[TowerTalk] Antenna Mast - guidelines for ratio in tower / out of tower

[chas]

john at kk9a.com wrote:
> I do not have a mechanical engineering background, however since no one else 
> has answered your post I will give it a try.  I believe that 1/3 in the 
> tower and 2/3 above the tower works fine for most mast installations.
> 
> John KK9A


I of course know nothing about this as I am not a Civil PE or a 
Structural Steel geek... but
your concern is not simple..
1. is overturning moment..
2.  #1 is dependent upon the load on the exposed mast AND the strength 
of the surrounding tower structure AND the guying at the top AND the 
fit/strength of the "guide plates" installed at the very top and which 
center the mast  --  whatever they are called

good example is to take a 12" tire tool and stick it into the neck of 
a long neck or similar glass bottle.  if you stick 4" in and then push 
the end sideways, you will probably break the neck off.  However, if 
you push half of it in and try to push it sideways, it just doesn;t 
want to go because the "tower" is keeping it from overturning.

play with the idea and you will probably come up with the proper 
ratio.  Personally, I think that I would get about 40-50% into the 
tower.  10' of exposed mast is plenty for most purposes.  in 
actuality, so is 5' <G>

of course, I know nothing about this except in another life, I was a 
sign inspector for the City of Houston (oK! we were really hungry and 
the rust belt had moved to SE Texas...) for a couple of years.  I 
watched a lot of signs being built and talked with the plan inspectors 
during a lot of lunch hours.

fwiw
chas  k5dam
-- 
chasm at texas.net   k5dam  Houston, TX

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