[TowerTalk] antenna mast guidelines

jim Jarvis jimjarvis at optonline.net
Mon Mar 23 19:42:14 PDT 2009

An interesting discussion... regarding mast loading, and how much  
should be
above the tower, versus inside....

K8RI wrote...

" ... so going much above the top of the tower
can add considerable force to the top of the tower."

Doesn't it matter whether we're talking about a flat-top tower with  
thrust bearing, or
a sleeve-topped tower?    Is the load rating any different for the  
two types?

(I'm no longer sure, but I thought the original question actually  
dealt with the strength of
the mast material, itself, rather than loading on the tower, or on  
the rotor.   All of
those factors are relevant, in engineering the entire system, of  

My real question:   Is there any specific load rating for taper-top  
25g which would
limit the mast extension above the tower top?

I'm contemplating running 20' of 2" x .250" 6061-T6 above 40' of  
25g.  4' of mast would
remain in the tower, either attached via rotor, or via tb-3 and  
accessory shelf.   I might put
a 6m yagi or a small 20-10 lpda on top.   In the latter case, I would  
need to calculate the
windload on the log, and lower the structure appropriate to the  
bending moment imposed
at the top of the tower.   Will need to get structural data on the  
mast, to determine what it will

If any ME on here happens to have data for 6061,  2" x .250",  I'd  
welcome the info.



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