Comprehensive Operating Manual & Guide to Metal Detecting
Comprehensive Operating Manual & Guide to Metal Detecting
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F75
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F75
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ground and lower it to within 1 inch
of the ground, about once or twice a second.
3. Turn the SETTINGS KNOB to adjust the setting.
The goal is to eliminate the sound as the coil is being pumped over the ground. In
some soils, the sound is not completely eliminated.
If the ground balance adjustment is incorrect, there will be a difference in the sound as the
searchcoil is either moving toward or away from the ground. It sounds like you are either
pulling the sound out of the ground, or pushing the sound into the ground.
• If the sound is louder as you raise the searchcoil, increase the ground balance setting.
• If the sound is louder as you lower the searchcoil, reduce the ground balance setting.
NOTE: Experienced users often prefer to adjust the ground balance to get a weak but audible
response when lowering the searchcoil. This is called adjusting for positive response.
Positive and Negative Response
The purpose of ground balancing is to adjust the metal detector to ignore ground minerals. If
the setting is incorrect, ground minerals will give either a positive or a negative response,
depending on which direction the adjustment is off.
POSITIVE RESPONSE
If the G.B. setting is too high a number, the response of minerals will be positive. This means
that when the searchcoil is lowered to the ground in PinPoint, Stat, or Motion All Metals mode,
the sound will get louder as the searchcoil approaches the ground. The sound will grow
quieter as the searchcoil is raised. What, if anything, you will hear in discrimination mode
depends on the discrimination setting.
When searching in an All Metals mode, if ground balance is properly set to cancel the ground,
and you sweep over a positive hot rock, the rock will give a “zip” sound similar to that of a
metal object.
NEGATIVE RESPONSE
If the G.B. setting is too low a number, the response of minerals will be negative. When the
searchcoil is lowered to the ground in PinPoint, Stat, or Motion All Metals mode, the machine
will be silent. The machine will sound off as the searchcoil is lifted away from the ground.
What, if anything, you hear in discrimination mode depends on the discrimination setting.
When searching in Motion All Metals mode, a negative hot rock will produce a “boing” sound
after passing over it, making it difficult to know where it is located. It will not have the sound
and “feel” of a metal object.
Ground Balancing (continued)
Search Techniques (continued)
The F75’s other processes have a reputation for lightning-fast response over targets, with the
result that the duration of the sound over a good target can be very short, especially in a
trashy area. The Boost process lengthens the duration of the target’s sound. Many users will
find this audio feedback less fatiguing; the Boost process makes it easier to listen through the
trash clutter to hear good targets. Whereas in Default process slowing your sweep speed
leads to a loss of sensitivity, the Boost and Cache Locating processes allow you to sweep
slower, without a loss of sensitivity
The Cache Locating process is primarily for locating large, deep objects while searching with
the searchcoil several inches off the surface of the ground. It is free of the gradual threshold
drift which can occur in the Static All Metals Mode. In general, its response is too slow for
ordinary relic hunting or coinshooting. But if you prefer a very slow sweep speed (for instance,
if you are accustomed to using the older technology of heavy and sluggish competitive
detectors) you can still achieve good results.
In areas which have been pounded to death and were seemingly hunted out, even by the
predecessor version of the Fisher F75, the Boost process can make such sites productive
again. By detecting targets which were just out of reach of other machines, or by lengthening
the duration of good sounds that were too hard to hear amid trash sounds, old sites are again
productive. If a site has been especially productive in the past, you may want to revisit it
using the Cache Locating process and utilize a very slow sweep.
Most of the foregoing techniques apply both to the Discrimination Mode where the process is
selected, and to the corresponding Motion All Metals Mode, whose response characteristics
are also modified when the Boost and Cache Locating processes are selected.
While searching in bP or CL process, you may also want to periodically toggle back to dE
process. Press-and-Hold the MENU button to temporarily engage the dE process. For users
familiar with the F75 default process, this can serve as a target check. Under some
conditions, the default process may identify targets more accurately. Targets yielding a
marginal response in one process may sound different in another process. If you are new to
the F75, toggling back to default process from bP or CL can serve as a learning tool to
understand the different response characteristics of the different processes.
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.
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