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ELF detectors

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Conundrum

Sat Jan 04 2014, 08:05AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Proud Mary wrote ...

Lastly, there is the tree antenna. Two nails banged into the trunk of a big tree a couple of metres apart will produce a small but detectable ELF output. (This really does work in practice, and a few peer-reviewed papers have been devoted to it.)

Amazing. One wonders how this works, do the tree roots somehow act as ELF rectifiers?
Also a synchronous rectification approach using zero voltage MOSFETs might be worthwhile, and bring in very small signals indeed.

-A
"Bother!" said Pooh, as his Bluray drive caught fire...

Proud Mary

Sat Jan 04 2014, 06:41PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Conundrum wrote ...

Rectification isn't something required of an antenna at any frequency.

A bit more complex than the VLF tree antenna, is this 1973 paper: Utilization as RF-Antennas of Live and of Lifeless Structures in Natural and in Man Made Jungles

and Performance of Trees As Radio Antennas In Tropical Jungle Forests

This phenomenon was first reported at Signal Corps Laboratory, Camp Alfred Vail, Little Silver, NJ, USA , and described by Major-General George O. Squier (Chief Signal Officer, US Army) in Electrical Experimenter July 1919, p. 204

As can be seen from the picture, the signal is extracted between a nail in the tree, and an Earth point. The later US Army experiments loaded trees via an impedance matching ferrite toroid.

Effective VLF tree antennas using removeable stainless steel screws to minimize damage to the trees have been reported by members of NASA's INSPIRE project.

And finally a real cracker from Nature 16th Feb 1978 ULF Tree Potentials and Geomagnetic Pulsations:

,d.bGQ&cad=rja

Conundrum

Fri Jan 10 2014, 08:42AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Amazing. Wonder how I could get permission to test this out, we have some enormous trees here.
Would a tungsten screw also work, as this is pretty corrosion resistant.

-A

Shrad

Fri Jan 10 2014, 08:48AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780

for an ELF detector, I'd use a DWARF

Proud Mary

Fri Jan 10 2014, 11:17AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thank you for your helpful input, Mr Shrad!

I haven't seen it suggested anywhere, but I wonder if the tree antenna isn't a special case of fractal antenna, which are supposed to be frequency and bandwidth invariant.

Proud Mary

Fri Jan 10 2014, 12:10PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Conundrum wrote ...

Amazing. Wonder how I could get permission to test this out, we have some enormous trees here.
Would a tungsten screw also work, as this is pretty corrosion resistant.

I can't see why a pair of tungsten screws wouldn't work, AndrÃ©. I guess the thing to avoid is using screws of different metals having different electrode potentials that would operate as a voltaic cell, setting up a potential difference between the two electrodes, and releasing noxious electrolysis products into the tree.

Long agricultural fences of wire stapled to wooden stakes might also be worth investigation as antennas at low frequencies. Some of them will be electrically continuous for miles. They will of course be shunted by the resistance of the wood at regular intervals, but in summer when the wood is dry the losses should not be too prohibitive, and might even be beneficial - some very long ELF antennas terminate in a resistance to ground of 600Î© or so to improve impedance matching.

I think VLF/ELF/ULF is one of those fields where the amateur with relatively simple equipment and a very small budget can still hope to discover things of interest - I'm sure that at heart we all hope to 'discover' something!

Ash Small

Fri Jan 10 2014, 01:02PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Conundrum wrote ...

Amazing. Wonder how I could get permission to test this out, we have some enormous trees here.
Would a tungsten screw also work, as this is pretty corrosion resistant.

-A

A 316 stainless screw would be more corrosion resistant than 304. If you're in the Channel Islands, Andre, you should be able to get these from any reputable yacht chandler/boatyard. They are also known as 'marine grade' or 'A4'. (don't use what the marine industry refer to as 'A2', as these are type 304.)

Edit: in 'tree sap', monel or phosphor bronze screws would be even better, although monel (nickel-copper alloy) is not easy to find these days.

Proud Mary

Fri Jan 10 2014, 01:33PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The 'no nails' tree antenna technique developed by the US military in the Vietnam era uses what looks from pictures like a large diameter (20 - 40cm) Rogowski coil wrapped around the trunk.

In experimental military HF use, the wrap-around coil was then loaded using ordinary antenna matching techniques.

How well this might work at VLF and below is another question.

Mattski

Fri Jan 10 2014, 09:00PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Conundrum wrote ...

I think this guy is onto something, a lot of research into wireless power transfer assumes that a small antenna simply cannot work but in fact if it is properly made the efficiency is actually higher than conventional knowledge predicts.

wrote ...
Please understand then, my expression of total disdain at the manner in which scientific theories in relation to magnetism and electromagnetic 'wave' propagation have been inculcated since the first intuitive attempts to explain same during the pre-electronic epoch. New conceptual exercises related to the investigation of physics fundamentals, plus the subsequent design of this new inductor have made me realise that dogmatic repetition, and worse, the indoctrination of erroneous hypotheses into formative student minds *including my own* by the so-called "know-men" of science who control education curricula in our schools, colleges and universities, had, for 45+ years (and I state this as being a genuinely truthful fact related to my own situation) quite literally prevented me ...

Interesting how this guy thinks he has discovered new theories but has not done a lick of math to test his results against the "conventional" theories that he disdains. I didn't read enough of his work to understand what he has done, and I know very little about antennas anyway, but I took enough EM to know that math gets heavily involved ;) I'd bet a shiny dollar that conventional theory explains his results just fine.

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