[TowerTalk] guy line anchor ?

[Roger (K8RI)]

Paul Young wrote:
> Hi Guys,
>
> a few have asked about the rotator and how it is mounted.
> It is mounted inside a cage that has a top bearing.
> I have added a photo of the type of cage used 
>
> you can see it here: http://www.g0hwc.com/latest_projects.html
>   

Having looked at the photos; It's a nicely designed cage.  I couldn't 
see how the rotator mounts other than a plate in the cage.  Two things 
to remember here is how the cage and rotator attach.  The Rotator should 
attach to both the mast/tower/pole and the cage as well as the mast to 
the antennas (out the top of the rotator), plus a thrust bearing/sleeve 
at the top of the cage. That way the wind load from the antennas is 
nicely distributed down the mast and there is no bending moment to the 
rotator.  If the rotator does not mount to both the cage and the pole, 
then the point where the cage attaches to the pole becomes a bending 
point.  With a good size tri-bander and multi-band vertical that could 
be considerable.  Remember that vertical is a really long lever whos 
load is almost entirely bending moment at the attach point..

As the mast plus rotator and cage is about 10 feet long, that makes the 
load at the top of the tower*about* ten times the wind load presented by 
the area of the antenna alone. So if you have an antenna with 10 sq ft 
of area presented to the wind  with a resulting force of  50 ft#, the 
moment at 10' down is 500 ft#  IOW the farther you go above the top of 
the tower/mast with the antenna the more you have to derate the 
tower/mast specs.

> Paul G0HWC
>
> Check out my website  www.g0hwc.com  *Echolink node MB7ICL-L  "381900"*
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