Detecting Depth Vs. Coil Size And Shape (long, Detailed)

[phrunt]

That Gold Bug 2 chart is real and carries over to all types of detecting.  I've had nuggets that a small coil picks up where as a bigger one won't see at all, and I've had coins where the 11" coil hits on them and the 10x5" coil misses them entirely.  Most of my coins are deep, If I use a smaller coil I'll only find the junk modern targets that are often more shallow and next to no silvers as they are deep.  Even with the GPX 6000 I found a nugget with the 11" stock coil that's JW's 17" GPX coil had no response on at all as the 17' just didn't have the depth of the 11" on this size target.

I've seen people wondering if the new 12x7" Nugget Finder coil for the 6000 will be as deep as the 11", I'm confident it is not in the right targets, but it will be deeper on smaller targets, there will be a sweet spot target where the 11" shines over the 12x7", that's just a fact and it's how coils work.

You use the coil that suits the job you do, for gold with my gold mostly being small but also quite deep I increase my finds by using smaller coils, for coins mostly being deep and not a whole lot of trash the bigger the coil the better. 

I'm fortunate to have a rather large collection of coils so I've had a lot of time using a variety of coils to work out which coils suit me best, especially with my GPZ where I'm fortunate to have almost every coil ever made for the detector so you get a bit of a feel about coils performance with target sizes and depths and if only buying one coil you want a middle ground coil that's good on everything but not the best of course, this is why VLF general purpose manufacturers have settled on this 11" size.

[EL NINO77]

The very use of different coils on the detector with which you detect ... is a bit of rocket science ... where the physics of the size of the coil determines the following depth and separation properties. not only in various tests ... but ... which you can also notice in practical detection on certain terrain...when you change different coils on your detector...and you have at least 50-100 hours of detection on such terrain....

First of all, you can notice...that on a modern detector with an adjustable recovery speed...the 11" coil can do a lot of work.....but it cannot detect all targets...whether deeper or masked by iron....

Remember that it's an 11 coil, it's a standard coil .. and it's a compromise between good depth and pretty good separation...

if you want better depth or separation ... you must have another coil ... of a different size ...
And that's why, in further detections, other coil sizes come into consideration... which can really pull out other targets in the field...

Many people think that the smaller the coil, the more it can unmask more targets than an 11" standard coil... but the truth is that really small coils can better unmask targets in iron only to a certain depth... and for coins masked at a greater depth already such small coils do not have enough power to unmask a deep target...

Now we can ask ourselves the question,,,,, what size coil can best unmask very deeply masked targets?....

From my observations from detection...from the field.....but also specialized... 3D deep separation tests confirm one thing and that is that the 8.5-9" coil can best detect very deeply buried and camouflaged targets quite close it depends....where not even 11" standard coils but even small 5-7" coils can do it so well... 

In.. *Super deph 3D Separacion test:  very small 14mm -0.45 gram silver hammered coin placed at a depth of 17.5 cm...in terrain..

1.test 8.3" x 9" DDcoil /23CM DD Rutus coil/

vs. 11" Standart Rutus coil.. in 2.Test:

------------------------------------------------

But if we take into account that we have a relatively clean field with a minimum of iron.. which is little or slightly mineralized.... then the best deep results are achieved by large coils..

in this next test, I tested different coils on 3 deep targets to find out what sensitivity I need to set on my detector in order to reliably hit all 3 relatively deep targets... 

The first marked column of the table is the minimum sensitivity when working on multi-frequency /M/, the second marked column is the minimum sensitivity required to detect targets on 1 frequency of 15.8 khz..

.The third labeled column/M/ indicates, for some coils, what minimum sensitivity we need when shooting at multifrequency to reliably detect the deepest target on my test field, a 50 euro cent coin at a depth of 37cm...

As you can see the ATrex on the big 15" coil needs only 55 sensitivity on one frequency15.8 and only 65 sensitivity on multi frequency out of.. 99 - maximum detector sensitivity .. to reliably hit all 3 deep targets... on my test field...

[GB_Amateur]

6 hours ago, Steve Herschbach said:

I should mention mineralization and EMI also. Large coils see more of both relative to target size. These two factors work against larger coil sizes and can negate some or all of the theoretical gains.

This point cannot be ignored but that seems to happen too often, even in some posts in this thread....  Certainly Eric Foster understood this and said as much in at least one of the two posts quoting him here.  "Know the assumptions!" is a lesson I was taught long ago but even with that and decades of experience I still lose track of it sometimes.  Air tests have assumptions.  If you ignore them you're eventually going to be wrong drawing conclusions when those assumptions don't apply.

[phrunt]

9 minutes ago, GB_Amateur said:

This point cannot be ignored but that seems to happen too often, even in some posts in this thread....

That's one of the under-rated performance advantages the Manticore has over the Equinox 800 and I would guess the 900, it's ability to handle EMI better, either by the detector itself,  it's long EMI noise cancel being better with EMI which to me it seems to be, and add the FACT that it's deeper in lower sensitivity levels than the Nox, this is a big advantage to the detector over the Nox.  The Manticore on 16 sensitivity seems to keep up with the Nox 800 on deep coins when the Nox is on 24 sensitivity.

It's why I believe I had good luck with the Vanquish over the Nox in high EMI areas, as the Vanquish handles EMI better than the Nox, to me the reason is unknown, frequency weighting? Frequencies being different enough to the troublesome EMI frequencies or the Elliptical coils perhaps.  I did very well finding coins that I had possibly missed with the Nox due to the Vanquish being able to run in higher sensitivity settings than the Nox in these areas.

You can see in this video I can run the Vanquish 1 notch off full sensitivity in jewellery mode (the most sensitive) with no real EMI troubles, in the same spot I have to wind the Equinox back to about 16 to get it as stable as the Vanquish in all modes, and with the Nox I'm using discrimination to knock out some of the EMI with all the default iron blocked out, if I go to all metal it's worse, the Vanquish I can have all targets wide open.

So the question is, is the Vanquish v12 12x9" coil being elliptical less prone to EMI? If that's the case it's a demonstration of why the Vanquish did better at this particular spot than the Nox with it's 11" coil as I was getting deeper coins missed by the Nox because of the Vanquish's coil being slightly smaller and elliptical being less affected by EMI so I could run my sensitivity higher thereby giving the smaller coil more depth.

I had the 11" coil on the Nox at this spot as with my usual 15x12" coil EMI was even worse, so the smaller coil was the better choice but dropping back to 6" cut the depth far too far and became counter productive, better with EMI but nowhere near deep enough to find anything worthwhile.  I didn't have the 10x5" at the time but it's not deep enough to find many of the coins I find in these areas, that's been well tested.

[phrunt]

Excellent post here by Steve relating to the same conversations

 

[Rad Rocks]

Coils,

    This happened to catch my eye while scrolling past some News sites.. Nowadays I tend to avoid the News like the plague. But, for obvious reasons, this bit coming out from Australia was just far too interesting to pass by without a look-see. I wasn’t quite sure what to think, but it is real and they claim that it does find Gold.  I just had to give it a little attention. 

   I have seen some pretty Small coils and I have also seen some Rather Large coils… But This one that they are using in Australia takes the Cake!l…..Well, 6 or 7 Cakes!.. They are Claiming 400 meters of depth!….  

Just wow!, Can you imagine!?..