Here is the straight skinny on 25G top sections:
Several years ago (ten or more) Rohn redesigned the 25AG2 and 25AG3 top
sections to use a 2.25 inch o.d. 14 gauge wall top support tube. After
galvanizing these top sections will fit with a 2 inch o.d. mast (also
galvanized) and have a clearance of about .050 inch left over.
Before the redesign a 1.9 inch o.d. mast would fit ok but a 2 inch o.d. mast
would bind in the top tube.
As a side note, Rohn also redesigned the TB3 thrust bearing to fit the 2 inch
o.d. masts instead of the older 1.9 inch o.d. masts.
I just tested a new 2 inch o.d. mast in a 25AG2 top section and the fit is
just right for free rotation of the mast. The clearance is close enough
though that without shims in a Ham 4 or T2X rotator there will be binding of
the mast. Also, the associated AS25G rotator plate is not exactly a precision
built piece of equipment and some "adjustment" of the mounting ears might be
required to center the rotator mast clamp with the support tube. Aditionally
the 25AG2 or 25AG3 top section suport tube can be out of plumb just enough to
cause binding; they are not exactly precise either. Adjustments of the
rotator plate can accomodate all of these errors but some patience might be
needed.
73 de Gerald Williamson/K5GW/Texas Towers
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