[Towertalk] Antenna Advice

[Wes Cosand]

This combination (a Force 12 230/240 and a 5BA) appeals to me, too.
>>What can anyone tell us about how properly to stack them?  In
>>particular, how far apart should they be on a single mast above a
>>70-ft. tower?  (I assume that the 230/240 should be above the 5BA.)
>>
>>-Chuck, W1HIS
>
>Natan told me 10 foot spacing would be fine. I never asked which would be 
>the topmost antenna but like you, I assume it would be the 230/240. You 
>would definitely need a chromalloy mast though!
>
>--
>
>73,
>
>Jim
>KJØM

I, also, am interested in the Force 12 230/240 and 5BA solution.  Here are 
some back of the envelop calculations about  what the yield strength of the 
mast would have to be for this application.  Let's assume 20 feet of mast 
above the tower with the 30/40 at 16 feet and the 5BA at 1 foot.  Lets 
assume 0.25" tubing wall.  I am not an engineer and these calculations are 
only for discussion purposes.  They are based on the method of W7NI's 
article.  (Do you really want a chemist doing your engineering?)


mast diameter    2"           2.5

90 mph             121K psi       72K psi
80 mph              98K           58K
75 mph              68K           40K

Wes, WZ7I