I have to agree with Barry (and Tom), but don't let that hold you back from
building one, Jim.
It's always fun to build stuff like that and even more fun when they work.
The advantage I see of the helical wound loop is, it will be much cheaper
than using aluminum or copper of the same diameter.
For those online demos, the antenna in use was located outdoors, in the
clear, with not much around to interfere with it.
That for starters is a big help!
I saw 3 different worlds with my 6' diameter commercial loop:
1) Indoors it was a poor performer - though it did work on some bands
2) It came to life when moved to the balcony
3) Mounted at 10' height, in the clear out in the front yard, it was as good
as the 40m dipole about 10' above the roof of my 3 story house.
I also had it mounted to a push-up mast on the back of my RV, but I only
used if for a couple of trips.
It wouldn't work at all when dropped into position for traveling, and it was
a pain to have to push it up and down all the time. It was not light. But
it did work quite well, once into position.
IMO, its single biggest strength is its ability to enable a decent signal,
even when you are prohibited from running wires. Too bad it's just so
narrow bandes.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Barry N1EU
Sent: Sunday, April 27, 2014 9:21 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Big TX Loops
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@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@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
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
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