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Some
of the basic coil types: |
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The most common
description for
metal detector
coils are:
concentric,
elliptical, and
Double D. |
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Concentric
Coil
A concentric
coil is probably
the most
commonly used
coil. Different
manufacturers
refer to these
coils with
different names,
however a
concentric coil
is a concentric
coil! These
coils are round,
some being very
thin in height,
some thicker,
some with open
holes in the
center, making
them shaped like
a flattened
donut, and some
are solid. A
few of the
manufacturers
have migrated
into designing
their concentric
coils into a
design which has
caused them to
be referred to
as “spider
coils” because
the bracing of
the coil’s
structure makes
the overall
appearance of
the coil to
resemble a
spider’s web. |
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Elliptical
Coil
This style
of coil also
gets its name
from the shape
of the coil.
Instead of the
round shape of
the concentric
coil, it is
merely has
elliptical
shape. Now if
the coils are
different only
in shape, you
are probably
thinking why
would one want
to buy an
elliptical coil
over the
concentric coil? |
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Overhead view of
a concentric
coil |
Let’s assume we
have a
8”concentric
coil (or round
coil). Let’s
also assume that
the coil covers
a path of 8”
wide each time
the coil is
passed over the
ground in the
sweeping motion.
Now, let us also
assume the coil
weighs 12
ounces. |
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Overhead view of
an elliptical
coil
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By making the
coil less in
width and longer
in length the
coil will become
elliptical in
shape. Lets
suppose the 8”
concentric coil
mentioned above
were to be
reshaped by
decreasing its
width by one
inch and
increasing the
length of the
coil by 1”. The
coil would be
elliptical in
design, and
would be, let’s
say, a 9” x 7”
coil. By doing
so, the coil has
increased the
amount of ground
it will cover
per sweep of the
coil by one
inch. We have
thus an
elliptical coil
with the same
size windings as
was in the 8”
concentric coil,
and the same
weight as the 8”
concentric coil,
but have a bonus
of 1” more
ground cover per
sweep. Had the
coil width been
decreased by 2”,
the length could
have been
increased by 2”,
making the coil
an elliptical
10” x “6” coil,
thus creating a
coil with two
inches more
ground coverage
per sweep of the
coil, with the
same overall
weight of the 8”
coil. (The
quoted
measurements of
the coil were
just for an
illustration,
not exact
measurements.)
The major
advantage of the
coil is the
ground coverage
versus the
weight, the
major
disadvantage is
that it usually
takes a little
more getting
accustomed to
the coil to
achieve the
precise
pinpointing of
the target as
compared to the
concentric
style. |
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Overhead view of
a Concentric
Spider Co |
Concentric
Spider Coil
A concentric
spider coil has
the same
windings
features as the
concentric coil
mentioned
previously. The
major difference
between the two
is appearance.
However, it is
my personal
opinion that the
spider coils
seem to be a
little more
sturdier, and
when bumping the
coil into small
twigs and
objects while in
the woods relic
hunting, the
amount of false
signals are
quite a few less
than the normal
concentric coil.
I think this
might be because
the windings are
held in place
within the coil
a little better
since most of
them have the
windings
imbedded in a
layer of epoxy.
This is just my
personal
opinion. |
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Overhead view of
the windings of
the Double D
coil |
Double D
Coil
The Double D
coil is a coil
which has the
winding in the
shape of the
letter D. Normal
winding are
basically shaped
the same as the
shape of the
coil from
overhead, for
example
concentric coils
have windings
which are also
round.
Elliptical coils
have windings
which are also
elliptical or
oblong. Double D
coils have
windings shaped
as the letter
"D" placed back
to back.
Double D coils
for the most
part are not as
deep seeking as
the other coils,
but enables a
wider scanning
of the ground
per sweep of the
coil, and also
offers the bonus
of not being
effected as
badly by heavy
ground
mineralization. |
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Treasure Finders |
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