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Rohn 25 Rotor Mounting

To: <>
Subject: Rohn 25 Rotor Mounting
From: (Stan Griffiths)
Date: Wed, 29 Jan 1997 04:49:10 -0800 (PST)
>.=A1=A6=05=D8=B8=03 dhand@DS9.MICRODES.COM
>I am in the process of putting up an 80 ft. tower with a couple of HF=20
>stacked on top.=20
>The plan is to have a TH7 about 2 ft. above the top and an a3ws (12/17m)=20
>about 8 feet above it. I figured to nest two sections of mast so the A3=20
>would be accessible from the top of the tower with the two sections=20
>collapsed. The problem/question arrises in that that puts the
>TX2 rotor down about 6 feet into the tower and I will have to cut the Z=20
>braces at that point to get the mounting plate and rotor in place.=20
>Is this advisable or will it cause an unacceptable weaking of the tower=20
>at tat point?=20
>Or is there a better solution that I havent considered??
>Dave Hand WB4HYP=20

Hi Dave,

This is what I have done:  I use a 1 piece 18.5 foot mast.  The rotator is
mounted at the junction of the top section and the section just below it.  I
had to cut out one horizontal at the bottom of the top section to get the
rotator into the tower.  I use a thrust bearing on top of a flat top Rohn
25AG4 and a rotator plate with a Rohn "wood bearing" where the rotator
normally goes.  This way I can remove the rotator for service and the mast
will not tilt since it is still held in two places.  With the rotator
removed, I can loosen the hardware onf the lower beam and telescope the mast
down into the tower to work on the upper beam.  I have also "stepped" the
mast and I can climb to the top beam without removing the rotator if I want=

I have a second tower with a very similar setup except I used a Rohn 25AG3
pipe top on that one.  I put the thrust bearing on a rotator plate where the
rotator normally goes.  The pipe top keeps the mast straight and vertical
with the rotator removed.

Both of these installations have been working just fine for me since 1973.

The problem that I see with telescoping the mast is that you have to reduce
the diameter of the inner (upper) mast section to get it to telescope inside
the lower (outer) mast section.  This will weaken it a bunch.  Too much, in
my opinion.  If you bore any holes through the mast sections to pin them
together, this will weaken it even more.


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