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GB_Amateur

Test Stand With Variable Depth Adjustment

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Cool little project, I'm looking forward to how your Ultimate coil goes against the competition 😀

I should make something like this up for a bit of fun.  Just waiting for winter to end at the moment before detecting can get into full swing.  I am guessing my little Garrett Ace will do very well in the depth testing...............

That's it, I'm going to make one, I need to know 🙂

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Cool.  I like seeing how others do it.  I usually make small vials with the lid drilled out to accept a knotted string.  If not going deep, then I can pull it up to different string lengths.  But this gets really hard after 6 inches.  That's why I have gone in your direction, at times, by using a vertical pvc pipe that I can raise the gold vial out on a string.  But yes, a 30/60/90 or a 3/4/5 triangle would let you make a simple chart for this and you would have more ground above the gold (to improve accuracy). 

Andyy

 

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There is a German ( Austrian? ) depth test out there on the web, that does a pretty similar thing. I can't recall if they 'drilled' the hole for the pipe to go in, so as not to disturb the earth.
I'll see if I can find it, there may be some tips to pick up from it.

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A similar setup was/has been used by Georgi who owns Nexus metal detectors,he used a small arbour/drill slightly larger than the coin buried,must admit he has not done it in the last few YouTube videos though.I guess with some of the crazy large GPX coils that he has been testing the holes at angles would be very deep.

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This is a very worthy project.  I'll spend time looking at some of those YouTubes.

I think this type of 'test stand' would allow for someone to learn how to hear fringe targets.  Each detector/coil combo will have an ultimate limit of depth on a target.  What does it sound like just above that? (If you are directly over it.)  What does it sound like when you are 'close' to it from the side? (Not directly over the target but kind of a side scan/off coil detection.)  The second measurement could determine how you set your grid pattern if you know a layer the gold or relics are in then you could 'open up' the pattern to find more in the same amount of detection time.  I think a third benefit of this type of 'test stand' would be to test the coil speed. (How fast/slow can you swing and still hear the target to maximize time and efficiency.)

I'm like Simon.  I need to do it so that I know what the coil sees and what I can hear.  It has been a few years since I've done it.  How much ground can I cover in an hour and be confident I didn't miss anything?

A question I would have is one about possible lack of halo.  You can't make a 'test stand' that is as natural as a long buried target or an unearthed target on virgin ground.  If the target is dry and encased in the pvc tube and perhaps other wrapper ... how close to natural is this?

Mitchel

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7 hours ago, mn90403 said:

A question I would have is one about possible lack of halo.  You can't make a 'test stand' that is as natural as a long buried target or an unearthed target on virgin ground.  If the target is dry and encased in the pvc tube and perhaps other wrapper ... how close to natural is this?

Good point, and it shows one of the weaknesses of this setup.  I did bury two coins (US 5 cent 'nickel' at 6" depth, US 1 cent bronze at 5" depth) for calibration/sanity-check purposes.  But those can have their problems, too, such as the depth and orientation changing over time.

I will point out that three engineers most of us have heard of (Dave Johnson, Carl Moreland, and George Overton) are skeptical that the halo effect even exists except for possibly iron.  But that's a whole 'nother discussion topic and doesn't need to be elaborated here.

In the end I think any controlled setup has its limits compared to real in-ground targets.  But I do think (and I see you and many others agree) that it's still informative and worth the effort.

 

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14 hours ago, mn90403 said:

A question I would have is one about possible lack of halo.

 

6 hours ago, GB_Amateur said:

will point out that three engineers most of us have heard of (Dave Johnson, Carl Moreland, and George Overton) are skeptical that the halo effect even exists except for possibly iron.

This^.  I was going to respond similarly, but you beat me to it.  The target orientation variabity and lack of direct contact with the soil are problematic, but still better than an air test IMO.  Can't wait to see your results.

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I just read a thread about mono vs DD coils that 'expanded' the usefulness of your 'test stand' features for users.  The first 2/3s of it required slow, deliberate reading (just like overlapping a coil) in order to get to the truth of a swing and what I should be hearing.  (The last 1/3 is more he said/she said which is a distraction.)

The thread talks about the coil field (I liken it to a nerf ball) but when swinging any coil over your 'test stand' the weak fringe targets should lead to the centered targets which means 'dig me' vs ground noise!

 

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3 hours ago, mn90403 said:

The thread talks about the coil field....

Thanks for the link, Mitchel.  I went back and reread it (probably need to do that again) and, yes, once the new (May 2019) replies start talking about the X-coils the informative discussion gets derailed.  Being the contrarian that I am, though, I'm reminded of Dave Johnson's article:  http://www.fisherlab.com/hobby/davejohnson/SearchcoilfieldshapeApril2012.pdf

where he warns: So to say what happens when you swing a target past the searchcoil of a simple motion discriminator requires computation of at least 26 variables. I doubt anyone has ever attempted to compute such a thing, although it’s theoretically possible. In any case, nobody will ever draw a picture of it.

Kinda like quantum physics.  You can get a pretty good idea of what's going on with a good verbal description, but to really understand it you need to get into the weeds (higher mathematics).  Just like detecting.  It's hard to swing a detector in the weeds, but sometimes that's where the really good targets are hidden.  😁

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      1994 Compass X-200                6 kHz    14 khz
      1997 Minelab XT 18000            6.4 kHz    20 kHz    60 kHz
      1999 Minelab Golden Hawk        6.4 kHz    20 kHz    60 kHz
      2002 Minelab Eureka Gold        6.4 kHz    20 kHz    60 kHz
      2005 Minelab X-TERRA 50                7.5 kHz    18.75 kHz
      2006 Minelab X-TERRA 70            3 kHz    7.5 kHz    18.75 kHz
      2009 Minelab X-TERRA 305            7.5 kHz    18.75 kHz
      2009 Minelab X-TERRA 505        3 kHz    7.5 kHz    18.75 kHz
      2009 Minelab X-TERRA 705        3 kHz    7.5 kHz    18.75 kHz
      2009 XP DEUS                  4 kHz     8 kHz     12 kHz     18 kHz
      2016 Rutus Alter 71        Variable 4 - 18 kHz
      2017 XP DEUS V5           Additional 14 kHz    30 khz    55 khz    80 khz options
      2017 Nokta Impact            5 kHz    14 kHz    20 kHz
      2017 Makro Multi Kruzer            5 kHz    14 kHz    19 kHz
      2018 Nokta Anfibio            5 kHz    14 kHz    20 kHz
       
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      1991 Minelab Sovereign            BBS
      1999 Minelab Explorer S/XS        FBS
      2001 White's DFX            3 kHz & 15 kHz (Simulates single frequency by ignoring half the dual frequency signal)
      2012 Minelab CTX 3030            FBS2
      2020 Minelab Vanquish             Multi-IQ
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      2020 Garrett Ace Apex   5 kHz or 10 kHz or 15 kHz or 20 kHz plus multi frequency options
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      Minelab - Metal Detector Basics and Theory
      Minelab - Understanding Your X-Terra
      White's - Spectra V3i Owners Guide
      White's - V3i Advanced Users Guide
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