SEARCH COILS BASICS
Detector search coils come in a wide variety of sizes and shapes. Generally, the coil shape is either circular or elliptical. A circular coil has slightly more detection depth and sensitivity and non-mineralized soil. Elliptical coils are widely used because their elongated length provides greater coverage area and elliptical coils are generally more maneuverable in tight spaces. Search coils range in size from only a few inches in diameter the more than a foot in diameter. The magnetic field generated from the coil as size and depth that correlates to the shape and size of the coil. The bigger the coil the larger the magnetic field.
Larger coils therefore generally detect wider and deeper than smaller search coils. This means covering a large search field will take pure sweets with a large coil in a small coil. But because of this large scan area, large search coils can be challenging and trashy areas were multiple targets will be encountered at once. Because of their diffuse magnetic field, large coils will be less sensitive over tiny targets.
Small search coils have concentrated magnetic fields making them ideal to use when searching for tiny targets such as gold nuggets. You will cover less ground with each sweep of a small coil but the smaller magnetic field makes small coils ideal for use in hunt areas where you'll encounter a lot of metallic debris. The small coil will help you locate good targets around trash they're lighter in weight and they are easier to maneuver in tight search spaces. In addition to search coil sizes and shapes, there are a variety of search coil configurations available.
The configuration refers to the arrangement of the transmitter TX and receiver or RX coil windings within the search coil shell. Five of the more common search quote configurations are Concentric, Double D, Mono, Imaging and 2 box. Concentric will consist of a TX coil and RX coil usually with a smaller RX coil located inside of a larger TX coil. With larger coil windings the concentric oil offers the largest possible detection field and greatest detection depth. The concentric coil has a very symmetrical detection field allowing easy in pinpointing and consistency in target identification. This uniform field also provides a better ability to discriminate iron targets like bottle caps and nails. Double D configuration coils have both TX and RX coil windings in the shape of a d. With the positive detection field running beneath the overlapping center section from front to back. The remaining portion of the coil actually produces negative or canceling detection fields making a DD coil more stable over the heavily mineralized ground. Many users find that a DD coil with his narrow detection field offers advantages and separating adjacent targets in a target-rich hot side. The concentric coil offers deeper detection depth and non-mineralized soil but notices that the DD coils performance becomes Superior as the level of ground mineralization increases.