My Magnetic Loop Antenna
Richard Robbins, WA8RR
I had read in several articles, the building and use of magnetic
loop antennas. I found the following website:
This web site allows you to enter various values for the main
loop. I was interested in 40 and 20 meters.
I decided on a loop of 10 feet in circumference using a piece
of ½ inch copper pipe. I wanted to run 100 watts because that
is what my ICOM 7300 could put out.
The calculations provided the following.
I found a piece of 10 foot copper pipe at a local plumber. I
located a capacitor that looked like it would work from the
Hamvention. I didn’t have any fancy tools. I hand bent the
pipe into an approximate circle.
It will never win any beauty awards. However, I constructed a
drive loop out of coax, connected the coax to my RigExpert
and found that the antenna would tune.
General observations. The antenna would tune 20 meters. To
tune 40 meters, I added a piece of coax in parallel to the
variable capacitor. Tuning is very sensitive. I used a 10 to 1
reduction drive to adjust the capacitor. Body presence and
metal affect the tuning. I ended up adding a remote control
to the antenna using a 1.2 rpm dc motor. With the
configuration as shown above, I was able to make several
contacts on FT8. I would use my RigExpert to tune it. The
tuning would shift as I was transmitting. This is a result of a
very high circulating current and heating of the separate
components. Encouraged by the results, I decided to take
what I had learned and redesign.
I found a 10 foot 1 and 1/8 inch thin wall copper pipe at
Menards. Located a local metal fabricator to bend it…the
process needs a roller bender. The results were good.
I replaced the variable capacitor with a vacuum capacitor. The
vacuum capacitor is expensive. However it seems to be the
goto device for this type of application.
It is big and heavy…It has a range of 5 pf to 250 pf at 20Kv.
To drive the capacitor, I obtained a stepper motor and driver, an
Arduino controller board and a four channel remote. I used some
sample programs to develop the code that would move the capacitor
at different speeds depending on how long the remote was pressed.
The final results are shown below.
Mounted on the tripod. Since this is a magnetic antenna, the loop should
be with in 1 diameter of the ground.
This shows the mounting of the capacitor and control box.
Close up details of the control box.
I added markings on the capacitor so I could quickly move to different bands.
Showing the tuning for FT8.
This shows the PSK reporter during operation with the antenna.
KE8O Update on N8OB’s sale
I’ve had success selling a lot of Bob’s equipment for Marcella.
The following are new items located:
LDG 600 Pro ATU w/box $200
Yaesu FT60 HT w/drop in charger AND programming software w/cable -
I plan to bring the following to the next meeting
2 Older bench model DVM’s
2012 ARRL Handbook
Misc jumper cables and connectors
Jamie in the park
(sung to the Chicago tune!)
Today I decided to see if my antenna pole would work with the antenna
attached. As it turns out the initial way I was thinking of using it as a free
standing pole was a fail. D'ohhhh.
It was far too unstable for my liking. I don't need a major failure that might
get someone injured. Namely me.
So I went back home to think about it. Ohmmmmm.
So I decided to use rope as guy lines at each section. That equals x3. I
already had the middle ready so I repeated the steps for the bottom and tip
top. This time the pole is very much more stable and adjustable for each
As seen in the images, I ended up with a mini tower where the antenna
feed height is at 22'. I was able to pull and release the antenna up and
down with no issues. The top support is about 18" from the pole and
should work well.
I didn't get to power the antenna but hopefully I can do that tomorrow. Oh,
I also made 10 and 6M wire to add to it. So this has the potential for 40, 20,
10 and 6M.
The top support needs a small mod to be a bit better. It took some time to
figure out the set up and is a bit more involved but I am making what I have
on hand work.
I'm tickled. So I need a name for this set up. What do you think it should be
Oh, with the wind the guy rope sings. How cool.
The Miami Valley Steam Threshers
2019 show is coming up in July.
Will, N8HDM, has been operating a special event station during the
show over the last several years but will not be available this year. He
has asked Ed, KE8ANU to head things up this year. He will need some
help setting things up and operating.
The show itself is a ton of fun so bring the family!
Please contact Ed or Will to volunteer. firstname.lastname@example.org
Help Wanted: Scouting Radio
Last June DELARA was asked to conduct a one day ham radio
demonstration during the Delaware District Cub Scout day camp. We
conducted three sessions with Arrow of Light kids only. The AOL kids
are in 5th grade. The camp staff was so impressed that they have
asked us to return this year, with one additional request - they want
us for the whole week and to work with ALL the kids. On camp that
week will be HUNDREDS of Cub Scouts in grades 1-5. The day camp
staff has been working more STEM (science, technology, engineering,
and math) activities into the camp program.
In order to pull off 5 days of hamming, we're going to need a lot of
help. Wally W8WLK, Joe K8MP, Bob W8ERD, Steve K8SWH, and myself
are already lined up. These fine gentlemen helped with the Scout day
camp event last June and/or with Jamboree on the Air (JOTA) in
October. We still need more help! Volunteers can opt to help for one
day to all five days, or anywhere in between. Partial day assistance (at
least four hours) could be useful, too.
Day camp will be June 24-28th this year. That is the week immediately
after Field Day. It also means we need helpers to set up antennas,
extension cords, tables, stations, etc. the Thursday or Friday before. I
know, it's the same time as Field Day setup, but how many
opportunities do we have to get HUNDREDS of kids on the air?
I think we'll need at least FOUR people each day for the five days to
operate radios, interact with kids, demonstrate HTs, mesh, DMR, CW,
or anything else we can do to keep them occupied while they wait a
turn on the microphone. Having SIX hams each day would be even
better. Even if you can just do one day of the event, or help setup or
tear down would be huge!
I have negotiated the following amenities to make this a successful
An open field surrounded by trees near the swimming pool
bath house (running water and flush toilets!) - lots of room for
A 10 x 20 barn with locking doors for our "shack" - setup radios
once for the week
A 10 x 20 portable garage (like a giant tent) for information
tables, sign-in sheets, etc.
A golf cart for our exclusive use - in case hams need help
getting from the parking lot to our area
Access to 110v power (via extension cords)
Please let me know if you can volunteer for any amount of time and I
will add you to the list. Like last year, I will conduct a series of
conference calls to plan and organize the event. I would like to host
our first call in the next week or two.
Ed Jones - K8MEJ - Lewis Center, Ohio U.S.A