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Old 20th Sep 2017, 8:20 am   #123
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

You'll find that with any loop antenna, the peaks are rather broad and the nulls are very sharp. So if it's rotatable you'll find yourself turning it to minimise your worst noise source rather han peaking the wanted signal.

For reception, a loop made out of whatever wire you have kicking around will be fine.The amplifiers used have much higher input impedances than the radiation resistance of the loop, so there is no attempt at matching.

For transmitting you'd like to match into the radiation resistance, but this is spoiled by the losses in the copper and whatever joints you have. The loops are usually resonated, multiplying the circulating current to get the best radiated mag field, but this increases the dissipation in the losses. So thick copper with no joints is needed, and something special is needed as a low loss resonating/tuning capacitor. Transmitting is much more difficult and the best care will get you up to merely poor efficiency. Lack of care gets abysmal efficiency!


David
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