Jeff,
This is an interesting idea, and I've wondered if it could be done. I
haven't pursued it because my TH-7's windload maxes out my MA-770's rating.
These towers aren't designed for a stacked configuration, but I can't think
of a reason it would be unsafe, as long as the combined windload is under
the tower's max rating. Besides, the lower antenna doesn't present the same
bending moment as the top antenna, so it could probably be up-rated.
I think the simplest method would be to use a pair of large u-bolts around
the MA-850. If you can get big enough u-bolts with saddles, and the saddles
are strong enough, you could drill holes in the saddles that line up with
the u-bolt holes on the antenna's boom-to-mast bracket. Then you can mount
the boom-to-mast bracket to the saddles with some short bolts. If you can't
find u-bolts with appropriate saddles, you could make your own out of some
angle stock.
The C3 uses a two-plate mounting system and there's a center bolt in the
mast plate. The head of the bolt is supposed to sit flush against the mast
so you can slip the boom plate over it easily when you mount the antenna. If
the u-bolt saddles are on the mast side of the plate, the bolt won't stay
in. It's no big deal -- the centering bolt is a convenience, not a
necessity. If possible, though, try to put the plate between the mast and
the saddles. That way, you might be able to use the centering bolt as
intended.
The downside to this method is that it may prevent full retraction of the
tower. It's not a safety problem because we're only talking about a few
inches. The problem is that the antenna mounting may slam into the top of
the next section down before the limit switch stops the retraction. If you
don't use the remote control option, or can see the tower from the remote
control location, you can manually stop the retraction in time. If, like me,
you use the remote control and can't see the tower, you may be able to move
the limit switch activation point by lowering the small piece of track it
rides on.
Another problem is that the mounting has to clear all the stuff at the top
of the section -- pulleys, cables, coax standoffs, etc. I think there's
sufficient room, but you need to give some thought to exactly where to place
the mounting.
Hope this helps, and let us know if it works.
73, Dick WC1M
To: <towertalk@contesting.com>
> Date: Fri, 20 Jul 2001 14:06:47 -0700
> From: "BATTIN" <jbattin@starband.net>
> Subject: [TowerTalk] US Tower MA850 Antenna Stacking
>
> I am in the process of putting up a US Tower MA-850 with rotating
> base. I would like to mount a small HF beam on one of the telescoping
> sections. At full extension each section is 16ft apart. If I can I
> would like to stack a pair of C3s or a pair of the new Fluid Motion
> antennas. One beam could be at 87 feet and the other could be at 55
> feet. The separation can also be adjusted by tower height. Does any
> one on TowerTalk know if or what would be the best way to mount an
> antenna to the top of one of the telescoping sections on a MA series
> tower?
>
> Jeff - Ko7p
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