There’s a joke in the world of radio that all you need for a HF antenna is a piece of wet string, but the truth is that rudimentary antennas rarely perform well. Random pieces of wire may pull in some signal, but along with it comes a ton of unwanted interference and noise. It’s thus worth putting in the effort to make a better antenna, and if you’re not fortunate enough to have a lot of space, your best choice may be a magnetic loop. [Robert Hart] takes us through the design of a receive-only coaxial loop. It’s referred to as a Moebius loop because the conductor takes a “twist” path between the inner and outer halfway around.

The idea of a loop antenna is simple enough. It’s an inductor intended to respond to the magnetic portion of the wave rather than the electric part. They’re normally made of a single turn of wire in a loop of diameter well below half a wavelength, and, in their transmitting versions, they are often tuned to resonance by an air-spaced variable capacitor. Coaxial loops like this one provide enhanced resistance to electrical noise. He’s using some rather expensive Andrews coax for its rigidity, but the less well-heeled can use cheaper stuff without penalty. The result, when put on a frame of PVC pipe and a speaker stand, is an excellent portable receiving antenna, and if we’re being honest, something we might also consider in our own shack.

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