[TenTec] Big TX Loops

[Rick - DJ0IP / NJ0IP]

Jim, this is an outstanding method of construction.
My worry would be the loss in the connection of adjacent segments.
Even a fraction of an Ohm resistance in such a connection can cause problems
with the high current running though this antenna.

On the other hand, by having the 45 degree bends, if he would make them say,
45.5 degrees, then he would place a bit of tension on all of the joints.
That might help.

Keeping resistance low is fundamental to this antenna.
All of the commercial manufacturers weld their connections.

By not doing that, it doesn't stop the antenna from working, it just adds
some additional loss.

The only problem is, Lee (who started this thread) wants to use the antenna
indoors, and large magnet loops indoors won't work.  You need to keep a
distance from the floor, ceiling and walls of at least the radius of the
loop, better is to keep the distance the diameter of the loop.  THIS APPLIES
TO OUR CONCRETE HOUSES her in Germany.  I don't know what would happen in a
wood house.  Perhaps it is not so critical.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Sunday, April 27, 2014 8:43 AM
To: Discussion of Ten-Tec Equipment
Subject: [TenTec] Big TX Loops

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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