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Planar Wound Loop for Medium Wave

planar wound loop

Yesterday, I converted my receiving loop from box to planar wound loop.

Initially, I used depth or side-by-side winding for my receiving loop. The loop is mounted on a cross frame made from 48 inch wooden dowels. This frame sits atop a stand on a servo operated pan-tilt mount. I custom designed and 3D printed all of the mounts.

During my early tests, I noticed that the multiple loops of wire depth wound made the loop front-heavy, not well balanced. So, I switched to planar winding, that is, with all the loops wound in the same plane. This resulted in a much better physical balance. Other changes included adding more turns to increase loop inductance, and increasing the space between the wires to reduce stray capacitance between the wires. Also, I switched to a heavier gauge wire for the pickup loop.

Early Performance of Planar Wound Loop

In theory, the performance of a planar wound loop should be similar to a depth wound loop. This seems to be true in practice. Although the antenna is still in the basement, I can get up to 50 dB gain when I tune to resonance, and a similar level of null when I rotate the loop so it’s broadside to the AM transmitter.

With the reconstruction, I now have a main loop of 7 turns and a secondary loop of 4 turns. Switched by a relay, this means that up to 11 turns are available. This provides enough inductance for tuning to below the bottom of AM Broadcast Band.

My daytime test station at the low end of medium wave has been CBK Regina (clear channel, 540 kHz) located in Watrous, Saskatchewan. This is a distance of around 700 km to the east. At the higher end of the band, KFBK on 1530 kHz ships up a great signal from Sacramento, around 1500 km to the south. With the antenna properly tuned to these frequencies, I can get a good strong signal or make the station disappear, depending on loop rotation.

Now it is time to build the wireless remote control circuit board, and move this loop out of the basement.

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