[TowerTalk] Mounting the OR-2800 in Rohn 25?

[Gary R. Hosler]

I have an Orion 2800 mounted 8 feet down in the Rohn 25G tower at the junction
of two sections.  The standard AS25G rotor plate works very well there.  As far
as the section joint not being big enough to accomodate the OR2800, I'm
confused.  I have been able to insert the rotor through the "Z" braces and
lowered down to the mounting plate.  No braces were removed or modified.  I also
have a 2nd AS25G mounted about two and a half feet above the OR2800 drive plate
that holds a thrust bearing.  This allows me to remove the OR2800 for service
and have a lower support for the mast.  This was NOT an easy fit!  The present
AS25G plate was not designed to work any place but between the sections.  I made
up a cardboard template of the AS25G and trimmed to fit while working on the
ground using the bottom tower section.  I then transferred the template outline
to the AS25G and used a metal cutting blade in a sabre saw to hack up the AS25G.
Once I could confirm that it would fit I used a spray "cold galvanize" to retard
rust.  I also enlarged the thrust bearing mounting holes to allow some slop to
account for any mast run out.  It works very well but I would not want to have
the modified AS25G take the entire vertical load of the antennas and mast as the
amount of material removed really weakens it.  It doesn't seem to be a problem
as far as lateral support and I use the top bearing to handle the load (as well
as the OR2800).  I built the same setup for a friend and he doesn't even snug
down the lower bearing bolts unless he is going to remove the rotor for service.

de Gary  W0AW




Michael Tope <W4EF@pacbell.net> on 05/05/99 12:31:49 PM

To:   "'towertalk@contesting.com'" <towertalk@contesting.com>
cc:    (bcc: Gary R. Hosler/KHI/Imation)
Subject:  [TowerTalk] Mounting the OR-2800 in Rohn 25?






I am trying to figure out how in the heck to get an M2 Orion 2800 "positioner"
into
Rohn 25. The 2800 has a triangular cross section which lends itself to fit
inside a
"rungless" portion of 25G such as found in the various types of 25G top
sections.
Unfortunately, I would like to place the rotator well below the top of the tower
(10 -
12 feet) to minimize the lever arm effect of the long mast outside the tower
working
against a short piece inside the tower.

One option appears to be to utilize the gaps in the Z-bracing created by the
section
junctions. In this case, the AS25G rotator plate would be mounted just below the
section junction junction (immediately above the highest set of horizontal rungs
on
the section below the joint).

Since the gap created by section joint isn't quite big enough to accomodate the
rotator, I would either have to cut the horizontal rungs just above the junction
(lowest set of horizontal rungs on the section above the junction), or somehow
increase the spacing between two sections using somekind of spacer tubes.
An extra six inches (plus overlap) of straight tubes with no bracing would
create
more than enough room for the rotator, and would make servicing very easy.

Does anyone know if Rohn makes spacers like that I could use to open a gap in
the bracing, or should I sharpen my hacksaw? This spacers would need to be a six
to eight inch piece of 25G leg material with a standard Rohn 25 swage on one
end,
no taper on the other, and holes for 25G leg bolts on each end.

Thanks again.

Mike, W4EF.................


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