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© Jonathan Porter 2003
A big monoloop coil requires fitness and
patience, you have to be prepared to dig
a big hole on spec and still remain
positive when it turns out to be ground
noise. But there are a few tricks to
help alleviate some of the frustration.
First and foremost: train your brain to
remember what the original response
sounded like and then use this as a
benchmark as you start excavations. With
this in mind you can then compare the
signal as the hole progresses,
theoretically the signal should improve
as you get the coil closer to the
target. However you can chase a ground
noise into infinity, because a big mono
can generate noise off the edges of the
hole as you dig, this can become more
pronounced the deeper you go.
When you suspect this is the case then
try this; when digging the hole make
sure all the spoil from the hole is
stacked well away so that you can get a
clear swing over the top of the hole
(making sure the coil is perfectly level
as it passes). If the signal is still
present then the chances are that it is
indeed a good target, but be careful
because sometimes when you disturb the
chemistry of the ground you could lose
the response until the coil comes into
the nuggets correct range again (this is
because of halo effect). This is why
when chasing these types of signals the
detector should always be placed in
fixed ground balance; let your mind make
the decisions about whether or not you
should continue to dig. Okay, you will
chase a few ground noises but you will
also learn from each one.
Dish out the sides of the hole so there
are no sharp edges, just a gentle slope,
this is so you can bring the coil into
the hole at a reduced angle to help
control spurious noises generated by
tilting the coil too far out of level
plain and also gives an increased chance
of identifying any improvement in signal
response. Once the signal becomes really
apparent you can then get stuck into
making as much mess as you like (I tend
to get a little excited when the signal
becomes a positive and dig like a mad
thing until I have the nugget in my
hand.) Remember though, you must re-fill
your holes no matter how disappointed
you are with the result!!
If you are using a coil as big as a 25”
Nugget Finder, then obviously you’re not
there chasing tiddlers. Depending on the
detector, you can reduce some of the
sensitivity (except the SD 2200) by
either using Ground balance one (1)
switch only (SD 2000 and 2100) or using
Salt mode on the GP’s. Every big nugget
I have found at depth (and most of the
smaller pieces too) have registered well
in Salt mode, which is just a timing
change for when the detector measures
the amount of decay left after the
ground has been charged by the pulse.
The
bigger the nuggets the longer the decay
will last, the smaller the nugget the
shorter the decay. Salt mode then
becomes smoother and quieter because all
the energy generated by the ground has
dissipated before the detector takes its
sample, hence a small loss in
sensitivity to small gold (Sensitive
mode is the reverse of this). When a PI
detector sends a pulse into the ground a
nugget will be charged by that pulse,
resulting in eddy currents racing around
in the nugget, those eddy currents then
reflect back to the detector; the
problem is mineralized ground can behave
in a similar manner which causes ground
noises.
When using my NF 25” mono I use the
following settings on my GP3000: Deep
mode; Salt or Normal mode
depending on the ground; Level adjust
- well before the twelve o’clock
position (anti-clock wise); Signal
control - ¾ to 4/5 (crisp initial
rise in pitch then tapering to a
controlled lowering); Threshold -
firm (not too loud or too quiet); DD
mode (better depth with mono coils
in this position).
A round coil will always provide the
best depth, especially when dealing with
coils of this size. A large out of shape
coil would be just as much a hindrance
in tight brushy terrain because of the
size and weight, but in the smaller
sizes can be an advantage because of
extra sensitivity gained on
close-to-surface targets with ease of
use in tight spots like creeks and
scrubby areas. A big mono will by its
very nature lose some sensitivity to
small gold, but has the added bonus of
smoothing out ground noise which all
helps in the search for nuggets at
depth.
Remember it is the ground minerals we
are trying to overcome, but it is also
mineralization that provides us with the
extreme depth capabilities of the PI’s
(halo effect). If we can effectively
control most of the mineral sounds, we
can then pay attention to those faint
deep responses without trading too much
off in performance.
Sometimes less equals more!!
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