a little confused

[sayvor]

Hey all,
Was at a hobby shop that was new to me, they sell Whites and buy gold etc.... sell too. I asked which coil is better 10"DD or 12" Spider coil... he asked am i looking for minerals???? I said huh? He was pushing the 12" because it goes deeper... i thought minerals are not what we want

.. we want elements ...metal ones.... no??? Please explain. I have both now so I just want to use the correct one for each own special features.
Eric

 

[widebody]

[size=large]that 12" is only good for trashless expances such as open fields and or sport fields where trash is few and far between. the D2 is great for hunting parks and sport fields with a fair amount of trash. the D2 seperates well but in trashy spots the smaller the better. the larger coils will null out and you won't find the targets but you'll have depth. depending on what you're looking for will dictate the coil needed as well as the correct machine. sounds like the seller knows not of what he speaks.

HH.[/size]

 

[Larry (IL)]

Some people who sell detectors don't have a clue what they are doing, especially at a hobby shop.

 

[a4wdguy]

Minerals in this context means gold ore, rather than gold jewelry.
When you detect gold jewelry, you are not detecting pure gold. Even 22 karat gold is alloyed with some harder metal, such as nickel.
When prospecting for gold ore, you are searching for nuggets or flakes in ground that is usually highly mineralized.
In highly mineralized ground, elliptical coils will ignore the mineralization better than concentrically wound coils.
The D2 is an elliptical coil. It is actually two elliptical coils back to back, so it emulates the concentric coil (such as the super 12) but is less sensitive to mineralization (such as the Eclipse coils).
Because it is 2 inches bigger than the 10 inch D2, the super 12 will get a bit more depth in lightly mineralized soil than the D2 will. But, if the soil is heavily mineralized, the D2 will get you more useable depth.
Because the super 12 is 2 inches bigger than the D2, in areas with a lot of trash, the coil will cover more targets at once than the D2 will, making separation of targets more difficult.
The super 12 has a bit more mass than the D2, which is multiplied by being at the end of a long rod as it is swung back and forth. This can contribute to greater fatigue than a lighter coil. One cure for this is to shorten your rod a bit.

Hope this clears up some of your confusion.

 

[Rob (IL)]

The D2 is a round DD coil made up of 2 D shaped coils that overlap in the middle. It is not elliptical in anyway. Elliptical refers to coil shape like the 4x6. Since the D2 is a round DD it doesn't emulate the 12" round concentric coil. DD and concenric refer to windings configeration not coil shape. You can get both round and elliptical DD coils and round and elliptical concentric coils.

 

[Larry (IL)]

Tit for tat............. but I have 5 minutes to kill before going to bed.

A DD coil can not emulate a concentric or vise versa, here is a good discription of the differences in the two designs: http://www.ohiometaldetecting.com/2/post/2009/09/shes-right-you-really-dont-need-an-additional-searchcoil.html

Normally, the windings of a DD coil do not overlap, they are back to back. The SEF coils (Symmetric Electromagnetic Field) are an advanced version where the windings do overlap in the middle and the windings are more commonly referred to as an OO style even though they are not truly circular.

 

[Rob (IL)]

Here is a essay by Dave Johnson Engineer and designer for Fisher and before that Whites.

Notice this line????

Some search coils (whether round or elliptical) are of DD construction. Double-D's comprise two overlapping D-shaped coils of approximately the same size.

http://www.fisherlab.com/hobby/davejohnson/searchcoils%20essay%20revised.htm

I'm no expert, just trying.

[attachment 269850 ScreenHunter_51Jul.0921.29.jpg]

 

[Monte]

Hey all,
Was at a hobby shop that was new to me, they sell Whites and buy gold etc.... sell too.

Just because a shop, a store, or an individual SELLS a product, it doesn't mean they really know or use that product.

I asked which coil is better 10"DD or 12" Spider coil...

Maybe you could have specified in your question what the coil was supposed to be better for? The type of targets you seek or the general site conditions you'd hunt. Better yet, when shopping for a detector or coils, ask the person what make and model detector THEY use? Their answer will lead you to more questions to know if they can really help you or not in the first place.

he asked am i looking for minerals???? I said huh? He was pushing the 12" because it goes deeper... i thought minerals are not what we want

.. we want elements ...metal ones.... no???

He might have wondered if you were looking for a detector to go after something like gold nuggets .. a mineral, yes, but you'd still be detecting it with the metal detection capability of the detector. Not knowing detectors he might have thought you'd want a larger coil to search deeper for raw gold, not really knowing the generally small-size nuggets we tend to find, and their shallow positioning as a rule.

Please explain. I have both now so I just want to use the correct one for each own special features.

Well, since you asked the dealer questions, I'll ask you a few.:

Which detector model do you own?

What types of sites do you generally hunt?

What size and type of targets do you usually try to find?

You asked which of the two coils was better, and now you say you have both of them .... why?

What coil was standard on your detector?

Do you also have a smaller-than-stock coil, such as the excellent, multi-purpose 6

 

[Larry (IL)]

Just because Dave says, does not make it true. This is White's patent drawing of their DD coil design old and improved.

[attachment 269866 improvement.GIF]

The overlapped DD or SEF design is patented by Detech to the best of my knowledge but like always, I might be wrong

 

[Flintstone]

Thanks Larry, That is one of the best post i have seen on coils. I had never seen that post before. Flintstone

 

[Rob (IL)]

The overlap is needed to achieve induction balance. If you are building it for a PI then IB is not really necessary, but can give better performance. Besides, if you don't use IB, then why make it DD? Just make it concentric.

- Carl

It's not important. How they work for us is all that counts. I didn't have anything better to do either.

 

[Larry (IL)]

Thanks Flintstone, if anyone is really interested in coil and detector design, here is where designers and engineers far smarter than I hang out.

http://www.geotech1.com/cgi-bin/pages/common/index.pl?page=main&file=main.dat

It is a technical forum with no ads or sponsors but owned by Carl Moreland, Engineering Manager at White's Electronics.

 

[a4wdguy]

When I said the DD coil emulates a concentric coil, I was referring to the shape of the cone in the ground, rather than the blade shape of the elliptical coils.
This is a characterization that I got from Carl Moreland several years ago (when the D2 was first introduced).

 

[Larry (IL)]

I think you have the search fields backwards a4wdguy.

I was one of the field testers working with Carl on the prototype D2 and the V3 that the D2 was initially designed to work with. The D2 is a true DD coil with the blade pattern characteristics of DD type coils.

The elliptical concentric is still a concentric with the conical search field, just squeezed in on the sides. The elliptical concentric is a great compromise for those wanting the depth of a concentric coil with better target separation and mineral rejection than the round concentric.

 

[a4wdguy]

I think you have the search fields backwards a4wdguy.

I was one of the field testers working with Carl on the prototype D2 and the V3 that the D2 was initially designed to work with. The D2 is a true DD coil with the blade pattern characteristics of DD type coils.

The elliptical concentric is still a concentric with the conical search field, just squeezed in on the sides. The elliptical concentric is a great compromise for those wanting the depth of a concentric coil with better target separation and mineral rejection than the round concentric.

Well there ya go. Thanks for setting me straight, Larry.

 

[Explorer]

The best diagrams of the shapes of the field patterns for the various coils is the work done by Jeff Foster in his "Digging Deeper with the DFX" pages 70-72.