Can a dinky 3-foot loop antenna really work? I decided to find out. Take a moment, if you please, to follow me through my experience of building and using several different magnetic loop antennas, one for 100 watts and two for QRP, and trying them in the real world of ham radio (Photo A).
At the start, I’d heard all the comments, mostly negative, about these antennas. “They’re hard to tune, they’re so sharp” — “Every time you change frequency, you have to retune” — “A small loop like that can never compete with my half-wave dipole.” — “What about capture area?”
Like the bumblebee, which theoretically can’t fly, yes, I found that mag-loops do work. A well-made mag-loop is a surprisingly good antenna and provides us with the ability to work stations from the confines of an apartment or private home where outside antennas are forbidden or at least severely limited by the Rules Police, also known as the homeowners’ association, or HOA.
I am not here to say that a mag-loop will outperform your three-element Yagi at 40 feet, or your half-wave dipole either. Of course not. But I do work stations all around the country while using CW on a QRP rig and a mag-loop antenna, all inside my home. Recently, while operating POTA (Parks on the Air) using QRP to my mag-loop, we worked Spain, among 20 stateside contacts.
A 100-Watt Mag-Loop Antenna
I designed my first loop to work at the 100-watt level with my Icom 7300 transceiver. It uses a 39-inch diameter piece of 1/2-inch copper tubing (Photo B). The 39-inch diameter wasn’t the result of a calculation, rather, the box of tubing I bought was about 10 feet in length and, when uncurled into a single turn, it yielded the 39-inch diameter. So much for scientific design.
I tune the loop with a motor-driven 40- to 300-pf vacuum
