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Interview With Brent Weaver, Senior Design Engineer, Garrett Metal Detectors


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11 minutes ago, phrunt said:

Yes, fine gold on the GPX certainly increases target response on some difficult nuggets that in sensitive extra could miss entirely, it still isn't great on them, but it will find gold sensitive extra will miss, and probably the same goes the other way around too.

Fine Gold is a misnomer and it will absolutely miss gold that you will hit in Sensitive Extra. Fine Gold should have been named Banded Iron Rejection as that is what it was made to do. It does really well picking up the gold it does pick up and that combined with the name made it a magic setting for a lot of people, but it has very aggressive ground cancellation and should not actually be used unless the ground demands it. It's a good dummy mode though and that is why it was used as a basis for the SDC 2300.

Per Minelab:

"Fine Gold is sensitive to smaller targets in highly mineralized ground. It provides a sharper signal on small gold compared to Enhance, and improves the detectability of rough/flaky gold and specimens, while ignoring most hot rock signals and false ground noises. Shallow, highly mineralized ground where gold has been found previously should be re-examined with Fine Gold, and best results will be had by using the optional 8” and 11” Commander Monoloop coils. Note: Sensitive Extra will provide superior results on small gold in milder ground." Emphasis added.

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yep, I run almost exclusively in sensitive extra except in bad hot rock areas, I have noticed as Minelab are pointing out there that fine gold does well on rough/flaky gold and specimens though, better than sensitive extra on some little bits, some sensitive extra won't see at all that fine gold does.

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Yep sensitive extra should be run anywhere the ground will allow. It's going to find gold better that fine gold in most US locations. I always start in sensitive extra and adjust if necessary.

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24 minutes ago, abenson said:

Yep sensitive extra should be run anywhere the ground will allow. It's going to find gold better that fine gold in most US locations. I always start in sensitive extra and adjust if necessary.

Me chasing big nuggets in Alaska I always started Sharp and maybe backed down to Normal if I had to. :smile:

"Sharp is similar to Normal but creates a more powerful detection field. It is capable of an improvement in depth, but is more susceptible to interference and will increase the severity of false signals in difficult grounds. This timing is best used in quiet conditions and can work well in combination with Deep Search Mode with a reduced Rx Gain setting. Sharp is an excellent tool for pinpointing faint signals due to the very "sharp" signal response. Sharp will work best with DD coils in most gold field locations."

Again, the ground rules all. This chart shows how Sharp outperforms in milder ground but falls on it's face in severe ground. Normal is better than Fine Gold in any ground where it can be run, which is all but the worst ground. People should be aware severe mineralization is actually pretty rare. The banded ironstones of Australia and Mother Lode serpentine belt of California are examples of severe ground.

minelab-timing-example.jpg

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5 hours ago, Steve Herschbach said:

But maybe we are just talking semantics. What you think of as a hole and I think of may be different things. To me a hole occurs when a detector will not pick up a nugget it should pick up due to whatever ground canceling method is in use also knocking out the gold target.

In a detector with only a single GB channel (like the TDI), it is possible to find a small range of conductivities at the conductivity transition point that are severely suppressed. When I air test the SDC with a continuous array of conductive targets, I can easily find the two transition points between the three regions. I could not find any range of suppressed targets with the SDC, target detection through both transition points was quite good. This tells me that the mathematical target holes are filled in.

Again, that's in air. If particular targets are then lost in particular ground, then that could be due to the way the tracking algorithm is working, rather than the mathematical target hole. I suspect the same thing would happen in a multiperiod detector. In other words, you can eliminate the mathematical target hole with either multi-TX or multi-RX, but you will likely still face the same issues with certain targets in certain ground. I can see calling that a "target hole" but it may be a completely different issue.

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Interestingly, Even with its dated technology, I find that with the TDI by using the Ground balance adjustment more for adjusting the ferrous non ferrous crossover point than for ground balance, with careful manual adjustment I can often ID iron more accurately than the newer machines, especially large iron that will overload most detectors and give a non ferrous response, and that includes the best simultaneous multi frequency VLF machines like the equinox 800. I am sure this is why relic hunters like the TDI as Steve mentioned.

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2 hours ago, Geotech said:

In a detector with only a single GB channel (like the TDI), it is possible to find a small range of conductivities at the conductivity transition point that are severely suppressed. When I air test the SDC with a continuous array of conductive targets, I can easily find the two transition points between the three regions. I could not find any range of suppressed targets with the SDC, target detection through both transition points was quite good. This tells me that the mathematical target holes are filled in.

Again, that's in air. If particular targets are then lost in particular ground, then that could be due to the way the tracking algorithm is working, rather than the mathematical target hole. I suspect the same thing would happen in a multiperiod detector. In other words, you can eliminate the mathematical target hole with either multi-TX or multi-RX, but you will likely still face the same issues with certain targets in certain ground. I can see calling that a "target hole" but it may be a completely different issue.

Yeah we are tripping over semantics. When I and the other guys sit around the campfire and talk PI detectors and the detection "hole" what we are all referring to is the gold that is lost in the "holes" in different timing scheme. From our perspective every GPX 5000 timing has a hole of some sort, in that gold you miss in one timing can be detected in a different timing. The gold "falls in the hole." So when people are talking here on this forum that is what we mean by the term "hole" - a layman's definition as opposed to an engineers mathematical definition. I am sure I do not know the exact reasons why this happens but it is easy to show in the field with a GPX 5000 and it's multitude of timings. The problem historically is most 5000 users really did not know the timings scheme well enough to do more than half guess at what they should be running, and often a favorite setting got used everywhere. The only way to do it right was to hunt a patch multiple times with multiple settings.

For me personally it feels like an over filtering issue. In bad ground with hot rocks I can apply progressively higher levels of ground compensation. As I ramp up the ground cancellation the machine gets quieter, but at the same time my gold responses drop off. My tuning methodology usually involves riding the edge as close as possible and dealing with some noise and some hot rocks. If I kill the ground completely, kill the hot rocks completely, I will inevitably do a full reset and start over. The Axiom in particular with its hot rock window I can force higher levels of ground and hot rock rejection, but then all the sudden I know I have gone to far, and do a reset. I just know for a lot of years of doing this that the more aggressive the ground cancellation, the more gold that gets missed. Gold grades imperceptibly with depth and mineralization into the ground signal until they are one and the same.

The GPZ 7000 was a direct answer to that in attempting to get a machine that would find as much gold as possible in a single pass with as few settings as possible. Garrett referred to this issue on the 5000 and earlier GPX models in their ATX advertising...

garrett-atx-ad.jpg

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