Axiom Focused Core DD Coils - A Must Read For All New Owners!

[Steve Herschbach]

When people familiar with metal detector coils hear certain terms, they think certain things. Here are the three classic coil designs, illustrated in many articles in books, magazines, and the internet. Mono and DD coils are common, concentric much rarer with modern VLF and PI detectors. A classic mono transmits and receives alternatively with a single coil winding, and so is only used on pulse induction detectors. DD and concentric separate the transmit and receive into two separate windings, and so can be used in both PI and VLF designs.

Metal detector coil types illustrated - concentric vs DD vs mono

Garrett has some unique coil designs, but refers to them by the old terms. This leads to some confusion and incorrect assumptions about how the coils will perform. In a classic sense, a mono combines the transmit and receive into a single coil. Since depth is connected to how large the receive coil is, a mono often had better depth on larger targets than a similar size DD coil. The DD has separate smaller transmit and receive coils enclosed in a housing the same size as the equivalent mono. The smaller receive area often puts the DD at a disadvantage compared to a mono for depth on larger nuggets.

A mono tends to be hottest on small gold very near the winding, around the edges of the coil. A nugget next to the winding gets the most benefit from both the transmit and receive phase, since the one winding is doing both. This leads to an odd effect with the smallest gold, where a mono coil has a soft, or non-existent signal in the middle of the coil. A clue to small surface nuggets is when a mono coil gives a double blip, one on each edge of the coil as it passes over the nugget.

A classic DD coil tends to have a milder response to small nuggets, since over a lot of the coil surface a small nugget is far away from either the transmit winding, or the receive winding. As a result, with small nuggets you get the best response in a narrow band down the middle of the coil, where the transmit and receive coils overlap.

In the last decade mono coils have been more popular than DD coils on pulse induction detectors for that edge on larger gold depth, and users have learned to hunt with the edges when chasing the smallest gold. But DD coils have some inherent advantages in ground cancellation and EMI handling, and Garrett decided to try something different when they made DD coils for the ATX. The main complaint was how narrow the response was on a standard DD coil, so what would happen if that area was opened up, made larger? Here is what they came up with:

The coil is wound like a standard DD, but the winding crossover is not at the toe and heel, but in the middle where the inner coil area is created. This creates a coil within a coil, and the secret to the Axion DD is that this is what is inside the solid exterior. It is not a standard DD, but a "Focused Core" DD, with a strong target area in the middle of the coil.

Please excuse this quick and dirty diagram I just whipped up. I may replace it later, but it gets the idea across.

Winding layout inside the Garrett "Focused Core" DD coil

The tones refer to the two different tones a PI detector will make on targets. The small item hi-lo tone, and the large item lo-hi tone. The design of this coil results in more complex tone responses than on a normal DD coil. This can be confusing at first, but actually gives a trained operator extra information about the size and depth of the target. Small targets will "tone-flip" front to rear, with the classic hi-lo tone in the center. Larger targets at depth will no longer tone flip, but just deliver a stand hi-lo or lo-hi response.

Here is the super critical information I wanted to get across in this post. People just automatically tend to assume mono coils are better on a PI detector, due almost everyone using them. Yet we have seen more interest in some concentric PI coils lately, which have a strong center response due to the way the windings are laid out. The Garrett DD is a unique coil in a class all its own, and it offers a very strong alternative as a small gold coil compared to their mono coil. With the mono and the smallest nuggets, you need to focus on the edges as where the hottest small gold response. With the Garrett DD, it is a more classic response in the middle of the coil. Anyone used to hunting with a coil and assuming the center is where you are going to get the best signal will take right away to the Garrett DD for hunting small gold nuggets. The only caveat is you have to really focus on that center area as being the hunt area of the coil, and overlap your swings appropriately.

Axiom Focused Core (FC) DD Coils from Garrett Metal Detectors on Vimeo.

Keep in mind that the Axiom Iron Check only works with the DD coil. I would submit that a really savvy operator, who pays close attention to the tone flipping characteristics in conjunction with the Iron Check feature, will be able to predict the nature of targets with the Axiom, better than any other PI yet devised. It will not be a VLF. It is something in a class by itself, and if you have a good ear for target responses on PI detectors, the Axiom offers a wealth of information to play with.

In closing, just do not forget this. Do not automatically assume the Axiom mono is your best choice and ignore the DD. It is a very bad habit many of us have fallen into, and I was guilty of this myself. I ran the mono almost exclusively early on. But then I made myself use the DD coil, and was surprised to find the more I used it, the more I liked it. All the gold I found on my last trip to Australia was found with the 11" DD coil, which has the same setup internally. It just seems more natural to me to be focused on the center of the coil instead of the edges when chasing small gold nuggets. It is also a quieter coil than the mono, which also helps when running higher sensitivity levels in bad ground.

The Axiom 13"x11" DD has a hotspot that is about 6"x5" in the center, where you should focus your efforts on smaller gold. The 11"x7" DD has a very hot 5"x4" center zone, roughly illustrated below.

As a final reminder, there are six coils available now, or very soon, for the Garrett Axiom. There mono, and three DD. All three of the DD designs including the 16" DD are actually the Garrett "Focused Core" DD in disguise. These coils are not protected by chips or anything that would block third party support, so I expect we will see more coils soon, either from Garrett, the aftermarket, or both.

[Steve Herschbach]

That was the long explanation. Here is the short one. The Garrett DD is like having a smaller mono coil built into the middle of a larger DD coil, with the benefits of both. You get the extreme small gold sensitivity of a small mono in the center, combined with the ground handling and depth of a larger DD coil. With Iron Check as a bonus. 

[Gerry in Idaho]

I've already had to explain this to a couple of my customers of the Axiom.  All of the 1st allotment I received were American version Axioms with 13" DD and the 11"MONO.  I feel that is the best for most folks.  But then it was brought to my attention, the videos I provided showed me using the 13" MONO.  So they wonder what is up with why I want them to get the 13" DD.  The main point....I was hunting for bigger gold.  Most folks want any and all nuggets.  I knew what you and Lunk were up to so I wanted to be different.

Thanks for the detailed explanation.

[UtahRich]

As a NOOB to PI's / nugget hunting, i was thinking the standard Axiom package was the way to go - 13" DD & 11" mono.  Should i reconsider?

Rich - 

[Gerry in Idaho]

57 minutes ago, UtahRich said:

As a NOOB to PI's / nugget hunting, i was thinking the standard Axiom package was the way to go - 13" DD & 11" mono.  Should i reconsider?

Rich - 

Most certainly and don't even look back.  The actual answer depends on your preferred detecting style, but since you mentioned NOOB, then go with the US version.  Here's the great thing about the Axiom.  Once they get all orders caught up and start working on coils, there is already 6 different options to select from.  Another bonus with Garrett (if we look at the past), is their coil pricing will be more reasonable than the other brand.  

If the Axiom sells good (and I don't see why not), then we might get options from other coil manufactures as well.  Options and more options is what we want.

[Steve Herschbach]

The 13" DD with 11" mono would be my preferred combo, with an 11" DD added. The 13" DD is hotter than you would expect, because there is that 6x5 hot inner area. I have to admit to having a real liking still for the 11" mono, as it is the lightest coil, and still super hot on tiny gold. Just remember to focus more on the edge sensitivity, and when down to the nitty gritty in a given spot, use the forward edge as a sort of search tool.

[UtahRich]

Thanks Gerry & Steve.  Appreciated

[Calmark]

This is a timely reminder about the unique center of the Garrett Axiom 13x11DD coil.  My Axiom arrived today (thank you Gerry) and I'll be sure to use the 13x11DD first thing once I get out on a hunt with it.  I may even go tomorrow for a half day just to give the machine a test.    

[cudamark]

I'm curious to know how that Garrett design DD coil would work on a multifrequency VLF machine. Have you heard of any testing or coil in the works for one......like the Equinox, Legend, or even Manticore? Even older model single freqs might benefit from one........

[Steve Herschbach]

7 minutes ago, cudamark said:

I'm curious to know how that Garrett design DD coil would work on a multifrequency VLF machine. Have you heard of any testing or coil in the works for one......like the Equinox, Legend, or even Manticore? Even older model single freqs might benefit from one........

The design is unique to Garrett PI detectors, and have never heard of anything like it being tried on a VLF.