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Steve Herschbach

Fisher Impulse AQ Discrimination Explanation

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2 hours ago, okara gold said:

Unfortunately 2 coil wire problems within the first year had me selling it right after the warranty expired. So now I wait on the new AQ and will be digging the extra mile.

Honestly a real shame Garrett never fully exploited the ATX circuit by hobbling it with a 7 lb box and a crazy coil design. I’ve screamed for years for an ATX that looks like the Impulse. All to the benefit of First Texas however so too bad for the neighbors in Garland. My incredibly crappy cut and paste “prototype” LTX from 2014.....

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Now There's something I'd be interested in!

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I have tried by writing quite a few different articles in slightly different ways to find the right combination of words to explain this complex subject. In response to some questions about the TDI I have given it yet another try. I will add a link to that thread to the original post here. It's all the same stuff just explained different ways and I am not the absolute know it all expert on all this. I'm just doing the best I can with the subject but frankly have run out of different ways to say the same thing. Hopefully anyone interested will dig into all my posts starting way back with the Garrett Infinium and through it all get a handle on what PI discrimination is all about. In the future any questions I get will probably just get a link back to these existing posts. It's a lot to study but if you forget about VLF discrimination and wishful thinking and just learn what these detectors can and can’t do I think the effort is worth it. I understand why people love VLF detectors but for me this stuff is much more fascinating and I am addicted to PI power. Instead of worrying about what they can't do I learn what they can do and then apply that for best results, including picking the proper locations to get the best results. But for some people, really, a VLF is a better choice. Not everyone is going to want to use a PI.

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The AQ uses the same basic electronic tools and realities of physics, but the two channels are handled somewhat differently to favor the largest range of gold jewelry while ignoring tiny low conductors and pushing the cut-off point for iron and high conductors high enough to allow detection of even some 24kt gold jewelry while using tone or mute discrimination.

I am not capable of explaining how this is done because even though it has been explained to me, I don’t have the necessary background in electronic and physics to grasp the details. Even if I did, It may be that going into the deep level of detail on this would be dealing with trade secrets.

Bottom line, the various explanations Steve have given all end up with the same caution - namely that whatever discrimination any PI analogue detector can do is way different from a modern VLF GB/ID detector’s discrimination.

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It’s still going to be a trade off. That is why there is a Reject knob. If the machine simply had an optimum set ferrous/non-ferrous rejection there would be no need for the knob. It will allow you to open up or restrict the ferrous acceptance and that in turn will allow or reject certain classes of good targets. Further, the ground balance is being employed here first and foremost as a discrimination system instead of an actual ground balance control. That is why there will have to be a different detector for gold prospecting... the inability of this model to finely tune for small gold in mineralized ground. That also means the discrimination aspects, if any, of the prospecting version will likely be quite limited. The reverse of that however means the Impulse AQ is trying to work around the lack of a fully adjustable ground balance system for dealing with both salt and ground conditions, necessitating a control like the Volcanic Sand control.

The bottom line is that for some time it has been quietly implied that the Manta/Impulse would operate to full PI depths while simply and easily eliminating ferrous targets... even seeing through ferrous targets. In my opinion reading between the lines on all this the reality is more complex and there are once again going to be the inevitable trades made between sheer performance and discrimination. I have no doubt the AQ is going to fine tune and advance the capability to a new level. My goal is not to take away at all from what is being achieved here. I’m right up there in line wanting a Fisher Impulse AQ. But it is not going to be a simple case of go dig rings at PI depths with no ferrous dug and no good targets missed. Like all things detecting, there is no free lunch.

But maybe I will be proven completely wrong and I would actually welcome that. :smile: Only time will tell. Check back by the end of the year and we will see.

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17 minutes ago, Steve Herschbach said:

Further, the ground balance is being employed here first and foremost as a discrimination system instead of an actual ground balance control. That is why there will have to be a different detector for gold prospecting... the inability of this model to finely tune for small gold in mineralized ground. That also means the discrimination aspects, if any, of the prospecting version will likely be quite limited.

Also, and I may have misinterpreted this, but Alexandre implied here that future specialized Impulse variants would likely use digital vice analog processing or at least different "technology" which might address the above limitations associated with the AQ version.

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Yes it's true.

Nothing is impossible at this level, it is just a compromise between the time to spend and the profitability of a detector of this type.

It already works and we know how to do it, but as in any development you have to produce it and do a market study

1 minute ago, Chase Goldman said:

Aussi, et j'ai peut-être mal interprété cela, mais Alexandre a laissé entendre que les futures variantes spécialisées d'Impulse utiliseraient probablement un traitement analogique numérique qui pourrait résoudre les limitations ci-dessus associées à la version AQ.

 

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13 minutes ago, Chase Goldman said:

Also, and I may have misinterpreted this, but Alexandre implied here that future specialized Impulse variants would likely use digital vice analog processing or at least different "technology" which might address the above limitations associated with the AQ version.

The leap to digital is critical to the future of this technology. It really is more about signal processing than anything and there is almost no limit to the signal processing you can do once you go digital and put a small computer under the hood. Part of my hope for the AQ is that it does succeed to the point of convincing the bean counters the money is well invested. The sky is the limit, but only if there are profits to pay for it. So really everyone should buy one even if they never use it just to support future research and development! :smile:

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With my tdi sl if I wanted to get gold on the beach I had to take out the coins of 1, 2 and 5 euro cents.  I would like to know if the fisher could discriminate?

I ask because the video I think is recorded in France

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Steve, I will leave it to Alexandre or LE.JAG to post something authoritative based on insight into the design (Alexandre) or long experience with a whole series of successive Manta/AQ prototypes (LE.JAG). But meanwhile - I think you have pretty much nailed it. My brief acquaintance with the AQ led me to test it on “tiny gold” - pretty much nothing. I asked Alexandre about that and said that it was “a feature - not a bug” (not in those words however) - that finding tiny bits of foil everywhere was too high a price to pay for an occasional tiny bit of gold.

It isn’t a general purpose tool - the design has a very sharp focus on one job - valuable gold jewelry at salt beaches.

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      References
      Da Costa, A.C.S, Bigham, JM, Rhoton, FE, and SJ Traina. 1999. Quantification and Characterization of Maghemite in Soils Derived from Volcanic Rocks in Southern Brazil. Clays and Clay Minerals, v. 47, no. 4, p. 466-73.
      Hunt, CP, Moskowitz, BM, and SK Banerjee. 1995. Magnetic Properties of Rocks and Minerals. In Rock Physics & Phase Relations: A Handbook of Physical Constants, Volume 3.
      Koch, C.B, Borggaard, OK, and A. Gafur. 2005. Formation of iron oxides in soils developed under natural fires and slash-and-burn based agriculture in a monsoonal climate (Chittagong Hill Tracts, Bangladesh). Hyperfine Interact 166, 579–584.
      Rivers, JM, Nyquist, JE, Terry, D.O., and W. E. Doll. 2004. Investigation into the Origin of Magnetic Soils on the Oak Ridge Reservation, Tennessee. Soil Science Society of America Journal, Vol. 68 No. 5 p. 1772-1779.
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