[TenTec] Big TX Loops

[Rick - DJ0IP / NJ0IP]

***"The helically loaded loop gets you the same performance of a magnetic
loop but at reduced size, supposedly.  IOW, the 80M loop that is 6' in
diameter can be 3 or 4' when helically loaded, so it is said.  I'm looking
at a one meter loop for 20-10M, then we'll see."***


You'd best take that with a BIG grain of salt.
BTW, I don't know if there is anyone making (and selling) good quality big
tx loops in the states but check out VE3UK on QRZ.com.  Seems to be a 4'
diameter loop.  Check out the tuning capacitor.

Take "that one" and compare it to the 4' helically loaded loop.  My money is
on "that one" and not the helically loaded.

It is very difficult to compare two different loops and then make a call on
their technology, because the "build quality" plays such a HUGE role in the
antenna's performance.  You must be sure both are built with the same
quality in order to compare technologies.

Of course those are still just peanut league. (hi)
I3VHF makes a MONSTER LOOP that is 13 feet in diameter.  It has 3" aluminum
tubing.
Takes about 4 people to hoist it up.  Now THAT's a BIG TX LOOP!

You have to be careful, though.  The loop must not exceed 1/4 wavelength.
If it does, it begins to pick up the electric component of the signal and
may suddenly become noisier.  

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


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Jim Allen
Sent: Sunday, April 27, 2014 9:58 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Big TX Loops

Yes, I read a good deal of that.  They have argued it, but no one has
demonstrated it, and AFAIK, no one has modeled one.  In the meantime, a good
number of folks, including some who are quite expert, say they are getting
gratifying results.  I know Tom is regarded as knowing what he is talking
about.  There is no way a loop is a superlative antenna, and you wouldn't
chose that if you had space, no restrictions, adequate budget
etc.   I certainly do not expect this loop to perform like my 4-4-5 quad on
60' tower years ago, but I didn't have HOA restrictions then, and was young
and healthy enough to manage the building and maintenance of such a project.

It's ironic that now that I have the money to do just about anything I want,
I don't want to, because it isn't a smart investment given my age and health
situation, and I am under HOA restrictions anyway.  If I went out and bought
a big place, like Tom, and started an antenna farm, I wouldn't live to
finish it.  Some of us are very content, indeed happy, to be on the air with
respectable signals, not multi-multi crushers.


Maybe it will be a bust.  It won't be the first time building antennas that
fell short somehow.  It beats sitting around watching Oprah Winfrey re-runs
or whatever it is that old people are supposed to do!

73 de W6OGC  Jim Allen


On Sun, Apr 27, 2014 at 2:20 PM, Barry N1EU <barry.n1eu at gmail.com> wrote:

> 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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