Mag Loop for HOA's??

Jack, W8TEE


We took Al's Double-Double mag loop:
Inline image
for a spin at FD. We ran 100W on 20M and 40M. First, we were surprised how well it performed for a "compromise" antenna. We worked 40M on Saturday and worked KS to ME, WI to FL. We even managed to work pileups, often towards the front of the pile. The stepper controller looks similar to this:

Inline image
although this photo was taken before the software was finished. Two encoders control the "target" frequency (e.g., 7199995) and the stepper motor, with the SWR calculated using an AD9850 as a signal source. The final version shows a 100-point plot of the SWR as you tune the cap to resonance on the target frequency. The cap position and frequency are very close to linear, so the final version will "fast step" to the target frequency and the encoder can then fine tune from there. We can tune to 1.1:1.0 on 40-30-20M. The display is a small 2.2" TFT display, but any SPI TFT using the ILI9341 driver could be used.

Quite honestly, Sunday wasn't as good. We concentrated on 20M and we were expecting better performance. (The models say it should perform better on 20M.) We didn't hear as many stations as on 40M on Saturday, but we're not sure if it was all antenna, band conditions, or a mixture of both. Al and I will be writing an article on its construction in a little bit after some testing that will give us some concrete numbers. We are devoting one chapter in the new Projects book to its construction and a second chapter to the stepper controller.

I will be trimming off the "spike" at the top for mine, which will allow it to fit in my car trunk. (I want to call it the "Luggable Double-Double", but Al doesn't like it.) Anyway, it will all be put into Open Source and we hope that some HOA-bound hams might find it useful since its 3' diameter might fit in an attic or somewhere else that the HOA considers acceptable.

BTW, I hope your club had as much fun at FD as we did...despite some rain.

Jack, W8TEE

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