Thoughts on search coil selection compliments of Tesoro Electronics
Searchcoils come in two types: Concentric and Widescan. Concentric are preferred for discriminating. Widescan are less affected by ground mineralization. All searchcoils are electrostatically shielded and waterproof.
In general, larger searchcoils will give better depth with larger targets and better ground coverage. However, sensitivity to smaller objects may be sacrificed. Smaller searchcoils will offer greater sensitivity to smaller objects and improved target separation in trashy soil.
A third style, the Printed Spiral, is made only by Tesoro for use with pulse induction circuitry. It offers good sensitivity to a broader range of target sizes and improved sensitivity to less conductive targets such as fine gold chains. All searchcoils are electrostatically shielded and waterproof.