[TenTec] Big TX Loops

Jim Allen jim.allen at longhornband.net
Sun Apr 27 17:46:50 EDT 2014


The problem here is the ground is so rocky that radials are all but
impossible to hold down and the HOA restrictions limit me to no more that
10' above the highest point on the roof, which effectively means about
35-39' depending on which part of the property I put it on.  It also
shouldn't be obviously visible from the street, which is not so much of a
problem with trees advantageously situated.  If they work decently, the
loop ought to be an ideal solution for me and many others similarly
situated, more and more of us.  Is helically loaded better than plain?  I
have no idea.  Some say yea, some say nay!

Higher is always better, I suppose, but these loops are reported to work
satisfactorily close to the ground.  Am I going to crack pileups with my
100 watts or less and these antenna?  Hardly, but I'm not fretting about
that.  I'm not going to be on the Honor Roll, no matter what.  I missed
Mellish Reef last month.  So what!  I'm on the air with the best signal I
can arrange in the circumstances, right now.

".... it's not practical to model it in most modeling software."

I bet if they wanted to, someone could.  They can model all sorts of things
these days, or claim to anyway.

"But it's those restricted conditions we're talking about."

That's where they will want to be used.  The ones that have been used are
claimed to work as expected.  Are they monobanders at 120'?  Nope, and
nobody claims otherwise.  Most of the users are happy to get close to
dipole performance if they can, or at least where they can get on the air.
Those folks are faced, in many cases, with no verticals (except flagpoles
in some areas), no horizontal antenna, certainly not at a respectable
height, no towers, no directional antennas as we have thought of them all
these years, not even a hex or moxon for the most part and even then not
high enough to really perform.

I spent quite a few years in San Diego as a Volunteer Counsel going around
trying to help get antennas through HOA boards or city councils/planning
departments, and this is a very daunting problem for someone to have a
really effective antenna.  The naysayers ignore the dozens of operators who
have these antenna and are satisfied that they are effective and as best
they could do in the circumstances.

73 de W6OGC  Jim Allen


On Sun, Apr 27, 2014 at 3:40 PM, Rick - DJ0IP / NJ0IP <Rick at dj0ip.de> wrote:

> 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 at 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 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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