Your smaller coil gives less depth - or maybe not

[luvsdux]

Recently read an article that made a lot of sense even though it was contrary to what most of us believer or have been told. It concerned actual working coil depth versus in air comparisons and even test garden comparisons. I'll try to condense the pertinent points here.

In more trashy areas, due to the multiple targets, larger coils often cannot readily deliver on their maximum depth whereas a smaller coil that isn't overwhelmed by the extra targets may still deliver its full potential or at least, more usable working depth.

In heavier mineralization one may get more depth from the smaller coil due to the fact that it's not reading as much ground interference and therefore can run with a bit more gain and again deliver more usable working depth.

I know from comparing the coils I own, that the normally accepted premise of the larger coils giving bit more depth versus smaller coils holds true in air tests. But these examples that consider true, working depth under different conditions are points worth considering and give another insight to how our detectors actually work.
luvsdux

 

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[goldentruth]

I like contacting the metal Detector companys repair tech and asking them if they have time to answer a question. I did ask about size of coils and they told me a MONO Concentric Coil os better for finding nuggets than a stock Double "D" Coil... The D coil will find gold too but the Mono 5 to 8 inch is more sensitive.
Please Note: If the gold nugget is large enough... Any coil and even a low cost $100 detector will hit a big nugget. A quote: Gold is where you find it! ( one day it is possible to be right on top of it if in the right area!)
Have a great day and good luck to you.

 

[luvsdux]

In theory, and in mild ground, what you posted is correct. However, it's my understanding that as the ground becomes more heavily mineralized, the DD coil would eventually catch and possibly pass the concentric. This would be comparing like sizes I'm sure. It's too bad that all nuggets aren't big enough to respond well to any machine, we'd all be rich.

What I felt was the main focus of the article I read was to keep in mind that there's definitely a number of things to keep in mind that affect the usable, working depth of our detectors depending on the conditions.
HH
luvsdux

 

[U.K. Brian]

DD coils should outperform concentrics on more heavily mineralised ground. Low or little mineralisation, a concentric is often the better choice.

A small coil not only picks up less mineralisation but also has more chance of a clear "view" of the target in the ground. So on ground thats got lots of rubbish from iron to silver foil and ringpulls its often far better to work between the bad signals to pick up the good inbetween that are being masked if a larger coil is used.

If the ground is mineralised fairly evenly all over (rather than having spots of mineralisation or just plain old rubbish as in the paragraph above) you can apply the old rule that if the target can only be detected at a distance of about half the diameter of the coil then switching to a larger coil size will give even less depth.

 

[Frankn]

The post is on coil size, so here goes. Smaller coils loose very little in the way of depth to larger coils. The advantage of larger coils is area covered at one time.
Now you might ask what gives depth! The simple answer is the separation of the transmit and receive coils. In most detectors, they are in the same coil casing. Now look at the two box systems. The coils are several feet apart. This gives great depth, but at a penalty of not picking up small objects. My two box will go down 12' but it will never find a single coin. Frank

 

[luvsdux]

That's interesting. I didn't realize the depth of two box detectors was due to the distance between the transmit and receive coils, nor how that distance plays on the performance of our typical detector/coil combination. I've been detecting for quite a few years and still occasionally learn something new.
luvsdux

 

[Frankn]

Learning is a never endind process, that is until you check out. I try to learn something new every day. I read about 12 mags every month, mostly technical. One prof. once told me knowledge is power.
Frank

 

[U.K. Brian]

You could look at the high power pulse machines that far outperform ANY two box hoard hunter and have the advantage that with the use of smaller coils individual coins can still be located. No distance between transmit and receive coils as its all done by the one coil.

For a more standard detector type but with coils spaced to provide extra depth its worth having a look at the Nexus range of machines.

 

[relicminer]

Great info, thanks!!!

 

[goldentruth]

As said, they are right. a Double "D" coil will pick up a coin covering a large area where trash is. The smaller 8 inch concentric will give more depth but rather than the "D" the concentric has a character to pin point to a smaller focus point also Sometimes deeper than the "D" a bit.

 

[Frankn]

Luvxdus. I don't want to give you the wrong impression. One of the reasons the 2 box detectors give great depth is the spacing of the coils, but there are other factors involved like one coil being horizontal and the other being 90 degrees off at vertical.
The thing is that most of the coil output shape pictures are basically incorrect. A basic coil radiates out in all directions. What is important is the the reflected angle of return. In a concentric configuration the reflection is almost straight back. That is why it pinpoints so well. Now the DD has a wider spacing between the coils thus the angle of return is "wider". This allowes it to basically look under other objects at an angle thus separating targets that are hidden from the concentric. It gets down to the question of what do you want more, Finding a little more or finding it easier. I us ally go for finding it easier, but the choice is yours. Hope this helped out. Frank

 

[goldentruth]

In theory, and in mild ground, what you posted is correct. However, it's my understanding that as the ground becomes more heavily mineralized, the DD coil would eventually catch and possibly pass the concentric. This would be comparing like sizes I'm sure. It's too bad that all nuggets aren't big enough to respond well to any machine, we'd all be rich.

What I felt was the main focus of the article I read was to keep in mind that there's definitely a number of things to keep in mind that affect the usable, working depth of our detectors depending on the conditions.
HH
luvsdux

Actually a guy posted he was in Alaska and his grandfather found gold nuggets over 1 1/2 Oz with a $100 Cheep MD! You can find nuggets if large enough any MD WILL PICK THEM UP!
Gold is where you find it, looks like they were right on top of it in the first place. thought you should know.