Big and deep or small and shallow?

[brucester]

Hello,

Just wondering, when it comes to PI detectors, what is the easiest to build for?

Big gold nuggets deep underground, or tiny nuggets near the surface?

With all the factors such as ground noise, the earth magnetic field, hot rocks etc etc, when it comes to generating and analysing signals, are big deep nuggets in high mineralised sand easier to generate technology for or are shallow little nuggets easier? Or are they both the same?

By easy i mean, timing of samples etc.

Hard to explain what i'm saying :P

Is it easier to cancel out all the other factors to process a signal for a big nugget, or do the higher currents required and longer time frames add to the complexity of the situation?


Bonus points if you can kind of understand what i am getting at :P

[Reg]

This is another interesting question. As to the detection of small nuggets, there are also problems with trying to detect those very small gold nuggets with a PI. I know, I built a low powered PI that could do a lot better than any other PI was presently on the market at the time I used that detector.

The key to this type of hunting is to be able to build a PI that works at below 10 usec and that is a real challenge. Using low power helps because it reduces the spike that has to decay, thus reducing the time it takes to do so.

Other problems begin to show up as you reduce the delay including the dramatic increase in ground noise that has to be dealt with, so this isn't exactly an easy task either.

One trick I used was the simple DD coil. It simply helped in different ways including making it easier to use shorter delays, the reduction of ground noise, and external and internal noise. So, you might keep this in mind.

Reg

[6666]

Hi Reg
interesting idea useing a DD.
Did you IB the coils useing the tx pulses as a reference signal.

[ApBerg]

This is another interesting question. As to the detection of small nuggets, there are also problems with trying to detect those very small gold nuggets with a PI. I know, I built a low powered PI that could do a lot better than any other PI was presently on the market at the time I used that detector.

The key to this type of hunting is to be able to build a PI that works at below 10 usec and that is a real challenge. Using low power helps because it reduces the spike that has to decay, thus reducing the time it takes to do so.

Other problems begin to show up as you reduce the delay including the dramatic increase in ground noise that has to be dealt with, so this isn't exactly an easy task either.

One trick I used was the simple DD coil. It simply helped in different ways including making it easier to use shorter delays, the reduction of ground noise, and external and internal noise. So, you might keep this in mind.

Reg

Thanks for this info !

[6666]

Brucester
some interesting reading here also
http://www.nuggetshooter.com/article...Idetector.html

[Reg]

I didn't balance the coils exactly but left them a little offset. It seemed like they would detect the smaller gold just a little better. At full balance it seemed like the really small stuff could be missed easier.

I do need to go back and do more experimenting with this design though. A lot has passed by since I originally built those DD coils.

Oh yeah, a lot has been learned since I wrote the Understanding the PI also. It takes time and a lot of experimenting as well as making a lot of wrong assumptions to get a better handle on PI's. I am still learning and wonder if I will ever really truly understand them. It seems about the time I feel I have things figured out, something new arises.

Reg

[6666]

Hi Reg
thanks for the reply
do you roughly remember the specs of the coils ?
thanks
6666

[Reg]

I tried several different values, but the one I decided on was 300 uh for the TX and about 450uh for the receive. One can go down a little on the TX to increase the depth a little but I wouldn't go much below 275 uh without doing more experimenting.

Reg

[6666]

Great thanks Reg
6666

[6666]

Hi Reg
Today I made some very crude 1st experiments with OO coils, just a couple of 300uH coils.
I used the surf PI as the TX, and hooked up the second coil to the CRO, no damping on second coil.
But it works, and I got some very interesting results in the waveforms in second coil, it has inspired me to do
some more testing.
6666

[6666]

This afternoon I hooked up a centre tapped differential coil for the second RX coil to the CRO.
Its 11 inch dia, 23 turns then 23 turns centre tapped, .47mm , all turns going in same direction
no damping.
Using the centre tap as earth ,
And wow what a huge signal, waved a couple of coins about the coil
and sure enough you could see the change on the CRO.