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Old 24th Feb 2021, 5:30 pm   #13
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Radiation resistance and gain of ferrite antenna

You do not want world record setting Q from an antenna.

Q is a measurement of the loss of energy from a resonator

You WANT to lose energy from an antenna

You just have a preference that the loss is into the radiation of an electromagnetic wave and not into the warmth of the hardware. You can treat reception as being reciprocal in most cases.

So your model of your antenna WILL contain resistance. Your Q should not be terribly high. The art lies in the partitioning of it between radiation and thermal losses.

Some years ago designs for copper loops a few feet in diameter (no ferrites, just a resonating capacitor) popped up in magazines and journals. some of them used straight lengths of plumbing type copper pipe and 135 degree Yorkshire fittings to make an octagon. Careful analysis showed that more oomph went into the 16 soldered joints than got radiated. The loop resistance (ESR) was small, but the radiation resistance was smaller. The sliding contacts in variable capacitors put the tin lid on it.

David
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