Hi Eric,
Thanks for the info. I am curious as to the program you are using simulate the flux distortion.
My observations regarding finding a nugget under or along side a highly mineralized rock (or a lump of mineralized soil) takes on two different senarios.
First, with VLF's, the detection of the nugget under a "hotrock" becomes much more difficult, and in many cases, almost impossible unless the detector is carefully adjusted for absolute minimum response or slightly positive response from the rock itself. Adjustment of the detector is extremely critical. If there is even the slightest negative response from the rock (ie the detector goes quiet) even a large nugget (ie 1/4 to 1/2 oz) can be ignored. It is easy to show how a golfball sized rock can easily hide a 1/2 oz nugget even if they are both very close to the coil.
My limited experience with PI's, on the other hand, indicates easy detection and possibly an enhancement of the gold when under or along side a hotrock. It has been my contention all along that the SD series aren't necessarily finding more nuggets simply because of increased depth capabilites, but because the iron oxide "hotrocks" do not masked or hide the nuggets on a PI like they do on a VLF.
On the downside, my limited experience with PI's shows that "hotrocks" such as magnetite and other simular members of the iron oxide family are detected as a positive target, as is gold. Obviously, detectors like the Goldscan and the SD series have additional circuitry to "subtract" the rock response. (I would add again that my Goldscan does an excellent job of elimininating most of the "hotrocks" and still easily find a nugget beneath or along side of it.) This is something extremely difficult to do with a VLF.
I have been experimenting with the Mark Stuart PI design to see how PI's work. I have found that shortening the pulse duration appears to effect the intensitity of the "hotrock" signal.
I have also been experimenting with different forms of autotuning, autotuning speeds, etc added to this detector. So far I have found a single high pass filter is extremely difficult to design to get the right autotune speed that doesn't lose depth and still maintain a constant threshold. However, I have just begun to experiment with a two filter design (4 filter if you count the low pass filters), and it shows promise. The trick is to find the ideal time constants for maximum sensitivity and maintain the minimum ground response. Right now, it appears this approach does a very acceptable job of typical ground signal elimination and still maintain high target sensitivity.
Getting back to the fundamentals, in my opinion, PI's show a very clear advantage as a detector of choice for hunting gold nuggets, especially if the hotrock and ground responses are minimized.
Again, my opinion is based upon limited PI experience, but extensive VLF knowledge and experience using and/or owning 10 or so different models of gold machines spanning most of the major manufacturers.
Sorry to keep altering the topic towards the subject of nugget hunting, but like I have said before, there are a lot of people like myself who are yearning for a light weight, reality priced, nugget hunting detector that gives them that added depth. I believe a PI design is the answer.
Reg
) The idea is that high mineralization beneath the coil will reduce the detection range above the coil, similarly to if the target was buried in the same ground. As I said, I haven't noticed this by testing myself, so when you try please let me know your results.