Metal Detector Search Coils

[49er12]

This is for all the experienced / experts of the hobby. Dumb question to some but could you explain search coils, yes some are bigger cover more area of course, smaller cover less area. But really are not the coils made the same inside with copper wiring etc. am I missing something please explain for us. Because some go deeper than other to the point are they programmed different what's really the difference other than size. I have 3 white's 950, dd 10 inch, and the 5.3 eclipse so there something to start with, I certainly respect all your knowledge, information is the way to learning, god bless and thankyou

 

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[RobRieman]

Most are made the same except you have a concentric or DD configuration. Larger coils go deeper than smaller coils but pick up more objects under the coil at the same time. Smaller coils don't go as deep but have good separation in trashy areas so you can pick out the good signals in the trashy area.
Concentric coils have a cone shaped pattern in the ground where as DD coils have a straight knife shaped pattern down the center into the ground. You have to overlap your swings a bit more on the concentric. Some are less acceptable to EMI than others also. Hope this helps a bit.

 

[Loco-Digger]

Sounds like you have quite an arsenal of coils. I have 3 coils. A 12" x 15" butterfly coil (Mainly for fields and non-trashy sites). The stock 11" DD coil (use the most) and the 5" DD coil (for trashy areas, under shrubs and flower beds near foundations). Aftermarket coils are normally a little cheaper than the coils from the MD manufacturers.

 

[Phantasman]

Here is a explanation by FTP Engineer Dave Johnson.

>About Searchcoils

Big Boys Hobbies has a pretty easy to understand info page on coils. They are a TNet supporter.

https://www.bigboyshobbies.net/double-d-coil-vs-concentric-coils/

 

[Tom_in_CA]

Rob gives good info.

Basically the larger the coil, the deeper it goes. However there's multiple "gotchas" with this formula:

a) there is a "point of diminishing returns" when it comes to coin-sized targets. So when you start talking about coils larger than 9 to 11", you get to where you can only find LARGER objects deeper, not coin-sized objects deeper. Hence you only add coverage swath, not depth, for coin-sized targets. This is why most detector's stock coils are about 9 to 11-ish inches. Because that's about the optimum size for coin-sized targets. Beyond that you're only adding depth for larger (cans, jars, etc...) sized targets.

b) Although you can increase depth and swath with larger coils, there's downsides: 1) more potential for masking, 2) fishier pinpointing, 3) less sensitivity to small objects (although this gap has been closed a lot in the last 30 years). 4) warbly performance 5) less ability in minerals, since you're "seeing" more minerals in the field-of-detection.