Understanding All-Metal Carry-Over Responses
When I began hunting with the Sovereign and Excalibur, I noticed that a lot of signals had this segmented quality that usually meant that something was very close to the coil. A signal would come in with a wide, drawn-out sound, give a normal tone in the middle, then go out with the same long tone. As I began to examine what was causing this sound, I recognized that these were almost always targets with some iron or steel in them. The exceptions were objects that were very small and right on the surface. These “carryover” responses can teach a lot about how the Excalibur performs. In effect, what you are hearing is the machine trying to form a “bridge” between the steel or iron in the object and the surrounding ground–just as it does with a false signal. The difference is that this false signal is interrupted by a good one–the non iron / steel part of the target. This good signal makes up the “blip” in the middle, and the carry-overs are basically a reflection–the interaction of signal and ground. What this means is that if you are hunting for objects with no iron or steel, listening for signal with less of this carry-over
effect can help you to tell which signals are not iron. This works well, although there are some exceptions. These exceptions show themselves by how much of the signal is in the middle portion versus the outside. As a rule, good signals will be louder in the middle, if they have any carry-over at all. Targets such as gold or coins with no steel will not make this sound, because there is no ferrous content to confuse the detector as to what is target and what is surrounding ground. Carry-over responses will be more pronounced with larger coils as these draw more response from the ground. Understanding them is a valuable tool for working in high-trash environments. Listening for this difference is especially good for telling bobby pins from earrings, chains or other small gold targets. As you progress in using all-metal mode to double-check responses, you should be able to tell which responses will give a discriminate tone before you switch over, by the width and carry-over properties of a signal. This should include recognition of steel alloys like most bottle caps too. Developing this skill will give your accuracy a quantum boost.
From: “Advanced Methods for Finding Gold in the Water with the Minelab Excalibur” by Clive James Clynick