Simple but brilliant LRL

[Funfinder]

Let's discuss and work together in this new LRL-case in an own topic!

But in the Iconos MD 807 thread
http://www.geotech1.com/forums/showthread.php?t=16625
I've reported already about the beginning developments (see schematics below) including these 2 clips 'til now:
http://www.multiupload.com/SHCZFGJA5H
http://www.multiupload.com/FJ82JS1ID5

Today I found a sieve 20cm diamater made out of metal and shaped like a half ball inclusive handle so it serves very well for small directional antenna tests.

And I found a highsensitive CA3130 opamp with FET Input on an old pcb! We electronical skilled treasure hunters are the real one, because we also can find real treasures in "eletronic junk" others throw away!

Estebans Zahori:
http://www.geotech1.com/forums/showthread.php?t=11674
uses one. This IC seems to amplifies already 2pikoAmpere weak signals and upwards:
http://datasheet.octopart.com/CA3130...heet-75654.pdf

btw. all those FETs work good together with photo-diodes so they also can be used for field temperature detection (metal or caves change the temperature of the ground) and perhaps I'll include such 2nd detection-circuit sometimes. Devices you can control by IR-remote use such often black photo-diodes.

My next test is if and how the CA3130 works (alternatives: CA3140, CA3240, CA3260).


@ Morgan:
Thanx for your answer and your suggestions. The diode is an OA95 (any glass-one may work) and an 1mOhm instead the 470k resistor is better, but for even more sensitivity you can remove this "pre-noise" circuit completly - it's not neccessary for the main one.
An included BFO circuit could be disturbing other important signals. And I read you detected the coin-cache (I hope you are a millionaire now! ) from 20m but directly over the coins you got no signals - perhaps because of overloading energies. We also should try to find a way how to solve this problem so the detection doesn't end at some level.

And I found out the FET at least needs some "minimal electrostatic current" until it starts to work! If the antenna has a big enough size you'll get always signal, or if the signal-source is near enough. A 10m long wire also works to get always a detection, but this is not practical.

However, for maximum gain the FET should be attached directly to the antenna or built into the antenna.

btw. this ring detection is very close to the range where the FET "switches itself on" and RRRRRRR's. And only a very small change in position results in a raising or vanishing ring signal.


@ detectoman
thanx for joining us here. I also invite Geo for sharing his experience and everyone who built already such kind of detectors.


See you soon guys!