Most of you know how much I enjoy playing with mag loops. I think I have something like 5 of them from different manufacturers, as well as my first one that I built myself. I showed a few photos of my homebrew baby on Ham Fun night a few months ago. My first contacts on 10 watts were to Maryland and then Hawaii a few minutes later on 17 meters from Morgan Hill. The really fun part about mag loops is that they don’t have to be hoisted high in the air. The two contacts I made that first day had the loop base about 2 feet above the grass in my front yard!
Just for fun, here’s a short clip of my Chameleon P-Loop in action. The station you’re hearing was 59 on 20 meters from Utah to Mississippi on my Yaesu FT-818 running 2.5 watts:
Anyway, I know that some of you would like to try building a mag loop, but that it might be a little fiddly or require some tools you might not have. I just happened across this video from K6ARK, a SOTA guy that’s really into super-light, backpack-able radios and antennas, and he shows one that only weighs 8.5 ounces and can be put together easily without bending copper or aluminum tubing into a loop:
I thought this interesting (QRP power only) build might inspire you to try making one of your own. This one is not super-hard to make, doesn’t require any specialized tools, and packs away into a very small space. You might have to come up with some minor accommodations if you don’t have simple metal-working hand tools.
For example, the nice bracket that he made for the BNC connector could be replaced by simply cutting and stripping a piece of RG-174 or RG-58 coax and using a hose clamp to connect the coax braid to the ground point. Then solder or twist a simple 8 to 16 inch length of any kind of wire to the center conductor of the coax to make the “gamma” match. You can use either an alligator clip as shown, or even just another hose clamp to attach it to the main loop body. Just move the connection points around for the best SWR.
The little plastic switch box with the tuning capacitor is maybe a bit more of a challenge, but you can even substitute it with a 18-30 inch length of coax (for 20 meters), if you’re OK starting with just a single frequency/band. The capacitance between the shield and center conductor of the coax replaces the capacitors in the box. Just attach the shield to one side of the loop at the top, and the center conductor to the other side, leaving an insulator between the two ends of the loop. Something like a piece of scrap plastic, pvc, or even just a chunk cut from a soda pop bottle would work.
Leave the far end of the coax open, and measure your resonant frequency with a NanoVNA or some other wideband SWR meter. Snip the length of coax shorter a half-inch at a time until it resonates on the frequency you want. There–done!
I’m embedding a video by VK3YE showing this “coax-as-a-capacitor” method on his mag loop. You don’t necessarily have to make a big copper loop like this, or copy his tunable capacitor made of scrap pc board and a rubber band. You can just simply cut the open end of the coax a bit at a time as I mentioned.
The interesting thing about this antenna is that you can run a full 100 watts through it. Note just how low to the ground it is. That wasn’t just for the camera. I know some hams might think it’s impossible to get out with something this small and stealthy, but it really works!
As I’ve mentioned before, the only real downside is that mag loops are very narrow-banded, giving you only about 20-30 kHz of the band without retuning. Maybe the scrap pc board and rubber band kludge isn’t such a bad idea in that case. But…let’s say you’re really into FT8, or just want to join a daily net. This might just be your ticket! Stick it up in your attic and away you go…