I think putting 5' of your 15' mast in the tower is a good plan. I also
think that two guy points should be very sufficient for a 70' tower. I
have attached guys to the top mounting plate with excellent results, however
for some people this is in the way when installing the antenna or they have
problems with the coax loop. If you are really concerned about twisting, a
star guy works much better than torque arms.
John KK9A.
To: towertalk@contesting.com
Subject: [TowerTalk] How to get PE wet sealed drawings for Rohn 55G less
than 100'? Masts and guys?
From: <trappaport@austin.rr.com>
Date: Sat, 1 Aug 2009 12:33:37 +0000
I am trying to get wet sealed VA engineering drawings for Rohn 55G towers at
70' height, as this is a requirement for the building permit application in
Montgomery County, VA. I already obtained the required soil samples that
shows
excellent ground for holding towers. I plan on putting up both a C31XR/HD
and a
Magnum 240N/HD on each tower (combined weight of 170lbs), and using Yaesu
2800
rotors. Wind load will be about 20 sq. ft. Being on a mountain top, I want
this
to be overengineered..But getting engineering drawings from Rohn has taken
over
6 weeks and I still dont know if they will be able or willing to provide
them.
Time is of the essence!
1. Any PEs out there who can do accurate engineered drawings for Rohn 55G
with
guys and windloads, in case Rohn fails me? Rohn's standard catalog for 55G
does
not go below 100' and I dont want to try and substitute 45G drawings that
don't
meet windload. I am a PE myself, but would prefer a neutral 3rd party to do
the
calculations.
2. Would a 2" steel mast pipe work, and what length/vendor/supplier would
you
recommend? should I get a 15' mast pipe and have 5' in the tower and 10'
above
the tower holding the 2 yagis? Is there a formula or rule of thumb for how
much
mast pipe protrudes above the tower and how much goes into the tower for the
rotor?
3. I plan on using 2 sets of guy wires (should be enough, yes?), and wonder:
Should I attach the top set of guy wires to either (1) a tower top mounting
plate (with thrust bearing); (2) a guy mounting bracket a few feet below the
tower top; or (3) a torque arm stabilizer a few feet below the tower top?
Which
one assures greatest stability in wind/ice on the mountain top? All of Rohn
standard drawins appear to show configuration(2).
Many thanks, Ted N9NB (trappaport@austin.rr.com)
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