IW5EDI Simone - Ham-Radio

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Magnetic Loops by W2BRI

Posted: 27 Jan 2018 01:41 PM PST
http://www.iw5edi.com/ham-radio/2346...ic-loops-w2bri


Article by W2BRI

After many requests by Ben W4KSY*, someone I consider to be my loop mentor,
I decided to post a page about my 80 meter magnetic loop. The idea for this
loop began with my purchase of a new vertical antenna. Now when you think
of 26 feet of antenna, it doesnt seem that large until you put it together.
Now add a couple of 1/4 wavelength 80 meter radials, and the vertical
antenna solution starts to get big. Now, Im into efficiency, and I wanted
to string four radials five feet above ground at 90 degrees, and set the
whole system up in the best possible way. However, when I moved into my new
house, I had the disturbing reality that I had many power lines running
across my property and I also didnt have close to the room for 1/4
wavelength or even 1/8 wavelength radials (even for 40 meters). So I
figured Id never get on the low bands and Id have to live with 20 meters
forever. Dont get me wrong, I love 20 Meters.



Its no secret, I am a big fan of Force-12 antennas. I own a Force-12 C3SS
triband beam, and cant complain a bit about it. I call CQ on that antenna,
and I get five people coming back to me almost every time. While I was at
the ARRL conference last year I met Tom, N6BT one of the owners of
Force-12, and picked up his book Array of Light. The book chronicles his
experiences designing, building, and putting up thousands of antennas (yes,
thousands!). It is a great book in my opinion, and a must read for those
interested in understanding the reality of antennas. As I went through the
book I found a chapter on magnetic loop antennas and their high efficiency.
The wheels in my head started turning, and I thought, I could manage
putting up an 80 meter loop in my backyard. Maybe 80 meters isnt out of my
grasp.

So I picked up the phone and called Tom at Force-12 and asked him what he
thought. He told me sure, hed be happy to build a loop for me but the
capacitor arrangement and the loop support would be my problem. I agreed
and after several emails back and forth and a couple of months (and
dollars), I received a very large box on the door steps of my house. The
box was filled with 2 inch 4 foot lengths of aluminum. Each piece was
tapered at the end so it would fit into another piece with about 3 inches
of overlap. Then a bolt was inserted between the connected pieces, and each
section was completed. the corners had a similar tapering, and it took a
whole 15 minutes to put it together by the garage.

At first I used coaxial stubs for a capacitor. Tom suggested this strategy.
You can cut coax and use it as a capacitor take several different lengths
of coaxial stubs equaling different amounts of capacitance, and move from
band to band. I even loaded the loop onto 160 meters, but thats another
story for later. I built two wooden supports for the loop with my friend
Steve, and we attached the loop into place. I was ready for 80 meter action.

Great, I had the loop built, but getting it to match and work was a whole
different story. I had read many articles by Ben W4KSY about loops, so I
thought since I was having some problems Id ask him via email what to do.
Well he was kind enough to instruct me about how the feed system works (the
one from Tom was too small), and how to re-work it and what to expect. We
emailed a bunch of times and I finally got it where I wanted it, 3.863 at
1.1 VSWR with about 10 KHZ in either side of bandwith (remember, with loops
you dont want a whole lot of bandwith but this was an acceptable range).

With excitment that first night I turned on the rig to 3.863, and heard a
bunch of guys in the bay area (from my QTH in Los Angeles). I popped my
call in with 100 watts, and they came back first time around. I heard
everyone in the round table, and everyone heard me. Night after night, QSO
after QSO, 99% of the time, everyone hears me and I hear them. No problem.
And this was during summer conditions. I worked many stations regularly
from Oregon to mobiles in Wyoming, stations in Arizona, and others up and
down the coast. Now when the propagation changes in early fall I am working
stations farther out, Texas, Colorado, and Oklahoma. I am looking forward
to winter conditions to give more reports.

I eventually upgraded the capacitor to a Jennings vacuum variable 5-750 pf
with a over 12KV rating (cost around 200 bucks), and fixed on a motor to
drive the capacitor up and down the bands. The motor controller is in the
shack and I use a pair of DPDT relays connected to momentary pushbuttons to
pulse the motor onto frequency. It works like a champ.

So, can you work 80 meters with a 1212 loop 6 inches off the ground, yes!
And youll have a blast doing it.

For more technical explanations I plan on adding more info relating to
large loops on the site, and will be happy to email.

73,

Brian, W2BRI



this article was previously available atÂ*
http://www.standpipe.com/w2bri/80meter.htm

The post Magnetic Loops by W2BRI appeared first on IW5EDI Simone -
Ham-Radio.

On 01/28/2018 02:47 AM, IW5EDI via rec.radio.amateur.moderated Admin wrote:

IW5EDI Simone - Ham-Radio

///////////////////////////////////////////
Magnetic Loops by W2BRI

Posted: 27 Jan 2018 01:41 PM PST
http://www.iw5edi.com/ham-radio/2346...ic-loops-w2bri


Article by W2BRI

After many requests by Ben W4KSY*, someone I consider to be my loop
mentor, I decided to post a page about my 80 meter magnetic loop.
Hello, and hams just won't stop bundling that descriptor "magnetic" with
loop antennas. When we're talking about far-field (at least several
wavelengths away, a receive antenna responds to a propagating
electromagnetic field (or photons if you're so inclined). The far-field
receiving antenna most certainly doesn't respond solely to the E- or
H-field of an incident electromagnetic wave. The fact that a given
axis/plane of the antenna might align with the E or H component of the
wave is just a coincidence of the antenna geometry and its attitude
relative to the incident wave. sign Maybe I need to design an
"electric" loop antenna. Sincerely, and 73s from N4GGO,
--
J. B. Wood e-mail: