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


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  • 1 year later...

Thanks for the transcript and commentary.

To us outsiders, it seems bizzare that Garrett hasn't "unleashed" the ATX from its carapace.

My pet theory is that they had many thousands of the resin casting sets for their Recon Pro mine detector due to the near total collapse of the mine detector market after the Afghan and Iraq buildups ending.  Assuming that there is anything to my theory (and likely as not there isn't), you have to womder if they had accountants and market analysists to tell them to stay the course or whether they were just too stubborn to write off the castings. We will probably never know. 

Now the window of opportunity is narrower.  Minelab's steady price cuts on the GPX series have made new and especially used GPX's cheaper.  In addition the entire metal detector marketplace is feeling the effects of the steady disappearance of the high end flagship product customer - largely due to that demographic getting pretty "long in the tooth".

 

 

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  • 2 years later...

An excellent read and explained it really well, now I understand, it means single channel ground balancing PI's like the QED are inherently flawed - that was previously beyond my understanding. 

I've likely read this and other threads before, but when you partially understand them it goes a bit over your head, once you understand what everything involved means its more informative.  It's like reading the manual to a new detector and then going out using it, as a non-experienced person you're rather clueless and the manual doesn't help all that much, after spending time on the detector and reading the manual again it all starts to make sense.

 

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Thanks for bringing this back to top Simon. Not only is it a great explanation of dual channel ground balance systems, but also highlights my pointed criticism of the ATX, and my never-ending quest for what I called the LTX (Lightweight ATX). Now finally seeing the light of day seven years after this original post, in the form of the Garrett Axiom. :smile:

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I must admit it was a bit intentional, as I think new comers like myself could benefit from reading it.  I'm glad Garrett has released the Axiom, a major step forward and something that desperately needed to happen! 

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  • 1 year later...

This was linked from another recent thread, and I don't recall reading it before. So another better-late-than-never reply.

Quote

From Brent Weaver:
"but if they are a single pulse detector, they are going to have a hole in their detection, period."

This is not necessarily true. The SDC2300 is a single pulse detector and it has no target hole.

The reason for a target hole is that eddy responses have an exponential curve and viscous ground responses have a power law curve. A "single channel" GB detector takes 2 samples of the response curve, and 2 samples (basically a straight line) are not enough to distinguish the two types of curves. Therefore, there will always be a 2-point eddy response that matches the 2-point ground response, and this gives you a target hole.

The target hole can be moved around in a number of ways. Changing the TX pulse width will do it, but so will changing the sample timing or even the bandwidth response of the preamp. So, as Brent says, you can create a detector that transmits 2 different pulse widths, with their own RX channels, and they will have target holes at different places so that, when combined, there is no overall target hole.

But you can do the exact same thing with a single pulse detector, by creating 2 RX channels that place the target holes in different places. Again, this can be done by using different preamps, or by simply creating 2 channels with different sample timings. Normally, each channel takes 2 samples but they can be combined. Above I said that 2 samples are not enough to distinguish the two types of curves... but 3 samples are. You can create a first channel that takes Sample1 and Sample2 and this will give you a target hole, call it Hole1. Then you take Sample1 and Sample3 and this gives you a different target hole, call it Hole2. Combine the 2 results and there is no hole.

You can actually hear this result in the SDC as it gives a wee-woo response for very low conductors (below Hole1), a woo-wee response for medium conductors (between Hole1 & Hole2), and a wee-woo response again for very high conductors (above Hole2). All with a single TX pulse width.

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I beg to differ. The SDC is based on the GPX 5000 Fine Gold timings and will absolutely miss certain gold nuggets due to it's extremely aggressive ground cancellation. Even with dual channel holes exist as eliminating ground or hot rocks at any level eliminates gold also. 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. That was the entire reason for the GPX multiple timing scheme - one timing getting gold the other timings missed. From my perspective there is no such thing as a ground cancellation method with no holes. You can reduce the issue as much as possible but you can't eliminate it entirely in my experience.

From a user perspective I'm not sure there is a discernable difference between timings and channels per se when both produce results that appear the same in the field. We have come a long way from Eric Foster and the Goldscan/TDI PI with a single knob adjustable ground rejection point. Now there are more ways to address the issue to get better yet similar results. For you it is the difference between two different motor types when for me they both get me from here to there in a similar fashion.

To be fair to Brent his interview was in January 2015 about 4 years before the SDC 2300 was released.

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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.

Even the GPX 6000 displays this trait to a certain degree with difficult sometimes picking up some nuggets better than normal even in an air test with no soil to change the results, not something you would expect.

 

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