Fisher Labs F75 User Manual

Metal Detector

Users Manual

The F75 is a multipurpose metal detector. Its most popular uses are coinshooting and relic
hunting, and it is also well-suited to gold prospecting.

PRODUCT FEATURES

• Light weight and well-balanced: best ergonomically engineered detector in the industry.

• Intuitive menu-driven user interface

• Large LCD screen

• Visual indicators of important values such as:
Target Identification
Target Confidence
Target Depth (both running-depth and pinpoint-depth)
Ground Mineralization

• Multiple Search Modes:
Discrimination
Static All-Metal
Motion All-Metal

• Trigger-actuated FASTGRAB™ ground balanci ng with manual override

• Waterproof 11-inch open-frame BiAxial™ searchcoil

• Trigger-actuated target pinpointing with variable audio pitch

• Fully Adjustable Arm Rest

• Display backlight for night and low -light conditions

• Notch and discrimination controls

• Covers provided for both the control housing and battery box.

If you have any questions, or need assistance with your metal detector,
Call 1-915-225-0333, and ask for Fisher Hobby Technical Service

Copyright Fisher Research Labs, Inc., February 28, 2007

2

TABLE OF CONTENTS

Specifications……………………………………… 3
Quick-Start ……………………………………… 4
Mechanicals

Assembly Instructions ………………………….. 5
Mechanicals………………………………………6
Arm Rest adjustment …………………………… 6
Using Headphones (not included) ……………… 6

Introduction to the F75

General information ……..……………………… 7
Controls…………………..……………… ………8
Menu System..…………………………………... 9
Ground Balancing….………………………...10-12
Motion All Metal Mode …………………………13
Static All Metal Mode……………………………14
Discrimination Mode…………………………15-17
PinPoint Feature …………………………………19
LCD Visual Display…………………………20 –23
Numeric Target Identification ……………... 20
Probable Target Identification……………... 20
Target Indicators ……………………………21
Depth Indicators……………………………..21
Confidence Indicator….……………………..21

Fe3O4 Graph…………………………….........21

Battery Indicator …………………………….22
G.B………….………………………………..22

Settings ………………………………….......22

Messages ……………………………….........22

Frequency Shifting ………………………………..23
Capabilities & Limitations…………………...24 - 26

Tips & Techniques
Search Techniques

How to sweep the searchcoil ……………..27
Pinpointing targets ………………………. 27
Estimating target size and depth…………. 28
False signals and chatter….……………….29
Adjusting Sensitivity …………….……….31
Tips on ground balancing ……………...…32
Detecting Activities
Coinshooting…………………………….…33

Relic Hunting ….....................................33-34

Gold Prospecting…………………….…34-35
Cache Hunting……………………………..36
Shallow Water Hunting……………………36
Salt-Water Hunting ………………………..37
How metal detectors work……………………….37
Warranty …………………………….……………..38

3

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 (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

Dynamic Balance: axial moment, 0.29 foot-pounds (0.39 newton-meters). Varies with

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
Basic Sensitivity: 6 x 109 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 30 hours with high quality alkalines, somewhat less with

Operating
Temp Range: 4 to +122 degrees F (-20 to +50 degrees C)

Operating
Humidity Range: 0-90% non-condensing

physiology.

adjustment and user’s stance and arm/hand physiology.

rechargeables.

4

QUICK START

Use your F75 right out of the box

1. Assemble the detector (see instructions beginning page 4).
2 Install four AA alkaline batteries. All positive (button-end) terminals point up.

Batteries are included with the detector.

3. Turn the knob, located under the armrest, fully clockwise.
This turns the machine on and sets audio volume to maximum.

4. When first turned on, the F75 starts out in the Discrimination mode, with:
Sensitivity preset to 60
Discrimination Level preset to 10
Number of Tones preset to 3
Process# preset to dE
Sweep the searchcoil from side to side, parallel to the ground. Keep the searchcoil
moving over the ground. If you stop moving the searchcoil, the sound will also
stop. Probable target type will be indicated at the top of the LCD screen.

5. If the searchcoil is not in motion and not close to metal, the detector should be
silent.

6. If you experience false signals from electrical interference, from the soil itself, or
from lots of trash metal, press the MENU button.
Sensitivity will be highlighted.
Rotate the Settings knob to the left (counterclockwise),
Reduce the sensitivity setting until the false signals go away.
After 7 seconds, the machine will exit the menu and return to
normal operation.

7. Toss a coin on the ground and sweep back and forth over it a few times to get a
feel for how the machine responds.

8. You are now ready to search.

9. Pull the trigger switch with your index finger to pinpoint the exact location of
targets, making them easier to unearth.

When the trigger is pulled, Pin Point is engaged ….
The searchcoil need not be in motion to detect an object.
The 2-digit numeric display indicates approximate target depth, in inches.

5

ASSEMBLY

1. Remove all components from box.

2. Attach searchcoil to lower rod by lining up the holes.
Notice that the lower rod is supplied with only one rubber washer.

It is designed to work with only one washer for maximum stability.

Push coil knob through hole and tighten knob gently.
You will tighten up the coil knob later.

3. Insert smallest rod into S-rod (S-rod hold s detector body).
Turn top locking collar counter-clockwise to open up.
Push in pin on small rod.
Slide small rod into upper rod.
Click pin into hole and tighten locking collar firmly clockwise.

4. Push lower rod into small rod as follows:
Turn locking collar counterclockwise to open up .

If plastic insert tab interferes, push it down, or turn tube upside down.
Push in pin to allow rod to slide in.
Slide lower rod in.
Click pin into any hole.

5. Remove velcro strip from lower rod.

6. Wrap cable around stem as follows:
Leave some slack in cable at base of lower rod.
Secure cable at base of rod with velcro strip.
Wrap cable loosely around entire stem up to bent part of upper rod.
You will re-wrap the cable later after sizing the rods to your height.

7. Push cable into connector on back of housing.
Do not twist the cable or plug.

Turn knurled cap nut only. Do not cross thread.

8. Tighten knurled cap nut by hand to secure cable connection to housing.
Do not twist the cable or plug .

9. Adjust to your height:
Hold detector, standing up, with your arm in the armrest.

Place searchcoil flat on the ground with back edge of coil 6” in front of your

toes.
Click pin on lower rod into nearest hole.
Firmly tighten bottom locking collar to secure lower stem.

10. Attach cable to top of rod with upper Velcro strip

11. Tighten up coil knob to keep searchcoil from flopping.

12. Insert batteries.
4 batteries are all installed the same way -- positive terminals pointed upward.

After establishing a comfortable length, firmly tighten the locking collars on the rods to
prevent the tubes from rattling. Rotate the collars a full 270° to engage and lock in place. If
you are unable to rotate a full 270°, use gloves for a better grip.

If the searchcoil appears crooked with respect to the pole, loosen both locking collars and
re-adjust. Hold each of the lower poles in the counterclockwise position as you tighten the
locking collars.

6

MECHANICALS

BATTERIES

The F75 required four AA batteries.
These non-rechargeable chemistries may be used: Alkaline, Nickel Oxy-Hydroxide
(Panasonic Oxyride or Duracel PowerPix), and lithium iron disulfide (Energizer L91).
Nickel metal hydride and nickel-cadmium rechargeable chemistries may also be used.

Zinc-carbon and so-called “heavy duty” batteries may not work, especially in cold weather.
Do not use these batteries.

Expect 30 hours of service in the field with one set of alkaline batteries.
Rechargeable batteries will usually deliver over 25 hours of service without recharging, but
when they start running low, they die suddenly with little warning.

Always install batteries which are of the same type and the same state of charge.
Otherwise battery life will be determined by the weakest battery, because the good batteries
cannot deliver their power with a dead battery blocking the current.

All 4 batteries are installed with the positive terminals facing upward.
The LCD screen shows battery condition on the right.

ARM REST

The arm rest WIDTH and POSITION are both adjustable.
Arm Rest Width : The sides of the arm rest can be bent inward and outward.

To best stabilize the detector to your arm and body movement, squeeze the sides of
the arm rest around your forearm. For a very secure fit, some users prefer to bend
the arm rest in tightly against the forearm such that you pry the sides loose each time you

place your arm into the arm rest.

Arm Rest Position on Pole : Remove the two bolts to position the arm rest farther forward or back,
to adapt to your arm’s length.

-- To reinsert the bolts, spin and twist them into place. Be careful not to damage
the power cable that runs through the aluminum tube.

-- Insert both bolts completely through both sides of the bracket
before attaching the nut to the opposite side.

-- After reinserting the bolts, tighten them very securely. You may need to use
gloves for a firm grip. As you swing the detector from side-to-side, you want the
bolts tight enough so that you do not feel any movement between the pole and
arm rest mounting bracket.

If you notice unwanted movement while swinging detector, check the tightness
of the locking collars. The locking collars must be rotated a full 270° to reach the

locking position.

HEADPHONES (not included)

The F75 is equipped with a standard ¼-inch stereo headphone jack at the rear of the unit, located
under the elbow as you hold the detector for use. Any headphone with a ¼” stereo jack should
work. Mono headphones will not work.

Using headphones improves battery life, and prevents the sounds from annoying bystanders. It also
allows you to hear subtle changes in the sound more clearly, particularly if searching in a noisy
location. For safety reasons, do not use headphones near traffic or where other dangers, like
rattlesnakes, are present.

7

Introduction to the Fisher F75

HIGH PERFORMANCE The F75 is a multi-purpose high-performance computerized
metal detector. It has the high sensitivity and ground balancing control needed for
professional gold prospecting, the discrimination responsiveness needed for serious relic
hunting under difficult conditions, and visual target ID considered essential in searching for
coins. The F75 operates at 13 kHz for good sensitivity to gold nuggets and jewelry as well
as to coins. The F75 comes with an 11-inch elliptical Bi-Axial searchcoil for maximum
detection depth in mineralized soils.

USER COMFORT The F75 is among the lightest and best balanced of all high­performance metal detectors, so you can hold and swing it almost effortlessly. The arm
rest position is adjustable to fit your arm. The grip is durable high-friction foam elastomer,
comfortable in any kind of weather. The controls are conveniently located and easy to
learn how to use. Locking collars on the tubes eliminate rattling.

EASY-TO-USE & INFORMATIVE INTERFACE The entire menu is always visible on
the LCD display. The LCD display indicates the electrical signature (target I.D.) of the
detected metal object. The display provides continuous information on battery condition
and on ground mineralization, which affects detection depth. Help messages are
automatically displayed on the bottom of the display when necessary.

LOW OPERATING COST The F75 is powered by four AA alkaline batteries, which will
typically last for more than 30 hours of use before needing replacement.

DESIGNED BY MANY OF THE INDUSTRY’S MOST TALENTED ENGINEERS The
lead engineers on the F75 design team were John Gardiner and David Johnson.
David Johnson’s previous Fisher design credits include the CZ-platform , the Gold Bug­series, most of t he 1200-series, Impulse Underwater Detector, CZ-20 Underwater Detector,
FX3 magnetometer, the Gemini 2-box locator, the XLT-16 Acoustical Leak Detector, and
the XLG-80 Ultrasonic Leak Detector. David was supported by fellow electrical engineers
Jorge Corral, Dimitar Gargov, and Mark Krieger. The mechanical design was a
collaboration among David Johnson, Brad Fulghum, John Griffin, and Tom Walsh.

MECHANICAL ENGINEERING
While the F75 is robustly engineered for outdoor use, it is not indestructible and it is not
waterproof.

RESET function
The F75’s microprocessor will save all settings which you input, even after the power is
turned off.
If you wish to reset the settings to the factory preset, follow this process:

1. Turn detector off

2. Press-and-hold the red MENU button and push-forward-and-hold the TOGGLE

SWITCH

3. Turn the detector on, while you are still holding the controls

4. Release the MENU button and TOGGLE SWITCH

5. See the F symbol. When the F disappears, the detector is reset.

8

CONTROLS

ON-OFF & VOLUME Knob (Under the elbow)
This knob turns the machine on or off, and controls speaker volume and headphone
volume. Knob position has no effect on detector’s sensitivity or susceptibility to noise

from electrical interference

The F75 has two controls on the front panel, MENU and SETTINGS.
MENU Pushbutton (Red button on right of the front panel)
Push the MENU button to :

1. Step through the menu selections on the display.
With each push of the button, the next menu selection will be highlighted.
The SETTINGS knob then allows you to change values for the highlighted

selection.

2. Recall the last setting which you adjusted.
After you have adjusted a setting, an indicator will remain highlighted next to this
menu selection. One push of the button will recall that selection and display the
stored value.

This recall function is useful for a value you want to adjust frequently, such as the
ground balance setting. In order to adjust a stored value with the SETTINGS
knob, you must first press the MENU b utton to reactive the user interface.

SETTINGS Knob (On the left of the front panel)
Rotate the SETTINGS knob to:

1. Change the setting (or value) of the highlighted menu selection you have chosen.

2. Select the operating MODE when the top line of the menu is highlighted.
When used to switch back and forth between the DISCRIMINATION mode and
ALL METAL modes, the detector changes modes as soon as the corresponding
selection is highlighted. The All Metal modes are used to detect all metal objects,
including small or deep objects. Use the Discrimination mode to ignore trash metal
such as nails, foil, or pull-tabs.

NOTE: When the menu selection highlight disappears, the SETTINGS knob is
deactivated. If settings values do not change when the SETTINGS knob is rotated, press
the MENU button to reactivate the user interface.

TRIGGER SWITCH (Under the display in front of your hand)
While the trigger is pulled back, metal objects are temporarily detected without the need

for searchcoil motion. This aids in pinpointing the exact location of objects which were
found while searching in the Discrimination or All Metal modes.

When the trigger is pushed forward, FASTGRAB automatic ground balancing is activated.
The internal computer measures the magnetic properties of the soil in order to cancel
interference from naturally-occurring minerals in the ground. After the detector measures
the soil in this manner, the detector then uses this information to control operation in both
the All Metal and Discrimination search modes.

9

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 modes 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, 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.

10

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 fro m 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 genera lly inaudible unless the discrimination setting is 0.

AUTOMATIC GROUND BALANCING PROCEDURE (FASTGRABTM)

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.

MANUAL GROUND BALANCING
In most situations, it is preferable to push the trigger switch to activate FASTGRAB
automatic ground balancing. Generally, it is best to first let the computer automatically
cancel interference from ground minerals. However, for gold prospecting, searching on a
wet saltwater beach, or searching in an area with so much metal trash that there is no clean
ground for the computer to sample, we recommended that you manually ground balance.
Manual ground balancing requires a bit of skill, acquired with some practice.

The range of ground balance settings indicated on the display range from 0 to 99; however,
each displayed number spans 5 detent steps on the settings knob. The actual internal
ground balance settings change with each step; there are a total of 500 different settings.
Under some ground conditions you may be able to hear the individual steps in the setting.

11

GROUND BALANCING (continued)

MANUAL GROUND BALANCING (continued)

The Fe3O4 bar graph on the LCD display indicates the amount of magnetic mineralization.
The searchcoil must be in motion to measure Fe3O4. The most accurate measurement is
obtained by pumping the searchcoil, as in the Ground Balancing procedure.

The two-digit G.B. Setting number displayed on the LCD indicates the type of ground
mineralization.
Some typical ground mineralization types are:
0 – 10 Wet salt and alkali
5 – 25 Metallic iron. Very few soils in this range. You are probably over metal.
26–39 Very few soils in this range -- occasionally some saltwater beaches
40–75 Red, yellow, and brown iron-bearing clay minerals
75–95 Magnetite and other black iron minerals

When manually ground balancing, try to “feel out” a spot on the ground to make sure
there is no metal present. In order to avoid locking onto metal, the computer will not

balance to ground where the GB setting is less than 40. Where the ground reads less than
40, manual ground balancing is required.

To perform the Manual Ground Balancing operation, do the following:

1. Select the MANUAL G.B. function
The legend G.B. SETTING appears.
The present ground balance setting is displayed (0-99).
The message PUMP COIL TO G.B. will appear.

2. 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.

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.

12

GROUND BALANCING (continued)

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 gro w 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 model 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.