I used a loop on the 73kHz band in the early days and had some interesting
results. The currents were very high - several amps for the same power that
delivered a few tens of mA into a same-sized vertical. The main disadvantage
of the loop was its directivity which is quite pronounced, even with the
lower part very close to the ground. This may be an advantage for a
point-to-point path, such as transatlantic and may result in lower noise.
GW4ALG used a loop and a vertical, and the vertical usually outperformed the
loop. He used the loop when it was not convenient to put up the temporary
vertical.
Another interesting fact was that signals from those using loops had more
fading at a closer distance than from those using verticals. This suggests
that the angle of radiation was higher. Perhaps an area for experimentation.
My matching method was to tune the loop with two (groups of) capacitors in
series, used as a potential (and hence impedance) divider. I was feeding the
antenna with a 3ohm source at the time.
A loop's independance from earth is a very attractive feature, but everyone
I know who has used one has eventually agreed that Guglielmo Marconi got it
right!
Mike, G3XDV
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