Re: LF: 160 years of Popov birthday

[James Hollander <mrsocion@aol.com>]

 

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