Most metal detectors models have a variety of different coils types that can be used. Most VLF detectors have 2 or 3 different coil types, while some of the PI detectors have dozens of different coil options, some of which cost over $500 each just for the coil! All of these different coils will have benefits and drawbacks, and we will discuss some of those issues below.
The size of the coil used has a lot to do with the ability to detect a target at depth. Generally speaking, a larger coil will detect a target at better depths than a smaller coil, and in many goldfields that have been hunted hard by other detectorists over the past few decades, the added detection depth provided by the larger coils are very important for detecting those nice pieces that others have missed. In many areas, swinging a very large coil is the best choice.
While the large coils will provide added depth, they certainly have some downsides. Larger coils “see” more ground at any given time, so they will often perform very poorly in highly mineralized grounds. This is especially true for VLF detectors, but even PIs can sometimes have a hard time dealing with hot ground using large coils.
Another type of area where large coils will perform very poorly is in places that have an abundance of trash targets. Trash targets that are right next to a gold nugget will often mask the sound of good targets. Smaller coils can work well at picking out these good targets amongst all the junk, while a large coil will get overwhelmed because it is covering so many different targets at one time.
Yet another consideration is the weight of the coil. It may not seem like much, but the weight difference between a small coil and large coil can make a huge difference in your comfort at the end of the day. Many prospectors prefer to use small/medium sized coils simply because of the comfort factor.
Also Read: The Best Metal Detectors for Gold
All metal detector coils come in two basic types, Mono and Double D. Each of these types also has their own benefits and drawbacks.
Mono coils have one wire winding that loops around on the inside of the coil. This type of coil give maximum detecting depth. It produces a cone-shaped detecting pattern which gets smaller at depth, so a slow and overlapping detector swing is very important to thoroughly cover an area.
Mono coils are the ideal coil when maximum detection depth is desired, but they will often be less stable in highly mineralized soils. You should also be prepared to dig all of your targets if you use a mono coil.
DD coils have two overlapping wire windings inside of the coil, which allows for better discrimination of the detected targets.
These are the ideal coil in trashy areas where good discrimination abilities is important. They also perform well in places that have highly mineralized ground. A DD coil will generally maintain a smoother threshold than a mono coil will in these conditions.
They give a more consistent detection pattern, which means that overlapping of your detector swing is less important. (The Fisher Gold Bug Pro has a small DD coil that works excellent in trashy areas.)
Making a Choice
A general consideration to keep in mind is how selective you intend to be with your targets. In very trashy areas, you may decide that digging all targets is not possible, and a DD coil will probably be the best choice to help you be more selective with your targets. If you are in an area that has less trash, and you are intent on digging every target that you hear, then a mono coil may be the best choice, assuming that it will operate smoothly in the ground conditions.
As with all things related to prospecting, you should try several different coils and decide for yourself which one you like best. Most gold prospectors have their own preferences on which works best for their particular area of style of hunting.
Also Read: Must-Have Gold Nugget Detecting Gear