[TowerTalk] Installing ham V in 25G

K8RI K8RI-on-TowerTalk at tm.net
Sat Apr 14 18:04:23 PDT 2012

On 4/14/2012 7:17 PM, W2RU - Bud Hippisley wrote:
> This is so "not a problem" by using either:
>       a.  Four standard 25G sections plus a 25AG4 top section; or
>       b.  Five standard 25G sections plus the 1-ft 4-in BAS25 Rohn bearing/accessory shelf section.

I'll have a Force 12 C19 XR about a foot above the top of the flat plate 
with a WARC 7 about 10' above it.  With the 4.9 sq ft of wind area from 
the WARC 7 that would produce the leverage, or bending moment  of 49  sq 
ft at the top of the tower. 58.8 if I went the full recommended 12'. 
Both far exceed the rating for a 50' guyed 25G.

   With the rotator mounted down in the tower the bending moment is 
mostly gone and it's more or less a side force.  On the 45G I mount the 
rotator close to 30 feed below the top.  The only places I've found the 
accessory shelf fits properly is between the sections.   Having worked 
on a lot of equipment I was always taught that if it has to be forces it 
doesn't fit.
> In either case, a TailTwister is easily mounted near the top of the top section, with provision for a TB-3 (2-in mast) thrust bearing a foot or so above the rotator.
> But I have also inserted a TailTwister into other Rohn 25 sections by angling it properly and putting a little bit of temporary pressure on one of the Z-braces.

The tail twister and Ham series are pretty much the same OD. It takes 
well over a 100# of pressure to bend either welded brace between a half 
to 3/4 of an inch to get the ham IV or V in there. The IV and V are the 
same rotator, only the control is a little different.  To me a "little 
bit of temporary pressure" is something I can do with my bare hands and 
that is definitely not the case here.

It's beginning to appear that the 25G is not suitable for these two, 
relatively small antennas.


Roger (K8RI)

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