[Antennas] Tower

Sat Aug 30 01:05:39 EDT 2008

de N4TGC Eric
Ignoring the over-wrought manufacturer's guidelines, the real issue is 
moment-arm: i.e., how much leverage will the tower and any antlers on 
it exert on the ground? While a hefty chunk of concrete will mask the 
effect, that's similar to ballasting a sailing ship: it'll still tilt 
when pushed enough. But unlike a ship, your tower won't (likely) right 
itself ...
The goal is too stabilize the base such that it will bend or break off 
before it tilts out of the ground. Around here, no concrete would be 
needed for such a short assembly; a tower section embedded in a 4' or 
deeper hole with the cherty clay compacted in and around it would 
suffice. In sand, any sufficiently broad-base structure will work: 
concrete cast in a 4-point star extending a foot or so out; hefty metal 
(or even pressure-treated wood) threaded thru the legs horizontally 
(sand anchor effect) and buried; etc. For my latest tower guy-post, I 
used a 3' long, 3-core concrete block, buried just beneath the surface 
and positioned perpendicular to the direction of pull, which the post 
bears against. Okay, so that's an unusual size, but the idea is to get 
enough soil bearing against the base that it's weight prevents the base 
from tilting out (the bottom of the post goes 2' further down, and has 
a concrete "wing" cast around it.) I did this 'cause the post doubles 
as a clothesline pole, and wet clothes can be quite heavy ...
The post is for my ground-mounted tower (the other three are on the 
roof; only the center one is tall enough to need guys), currently 53', 
is simply embedded in bare soil, as it's fully guyed, and tilting out 
is not an issue (theoretically it could sink straight down, but it 
hasn't yet ...) This also makes it "self-grounding" (concrete is 
largely an insulator, despite being water-entraining), and allows the 
legs to drain any condensate (I've lost count of the split legs I've 
seen, for lack of this!) But since the tower in question is to be in 
sand, as long as one doesn't allow concrete to plug the legs, this 
shouldn't be an issue - esp. in Florida. But consequent rust might be 
...
	e