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Why evolution by natural selection didn't make use of RF?
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coppercone2:
some how derailing this thread to yell about harmonics is just not cool
Bud:

--- Quote from: RoGeorge on August 31, 2023, 04:47:32 pm ---
For example, if we take a square wave of 1kHz, such a signal is supposed to have plenty of sinusoidal 3kHz in it, according to Fourier.  However, one can make a filter that will only respond to a sinusoidal shape of 3kHz, and no other shape than sinusoidal.

--- End quote ---
No, one cannot  :-DD
tggzzz:

--- Quote from: Bud on September 01, 2023, 03:29:31 am ---
--- Quote from: RoGeorge on August 31, 2023, 04:47:32 pm ---
For example, if we take a square wave of 1kHz, such a signal is supposed to have plenty of sinusoidal 3kHz in it, according to Fourier.  However, one can make a filter that will only respond to a sinusoidal shape of 3kHz, and no other shape than sinusoidal.

--- End quote ---
No, one cannot  :-DD

--- End quote ---

How about capturing the signal, doing an FFT, and seeing if there is any frequency other than 3kHz :) Oops; that contains the "invalid" word "Fourier".

Or an analogue variant: a bandstop filter centered on 3kHz, plus a switch. If the filter's output is non-zero, the switch is opened. Oops; that depends on the concept of the equivalence of time and frequency domains, as defined by Fourier.
Bud:

--- Quote from: RoGeorge on August 31, 2023, 04:47:32 pm ---Such a 3kHz filter won't respond to a square wave of 1kHz, which indicates there is no sinusoidal 3kHz in our 1kHz square.  I'll say that's a proof Fourier spectrum is not really there.

--- End quote ---
That is exactly what a 3kHz filter WILL DO, you just have not tried or have not measured properly.
coppice:
Its sad how many of the messages in this thread come down to "that can't happen. because I've never seen it happen", rather than "here is a physics road blocker which means that can't happen".
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