DEUS HF DD Round Coil vs. Elliptical

[vferrari]

Since the ground tracking thread is getting very long, I wanted to start a discussion regarding Separation and the Actual Detection field of the Deus HF DD 9" Round vs. 9.5" Elliptical.

tnsharpshooter has provided data that shows the the 9" round detects deeper or at least you can have more of an air gap between the ground and the coil than the elliptical to detect a target at a given depth. That seems consistent with my understanding of how a round vs. and elliptical DD coil of approximately the same "long axis" dimension (for a circle that would simply be the diameter of the circle and for an elliptical coil it is typically the active length of the coil with the long dimension running for and aft vs. sideways).

I have always argued that ALL THINGS BEING EQUAL (which we know they are usually not) the round 9" coil would "out depth" the elliptical 9+" inch (long dimension) coil and that the elliptical at a given frequency would not separate better (side-to-side) than the HF round because the active wideth of the field (where the two "D's" intersect down the spine of the coil and where most of the active detection field penetrates the ground) is approximately the same width for the two coils. So, in theory, the only thing that makes the elliptical coil separate better would be the fact that it can operate at a higher frequency than the round coil and can, therefore, resolve smaller targets better.

Anyone like TN or Charles who has actually built coils care to comment?

 

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[Gravelwasher]

In general I here the round shape is better at depth and the elliptical may sound off on slightly smaller targets.
I here its the shape on the round that aids it(perfect circle forms a better cone than oval) and the ellipticals tip with a shorter radius or distance between the wires allows smaller targets to get recognized better.
Thats just my understanding of the general nature of all metal detector coils vs brand specific.

 

[smokeythecat]

I was out with the elliptical running version 4.0 and 28.8 khz. The place has been pounded ESPECIALLY with people with trash can size coils on their White's, Minelabs and Fishers.

I got my share of junk but pulled a squeaker of a target, a small musket ball, from about 9" down. It sounded a high tone, but no numbers on the meter. I think the big coil would have missed it. I noticed that on the Tesoros, the bigger coils MISS the little, deep stuff.

 

[vferrari]

In general I here the round shape is better at depth and the elliptical may sound off on slightly smaller targets.
I here its the shape on the round that aids it(perfect circle forms a better cone than oval) and the ellipticals tip with a shorter radius or distance between the wires allows smaller targets to get recognized better.
Thats just my understanding of the general nature of all metal detector coils vs brand specific.

Concentric coils produce a cone shaped field or coaxial ellipsoid cone field, DD's do not. It is more like an Axe Head penetrating the ground, deep but narrow, the width of the center spine of the detector where the two D coils intersect. This is independent of the shape of the coil, which generally just affects the field strength or depth the field penetrates the ground. That's why I am asking about how much shape matters when talking DD coils. It certainly makes a difference on concentric/coaxial coils, but from what I can tell, not that much difference (as far as separation is concerned) on DD coils (at least at the same operating frequency) and maybe a slight hit on depth for the elliptical with the same long dimension as the diameter of a circular coil.

 

[CharlesUpstateNY]

Concentric coils produce a cone shaped field or coaxial ellipsoid cone field

Correct, the TX (transmit) winding is the larger outer round winding, RX the receive winding is smaller, much smaller and centered inside the transmit winding producing the cone shaped detection area below the coil. Concentric coils get a bad wrap, a small concentric coil for a DD machine can out snipe a DD coil in heavy trash/iron its like hunting with a pin pointer at say 6 inches off depth. I built one once for my Explorer Se Pro.

It is more like an Axe Head penetrating the ground, deep but narrow, the width of the center spine of the detector where the two D coils intersect.

Its only a perceived axe head, this is important to understanding the difference between the round and elliptical DD coils and how coil geometry (shape) effects depth and achieved depth in mineralization. CLIFF HANGER is it coil length front to back or coil width left to right which most determines coil depth?

Look down at your DD coil, there are two separate D shaped windings of magnet wire in the coil. For the purpose of the discussion lets say the left D shaped winding is the transmit winding TX and the right D shaped winding is the receive winding RX.

The two windings overlap each other down the center of the coil, why? This is to balance the coil, the purpose of balancing is to make sure the receive winding RX is not detecting any of the signal being transmitted by the transmit TX winding. This is also true for balanced concentric coils. Imagine, TX is blasting out a strong signal you don't want the receive winding which detects the targets to be detecting this strong transmit signal right, with me so far?

If you connect the coil to an oscilloscope which you must do to balance a coil, you can see the transmit signal on TX typically a sine or square wave pattern on channel 1 of the scope. If the coil is somewhat out of balance you will see a mirror image of this transmit signal riding on the receive RX winding, you need to get rid of that. Adjusting the overlap of the two windings precisely, get it just right, and poof the receive winding RX flat lines, no TX signal. A tiny nudge too much or too little overlap and the transmit signal reappears on the receive RX winding.

Ditto for balanced concentric coil. I mention them because they help explain how and why a DD coil is constructed, why the windings are D shaped, this is simple stuff so lets take the mystery out of it. On a balanced concentric coil, lets say a concentric co-planer coil, the large outer round winding is TX transmit, then there is a 2nd smaller inner winding inside TX that's the receive winding RX, and to this you wind a few more loops of RX but in the opposite direction, this is how you balance the coil. I might be say 6.5 loops that brings the coil into balance, or 6.25 it can be that precise. There are other methods and some manufactures leave another even smaller bit of winding loose, pour the epoxy to setup the coil, then move this small bit of winding around the coil to fine tune the balance and secure in place.

Now DD winding shape, do they have to be shaped into a "D" no. In fact some manufactures make a OO coil where instead of a D shape each winding is O shaped so a double round or double circle if you will. They also overlap down the center. They won't cover as much ground per swing as a DD but they will go deeper which brings us to the cliff hanger above. Is it coil length front to back or coil width left to right which most influences coil depth, the answer is coil width left to right and by that I mean winding width.

Which coil goes deeper, a 12 inch round coil or a coil that's 12 inches long front to back, but 18 inches wide left to right? Yep the 12x18 I built one once. I was looking for more depth, I was not looking for more soil mineralization signal so I had the width and most of the depth of a 18 inch round coil, but at only 12 inches long front to back, down the center spine where detection is the strongest, it was gulping 6 inches less soil mineralization. Which is an extension of the DD advantage over a concentric, that they see less soil mineralization bounce back vs concentric coils, I just took it a step further. You could orient your coil windings into a D shape, O shape, square, depends what you are trying to achieve with your coil design.

Finally back to the DD axe head description, I called this a perceived axe head. In reality the transmit winding on a DD round coil is about 70% round and its producing about the same amount of soil mineralization bounce back as a concentric, but on a concentric its center positioned receive winding is getting hit in the face by the full mineralization bounce back where on the DD with the receive winding being positioned way off center of the transmit winding soil mineralization bounce back is much reduced. DD's are hot down the center, far less so at the outer edge of the coil. The concentric coil is actually a deeper coil vs the same size DD, in low mineralization I could make a case where that's the better coil.

 

[CharlesUpstateNY]

Coil magnetic field SIZE vs coil magnetic field DENSITY. The size of the magnetic field a coil produces is pretty much governed by the size of the transmit TX winding. The bigger the winding the larger the field and the deeper the coil reaches. But there's a catch, the strength of the magnetic field density. The more magnetic field lines a coil produces that strike your target, the stronger the signal you get back from the target. You could build a 12 inch coil but if you only used 2 loops or turns of magnet wire for the TX transmit winding while that field is reaching into the ground like a 12 inch coil, the field density is very weak and producing few field lines.

Okay fine, can you just add more turns to increase field density? Heck why not double the number of turns make it super hot? If you measure a Minelab Explorer 8 inch coil, 10, 11, the small Joey elliptical, the monster 15 inch WOT coil you will find they all measure in a very narrow band, TX and RX specs are tight across all coil sizes. The resistance of the TX and RX winding, the capacitance, the inductance, and Q all within narrow windows. You can't just add more magnet wire to a larger coil to make it as hot or as dense a magnetic field as a small 8 inch coil and stay within the narrow coil specs for the machine.

So the info nugget here is, small coils hot, dense magnetic fields, not deep but smacks smaller targets and generally give a strong signal. Large coils somewhat less hot, less dense magnetic fields but deep. I have found 15 inch coils to be quite excellent performance wise. But 18, 20, 24 inch coils at some point the magnetic field density drops too far and the coil falls on its face. Yes I built a 24 inch coil once FAIL! lmao

 

[CharlesUpstateNY]

That's why I am asking about how much shape matters when talking DD coils.

Absolutely matters. Explorer XS and Explorer II coils look identical but are actually quite different. The original XS coil overlap down the center is real fat at the rear of the coil, and quite narrow at the front that overlap is not even front to back at all. On the II Minelab changed this and the overlap was more even front to back. The original coil SMACKED nickels hard, made them big and fat sounding. You could wade into a pile of tabs and call your shot on nickels. On the II poof that advantage was gone.

Coils are weird spooky things. They seem simple but are far more complex to build than you would think. If I can buy one I won't even attempt to build one they are that difficult. Deus concentric coplanar coil I might attempt that but would have to sacrifice a Deus coil to get the electronic guts and make some measurements of the windings. I'm not kidding that concentric I built for my Explorer, a trash sniping monster. First target I dug with it was an indian cent about 6 inches deep, solid, no hint of trash, dug a 6 inch plug and there was trash in the side of the plug.

 

[gene the machine]

CharlesUpstateNY... Say what lol... quite the seminar on coils mister. I loved it and I even understood most of it too. I love techie stuff so this was enlightening. So why don't you build me a coil for the Deus that hits hard on GOLD!!! lol... you would make a fortune. I'll be your distributor, ok? Keep that kind of stuff coming. Thanks for the great write up.

 

[vferrari]

Charles you did not disappoint. The snippet of coil discussion in the ridiculously long GB Tracking thread inspired me to start this one so you could lay it all out there. Thanks.

 

[smokeythecat]

First rule: Get off the computer and detect some! I'll never understand the intricacies of the coils, but I dug a target today a good 18" deep with the 9" elliptical. 'Bout killed me!

 

[Gravelwasher]

Very good info,thanks!!

So does XP Deus maybe thinking of putting out a new concentric, mono style coil?

Or would the discrimination and target ID still perform?

I know with my minelab a mono coil in mild soil will punch harder than a DD.

There is still more complexities to coils when it comes to the wire used from what I understand. Like flat wire tech on the newer evolution coils and elite coils from Nuggetfinder and coiltek.
Whatever they did internally the 14"mono coil got sensitive enough to hit .05-.10 gram gold nuggets.

 

[vferrari]

First rule: Get off the computer and detect some! I'll never understand the intricacies of the coils, but I dug a target today a good 18" deep with the 9" elliptical. 'Bout killed me!

I would if I could, spent the day shuttling my daughter back to college. Though, I will basically be detecting continuously for the next week in various spots in central VA including Fredericksburg, Orange Virginia (Colonial relics), and good old Culpeper to open my Fall relic hunting season. Oh, yeah.

 

[vferrari]

Very good info,thanks!!

So does XP Deus maybe thinking of putting out a new concentric, mono style coil?

Or would the discrimination and target ID still perform?

I know with my minelab a mono coil in mild soil will punch harder than a DD.

There is still more complexities to coils when it comes to the wire used from what I understand. Like flat wire tech on the newer evolution coils and elite coils from Nuggetfinder and coiltek.
Whatever they did internally the 14"mono coil got sensitive enough to hit .05-.10 gram gold nuggets.

For deep seeking, XP is focusing on a two-box coil design for their next trick though that one has been in the works for about 5+ years. They have shown no interest in producing a concentric coil, and yes, that would probably necessitate a major code rewrite for compatibility.

 

[CharlesUpstateNY]

Very good info,thanks!!

So does XP Deus maybe thinking of putting out a new concentric, mono style coil?

Or would the discrimination and target ID still perform?

I know with my minelab a mono coil in mild soil will punch harder than a DD.

There is still more complexities to coils when it comes to the wire used from what I understand. Like flat wire tech on the newer evolution coils and elite coils from Nuggetfinder and coiltek.
Whatever they did internally the 14"mono coil got sensitive enough to hit .05-.10 gram gold nuggets.

I doubt they would release a concentric coil, first everybody has DD coils on the brain. Its also a global market, its not cheap to bring a coil to market so unless it would sell in large numbers globally I doubt a specialty coil would released by the big manufacturers of any configuration. I don't think a concentric would require a rewrite of the Deus code if the windings were held to the same specs as the Deus coil. Lets say I sacrificed a 9 inch LF coil to get the electronic bits, so long as the concentric coil windings measured similar to the 9 inch LF coil windings, the only real difference would be the larger soil mineralization bounce back on the concentric vs the 9 inch DD, certainly an impact but could possibly be adjusted for with GB and sensitivity.

On the other hand, there are electronic bits and a battery in the Deus coil shell, metal components in the coil probably requires careful positioning which may not be possible with the centric bulls eye shape. It would be interesting to xray a Deus coil to have a look inside.

Minelab uses rather expensive woven Litz wire for the transmit winding on at least some coils for some spooky weird reasons so I could see them using flat wire, coils only look simple, its definitely one of those things where the devil is in the details. For the RX winding how loose or tight you wind the wire can throw off the specs, tighter increases the inductance, in coils I built with tightly wound RX windings they were much noisier and more prone to falsing even though the coil measured within specs. So not too loose but also not too tight, stuff like that.

Then there is shielding the coil, which isn't complicated just use the right shielding paint, typically carbon black the nickel shielding paint can actually be detected, shielding paint can't be too conductive. So while not complicated...its complicated during assembly of the coil. You have the windings which must be encased in epoxy, there needs to be some space between the windings and the shielding paint, so encase the windings in epoxy, then coat the entire assembly with shielding paint, then that paint has to be entirely encased in epoxy, then finally secured in an outer plastic shell.

 

[CharlesUpstateNY]

This one is for TN and his 3D testing...imagine an elliptical coil built on an angle to angle the signal into the ground at say 30 degrees instead of straight down. The 15 inch WOT coil got me thinking about this, sites pounded for decades detecting only straight down on the target/iron/trash matrix. Now go detect it at an angle...

 

[Gravelwasher]

Wow thats a lot to think about..lol

 

[Tedyoh]

This one is for TN and his 3D testing...imagine an elliptical coil built on an angle to angle the signal into the ground at say 30 degrees instead of straight down. The 15 inch WOT coil got me thinking about this, sites pounded for decades detecting only straight down on the target/iron/trash matrix. Now go detect it at an angle...

Interesting indeed.....may be with a shot just tilting the coil 30 degrees at a heavy trash relic site to try and unmask shallow relics....

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[fred57]

I would love to see a comparison between the two new HF coils on how they perform with on edge coins.


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[smokeythecat]

Fred57, I'm not sure about the difference, but I went over a hammered spot last week and pulled out three very old buttons from a place with the HF coil the regular one missed. All the buttons were on edge. Not sure about coins. Most of my coins lie flat. Or I just am not doing it right. Got skunked Saturday except for clad. It happens.

 

[fred57]

Thank you, Smokey. I’m very interested in acquiring one of the new HF coils, I’m just on the fence about which one. I mainly hunt coins in iron infested areas and parks/schools. The idea of being able snag on edge coins left behind is intriguing.


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