As you know, a metal detector consists of several parts - a control block, a stick and a coil. Replacement of the coil is much more common among detectorists.
✔️ Concentric coils
They are very good at discrimination and pinpointing the target. Thanks to it's concentric shape, the signal falls more accurately on the target. However, these coils are very sensitive to electromagnetic interference. They also do not have very wide coverage and depth, which could make you miss some targets which falls on the edge of the coil.
✔️ Elliptical Coils
These are similar to concentric coils except that instead of being round they are oval shaped. By making the coil is longer front to back and shorter side to side, elliptical coils will cover more ground with each sweep of the coil. Like the concentric coil, the signal reaches the deepest in the center of the coil so you should overlap you swings to achieve maximum depth.
✔️ Double-D coils
They have a great depth of detection, good resistance to disturbances, and are more productive than concentric coils, especially in mineralized soils. In addition, the shape of the winding of the wires inside the coil can affect performance. With DD-coils it is good to work on sea sands as well as in those areas where the soil type often changes.
The disadvantage of these coils is that it is difficult to determine the exact location of the target, it would be nice if your detector is additionally equipped with a pin-point function.
They are suitable for searching everywhere, in the woods, in the park, in fields or on the seashore.
For coin searching, the best to have is a medium sized coil, which is a compromise in terms of depth and sensitivity to deeper smaller targets. The best search coin size can be considered as a 10-12-inch or 24-30-cm diameter coil.
However, if the soil is heavily polluted, it is better to work with a 5 to 9 inch coil that is suitable for searching in abandoned houses, wells or places with many targets. With larger coils, discrimination is usually worse or completely missing after 20 cm in the soil, so it is unclear whether the target is a gold coin or rusty iron.
My personal advice would be to have 2 types of coils, one big for pastures and fields and one small for beaches and harsh conditions. Many times I've been reading how someone wants to buy a big coil to "go deeper" in a thrashy environment it's not going to happen. Therefore, the real difference between the two coils is how well you "feel" and how satisfied you are with the end performance, and if the coil you choose is a good match for the detector you are using, the settings chosen, and most importantly, the sites selected to hunt.
Hope this post helps you choose wisely. Thank you and good luck.
To be continued with other metal detecting related posts. ®