P.I. Response to Magnetic Ground and Hot Rocks.

[Anonymous]

PI

 

[Anonymous]

Eric,
Thanks for the fantastic article. How do you think that a concentric coil would work if you formed the loops into elipses? I was thinking about trying a large eliptical transmit coil with a smaller receive coil inside it. A feedback coil would be wound around the receiver coil. Dave. * * *

 

[Anonymous]

Hi Dave,
I see no reason why it should not work just fine. It would give you a more elongated front to back response, which is desirable. I'm not sure how it would compare to a DD elliptical, but I suspect the DD would have the edge on range as the receiver coil is bigger. By the way, you can use a small piece of Magnetite positioned between the windings to get a fine balance.
Eric.

 

[Anonymous]

Hi Eric
Very nice and very educating post.
One of the worst places for the ground cancellation circuit of a IB detector I have found is at the edge of the beach between the wet and the dry sand. If it is one of the beaches where you also can find black sand, it can be nearly impossible to use a IB based detector. Try to swing from dry to wet sand following the edge, and the VLF's ground cancellation will course a "beep" when the line is crossed.
I have tried with a home build PI unit and could not find any reaction at all. I tried to switch between the PI unit and the VLF when a target was found. In most cases I could adjust the VLF to see it, but I guess that I would not have found it if I was only using the VLF.
Regards
Mark

 

[Anonymous]

Eric , I seem to remember reading about some detectorists that used a portable generator with positive and negative probes set in the ground 50 metres apart thus charging the ground and highlighting metallic targets . Is this the same principle that you mention with your large transmit coil? regards Ron.

 

[Anonymous]

Hi Ron,
No, it would not be the same. There are prospecting techniques that involve putting probes in the ground and passing an alternating current through them, but these are usually for measuring ground resistivity. I am not aware of any electrical mechanism that would highlight small metal objects in this way. It can be used for locating large metallic ore bodies as the current would gather, or concentrate, in areas of higher conductivity. Some Long Range Locators that are advertised utilise probes that are put in the ground and are claimed to excite metal objects at great distances. However, this is a very controversial subject and not one I wish to get into here.
The large ground loops that I use simply transmit a pulsed magnetic field, but over a much larger area and to a greater depth than is possible with a hand held coil. Generally this technique is only good when looking for objects of cannonball size and upwards.
Eric.