Specifications - Fisher F75 SPECIAL EDITION User Manual

F75
LIMITED
Comprehensive Operating Manual & Guide to Metal Detecting

Specifications

Mechanical: S-rod with electronics housing mounted on handgrip, 3-piece
breakdown, batteries under elbow, 2-way armrest adjustment —
forward/backward & around forearm.
Searchcoil: 11" (28 cm) open-frame elliptical double-D, waterproof.
Batteries: 4 AA, alkaline (not included).
Weight: 3.5 pounds (1.6 kg) with alkaline batteries installed.
Static Balance: force in vertical plane normal to elbow 0.47 pounds (0.22 kg).Varies
with adjustment and user's stance and arm/hand physiology.
Dynamic Balance: axial moment, 0.29 foot-pounds (0.39 newton-meters). Varies with
adjustment and user's stance and arm/hand physiology.
Sweep Effort: lateral moment 5.2 foot-pounds (7.1 newton-meters).
Operating Principle: VLF induction balance
Operating Frequency: nominal 13 kHz, quartz crystal timing reference
13158Hz, 13100Hz, 1043Hz, 12987Hz, 12931Hz, 12876Hz, 12821Hz
9
Basic Sensitivity: 6 x 10 root Hertz (detectivity)
Lag Coefficient: 78 milliseconds
Reactive Overload: approximately 10,000 micro-cgs units (volume susceptibility)
40,000 micro-cgs units with sensitivity < 30.
Resistive Overload: approximately 1,200 micro-cgs units (volume susceptibility)
4,800 micro-cgs units with sensitivity < 30.
Ground Balancing Range: From ferrite to salt, inclusive
Discrimination
Ground Suppression: combination of second and third order methods
ID Ground Suppression: third order
Battery Life: Typically 40 hours with high quality alkaline batteries
Estimated 80 hours with nickel oxyhydroxide batteries
Estimated 65 hours with lithium iron disulfide batteries
Operating Temp Range: 4 to +122 degrees F (-20 to +50 degrees C)
Operating Humidity Range: 0-90% non-condensing
4
Comprehensive Operating Manual & Guide to Metal Detecting
How Metal Detectors Work
Most hobby metal detectors use VLF Induction Balance technology. Here's how they work.
The searchcoil (also called search head or loop) contains two electrical induction coils which
are like antennas. One coil transmits a rapidly alternating magnetic field, illuminating the
region surrounding the searchcoil. If metal is present, its electrical conductivity distorts the
magnetic field. If iron metal is present, its magnetism also distorts the magnetic field, but in a
different way, allowing the metal detector to distinguish between ferrous and nonferrous
metals.
The other coil is a receiving antenna which detects changes in the magnetic field caused by
the presence of metal. Electronic circuits amplify this weak signal, analyze it to determine the
changes which occur as the searchcoil sweeps over the target, and then convey the
information to the user in the form of a visual display or audio tones. Most modern metal
detectors perform many of these tasks in software running on an internal microcomputer.
The iron minerals which are present in most soils also distort the magnetic field, obscuring the
weak signals of small or deep objects. This can cause the object to go undetected, or to be
misidentified when it is detected. Much of the technology that goes into modern metal
detectors is devoted to the task of eliminating the unwanted signals from iron minerals in the
soil, while not losing the signals from metal objects.
This device has been designed to operate with the antennas listed below, and having a
maximum gain of 3 dB. Antennas not included in this list or having a gain greater than 3 dB
are strictly prohibited for use with this device. The required antenna impedance is 53 ohms.
10COIL-F70, 11COIL-F75, 5COIL-F75, 6COIL-E
The following statement is not relevant to metal detectors but is printed here to satisfy
legal notification requirement:
"To reduce potential radio interference to other users, the antenna type and its gain should be
so chosen that the equivalent isotropically radiated power (e.i.r.p.) is not more than that
permitted for successful communication."
The following countries allow free movement of this product within the European community:
FIN,LVA,SVN,SUI,BIH.
F75
LIMITED
45