My neighbor, W6GJB, has built a large TX loop Here's how described it to
another ham. The "army mast" he's talking about is a bunch of 4 ft
sections of 2-in o.d. Al tubing that fit together, and fit into a
triangulsr base. They've been sold at Dayton and other flea markets for
several decades, and are quite useful. With a tripod section made from
two sections per leg, it's easy for one guy to push them up, then slip
another section under it at the bottom, and so on They will, for
example, support a small tribander like a C3 at 30 ft if guyed properly.
We've also used them to build a 2-element vertical array for 40M.
= = = = = = =
The mag loop is homebrew, made of 8 segments of Army mast bent (very
carefully) in a pipe bender. The whole thing can break down and go into
the big green bags that go with that tubing. The air-variable capacitor
should be able to handle 500W, but I have not tried that yet. Running
100W at this point with a KX3+KXPA100.
With 8 segments it is close to 1/4 wave on 40, which should be over 90%
efficient with some of it going into low angle radiation. Should be
better than a low dipole. I can add fixed capacitance to tune it on 80,
or add another 4 tubes and it should be better than 80% efficient on 80.
= = = = =
So to clarify, his loop consists of four sections of mast that are each
bent twice at 45 degrees. They go in the four corners, then a straight
section goes between each of the four sides. That's the 40M loop. So
what he's saying is that to build it for 80M, you simply add another
straight section on each side.
This is a current project for him, and he's in the process of on-air
testing using RBN to get comparative signal reports with his other
antennas.
This is fairly inexpensive to build (I'd guess around $500), but you
need a good pipe bender, some practice, the sections, and suitable HV
caps. I've given him several big air variables from my junk box to play
with.
An objective is for something he can throw in the back of his truck and
set up quickly for FD or CQP.
73, Jim K9YC
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