Hi All and Happy Holidays,
I'm in the process of trying to put together an installation of Rohn 25g
somewhere between 39 to 49 feet high as the first of several towers for my
QTH.
However, I have been unable to find enough sufficient information in the
Rohn published specs to put together what I believe is a suitable engineering
package to request a building permit.
My proposed installation is as follows: Concrete base 3.5'x3.5'x3.5'
reinforced with a rebar cage and utilizing a Rohn SBH25G (short tilt tower
base
section) encased in the concrete base, tower bracketed to the house at the 21
foot level, bracket (Rohn HB25CG) bolted to the house with 4 threaded rods
extending 6 - 8 feet into the attic, double bolted through multiple arrays of
2 x
4 wood joist stud supports, and extending the tower another 18 to 28 feet
above the bracket without any guys. The antennas (VHF/UHF yagis) will be
mounted to a Glen Martin Hazer H-4 with a total windload of around 10 square
with
the hazer only extended during times of station operation.
What are your thoughts concerning my proposed installation and what is the
best way to convert the data provided by Rohn? The specs provided by Rohn for
bracketed towers don't cover anything bracketed below 30 feet and extending
to 39 feet, or bracketed with one bracket. I can use two brackets, but the
lower bracket would not provide much support, because I can only attach it to
the 4 inch wall studs or use anchors behind 3/4 inch plywood without
performing modification to the wall framing of the house. I know using
less/lower
bracket support devalues the tower load rating, but by how much? The tower
would probably never need to be climbed above 30 feet as the hazer can be
lowered down to 21 feet which allows the antenna system to be worked on at or
just
above the roof top level, and if necessary the tower could also be tilted
over.
I previously performed a similar installation at a prior location with the
bracket at 18 feet, tower to 39 feet, with a windload of about 16-18 square
(stacked Cushcraft X-7 with X740, under a 13B2 and a A50-5S, H-4 Hazer, single
12 foot Hy-gain mast, Yaesu SDX 800 rotor). The installation was very secure
without any problems even during an ice storm with 3/4 inch ice loading, but
I installed it without obtaining any permits, therefore I don't have any
engineering calculations from the last time.
Thanks for any input.
Jim, AB4D
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