14
thereby appearing larger
to
the
detector. The
worst
conditions
for
detecting are on loosely compacted
or
freshly dug ground
or
when the object
has
only
recently been buried.
In
these
conditions
detection
range
will
be reduced. 90%
of
all artefacts are
found
within
6"
of
the
surface.
N.B. Adverse soil
conditions
can reduce
depth
of
detection
by
more than half.
Determining
the
Target Size and
Depth
An
operator
who
is
familiar
with
his
instrument
will
be able
to
do
an
excellent
job
of
determining
object size, shape, and
depth
before he digs. This technique
is
learned
from
careful analysis
of
the
audio signals coming
from
the
detector. Each
time
a signal
is
heard,listen
for
any peculiar characteristics
it
may have,
determine
over
how
large
an
area
you
get a
detector
signal, and
try
to
"outline"
the
object before
you
dig. Listen
for
the sharpness
or
dullness
of
the signals and
determine
the magnitude
of
strength
of
the signal. A
coin
for
example
will
have a sharp signal, a nail a
fuzzy
signal.
After
digging up
the
object, compare the object size, shape,
depth
and
position
in the ground
with
signal
information
you
received
before
digging.
After
careful analysis
of
many digs,
you
will
learn
to
"read"
the hidden target before digging.
Detecting
To
test
for
the
type
of
signal
you
will
get,
take
a
coin
or
metal
object
and
with
the
detector
set
up
on
a table tuned
as
previously described, move
the
metal object towards and across the search head.
You
will
note
that
the volume
will
increase
quickly
as
the
metal object
passes
across
the
search head,
with
the loudest sound occurring when the search head
is
immediately
centred over the metal object. As
the object
passes
beyond the search head the sound
will
quickly
fade.
Since the detectors
employ
a
Total
Response search head
the
object can be detected across the
full
width,
back
to
front,
of
the
search head.
Maximum
sensitivity
down
the
middle
of
the search
head.
Pinpointing
(i) The strongest signal
will
always be received when
the
object
is
directly
beneath
the
centre
of
the
head
(see
X
in
Diagram 12).
To
poinpoint
the
find,
stop
the
search head when
you
are
directly
over
the
target
object,
then move
the
search head
through
90°
and sweep again, thus
forming
a cross
with
the
two
sweeps
as
shown in Diagram 12.
(ii)
To
'focus'
the
target signal
further
raise
the
search head, retuning
if
necessary, and
pass
the search head over
the
object
until
only
a
faint
signal
is
heard.
The
faint
signal
will
then be occurring at
point
X under
the
centre
of
the
head (Diagram 12).
More
accurate
pinpointing,
particularly
of
deeply
buried
objects can be achieved
by
finding
the centre
of
the
target object
as
described above and
fixing
its
position
in
the
'minds
eye'.
Turning
your
detector
through
90°
and sweeping across
the
target again
will
give a second
reading, accurately
determining
the centre
of
the
object
(Diagram
12).
.
Digging carefUlly
at
point
X
will
reveal
the
find.
With
little
practice, size, shape and
depth
of
an
article
may be estimated in
this
way
before
digging.
DIAGRAM
12.
Plclc
·up
A
...
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