Although I understand the basic concept of how a Metal Detector and Coils work I will be the first to admit my knowledge on the intricate workings are lost on me. I’m not one who can start talking intelligently on the circuits, boards, capacitors, Coil windings etc that make up a Metal Detector but what I can do is share my experience through thousands of hours of experience on many different Metal Detectors and Coils.
Concentric Coils have really seemed to go out of style over the last several years and DD Coils have become the preferred choice of most detectorists. Some Metal Detectors that are currently on the market don’t even offer a Concentric option nor does any of the aftermarket manufacturers.
DD Coils vs Concentric Coils
Before I get into exclusively talking about Concentric Coils I think there are a few things you need to know and understand first.
If you look at the picture below you can see that the DD Coil signal is narrow but runs from front to back. Now if we take a look at the Concentric Coil the signal is going into the ground from the outside edge of the Coil and gets narrower as it goes down.
It’s also important to not that in general if you compare the depth capabilities of the same size Coils the Concentric Coil will go deeper but it’s important to add at its deepest penetration it is very narrow. If using a Concentric Coil, I highly recommend tightening up your overlap sweep.
If you look at the image again you will notice that the DD Coils narrower search window is only picking out the good target while the Concentric Coil has the bullet and the junk under the Coil at the same time. This is a bad thing because in many cases your Metal Detector, if equipped with the Concentric Coil, will not give good signals on the good target because the junk will skew the signal, make the VDI jumpy and the tone not as clear as if you were just picking up the good target. The junk could also potentially completely mask out the good target to where you don’t get any good numbers or tone on it.
So, if you look at the diagram and after reading the differences between the two the DD is the clear winner right? In my opinion absolutely not!
In my experience, while metal detecting in sites with a lot of trash or iron, the Concentric Coil is my go-to Coil. As many of you know I’m a field hunter, searching out where houses were but have been gone for a hundred plus years. These sites are inundated with large amounts of small iron and no matter what Metal Detector I use I’ve found over and over again that Concentric Coils work through the iron better.
Another great advantage of a Concentric Coil is they usually run deeper that the same size DD Coil like I mentioned earlier. For me, metal detecting in the iron infested fields this is another big advantage. When I’m in the thickest of the iron I will run very small Coils 8 inches or smaller. As we know the smaller the Coil the less depth, the larger the Coil more depth but also less separation between targets. When I have to run a really small Coil for example a 5 inch, to really get through the iron I know using the Concentric Coil I am getting more depth out of it than if I was running a 5 inch DD Coil.
The one big advantage DD Coils have over Concentric Coils is they work better in mineralized ground or so I’ve been told. I would say 99% of my metal detecting is in at least fairly unmineralized ground but I have used Concentric Coils in mineralized ground with success.
In my quest to understand why I have found in my conditions the Concentric Coil to be the clear winner over and over again I asked a lot of friends why I have been much more successful using Concentric Coils.
I was talking to Keith Wills who has been repairing Metal Detectors since the early 80’s. Keith told me I was looking at it all wrong. Forget the diagram and how each Coil sends its signal in the ground and instead think of the ground itself. The Concentric Coils are working so well because the majority of the ground I hunt in isn’t mineralized where if I was in heavily mineralized ground the DD Coil would be the clear winner.
Although I am not educated enough on the matter to confuse you with how the electronics work I can, after thousands of hours of metal detecting, recommend giving a Concentric Coil a chance!