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Ground Coverage Difference Between GPZ 14 And GPZ 19 Coils


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Minelab just updated the October 26 blog entry at http://www.minelab.com/usa/go-minelabbing/treasure-talk/the-gpz-19-coil-does-it-really-detect-30-deeper to add the following information at the end of the entry. Note that to get good coverage it is the smaller receive windings that matter, not the larger center transmit winding.

ground-coverage-compared-gpz-19-and-minelab-gpz-14.jpg

minelab-gpz-14-and-gpz-19-coil-size-compared.jpg

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Hey Steve
Did you notice they have also added a disclaimer asterix to the "30% deeper" claim. That asterix wasn`t there a week ago.
My experience so far with the 19" has been very disappointing but my intention is now that it is on it is staying on. There has got to be some advantage to it somewhere.
  I`m interested to see how the coil performs in the States.
cheers Dave

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Hi Dave,

Actually the disclaimer has been out there since day one though now it is more detailed, as can be seen in the post of the materials originally at http://www.detectorprospector.com/forum/topic/2584-minelab-gpz-19-coil-full-official-information-release/

Not that it matters. Either you are happy with the coil or you are not - I hope things improve for you on that score.

 

 

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This talks about sweep length, but doesn't take into account sweep speed. Now I haven't done a direct comparison on sweep speed in a technical way, but I believe you would lose all of that advantage and maybe a bit more on the loss of sweep speed. Of course sweep speed is not solely dictated by coil size, other factors come into play, like ground depth and type or the likelihood of gold at depth, but all of that comes down to the detectors response and the operators ability to hear.

 

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Excellent point Steven. Usually a larger coil does cover more ground in a given period of time and that alone can result in more gold. However, for myself at least the GPZ 19 would not be a general hunt coil but one intended for hunting specific areas very carefully looking for suspected deep, large nuggets. When used like that I would very likely slow way down, especially given the extra weight of the coil and need to keep it under careful control for best performance.

There may be those who can swing that big coil all day long just as fast as they can swing the GPZ 14 but I am not one of them.

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Couldn't agree more, I think I could swing it Ok for a day or maybe two. But for me the coil is too difficult to maintain coil control for everyday detecting in my area, there is just too many things to snag on and to go around. I would be more likely to target specific areas of a patch, such as further down a wash as it slowly drops into deeper ground or a rock bar trap downstream from a patch. But this coil will mean different things to different people depending on the ground type and their ability to swing it.

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Another piece of errata from this blog, they state the RX area is 96% larger than the 14's. So, if these numbers are correct and there isn't some other piece missing, that means the RX area is not scaling linearly with coil size (outer diameter) like a mono because a 19x18 ellipse is 87.9% larger than a 14x13 ellipse. This is a possiblity I brought up on 4umer before the blog was editted - the fact that the super D need not scale like a mono, and it appears to be the case. Except in the opposite direction I had suspected because it looked to me like the space between the D's was larger on the 19 so I assumed the area might scale less and not more.

So if anything the 19 should be getting a bit more depth than might be assumed since the total RX area is proportionally larger in the 19 than it is in the 14. Even if the D's are configured to act differentially, they should be the same size as each other (in the same coil) so this still applies. Yet it seems to be underperforming.

I have an idea why this might be...tinfoil hats and all. :tongue:

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Hi Jason,

You are using the outside diameter of the coils to figure area of an ellipse, whereas the blog entry referenced is using a best fit at the outer edge of the TX and RX windings. This makes the 19" x 18" coil closer to 18.68" x 16.65" and the 145" x 13" coil closer to 13.27" x 11.96". These measurements in turn deliver the 96% (95.8%) larger area as referred to in the blog entry. See the diagram below.

I think the basic premise that the coil is underperforming is flawed and so attempting to figure out why that may be is an exercise in futility. Again, I think this all comes from Minelab trying to get all scientific about things and put numbers on relative performance. It gets them in trouble every time, but here we go again. Same story, different act. New Minelab item comes out, much pulling of hair commences, product deemed deficient compared to people's expectations. Then time passes and item praised later as best thing ever as expectations adjust to reality. Most recent examples, GPZ 7000 itself and SDC 2300, and earlier virtually every SD, GP, and GPX model.

I never thought a larger coil was going to be magical myself as every oversized coil I ever got in the past came with too many expectations that quickly were dashed on reality. Reality is those big deep nuggets just out of reach are far rarer than people think.

Oh well, I should just let it all settle out without comment as I come off sounding like I am making excuses for Minelab. It is just all so predictable however.

minelab-gpz-14-19-area-comparison.jpg

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