On 3/17/2012 1:59 AM, Jim Brown wrote:
> On 3/16/2012 7:52 PM, Joe Barnes wrote:
>> I don’t see much info out there about this tower
> That's not the official name of it, but it is what it is commonly
> called. It s really an OEM part made for Motorola, and I think it's
> been discontinued for years. I was lucky enough to find four straight
> sections and a pointy-top, and it's currently holding up mono-banders
> for 20M and 15M. I had a friend make a rotor plate to fit it.
>
> For those who don't know, "Rohn 35" is heavier gauge and has wider
> spaced legs than Rohn 25, but less than Rohn 45, so it's pretty robust.
> I suspect you can find the "real" nomenclature for it by Googling Rohn
> 35 and Motorola.
>
> I have been told that pointy-top sections should not be used in place of
> thrust bearings, so you might want to consider buying a real thrust
> bearing and using that if you can't find a pointy-top.
Flat top plate sections are easy to build for a welding or machine
shop. They are simply a piece of 1/4" (or 3/8") flat plate with a
center hole, mounting holes for the thrust bearing, and 3 tubes to fit
the top of the tower welded in place. Of course those 3 tubes need 2
holes in each, of the proper size and are likely to be painted instead
of hot dipped galvanized. It helps to make a fixture to align the holes
when drilling. At least it makes it easier to get the three of them
aligned. Basically mount the 3 tubes (of the same length) on the top
tower section and then weld them to the top plate. It'd probably be a
good idea to bend the corners down just as the regular flat top plates
are done.
Of course it becomes a LOT easier if you have dimensional drawings for
the top section with the flat top plate.
73
Roger (K8RI)
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