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Comprehensive Operating Manual & Guide to Metal Detecting

Comprehensive Operating Manual & Guide to Metal Detecting

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F75

F75

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)

GROUND BALANCING

To achieve maximum depth in any detection mode, as well as when using the PinPoint
feature, the 

F75 

offers the ability to cancel out ground minerals either by manual adjustment,

or automatically using the FASTGRAB feature.

If you do not perform the ground balancing operation, the Discrimination mode will usually still
work fairly well, but the ALL METAL modes will not.  The Pinpoint feature can be used for
pinpointing objects at moderate depth in most soils without prior ground-balancing.

The internal computer will not cancel salt water, so when detecting on wet ocean beaches,
ground balancing must be done manually.

DISCRIMINATION

Discrimination refers to a metal detector's ability to ignore metal objects in selected categories,
especially iron and aluminum.  This makes searching much more pleasant in an area with a lot
of metal trash.  The 

F75 

offers a wide variety of discrimination features which you can select

according to the search conditions and your personal preference.

DEPTH READING

The estimated Depth Reading displayed when pulling the PinPoint toggle is based on the
strength of the signal.  It is calibrated to coin-sized objects.  Smaller objects will read deeper
than they actually are, and large objects will read shallower than they actually are.

AIR TESTING

There may be times when you want to test or demonstrate the metal detector without sweeping it over
the ground, for instance, if not fully assembled, or if you are indoors. To air test, place the searchcoil in
a spot where the detector is stable and more than two feet away from any large masses of metal,
including the reinforcing steel usually present in concrete.  If you are wearing a wristwatch or jewelry
on your hand or arm, remove it.  Then, test or demonstrate by waving metal objects over the
searchcoil; wave objects briskly, several inches over the top of, and parallel to, the searchcoil.

Ground balancing cannot be tested or demonstrated in air unless you happen to have
appropriate specimens of iron minerals available.

SWEEP SPEED  

The 

F75 

is noted for its quick response.  This gives it unsurpassed ability to locate and identify

good targets surrounded by trash.  It also permits the user to sweep the searchcoil quickly in
order to cover more ground with very little risk of losing targets.  In general, if you are
searching an area where the desirable targets are more than 8 to 10 inches deep, a faster
sweep speed will detect to a greater depth and yield more accurate target IDs.  

CHECKING A TARGET

In order to most accurately verify a detected target with most other metal detectors, users will
narrow their sweep and loiter over the top of the target. The 

F75 

is different. The 

F75'

s quick

response and advanced signal sampling system produces the most accurate target IDs with
deliberate (shoulder width) sweeps all the way across the target, even if there are other
targets nearby.  If you check targets using sweep techniques learned on some other detectors,
you run the risk of getting less accurate target IDs. You can use the confidence level indicator
to improve your technique.

Capabilities And Limitations (continued)

F75-MANUAL.qx6  8/15/07  9:42 AM  Page 16

Summary of Contents for F 75

Page 1: ...Metal Detector Users Manual ...

Page 2: ...pth Ground Mineralization Multiple Search Modes Discrimination Static All Metal Motion All Metal Trigger actuated FASTGRAB ground balancing with manual override Waterproof 11 inch open frame BiAxial searchcoil Housing constructed of a carbon fiber polycarbonate blend Trigger actuated target pinpointing with variable audio pitch Fully Adjustable Arm Rest Display backlight for night and low light co...

Page 3: ...entification 24 Probable Target Identification 24 Target Indicators 25 Depth Indicators 25 Confidence Indicator 25 Fe3O4 Graph 25 Battery Indicator 26 G B 26 Settings 26 Messages 26 Frequency Shifting 27 Capabilities Limitations 28 30 Tips Techniques Search Techniques How to sweep the searchcoil 31 Pinpointing targets 31 Estimating target size and depth 32 False signals and chatter 33 Adjusting Se...

Page 4: ...cy nominal 13 kHz quartz crystal timing reference Basic Sensitivity 6 x 10 9 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 f...

Page 5: ... 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...

Page 6: ...es 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 ...

Page 7: ... 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 ...

Page 8: ... 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 bat...

Page 9: ...erting 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 reac...

Page 10: ... 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 40 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 ...

Page 11: ...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 On Off Volume Switch Menu Button Settings Knob Dual function Trigger switch ms g is n s a dly sts nd eft ual a u ...

Page 12: ... 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 ...

Page 13: ...alance 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 ...

Page 14: ...n 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 ...

Page 15: ...he 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...

Page 16: ...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...

Page 17: ... signal gain and is adjustable from 1 to 99 In the presence of electrical interference high ground mineralization or variable ground mineralization operation will usually be too noisy wobbly and erratic sound if the sensitivity is set too high At settings above 90 the internal circuit noise of the machine will probably be audible The sensitivity level setting is largely a matter of personal prefer...

Page 18: ... noise and or a slight amount of ground response If you do not hear these noises you will sacrifice detection depth If the background chatter is too annoying or the ground noise is so high that it impedes operation reduce sensitivity Such a downward adjustment in sensitivity improves depth detection as you can now hear weak signals better The sensitivity system has two stages 1 29 low gain and 30 ...

Page 19: ...noise increase You may need to adjust to a setting of 29 or less to silence electrical interference or to prevent overload on highly mineralized ground or in salt water You may also notice a shift in the ground balance setting over difficult ground conditions as you cross this transition DISCRIMINATION LEVEL This is adjustable from 0 to 65 and controls the range of objects to be eliminated from de...

Page 20: ...ct target ranges equal to 1 2 of each category for inclusion or exclusion from detection As you rotate the knob the target indicator will appear above the range currently selected If you set the notch value anywhere within the range the notch value will not necessarily stop at this number notch ranges are fixed as follows 1 1 7 iron 6 31 35 nickel 2 8 15 iron 7 36 45 tab 3 16 20 foil 8 46 55 tab 4...

Page 21: ...different tones The OF TONES selections are 1 SINGLE MEDIUM PITCH TONE All types of metal induce the same tone 1F MEDIUM TO HIGH PITCH TONE varying in proportion to target signal strength Large shallow objects will produce a squeal The variable audio pitch provides you more information about the detected object but some people find the sound on strong signals too annoying 2F TWO TONES Similar to 1...

Page 22: ...un noisier in trashy areas bc BOTTLE CAP MODE Response is modified so that steel bottle caps will usually produce inconsistent or non repeatable tones and broken sounds There may be a slight reduction in the ability to separate adjacent targets Use this process in areas with a high concentration of steel bottle caps Also refer to the Capabilities Limitations section for sweep techniques to aid in ...

Page 23: ...ch 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 ...

Page 24: ...oins will fall into the same range as the modern U S 1 Eagle OBJECT TARGET I D Most iron objects 4 12 foil from gum wrapper 16 25 U S nickel 5 coin typically 30 aluminum pull tab 33 55 aluminum screwcap 60 70 zinc penny dated after 1982 typically 60 aluminum soda pop can most often 63 69 but can vary widely copper penny clad dime typically 70 U S quarter 25 coin clad typically 80 50 coin modern cl...

Page 25: ...ntification it has assigned If all 6 segments are displayed you can be confident that the target ID is accurate If 3 or fewer segments are displayed the confidence is very low Junk targets tend to produce lower confidence indications than coin targets of similar electrical conductivity Sloppy sweep technique also reduces the confidence indication You can use this indicator to train yourself to swe...

Page 26: ... is overloading the circuit the message OVERLOAD RAISE COIL will appear Such overloads will not harm the detector but the detector will not detect metals properly under these conditions Raise the coil until the message disappears the siren sound will also stop Resume normal detection The message RAISE COIL only appears when using the bc process accessed through the PROCESS menu selection This mess...

Page 27: ... interference If you suspect electrical interference you may change the F75 s operating frequency This is a trial and error method to try to find a frequency different from the suspected source To shift frequencies 1 Hold the MENU button down Do not release the button 2 Push the trigger forward OR pull the trigger back to change the frequency Each frequency change requires a push of the MENU butto...

Page 28: ...ty In general smaller objects and objects made from lower conductivity alloys such as iron bronze brass lead pewter and zinc will read lower on the effective conductivity scale Larger objects and objects made from higher conductivity alloys such as silver copper and aluminum will tend to read higher The notable exceptions are gold which usually reads low because it is rarely found in large pieces ...

Page 29: ...nce if not fully assembled or if you are indoors To air test place the searchcoil in a spot where the detector is stable and more than two feet away from any large masses of metal including the reinforcing steel usually present in concrete If you are wearing a wristwatch or jewelry on your hand or arm remove it Then test or demonstrate by waving metal objects over the searchcoil wave objects brisk...

Page 30: ...searchcoil the crossed magnetic fields of the Double D construction can produce anomalous responses If the object feels shallow strong signal narrow response or multiple responses in a single sweep and is giving consistent high readings like a coin raise the searchcoil 2 to 3 inches and try again A coin will almost always continue to give consistent readings unless it is right next to an iron obje...

Page 31: ...ased 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...

Page 32: ...practice this by laying a coin and a flattened aluminum can on the ground you will quickly understand how to differentiate the two and you will probably never have to dig another aluminum can And you will know whether it was deep or shallow This technique works well in the All Metal modes and to a lesser extent in Discrimination mode Objects which are ring shaped or flat and round like coins tend ...

Page 33: ... nonferrous targets in the proximity of iron indicating ID numbers higher than would be obtained in an air test This tendency is connected with the F75 s enhanced see through ability that is the ability to find valuable targets in an area where there is a lot of iron trash False Signals and Chatter At times the detector may beep when there is nothing there or it may seem like there is nothing ther...

Page 34: ...ways 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 salt water th...

Page 35: ...e a gold nugget and are common in many gold prospecting areas They are usually but not always drawn to a magnet They are most often reddish in color but are often black brown or yellow On relic hunting sites red clay bricks and rocks which have lined a fireplace or a campfire will often be hot rocks The discriminator will usually eliminate them without difficulty if widely scattered but if there i...

Page 36: ...o 90 and then use the machine without ground balancing In most areas once you have ground balanced the ground balance setting will remain satisfactory for a long time However if the soil has been disturbed by digging or the addition of fill dirt or if you are in a geologically complex setting such as is commonly encountered in gold prospecting areas you may have to frequently perform the ground ba...

Page 37: ...rty owner Most of the public places where one is likely to do coinshooting are city county or school district property There is usually no ordinance prohibiting use of a metal detector as long as you are not causing damage Sometimes such ordinances do exist Administrators and security personnel often have the legal authority to prohibit any activity they do not like even if there is no ordinance a...

Page 38: ...h public and private land are protected by law from relic hunting If there is a metal detecting club in your area some of the members will probably know what the laws are in that area and which sites are and are not off limits Relic hunting is most rewarding if you have an avid interest in history In many cases the value of a relic is not the object itself but the story it s a part of what histori...

Page 39: ...s Alaska and in a few localities in the Appalachians The old saying Gold is where you find it means that to find gold you should look in areas where the yellow metal is known to be present Hillsides are the best areas for gold prospecting using a metal detector because hillsides cannot be cleaned out by panning and dredging the way streams can Also gold on hillsides not far from its source vein te...

Page 40: ...netite black sand If you know this to be the case in the area you re working you can maximize your gold recovery by concentrating your effort on areas where the bar graph indicates higher amounts of iron mineralization Gold prospectors are mostly a friendly bunch and willing to spend some time showing a beginner how to increase his odds of finding the yellow stuff Many will invite you to search on...

Page 41: ...lieved to have hidden the cache The ownership of a cache is not always clear Sometimes it belongs to the person or heirs of the person who hid it sometimes it belongs to the owner of the property on which it is located and sometimes it belongs to the person who finds it or some combination of the above If the contents of the cache were stolen this fact can also complicate the question of ownership...

Page 42: ...f a special sand scoop for recovering valuables from the sand quickly most metal detector dealers sell these The electrical conductivity of the water itself can pose some challenges You may get false signals when going into and coming out of the water making it necessary to pay careful attention to keep the coil either in or out of the water but not to touch the surface This effect may be observed...

Page 43: ...s 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 th...

Page 44: ...etector for service please first contact Fisher Labs for a Return Authorization RA Number Reference the RA number on your package and return the detector within 15 days of calling to Fisher Research Labs Inc 1465 H Henry Brennan Dr El Paso TX 79936 Phone 915 225 0333 ext 118 Warranty coverage does not include the cost of transporting the detector back to an owner who is located outside of the Unit...

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