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DD COIL CHARACTERISTICS
A DD coil is superior to a concentric coil, but sometimes requires a
different sweep technique.
Advantages are
1
.
1
.
Better target separation
2
.
2
.
Superior performance in highly mineralized ground
3
.
3
.
Broader Sweep- cover more ground with each sweep
If you experience multiple responses on a shallow target, you can
raise the coil, or narrow the sweep over known targets to only
intersect the center section of the coil.
BOTTLE CAPS
The disadvantage of the DD coil is its propensity to
classify steel bottle caps as coins.
If you hear a high tone in DISC mode and believe
that it is a coin, make sure it is not a bottle cap using
the following method.
1
.
1
.
If a repeatable ID# around 68 to 72, then it
should be a dime or copper penny.
2
.
2
.
If not in the range of 68 to 72, then:
a
.
a
.
Sweep the back end of search coil over
the target. If tone changes from high to a
low tone, it is probably a bottle cap.
b
.
b
.
Sweep search coil fast
across target.
1
.
1
.
If tone and ID-value
drop, it is probably a
bottle cap.
2
.
2
.
If a bottle cap, the
faster you sweep, the
lower the tone.
SWEET SPOT
The "center" of the DD-Coil is elongated (elliptical) from top to
bottom of the coil. With some practice you will find where the center
of this ellipse lies on your coil. Use this center point as a reference in
pinpointing.
Sweep back end
of searchcoil over
suspected bottle cap.
(Low Tone = Bottle Cap)
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7
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