Menu System - Fisher F75 SPECIAL EDITION User Manual

F75
LIMITED
Comprehensive Operating Manual & Guide to Metal Detecting
Search Techniques (continued)
NUISANCE BURIED OBJECTS
In some areas there is a lot of metallic trash which produces weak signals. These could
include deeply buried objects, little bits and pieces of rusty iron and corroded foil. These items
can be detected, but are difficult to pinpoint due to their depth and small size. When you dig
and find nothing, it may seem like the machine is beeping at nothing even though there is
actually something there. The best solution is usually to reduce sensitivity.
If searching a very trashy area and unwanted signals are a problem, search with the
searchcoil 2 inches away from the ground. Trash objects very close to the searchcoil will
sometimes not be completely eliminated, even when the discrimination setting should have
eliminated the target.
Metal detectors are designed to see one metal object at a time. Where there are two iron
objects near each other, the detector can be fooled into thinking that the gap between them is
nonferrous metal. This is a common condition where a wooden building has burned or been
torn down, and the site is littered with nails. A signal from a nonferrous metal object such as a
coin will usually be repeatable, whereas a false positive signal resulting from multiple or oddly
shaped iron objects will seem to wander around and even to vanish. Experienced detectorists
call these non-repeating signals and usually do not bother digging them since nonrepeating
signals are almost always trash.
GROUND MINERALS
Conductive mineral salts usually produce broad signals which will not be mistaken for a
metallic object. Common causes are concentrations of mineral fertilizer, spots where
evaporation has concentrated naturally occurring mineral salts, residue from de-icing salts,
and urine from livestock. Unless dry, "cow pies" can sound off like they are metal. Ocean
beaches have saltwater—that subject is discussed toward the end of the manual.
In spots where there has been intense fire, such as a campfire site or where a stump was
burned during land clearing, the soil minerals may be altered by oxidation so that their ground
balance setting is lower than that of the surrounding soil. In such cases, search slowly and
change the G.B. setting as frequently as necessary.
In some areas, electrically conductive industrial minerals such as fuel coke, slag, clinkers (left
over from burning mineral fuels), or charcoal have been dumped or used as landfill. Individual
lumps of these materials can usually be quieted by reducing sensitivity and searching with a
discrimination level of at least 25. However, where the ground consists primarily of such
materials, you may not be able to search quietly. In that case, do not dig unless a signal is
crisp and repeatable.
Electrically conductive natural minerals such as graphite, graphitic slate, or sulfide ore
minerals are rarely encountered except when gold prospecting. When gold prospecting, you
need to be able to hear everything, and you can expect to dig conductive minerals that turn
out not to be gold. In a given locality you may learn to recognize what type of rocks these
minerals are found in, and to ignore them if people in the area say that gold is not found in
rocks of that type.
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Comprehensive Operating Manual & Guide to Metal Detecting
The Menu System
The entire menu is printed on the LCD display. The display highlights the mode and settings
which are in use.
There are three search modes: Static All Metals, Motion All Metals, and Discrimination. To
change between an All Metals mode and Discrimination mode, the top line of the menu system
must be highlighted. Press the MENU button until the top line of the menu is highlighted.
When either All Metal or Discrimination is highlighted, rotate the SETTINGS knob to move
between the two categories.
Each search mode has several adjustable function settings:
ALL METAL: Threshold (not adjustable in stat mode), Audio Pitch, Sensitivity, and
Manual Ground Balance
DISCRIMINATION: Sensitivity, Discrimination Level, Notch, Number of Tones, and
Process Number.
To select a function, push the MENU button and continue pushing in order to move to the
function you want. The word SETTING will pop up in the middle of the display, and the
present setting of that function will be displayed as a number.
To change a setting, rotate the knob.
To increase a value, rotate to the right (clockwise)
To decrease a value, rotate to the left (counterclockwise)
If you select a function and
do not make a change to
that function after 7
seconds, the detector will
exit the menu system
automatically, deactivate
the SETTINGS knob, and
resume normal operation.
If you press the MENU
button while the machine is
in normal operation, the
user interface will return to
the last menu feature
setting. This feature allows
you to have quick access to
a function that you want to
adjust frequently.
F75
LIMITED
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