[TowerTalk] Re: Ham IV vs. 25G

[Stan Griffiths]

>In a message dated 98-04-12 16:41:28 EDT, gwolf@gte.net writes:
>
>> I'm not sure if this questions has been asked before or not... My apologies
>>  if it has...
>
>     If you don't know the answer to it, then it's news to you.
>
>>  Can one put a Ham IV rotator in Rohn 25 ?  I'm asking whether it can be put
>>  in a non top sections w/o any alterations to the section.
>
>     Yes, the Ham IV will fit in 25G. You can squeeze it through the braces
>with the proper application of huffing, puffing and liberal use of American
>colloquialisms.
>
>     The question really, though, is where can you fit the AS25G Accessory
>Shelf/rotator shelf. It will only fit at tower sections junctions or in the
>open faces of tapered top sections or BAS25G Bearing/Accesssory Shelf. 
>
>     I think W7NI had a scheme/design for a modified AS way to mount the
>rotator anywhere in the section. An update, Stan?
>
>Cheers,  Steve  K7LXC

As Steve says, the Ham IV will fit in a Rohn 25G section, but once you get
it in there, it will not slide freely up and down the tower.  The bell
housing is too large to get past the horizontal braces and it will hit the
diagonal braces as it rotates except in a very specific narrow range of
vertical positions.  So you have to mount it exactly right.

I made a sample shelf out of plywood just to see if I mounted it on top of a
set of horizontal braces, the Ham IV could sit on this shelf and rotate
freely, missing the diagonals.  It looks like it can.  One COULD make such a
shelf out of steel plate and mount it to the horizontal braces with small
u-bolts (1/4" cable clamps).  It might not be a good idea, however, since
all the torsion applied to the rotator by the mast would be transmitted to
the shelf and then to the horizontal braces and then to the welds that hold
the horizontals to the tower legs.  The main question is:  Can those welds
stand up under this type of stress?  I don't know the answer to that question.

I am still thinking of making a real steel shelf like this and installing it
on one of my towers.  The next question is:  How long does it have to stay
there without a problem before we believe it is a good idea?  The REAL way
to answer that question is to engineer the project and calculate all the
stresses and know how strong the welds and horizontal braces are in this
type of service.  This is a job for a REAL PE, which I am not . . . So the
only approach I can take is to build one, put it up, and wait.  Not really a
very good approach but I don't see another choice for me.

You know, if you took a standard AS25G, rotated it inside the tower 60
degrees, and bolted it to a set of horizontal braces with 1/4" cable clamps
used as u-bolts (discard the saddle), you could try this experiment
yourself.  You might have to shim the plate where it rests on the horizontal
braces of the tower section so it is perfectly parallel with the bottom
surface of the rotator.

Try this at your own risk, but let us know how it works out, OK?

Stan  w7ni@teleport.com


--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search