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[TowerTalk] rohn 25 flat or tapered top section

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Subject: [TowerTalk] rohn 25 flat or tapered top section
From: aa4lr@arrl.net (Bill Coleman)
Date: Tue, 11 Dec 2001 09:52:54 -0500
On 12/10/01 5:26 PM, David Robbins at k1ttt@arrl.net wrote:

>> You probably don't need it. The tapered top section will do the work that
>> a thrust bearing would.
>>
>
>the tapered top doesn't do what a thrust bearing does, put a plate below 
>it with the thrust bearing. 

For the installation he specified, he doesn't NEED a thrust bearing. 

> a thrust bearing holds up the dead weight of the mast 
>and
>antennas, 

There's some debate about that -- given the construction of your typical 
Rohn thrust bearing. It does more to keep the mast straight and keep the 
bending stresses off the rotator. The pointy top is more than capable of 
doing that.

In any case, he didn't specify a weighty stack of antennas and masts. The 
rotator he is using is more than capable of holding the weight of the 
stack.

>it also makes service on the rotor easier since you can just 
>pull it
>out without having to lift the weight of the mast and antennas off of it.

Several of the Rohn pointy-tops have set screws which can be used to hold 
the weight of the mast and antennas while you swap out the rotator. My 
25AG4 top does, I cannot remember if the 25AG2 does or not. In any case, 
you can use a muffer clamp at the top of the tower to accomplish the same 
end.

It wouldn't hurt to use a thrust bearing, but it would cost more and it 
wouldn't really do a lot of good. 

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901


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