Building a Magnetic Loop Antenna Series for Beginners [Video]

This is the introduction to the Building a DIY Magnetic Loop Antenna for Beginners Series. Chameleon Antenna was kind enough to provide their new magnetic loop starter kit making this series possible. In this series we will show the operator how to use the DIY Magnetic Loop Antenna starter kit to build their own mag-loop antenna, according to their budget, their requirements, their specifications. I'm also new to the Starter Kit, and have only once built a 6 meter magnetic loop antenna to use with my Yaesu FT-817ND. So we are all kind of new to this.



I'm giving a little more description that normally, because people who are not signed up for YouTube have complained about not being able to see the full description and links on an embedded video posted to QRZ.com

Magnetic Loop antennas for amateur radio are increasing in popularity these days. The light weight, easy deployment characteristics of a magnetic loop antenna make them a popular choice for HOA restricted Ham radio operators, or for anyone who can't or doesn't want to deploy traditional supported dipole or wire type antennas in the field.

Getting Started
- First thing you might want to join the DIY Magnetic Loop Antenna Facebook group

- Second, get yourself the Starter Kit from Chameleon Antenna, or source the components yourself http://chameleonantenna.com/ACCESSORIES/ACCESSORIES.html

- Next (only if you're interested, read the the OH8STN blog post which outlines his build plans for the series. You can find that blog here http://www.survivaltechnology.net/magnetic-loop-antenna-builders-buying-or-building-it-yourself/

- Optionally, If you're not already a subscriber, subscribe to OH8STN at the SurvivalTech Nord Youtube channel www.youtube.com/user/survivaltecheu

The first video should be out in late January. New videos will be posted in the DIY Magnetic Loop antenna facebook group. I'll also spend time to provide help and feedback in the DIY Magnetic Loop antenna facebook group to help you with your own project.

 

I nearly forgot the link to the Facebook group.
https://www.facebook.com/groups/DIYLOOP/

 

An Eham review on the loop antenna said "
"The awaited CHA RT-RR (mini Remote Tuner - Remote Rotator) will definitely increase the operating pleasure."

I couldn't find it on the Chameleon website, but it is listed elsewhere.

https://www.dxengineering.com/parts/cha-rt-rr

That should make things a bit easier for tuning without having to be right next to it to tune it.

 

Magnetic Loops are easy to build for DIY projects. Started with a loop made with hard line coax. Then went with 3/4" aluminum stock from Home Depot.
Finally found a Cardwell 154 (12 - 244uf) variable capacitor with gear reduction to make tuning easier. Works great for QRP and portable operations!

 

Just picked up the kit, so how about we get started?

 

Great video, Julian!

 

You can find the CHA RT-RR here:
http://chameleonantenna.com/PORTABLE ANTENNA/CHA F-LOOP/CHA CHA RT-RR/CHA CHA RT-RR.html






- C

 

I will never have a Face Book account. Please share anything relevant here.

 

So the title of this is more entice people to buy a product, than show how to build a loop.

Or maybe I am missing a link?

 

OH8STN has the task of building a Mag Loop and posting the results. I may have mine built before OH8STN gets started.

 

If you search ebay, look for an open air variable capacitor rated somewhere around 12pf thru 400pf. Physical size will determine how much power you can run using this antenna. Make the inside loop out of a piece of #4 awg copper or aluminum stock. You will need to attach your feed line to this loop. Center conductor to one side of loop and shield to other. Using another piece of aluminum stock or 3/4 inch copper tubing, make the larger loop 5 times the size of the smaller loop.( A 7 inch diameter loop would require approximately a 36 in diameter outer loop) You can use PVC pipe with T-Connectors to form a vertical and horizontal support for the outer loop. You will need to attach the variable capacitor near the bottom where the two ends of the outer loop meet. Leave about 1 inch space between the ends of the outer loop. Try to attach your variable capacitor on the PVC support. Connect one end of outer loop to frame of variable capacitor and other end of loop to the lead connecting to the moving plates.

Your will need an SWR meter to find the sweet spot when attaching the smaller loop at the top of the outer loop. (An antenna analyzer would be easier to find the best distance to space the small loop from the outer loop). You can try to attach the small loop with tape or tie wraps so that you can slide it up and down the vertical PVC frame until you find the best SWR setting before permanently attaching it. Make sure the loops do not touch unless insulated. Set the antenna on a stand and connect your rig. Start on 20 meters and listen for the noise. Slowly start turning the insulated knob on the variable capacitor until you hear a "peak" in the noise. Turn the knob back an forth to find the peak noise. Use an SWR meter at no more than 5 watts to check the reading. Then make a small adjustment to the small loop by sliding it about a 1/4 inch. Check SWR reading. Continue making small adjustments to small loop until lowest SWR reading is found. You may have to tune the loop again until the peak noise comes up and repeat. It takes several attempts to find the sweet spot so be patient! Make sure you are not near the antenna when making a reading. Any contact will de-tune it and you will not get an accurate reading. After finding the lowest SWR reading, secure the smaller loop. Now try and tune to a new frequency on the rig and then slowly turn the knob on the antenna until you hear the peak noise. ALWAYS CHECK SWR with 5 WATTS or less before using more power for your transmission. Hope this helps! 73 and have fun!

 

Thanks a bunch! I have been hunting on line for several evenings, looking for a "Mr. Rogers" level, step-by-step set of instructions. The antenna calculator I found said that 5/8 OD copper will work for the big loop and I'll need 10 feet for a 20 meter loop. The calculator never mentioned what size the smaller loop should be.

I plan to buy the copper at Home Depot ($24.00) and a tube bender from Harbor Freight so I can get a nice, clean, round loop.

What bothers me is the idea of RF going down the center conductor and then right back to the radio through the shield, this is contrary to everything I know (and that ain't much). Is an RF choke needed?

 

I was really wondering that same thing when I made my 1st mag loop using the shield portion of a piece RG-8 about 18 inches in length. When I made it into a loop it was roughly 7 inches in diameter. Then I cut another piece of RG-8 about 91 inches (5 times the inner loop) and connected the variable capacitor to each end using the shield portion. I used a PVC box to house the variable and used coax connectors to connect the outter loop. You would think that little loop would not work being a direct short but when tuned properly with the outer loop, the impedance matching begins to happen and the rig will see around 50 ohms depending on how low your SWR reading. I have not used a choke in my set up so far. Have not had any problems with RF getting reflected back on the coax.

5/8 OD copper tube should work great. It will be more efficient than shield on coax. I used aluminum flat bar to keep it lighter but copper is a better choice for performance. I would say if your outer loop is 10 feet in length, the inner loop should be 1/5 of that or approx. 2 feet in length using a smaller size copper tubing to make the turn needed to form a loop. Try to keep your feedline at least 25 feet minimum.

Keep us updated on your progress.

73,
N4UVR

 

Thanks for the update Cory. You answered another question before I asked, as I have read one person linked the shield to the center core, I could only envision a huge mess trying to do that!

Looks like the 12 feet of LMR 400 that came with the kit will be used for something else...

I plan to have this loop ready by Winter Field Day.

 

I'm not a fan of Facebook either. I'll share everything I do with the series in the announcements here.