I'm intending to put up my "retirement" antenna and tower soon. The tower is a
Trylon T400 self supporting model, with a Cougar belay system The base calls
for 6 yards of concrete with a rebar cage.
I have a length of schedule 80 1 1/2" T6061-T6 aluminum pipe for the mast.
This is od 1.90" with a .200 wall thickness. I know that 2" tubing with .250
wall would be better, but it is difficult to get in my area, and funds are
finite. The mast will be mounted 16' in the tower and turned by a Tail
Twister, with a Steppir 4 el mounted as close to the top bearing as possible.
The Steppir 4 el is rated at 9.7 sq. ft. I figure the boom will be about 1.5
feet above the bearing at the most, with 3' above that to accommodate the boom
truss, and possibly a uhf/vhf vertical. I know that some have found the Tail
Twister to be somewhat unreliable, but that is what I have to work with for now.
I used K7LXC's antenna/mast calculator for this combination using 24000 psi
mast yield strength, and it seems to say it would be good for 100 mph wind
speed. Did I do this correctly, and does it seem okay? I guessed that adding
a uhf/vhf vertical would add 2 sq ft at the most.
My next worry is that the 2" boom plates to mast u clamps supplied by Steppir
might turn on the 1.9 od pipe. I am thinking of getting some heavy duty ones
from DX engineering. They are also designed for 2" od tubing, but they look
like they would have much more surface area with which to grip the slightly
smaller mast. The Tail Twister is designed to pin the mast at the rotor.
Could I pin the boom plate to the mast as well or would this weaken it too
much? I will be using stainless shim stock to center the mast in the rotor;
could I shim the mast u-clamps? If I use stainless shim stock, should I use
Penetrox or similar to inhibit corrosion? Would this make it too slippery, and
allow the antenna to turn on the mast?
I am also considering the optional Steppir Connector Junction Box. I figure
this will make it easier to take down and trouble shoot if necessary.
Any thoughts or suggestions would be greatly appreciated.
Thanks, VE7YMM, Mark.
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