>
Subject: [TowerTalk] Antenna 6 feet above the top of an AB-577
I am planning to put a 3-element 6-meter yagi 6 feet above a C-3E
tribander, which in turn is supported by a Yaesu G-1000DXA rotator on
the top of an AB-577 tower. An engineer ham friend has raised the
question about whether one can do this successfully, given the side
loads that could be applied to the rotator's case by wind, a 6-foot
lever arm and this small yagi (1.8 square feet of wind area in a pretty
sheltered location).
Yaesu, characteristically, shies away in horror from any such thing -
the manual recommends only using the rotator *inside* a tower, with a
thrust bearing above it to carry mast loading. On the other hand, my
C-3E has survived 5 years mounted on top of the AB-577. Their manual
writers are extraordinarily conservative, so I'm asking for real-world
experience. Have you mounted a small yagi like this above a G-1000DXA,
and if so, what and how far above?
--
73, Pete N4ZR
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