Understanding Double-D (DD/Wide Scan) search coils:
The Double-D configuration is designed to significantly reduce ground interference and, thereby, recover the performance lost by a concentric coil over mineralized soil. With the Double-D, it is the arrangement of the TX and RX coils that produce a canceling effect of ground signals.
This configuration is called DD because both TX and RX coils are in the shape of a "D". The positive detection field of the DD runs beneath the overlapping center section from front-to-back. The remaining portion of the coil actually produces negative (i.e. canceling) detection fields. It is this canceling field that allows the DD coil to maintain performance over mineralized ground.
Because of its small positive detection field, the DD is inherently less sensitive than a concentric search coil of the same size, over non-mineralized ground. The Double-D will, however, significantly out perform the concentric coil over mineralized ground. For this reason, it is highly recommended when hunting over mineralized ground commonly found when prospecting and relic hunting.
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