Minelab Metal / Gold detector modifications SD2000 SD2100 SD2100E SD2200 SD2200V2 GP Extreme GP3000 GP3500 GPX4000 GPX4500 Detectormods is part of Link Technologies.
I have written this as a means to identify ground noises and differentiate these from real metallic targets.This works in conjuction with the upgrades we carry out on Minelab detectors.
How does one determine if a signal from a deep target is just ground noise or a real target? Even the experts and full time professional prospectors find it hard to work out. Most deep targets have a broad detection area due to the wide flat return signal from the target, it is very different to the shorter sharper signal from a target close to the coil. Most prospectors basically scrape off some soil and listen if the target response increases or decreases, this is not the way to accurately determine if the target is metallic or not.
Beware! many people walk away from ground noises only to find that the next prospector comes along and digs out a multi ounce gold nugget. On our modded detectors we have a 3 position switch that changes the pulse of the detector and this in turn changes the response from both ground noises and metallic targets.
The following is from my own experience and testing of this method, ground noise in general and in most cases drops away in sound intensity with a longer pulse length as this also increases the time it takes for the receiver in the detector turns on. I have found that in many cases a metallic target at depth will not change but ground noise will in most cases significantly decrease. This corresponds to detecting with our modded detector in position 2 and switching into position 3. Another way but a bit more complicated is to switch the 3position switch into the 1 position, this decreases the pulse width but turns the receiver on faster.
By switching into position 1 if you have been detecting in position 2 the target may get louder and in most instances it means the target is not as deep or as large as first thought and if still broad in response it is most likely a ground noise. Now if you are detecting in position 1 and get a broad signal you can put the detector into position 2 and if the signal increases i would definitely dig it. If the response drops slightly the target, if metallic would be small and close to the surface and would not give a broad signal in the first place. Some points to remember....Large deep targets respond with a greater signal strength if the transmitter pulse is made longer to more fully energize the target to develop a larger field via generating stronger Eddy currents in the target, if its size and structure can build up to a greater point before saturation. Most large objects can give a better return signal with pulse lengths over 500 microseconds. Ground in most cases saturates at less pulse on time and increasing the transmit pulse will not give any increase to most ground noises. I am trying to keep this simply written so that you do not need to have an engineering degree to understand it, but i find that the words i use to replace technical terms sound a tad funny.
Metal Detectors as supplied by the manufacturer in most cases are a compromise in design as no detector can be excellent in all prospecting environments. Mods / Upgrades can bring out enhanced functionality for specific prospecting.
Here is an explanation of these settings, plus why pro’s use the extreme
settings they do.
Higher adjustments are used primarily to consistently find both large and small
gold in highly mineralised ground.
Coil / Rx Setting = Mono with a Mono coil.
We use the Mono setting with an 18”in NF Mono coil, M/Lab recommend using the
Mono position too, not the DD position.
It has been found that to exceed this coil size for general prospecting, brings
in EMI to an unacceptable level.
Ground Balance = Fixed, when using Enhance.
Fixed is recommended, after a careful G/Balance, GB is crucial in Enhance
timings.
Even though the machine sounds GB'd, get into the habit of G/Balancing
often.
Using Tracking can G/B out a faint small or deep target in 2 sweeps of the mono
coil.
Soil Timings = Enhance with a Mono on hot soils.
Enhance is the best thing the 4500 has going for it in hot ground conditions,
this timing gets most of the missed gold, (Large & Small), plus its quiet
running lets you hear the faintest of responses.
Search Mode (Front End Cap) = Deep, in deep ground. (1’ft to
3’ft+).
We recommend this mode with the Digital settings below, as it has proven
to us that the 4500 differs from what settings we had used on the GPX 4000.
Digital Menu
Backlight Off (Unless detecting at night)
Battery Test = 8.0+V (Recharge battery each night)
Volume Limit = Headphones = 15 ------ Speaker with adjustable amp. = 18
Experiment with this, don’t go below 12. It can also be run at 20
GB Type = General
Specific is too much of a handful, its use is only recommended in highly
magnetic soil conditions.
Man Tune Find the best response over a known deep buried target, try in
the range of between 80 to 110, all machines are different to get their
ultimate frequency position. (It does make a difference).
Only tune out EMI up to 5 digits either side of your detectors best setting.
Have the machine always set on Man / Tune while detecting, as the EMI
interference waves come through, reach down and adjust the right hand knob a
few digits up or down to get a quiet frequency. We don't use the auto tune
button.
General Menu
Motion = Slow -------- or use (Very Slow), if there is bad
EMI.
RX Gain = 12 for the deep quiet ones, if EMI is nonexistent, try
13.
Why would you not have your detector near to maximum gain?
When it has been proven to produce large gold at depth.
It also gets the Fly Sh!t down to . 2 of a gram with this gain setting.
Audio = Normal -------------- (Less EMI and spurious noises).
Do not use Deep setting here when Deep is used on the F/E Cap,
as the Signal to Noise ratio is infringing on the faint responses.
With the 4000 you could use Deep / Deep, but on the 4500 it's noisy.
Audio Tone = 33
A lower tone is more suitable for the low growly deep faint signals; it is also
less annoying to the ear over many hours of detecting.
The small gold signals still comes through with their rising pitch.
Stabilizer = 11
Factory pre set is 10, with what you are looking for, (better size
gold), a tweak up is better than down.
Signal Peak = 19
This helps to determine target responses from ground signals, set high; it
provides a sharp clear target response with a quicker diminishing fall away.
Target Volume = 10 for headphones, ----- 12 when using an
external speaker amp with adjustable volume control.
Response = Normal
This gives the best chance on the smaller bread and butter gold, usually with a
sharp high rising response. Yet Normal response still responds well to
the large deep gold, with that unmistakable dipping growl.
In fact the majority of nuggets, say from 5” or 6”inches deep, will give this
reverse pitch dipping signal when using Enhance.
Most ground noises give a wide rising pitch signal, this is usually not
consistent from all angles of the coil sweep, and with practice many can be
eliminated.
When in doubt have a dig, also after rain with the dry & wet patches, or
wet charcoal under the surface, you do get some dipping ground noise
responses, these tend to make you dig more, but better to be safe than miss
one.
Tracking = Slow.
The reason: - When in Fix and your Ground balancing, the switch holds it
in tracking for a short time.
Using Slow Tracking restricts the EMI noise at this time and helps the GB
process.
Iron Reject = OFF It will not work with a Mono coil
Remember the ground conditions have to be of a highly mineralised and
variable nature to use the Enhance timing, so if the conditions are mild,
you should be using Normal timings for better depth.
To get the perfect G/Balance
Note; Keep the coil parallel with the ground during the pumping
procedure.
Keep your coil stationary 30mm above the ground. Hold in the green button on
the handle, now pump the coil using small even movements of about 30mm to 40mm
up & down, (at this height above ground).
Bring the coil down slowly to the lowest point of the pump, (30 mm from the
ground), be sure to hold it really steady when you release the button.
Never release the Q /T Button whilst the coil is moving or twisted, as this can
affect the accuracy of the G /Balance.
Be prepared to go through this same procedure 2 or 3 times to get it just
right, as sometimes conditions make it hard to get it to G/B the first time.
