Mag Loop

[Elecraft mailing list]

Hi Group:
OK... here's my mag loop story:
I have two AlexLoops.... and one is the original version that uses copper tubing for the main loop.  I used that loop to make an RTTY QSO with a station in Moldova.  I had set the loop up indoors (in my sunroom, which has a lot of windows) and worked that station on 40 meters... running 3 or 4 watts.
OK, it was during a contest... the contact was quick, but acknowledged both ways... so a Q is a Q.And, that was my best DX with that antenna.  The fact that it was 40 meters, the loop's least efficient band, is amazing to me.  I suspect that the other guy was using a much better antenna, and likely more power.
73 de Ray    K2ULR    KX3 #211    
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[Gwen Patton]

I made a small transmitting loop a couple of years ago as an experiment
with a material I wanted to try. One of the materials was not appropriate,
but I made it work for the sake of the experiment. I plan to make another
loop at some point from a different material so it's not an issue, but that
was only the *support* material for the loop. I wanted a loop I could fold
or roll up into a small package to take it to parks and such, that wouldn't
require stakes or lofting things into trees, in case the local authorities
don't like that.

The support material was some plastic perforated strap for supporting
pipes, conduits, and BX cables in basements and attics. The holes are an
inch apart on centers, and the stuff is VERY strong. It's also
flexible...but TOO flexible. It had no supportive strength whatsoever,
which was a problem for this project. I wound up making supports for it out
of thin wood, which worked, but it wasn't what I originally had in mind.
But it's not the support material I'm writing this to mention. I'm talking
about the conductor.

I used 1/2 inch wide adhesive copper foil. The adhesive is also conductive.
It's not very strong, but it's VERY conductive, and it's lack of thickness
isn't an issue because it has a lot of surface area, where the RF is
actually conducted, so it should have great bandwidth. I had a decent
variable air-gap capacitor, with a 10X vernier control on it, and used a
small wooden base, like a miniature pallet, as a platform for the entire
thing. I priced thin wooden furring strips for the rest of the supports,
but they were more expensive than I liked. So I bought a dozen wooden
meter-sticks for about half what the furring strips would have cost. They
work very well for situations where you need a thin but strong piece of
wood. I ran the copper foil tape the length of a piece of the plastic strap
to give me a loop I calculated for 40m-10m. The copper foil takes solder
very nicely, so it was simple to work with. The wooden supports I made were
a six-pointed star, the bottom being flattened for the connections at each
end of the loop and the capacitor. I made a coupling loop out of a similar
piece of plastic strap and the same foil tape, and connected it to the
coax, about 15 feet of RG-174.

I used this loop indoors, on a wire rack next to my workbench, and used it
with FT8 at various output power levels. I used a laser thermometer to
check the temperature of the conductor in multiple places, and it only
showed a tiny increase in temperature above room temp when I tried it with
100W. (KX3 + KXPA100) It was easily tuned on the bands I expected to use it
with, and with the internal tuner of the amp I managed to tune it on 80m,
but didn't expect any significant efficiency, and was right not to expect
it. But on 40m through 10m it was very serviceable. I'm in the Philly area,
and managed to have FT8 contacts as far as Fargo, ND and a couple in Cuba.
The bandwidth was fairly wide as I expected. I haven't used it to try and
make CW or SSB contacts, but I see no reason why I couldn't, though it is
firmly in the "compromise antenna" category for those emission types. It's
a proof-of-concept, mostly, but a functional one.

I've attached pictures, so you can see what it looks like.

-=-=-=-=-=-=-=-=-
73,
Gwen, NG3P


On Wed, Jan 20, 2021 at 10:50 AM Raymond Sills via Elecraft <
[hidden email]> wrote:

> Hi Group:
> OK... here's my mag loop story:
> I have two AlexLoops.... and one is the original version that uses copper
> tubing for the main loop.  I used that loop to make an RTTY QSO with a
> station in Moldova.  I had set the loop up indoors (in my sunroom, which
> has a lot of windows) and worked that station on 40 meters... running 3 or
> 4 watts.
> OK, it was during a contest... the contact was quick, but acknowledged
> both ways... so a Q is a Q.And, that was my best DX with that antenna.  The
> fact that it was 40 meters, the loop's least efficient band, is amazing to
> me.  I suspect that the other guy was using a much better antenna, and
> likely more power.
> 73 de Ray    K2ULR    KX3 #211
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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[Eric Norris-2]

I built two mag loops, one with an MFJ butterfly cap, and one with a
massive 60pf bread-slicer I found on Ebay--if my calculations are correct,
the monster should take a kw of power on 20m.  The MFJ capacitor is not
high quality, but it works over a wide range.  However, I much prefer my
AlexLoops for portability and ease of setup--they set up on a cheap photo
tripods with the heads removed.  My homebrew loops require guys because of
their size and weight.  The AlexLoop sets up in less than 60 seconds, as
shown here in a video I shot near a salt-water amplifier:

https://youtu.be/TVsm-Mpwj6c


73 Eric WD6DBM
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