Coils for LRL

[Funfinder]

I found essential info about the most important part of any short or long range MD - the coil!

Read this:
http://www.vlf.it/matteobruna/ULF_Induction-Coil.htm

On some other article of this page
http://www.vlf.it/minimal2/minimal2.html
i found this info:

Mechanical stabilization Let’s return to the practical problem. One of the worse troubles we find in using the minimal loop is the microphone effect: a loop millimetric mechanical oscillation produces a big interference, this is because the antenna works fitted in the terrestrial magnetic field. Since we can’t turn off the heart magnetic field, we need to make the loop perfectly stable.

and:

We can't place the receiving loop near metallic fences or other iron structures: their mechanical vibrations deform and modulate the earth magnetic field, producing the same microphone effects described before.

We should keep this in mind if we want to detect metal from far distances.


And if the Alonso PD really works at around 60kHz, the coil would need alot turns. And the thicker the copper wire the better, because of the electric resistance of the copper.

Here's the easyloop receiver:
http://www.vlf.it/easyloop/_easyloop.htm

Just we don't want to listen to VLF (very low) or ELF (extremly low) signals but need those low freqz. for better ground penetration.

The coil has to be unshielded for most gain and will detect the magnetical "interference" between earth and buried metal object (plus perhaps the electrostatic).

We should find out what coil has the best gain.

An usual air-core-coil or a ferrite-core-coil.
The directional effect should be the same, but instead of air the ferrite or other high permeabe material cored coil would be much smaller and light weighter.

1000-2000 turns around a 15cm ferrite should work. For making it more broadband and less "selective" scramble winding could be used.

For the beginning I guess also not very-low-noise op-amps will do it. Because we want to detect the change in electroMAGNETIC-field metal objects cause and not 1000km away radio-signals.

Perhaps also a VLF-transmitter should be used if the "background energy level" isn't strong enough.

btw. if the special magnetic coil really is very very sensitive and directional, it could detect even far metal only by "impedance changing effect".

In this case a very sensitive and stabilized oscillating coil would detect the magnetical losses or changes if some metal is "near". Using high voltage this circuit also would recognise if an electrode or cathode = the attracting metal object, is near. Depending on the humidity even buried ones.

Combining those both techniques including very selective and sensitive electrostatic plus eventually extra gradio- or magnetometer at least has to lead to some real working LRL device!


I'm just hoping I'll finding more and more such important info by for getting puzzle piece by puzzle piece the whole picture...