[TowerTalk] U.S. Tower rotor shelf position

[K7LXC@aol.com]

In a message dated 05/03/2000 2:00:51 PM Pacific Daylight Time, 
k0myw@worldnet.att.net writes:

> I'm in the process of topping a new heavy-duty 55-foot U.S. Tower
>  crankup with TX2 rotor, mast and a couple of medium-size antennas.
>   Although I cannot cite any solid engineering reasons, I would feel more
>  comfortable if the mast extended deeper into the top section of the
>  tower than the factory rotor shelf, which is a mere four feet from the
>  top.
>   The factory shelf is welded into place, so moving it is not practical.
>  However, I'm wondering if anyone has experience with extending a mast
>  through the factory shelf (perhaps incorporating an additional thrust
>  bearing there) to a second rotor mounting shelf installed, say, another
>  four feet deeper into the tower section.

     You didn't mention how long your mast is or the antennas are but using 
the existing rotator shelf for an intermediate 'holder' for the mast sounds 
fine. I wouldn't use an additional thrust bearing though - too much of a 
chance for binding plus just the shelf itself will act as a FB lateral 
stabilizer.

>   I believe U.S. Tower sells separate rotor mounting shelves, but I don't
>  know if they are bolt-in units or if they, too, require welding. I know
>  I can easily ascertain the answer to that question by contacting U.S.
>  Tower -- but before I do, I thought I'd solicit the collective wisdom of
>  this group concerning the advisability of such a modification.

     I've seen UST non-welded shelves.

>   Perhaps I should just do what Steve frequently advises and just go with
>  what the manufacturer provides (even if seeing the rotor so close to the
>  top of the tower does make me a teeny bit nervous)...
>  
      Greene County is only a 70 MPH windspeed zone so only moderate wind 
forces to deal with. I'm pretty sure that the top of the tower has 4-6" of 
tubing that the mast sticks through. It's welded into everything and is 
substantial enough to probably handle quite a bit of the forces you're 
worried about.

      Don't forget that the lower you mount the rotator - the more the tower 
has to be extended so you can reach it to install everything. Unless you've 
got a really big mast and load, I think I'd stick with the way it came from 
the factory.

Cheers,   Steve   K7LXC
Tower Tech 

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