Rotating Tower Sections
Sun, 6 Oct 1996 10:37:20 -0400

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

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