In a message dated 96-10-06 00:38:58 EDT, you write:
> I am interested in rotating 1 or 2 sections of Rohn 25G (stacked
>vertically, in the normal manner) on top of 130' of Rohn 45G, which will
>remain stationary. My basic plan is to build an industrial size "Lazy
>Susan". I would like to hear from anyone who has experience in this area so
>as to gather more information & ideas. The 45 has the flat top section on
>it, which will serve as the base for the 25.
Hi, Rob --
Here's scheme that I like but confess have never tried myself. The top
of the 45G has a flat plate and TB-4 (3 inch) thrust bearing. It also has an
accessory shelf with another TB-4 on it below the top of the tower in
addition to the accessory shelf below it with the rotator. Install a
suitable 3 inch mast so that half of it is installed in the tower and half is
sticking out. You'd probably need a mast at least 12 feet long (six feet
below and six feet above).
Now you invert a flat 25G top section with another TB-4 on it and
install it over the mast sticking out. This will sit the 25G flat top plate
on the top of the TB-4 on the 45G. (The thrust bearing on the 25G is just to
hold it in place and centered. If you can figure out a way to center the 25G
and hold it securely, you could skip this TB-4; perhaps the angle iron +
U-bolt approach.) Now you need a method to fix the mast to the top 25G tower
section. You can probably use a 25G accessory shelf with a piece of angle
iron attached to it with a 3 inch U-bolt through the angle iron and around
the mast to secure it. The trickiest part of this installation is lifting
the 25G over the mast. A regular Rohn ginpole doesn't have enough overhead
to do this with its 12 foot mast.
I would recommend this approach rather than a 'fabricate it yourself'
method because 1) you're using standard parts and 2) they are designed for
outdoor use. Anything that is fabricated should be hot dipped galvanized at
a minimum. The only fabricating you have to do with this scheme is
installing the angle iron piece and the U-bolt.
> BTW, I have talked to Dick Weber of RTS & am aware of his fine
>products; I am looking for a more economical solution. I plan to assemble an
>array of VHF/UHF antennas on this climbable mast once it is in place.
While I respect Dick and his products, everyone is looking for a more
economical solution. With your relatively small antenna system, the 25G
should be okay. Otherwise, I would go with 45G up above as well.
73 and good luck, Steve K7LXC
TOWER TECH - - professional tower supplies and services for amateurs
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com
Sponsored by Akorn Access, Inc & KM9P