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Old 29th Jul 2020, 11:43 am   #47
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: ATU vs. Preamp vs. Active Antenna

Not much advantage for a receiver. Huge advantage for transmitting.

With a typical loop well under a half wavelength in size, resonated to the wanted frequency with a capacitor, the effective radiation resistance can be sub-Ohm. So you neew the losses at the wanted frequency to be less than this. Due to skin effect, pipe is most efficient. Copper is low resistance and you do need plenty of surface area.

If you can only get the RF frequency loss resistance down as low as the radiation resistance, then 50% of your power heats the loop. So you want to get well below the radiation resistance. So big diameter tube, and copper-welded joint. Solder is not so good. My variable capacitor was made of plates copper welded into slots in the pipe.

Serious mechanical engineering.

David
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