Just interested really.

[JohnW2]

Probably the same aggravation while trying to sense (and amplify) tiny biological signals from "nudging molecules" or even intra/extracellular potentials formed during nerve depolarisation though I expect (but am not sure) that peripheral nerve depolarisation potentials (and resultant signals) are quite large compared to say signals in nerve axons of the brain or inter-molecular signals?

Indeed, as you say, if one measures intra-cellularly, or even on the surface of a cell, depolarisation potentials/ 'action potentials' in nerve and muscle cells are relatively 'large' - the resting potential across those cell membrane is around 70mV, so the changes one sees on depolarisation are at least that large. However, when one has an interest in what happens at, say, neuro-muscular junctions, one may wish to look at the ('sub-depolarising') changes in membrane potentials resulting from the release of single 'packets' of chemical transmitters, and those potentials can be well under 1mV, even when measured locally.

In clinical applications, of course, one is usually measuring 'at a distance' (e.g. ECGs and EEGs) i.e. looking at the field created within the conductive human/animal body created by the distant 70mV+ cellular potentials. As a result, surface-measured ECGs are of the order of 1mV and surface-measured EEGs as low as 10uV. In contrast, 50Hz and 'Radio 2' picked up by a human body can be orders of magnitude larger - and one has to rely on a mixture of low-pass filtering, 50Hz band-stop filtering and the common-mode rejection of differential amplifiers to get rid of most of that ... but then, to take one back to where we started, the amplifier then has to be somehow protected from picking up Radio 2 (and all sorts of other things) itself.

Kind Regards, John.

 

[sparkticus]

Maybe, although it's far from obvious why 'historic' stuck with wavelengths below 10cm but not those above ... and, of course, you've missed out a step of history - with the longer wavelengths, we first went through the phase of specifying their frequency in cycles/sec (which seemed so logical) before we ended up with Hz!

Yes, I was just generalising with historic because I don't know or maybe can't remember why we interchange the terms like that. What is true is that waveguide designers (including for mobile phone technology) do talk in terms of wavelength. I suspect that is because the wavelength (half and quarter wave) is critical to the "mechanics" of the design of the waveguide. Could it be that the terms are interchanged simply out of convenience? For example a waveguide designer talking wavelength and the pre-amp/PLL designer talking Hertz. I guess 10cm is 3 Giga Hertz, just wondering if that is some magic threshold but its too early in the morning for my aging brain to function or remember anything of significance

 

[JohnW2]

What is true is that waveguide designers (including for mobile phone technology) do talk in terms of wavelength. I suspect that is because the wavelength (half and quarter wave) is critical to the "mechanics" of the design of the waveguide. Could it be that the terms are interchanged simply out of convenience?

There's certainly obvious convenience in a waveguide designer talking about wavelength. However, the same is really true of 'radio waves' across the spectrum, again because of antenna design - of which the half-wave dipole, quarter wave vertical etc. are still the foundations.

I guess 10cm is 3 Giga Hertz, just wondering if that is some magic threshold but its too early in the morning for my aging brain to function or remember anything of significance

I just picked 10cm/3GHz because it more-or-less represents the boundary between 'radio waves' (VLF, LF, LF, VHF, UHF, SHF, ELF etc.) and the lower wavelength stuff that we think of in other ways (IR, visible, UV, X-Ray etc.). It's really only the 'radio waves' for which we generally use frequency these days.

Kind Regards, John.

 

[ban-all-sheds]

The Light Programme. 1500m Long Wave (or 200kHz in new-speak). Takes me back a day or several!

You used to be able to listen to that on fences near the transmitter.

The rust on the fence wires acted as a rectifier.

 

[JohnW2]

The Light Programme. 1500m Long Wave (or 200kHz in new-speak). Takes me back a day or several!

You used to be able to listen to that on fences near the transmitter.
The rust on the fence wires acted as a rectifier.

Indeed, and you could light up fluorescent tubes by simply holding one end of them in the vicinity of the transmitter; as I said, it pumped out an awful lot into the ether!

Kind Regards, John.