I think you're going to find out that for the height you want, your
tubing will prove to be too skinny and rickety. I'd start out with a
bottom diameter of 4 or at least three inches. I'd work out a scheme
to taper to about an inch at the top. As you have probably guessed,
this is not going to be a cheap vertical but when you start talking
about 1/4 wave verticals for 75 and 160 meters it gets hard to get
around the fact that you need more and bigger metal and quantity of
mass drives the price up. I've spend some time sitting around in the
past trying to figure out the cheapest way to get height with a
permanent vertical and eventually figured out that up to around 50
feet, a steel push up mast is cheapest and beyond that, a combination
of used R20 or R25 tower sections for the bottom half and some kind of
tubing for the top 30 feet is best for 75 meters. The trick is that
you have to be sure the used sections are pretty good, and you're not
using them for anything other than a vertical antenna you won't be
climbing. At some point in height, it might be cheaper to get your
structural strength with 1 foot face lattice aluminum tower sections
than to employ flag pole width aluminum tubing at the bottom.
If you still want to use the narrower tubing you mentioned, I'd go up
no more than 2/3 of the way and then run a horizontal wire off the
top, i.e. an inverted L. I bet you would not notice much if any
difference between that and a 60 or 70 foot tall antenna.
73
rob / k5uj
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