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

[K7LXC at aol.com]

In a message dated 6/8/2009 3:08:08 A.M. Central Daylight Time,  
towertalk-request at contesting.com writes:

>  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.


    The T2X should be fine with this antenna. As long  as the rotator has 
been checked out and bearings re-greased before you install  it, it should 
work FB for years. 

>  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.
 
    Looks like you're good to go mast-wise.  

>  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.  
 
    Well, 2" is 2" so there will a little slop in  there. The SteppIR mast 
clamps are also close tolerance so they'll work as  well as the DXE 
versions. 
 
>  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?  
 
    Well, I wouldn't pin the mast to this rotator -  you'll just find the 
next weak link in the system. And in this case it's the  brake wedge and then 
the transmission ring gear. Better to let it possibly  slip in the wind and 
realign it if necessary. 
 
> I will be using stainless shim stock to center the mast in the  rotor; 
could I shim the mast u-clamps?  
 
    You could try it but I've found it to more work  than it's worth. You 
didn't mention if you'll be using a thrust bearing or not  but if it was me, 
I'd just let the rotator turn the mast a little  eccentrically and not worry 
about it. There's usually enough slop in the  system that it won't hurt 
anything. If you do have some serious bind, then  pursue the shimming. One 
thing you can do is loosen the rotator base bolts as  the last step and then 
re-tighten them. This will let the rotator center  itself slightly to the 
installation. 
 
>  If I use stainless shim stock, should I use Penetrox or  similar to 
inhibit corrosion?  
 
    You don't need any. This is a mechanical function  (and it's stainless 
steel) - not electrical (which is what an antioxidant  like Penetrox is for).
 
>  Would this make it too slippery, and allow the antenna to turn  on the 
mast?
 
    See comment above. 

>  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.
 
    I don't think it's worth the several hundred  bucks they want for it. 
It's slightly useful but not at that cost. The way  they do it by stuffing 
the  wires in a little slotted PVC tube is  kludgey but works fine. I've never 
had one fail on me. 
 
Cheers & GL, 
Steve     K7LXC
TOWER TECH-
Professional tower services for hams
Cell: 206-890-4188
Installer of more SteppIRs than anyone else in the world.  





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