Fisher Gold Bug/Teknetics G2 Forum

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Gold Bug Pro and Bottle Caps :detecting:
Posted by: Dave J.
Date: November 11, 2010 08:28PM
Most modern discriminators have difficulty with flat iron, especially steel bottlecaps. It has to do with the way the discriminator works, not with alloy plating as some people have speculated. Beginning with the T2 several years ago, our discriminators have been on the leading edge of discriminator design, and the things they do well have made them very popular. However they do have a lot of difficulty with steel bottlecaps.

There are a number of clues that a target may be a steel bottlecap: subtle differences in the sound, seeing the iron mineral bars jump up, tendency for ID # to drop 'way down on some passes over the target, and target ID becoming much bouncier when you X the target. Using these techniques takes a bit of experience.

For decades, DD searchcoils have been well known for having difficulty with steel bottlecaps, especially shallow ones. This is why for many years discriminators used only concentric searchcoils. However DD searchcoils have certain advantages, too, and those advantages eventually came to be appreciated. .......The weakness of the DD on steel bottlecaps comes from the extreme variations in the shape of the field response within several inches of the coil. This, as it turns out, can be turned into an asset. A normal straight sweep across the target will tend to give the highest ID reading on a steel bottlecap, but if you go off toward the side or to the front and rear, the ID will usually start jumping around a lot more than it would with a coin. Some people use such techniques to good advantage but some folks find them hard to learn.

My favorite technique, which seems to work best with the 5 inch searchcoil, is to tilt (rotate) the metal detector 90 degrees turning the searchcoil into the vertical plane and sweep across the target that way, searchcoil edge just about touching the ground. This usually throws most of the ID's clear down into the iron range-- at least for me.

--Dave J.

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