[TowerTalk] Steppir 4el on 56' unguyed Trylon T400

[Mark Mellish]

Hi All,
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.