Manual
Comprehensive Operating Manual & Guide to Metal Detecting
Comprehensive Operating Manual & Guide to Metal Detecting
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F75
F75
Ground Balancing
What is Ground Balancing?
All soils contain minerals. Signals from ground minerals are often tens or hundreds of times
as strong as the signal from a buried metal object. The magnetism of iron minerals, found in
nearly all soils, causes one type of interfering signal. Dissolved mineral salts, found in some
soils, are electrically conductive, causing another type of interfering signal.
Ground Balancing is the process by which the metal detector cancels the unwanted ground
signals while leaving signals from buried metal objects intact. This is accomplished by
establishing the detector’s internal Ground Balance setting; this setting is calibrated to the soil
and eliminates the signal produced by ground minerals.
Calibration to the actual soil condition will result in deeper target detection, quieter operation,
and more accurate target identification. This calibration, or Ground
Balancing, can be accomplished automatically with the detector’s internal
computer, by pushing the Trigger Switch forward, or manually in the All
Metal menu.
The ground balance setting carries through into all operating modes. In
Discrimination mode, the ground signal is generally inaudible unless the
discrimination setting is 0.
AUTOMATIC GROUND BALANCING PROCEDURE (FASTGRAB™)
1. Find a spot of ground where there is no metal present.
2. Hold the detector with the searchcoil about one foot
above the ground.
3. Push the TRIGGER SWITCH forward with your index finger.
4. Physically
pump the searchcoil and detector up and
down over the ground.
Lift it about 6 inches above the ground and lower
it to within 1 inch of the ground, about once or
twice a second.
5. A 2-digit value will appear on the display. This is
the Ground Balance setting.
If the detector’s internal computer is unable to ground
balance, an error message will appear:
• If the message OVERLOAD RAISE COIL – CAN’T
GB
appears, you will also hear a siren sound.
You are probably over metal.
• If the message
CAN’T GB appears, you may
not be pumping the coil, or you may be
over a small piece of metal.
Note: FASTGRAB will
not automatically
balance over highly
conductive soils, such as
a wet salt water beach.
Search Techniques
Sweeping Searchcoil (this does not
apply to Pinpointing with the trigger
switch) Keep the searchcoil in motion to
detect targets. Sweep the searchcoil
parallel to the ground; do not lift the
searchcoil at the end of the sweep.
When you have located a target and
continue sweeping back and forth for
verification, use broad, deliberate
sweeps across the target for the most
accurate target ID. Do not use short
sweeps as you might with other metal
detectors.
Shallow Targets
Shallow targets tend to give multiple
responses, with the last response being
the one that remains illuminated on the
visual display. This last response is usually sampled at the edge of the searchcoil and will
tend to be inaccurate. If you suspect a shallow target (within 2 to 3 inches of the searchcoil),
lift the searchcoil slightly, and slow down your sweep speed until you notice a single response
consistently in the same place.
Large shallow targets can cause signal overload, indicated by the siren sound. In these
instances, raise the searchcoil until the overload warning disappears, and sweep at this
increased height.
Large Targets
If an overload warning is not confined to a small spot, you are probably overloading on a large
object, for example, a large iron pipe, reinforcing steel in concrete, or buried sheet metal. It is
usually not possible to locate objects, such as coins, in close proximity to large masses of metal.
Pinpointing With the Trigger Switch
When you turn the F75 on, the ground balance setting is preset to give a positive response on
nearly all soils. This means that if you are pulling the pinpoint trigger, the audio tone will get
louder as you lower the searchcoil to the ground. But you do not want to hear the ground; you
just want to hear the target. So always Ground Balance first.
After you have discovered a buried metal target using the ALL METAL or DISCRIMINATION
Modes, use the trigger switch to pinpoint its exact location.
Position the searchcoil an inch or two (2.5-5cm) above the ground, and to the side of the
target. Then pull the trigger. Now move the searchcoil slowly across the target, and the sound
will indicate the target’s location. As you sweep from side to side, and hear no sound at the
ends of the sweep, the target is located in the middle of that zone, where the sound is loudest
and the audio pitch is highest. If the sound is loud over a wide area, the buried object is large.
Use the PinPoint feature to trace an outline of such large objects.
WRONG
RIGHT
F75-MANUAL.qx6 8/15/07 9:42 AM Page 14