[TowerTalk] antenna/mast height above tower

[Jim Lux]

At 12:02 PM 7/23/2007, Alan NV8A wrote:
>But I suspect that that is so they can quote the largest possible area
>and hope that nobody notices that it's for an antenna only 1' above the
>top of the tower.


I'd suspect that the "tower" load spec is at the "top of the tower", 
since they don't have much control over what you put on it for a 
mast. For a tower over 50 feet tall, adding a foot is going to change 
the bending moment load (at the base) by 2%, which is down in the 
noise.  For a shorter tower, the percentage change is greater, but, 
then, the bending moment is smaller because the total lever arm is smaller.


If one goes and puts, say, a 30 foot extension (say a self 
guyed/trussed arrangement, for example), then clearly you're loading 
the tower in a way not covered by a simple "flat plate area at the 
top of the tower" which is probably considered as a single point load 
with no moment.

Jim, W6RMK