What would I do as a non engineer?Materials, if you can get it, ungalvanized
pipe, comonly called "black pipe", it is a better quality than galvanized,
which is typically full of defects and camoflaged by the galvanizing.Make a
three leg tower, with legs made up with three lengths of pipe (your spacing )
and lattice braced to the strength you desire) couple the individual leg
elements with threaded couplings to your desired height, stagering the
couplings to each vertically (no joints opposite each other). Taper each leg
having the three elements meet at the tower top, thus making stronger legs than
possible with a single pipe. Situate the triangular legs to your desired
dimension at the base. This will be a three legged tower with a triangular
plan view. Taper the tower up to the size apex plate you desire.Lattice brace
the three legs to each other on up the tower.Paint the tower heavy, with a
brush, for corrosion protection.I would paint every year for three consecutive
years and then stand back and see when it might need it next.There is a paint
called rust bullet, although expensive, possibly you can get some,
JIM, W4QBQ
From: Roger (K8RI) on TT <K8RI-on-TowerTalk@tm.net>
To: towertalk@contesting.com
Sent: Sunday, June 28, 2015 3:33 PM
Subject: Re: [TowerTalk] Homebrew tower
I would be careful adding extra braces. Much of the brace strength
comes from the angles between the brace and legs. Using lesser angles
reduces the strength, requiring still more braces. OTOH. I doubt the
extra braces would cause the tower to collapse under its own weight.
The braces serve to keep the tower legs parallel, which adds a lot of
strength in the lateral plane (resistance to bending in the wind) It
adds little to the ability support a load. IE: dead weight. They also
keep the tower from bending when "tipped up" in one piece. I believe
"X" braces bolted, or welded together where they cross will add strength.
This tower is only going to be about 40 to 50 feet tall and will support
a small beam/tri-bander. I have my doubts about the wind load and
leverage from a mast supporting a 5L 6-meter Yagi and a small 40 meter
beam at the required spacing. I'd be more inclined to use a series of
sloping dipoles on 40 and limit the wind load to a single, small tribander.
I'm assuming that the limitations are materials and budget as they are
for most hams and suitable used towers are not available. That adds
another dimension to the requirements: Durability. To me, it sounds as
if failure of the tower is not an option. Here in the states, we have
the options of used towers and lots of suitable materials to build and
rebuild towers. This does not appear to be such a case. If budget is
the problem, then I'd go conservative on the antennas.
73
Roger (K8RI)
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