[TenTec] Big TX Loops

[Barry N1EU]

Good luck with the helically loaded loop Jim.  Perhaps you're already
aware, but several folks (including W8JI) have argued that helically
loading the mag loop buys you nothing compared to a simple loop of the same
diameter.  But I know those youtube videos sure make it look good   ;-)

73, Barry N1EU


On Sun, Apr 27, 2014 at 12:55 PM, Jim Allen <jim.allen at longhornband.net>wrote:

> Let me add to what Ric has said, that there are very high voltages and
> currents developed in these small loops, 5000 v or more even at 100 watts.
> According to one calculator, a 5' diameter loop at 40M and 500 watts would
> develop nearly 10,000 volts.  It is essential to keep living things away
> from these loops while transmitting is possible, and not a good idea at all
> to be close to them while transmitting.
>
> I'm in the process of gathering the materials to build a helically loaded
> magnetic loop for 20-10M, with a vacuum variable tuning capacitor, using
> copper 3" wide wound on a flex PVC loop about 40" dia.
>
> 73 de W6OGC  Jim Allen
>
> 73 de W6OGC  Jim Allen
>
>
> On Sun, Apr 27, 2014 at 1:43 AM, Jim Brown <k9yc at audiosystemsgroup.com
> >wrote:
>
> > 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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