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