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| Subject: | Re: LF: 160 years of Popov birthday |
| From: | James Hollander <[email protected]> |
| Date: | Mon, 18 Mar 2019 16:40:27 +0000 (UTC) |
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TU emails from Gaj Kumar and Bob Riese.
RRR.
Re google info, see various coherer designs: https://en.wikipedia.org/wiki/Coherer Principle of operation: microwelding in some coherer designs. I’d think attraction of opposite charges and
same-directed currents might also be involved with ratio of particle surface
area to mass this extreme. The article
recognizes that a coherer simply detects presence or absence of RF so it’s not
an AM detector which isn’t used in ham LF anyway. Presumably, a coherer creates some noise of
its own as the particles change their constellation of electrical contacts with
each other.
Because a coherer is not frequency-sensitive
and does undesirably respond to noise peaks, a lot of filtering, noise
rejection and AGC tied to noise level could need to come ahead of it. For CW
signals spaced quite some way apart, no problem. For FSK and MSK, the filtering would need to be
more exacting. Perhaps rake RX as you say.
With all that, suppose a
coherer could detect presence of signal voltage down to 10% of noise
voltage. That would be SNR = -20dB -10
log10(2500/b.w.) in a 2.5KHz
bandwidth where b.w. is filter bandwidth in Hertz.
At the end of the day, why not just use a
diode detector or and forget all this.
Or do FFT (fast Fourier transform) and deep error correction like we
have now. No matter how you simulate a
coherer, it still just detects whether electricity exceeds some threshold. Pretty solid objections, right?
Software could simulate particle sizes even
finer than any realizable in known coherers.
Software could simulate particle shapes in a more systematic way than
the randomly ground particles in a hardware coherer. Software could represent particle responses
individually to electrical currents and magnetic fields in the coherer that
might depart from F=ma and usual electrodynamics--perhaps even diversely as to some particles vis-à-vis others.
In this
age of nanostructures, nanoparticles and quantum mechanical insights, I doubt
we have fully probed the properties and capabilities of colossal numbers of
individual particles to respond collectively to signal and not noise. While there’s no need to get carried away
over this topic, I think the coherer concept deserves a seat at the table of LF
topics occasionally, hi.
GL & 73, Jim H W5EST
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