10-40 Meter Magnetic Loop Antenna
I thought that maybe it was time that I would build a MLA (Magnetic Loop Antenna) to see what all the hype was about.
Before gathering the materials, I had to decide what I would want to use the antenna for, and as to what bands I would build it for.
It was a given that the MLA would have to be capable of breaking down into a small package, as I knew that the MLA would be perfect for my Manpack that includes the Yaesu FT-897D running on internal batteries.
Because the 897 running on internal batteries is limited to 20 watts out, and after doing research as to what was available for a variable capacitor in the marketplace, I found a source for a variable capacitor rated for 25 watts out and ordered it up.
This variable capacitor is a very nice build with a geared 6-1 front end making for very fine adjustments when tuning the MLA.
Because the primary loop had to break down for storage, I decided to build it from LMR 400 coax cable, as it coils readily when removed from the main housing for storage, yet retains a nice round footprint when assembled..
I should mention that I decided upon starting this project that I wanted the MLA to be fairly compact, and for that reason, I designed the MLA to cover 10 through 40 meters. with the main loop measuring 36" in diameter when assembled.
The mast parts were made from non-conductive composite material, and the joint connectors I made from white Delrin.
Not shown in the photo is the lower 36" mast section that mounts on the frame of the manpack, and is made from the same composite material as the loop support components, and supports the MLA when set up for operation .
The feed loop where the SO-239 connector resides for the transceiver to connect to, is constructed from flat bar-stock aluminum, and this also was by design so that when assembled the mast and the feed loop along with the control box become a ridged assembly to which the main loop mounts to and holds its form.
Of course there was a lot of one off pieces formed in my workshop, and the one component you see that resides at the very top of the feed loop was formed from Delrin, and has a channel cut in at the very top that the LMR 400 primary loop drops in to upon assembly of the antenna.
The lower portion has a 3/8x16 tpi thread that screws in to the feed loop, allowing for the SWR to be adjusted by varying the space that resides between the feed loop and the primary loop.
So, for the moment that's it, but over the following days while I running tests with the MLA mounted in place on the frame of my manpack and connected up to the FT-897D......Stay tuned.
Here's a look at the mag loop in the field being operated.....