GMT Super Pulse
Owner’s Manu
al
GMT Super Pulse
Ow
ner’s Manual
Controls
Threshold
The
T
h
res
hold
control sets the level
at which the background audio tone is
heard. In most cases,
f
ain
t tar
ge
t sig-
nals are eas
ies
t to hear when the thres
h-
old is set to a low but clearly audible
level. A higher threshold level can
result in audio fatigue. T
oo low of a
threshold level mean
s that a stronger
tar
get signal is required to
produce an audible change.
Thr
esh-
old
is best determined at a low gain setting where there is no
ch
atter
.
The threshold can be set low enough to ef
fect a “silent
search” audio. Some pe
ople prefer silent
search to prevent
audio fatigue. If you choose to do
this, increase the threshold to
the point where you can hear th
e threshold tone, then slowly
back of
f until it is barely ina
udible. Reducing the threshold any
more than n
ecessary requires st
ronger tar
get signals to produ
ce
an audio response. Othe
r controls — including
Gai
n
and
Ground
Bala
nce
— are best adjusted with an audible threshold.
Power/Gain
The
Gain
control increases or
decreases the ampl
if
ica
tion of the
receive s
ignal. Normally
, this deter
-
mines how deep the detector will “see”
a tar
get.
However
, increasing the gain not
only increases the am
plif
ic
ation of
tar
-
get signals, but also that of
ground signals and electromagnetic
interference (EMI) as
well.
A common mistak
e is to assume
that higher gain will al
ways give better dept
h. I
n air tes
ts this is
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Page
7
generally true, but ground result
s can depend on the amount and
type of mineralization.
W
ith the coil on the ground, increase the gain until the
detector exhib
its
ch
atter
, then
back of
f slightly for a reasonably
steady threshold tone. Proper
ground balancing will minimize
chatter due to mineralization.
The
Gain
control is a
lso us
ed to
tu
rn the detector on and of
f.
Ground Balance
This control is used to balance out
the signal from ground mineralization.
There is an
OFF
position for which
GMT Super Pulse
runs in straight PI
mode with no ground balance.
To
ground balance
GMT Super
Pulse
set the
Gai
n
to about the mid-
point or until the audio just begi
ns
to cha
tte
r. Pump the s
earc
h
coil up and down from about one
inch of
f the ground up to 6-8
inches above the ground while listen
ing for a change in the audio.
If
the GB is too lo
w
, the audio will have a
high tone when the coil
is lowered to the ground; if the
GB is too hig
h, the audio will
have a low tone. Adjust the
Grou
nd Balan
c
e
control for minimal
audio changes. For most moderate
mineralization,
this
will be
around “8”. A simple technique is
to start with the GB set inten-
tionally too low (say
, 5); pump th
e c
oil and incr
eas
e the GB until
the high tone begins to transition to a low tone, then back of
f
slightly
.
If you begin to hear ground
noises (false signals) as you
sweep the coil you should check the ground balance.
There are s
ome c
ases
where a
particular tar
get will fall
exactly on top of the
ground balance point and
GMT Super
Pulse
w
il
l n
ot
b
e a
bl
e t
o d
et
ec
t i
t a
t a
ll
. T
ar
ge
ts
th
at
a
re
c
lo
se
to
the ground balance point may have
their tone response shifted if
the
Grou
nd Balan
c
e
c
ontr
ol is
a
djusted.
For example, a given
tar
get may have a hi
gh tone response with
GB=9 but a low tone
