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F75-MANUAL(122811).qx 12/14/12 9:04 AM Page 17
F75
Comprehensive Operating Manual & Guide to Metal Detecting
Capabilities And Limitations
DEPTH
The F75 can detect U.S. coins to a depth of up to 15-16 inches (37-40cm) under good conditions. Large objects (55 gallon drums, manhole covers, etc.) can be detected to a depth of up to several feet (1-2 meters).
Electrical interference from power lines and from electrical appliances and electronic equipment can reduce detection depth, or cause audible interference, making it necessary for the user to reduce the sensitivity setting. Soils with large amounts of iron or salt minerals may also reduce detection depth or necessitate a reduction in the sensitivity setting.
TARGET IDENTIFICATION
The F75 identifies the probable type of metal object by measuring its effective electrical conductivity, which is displayed as a number from 0 to 99 on the LCD screen. The effective
electrical conductivity of an object depends on its metallic composition, size, shape, and orientation relative to the searchcoil. Since coins are minted to tightly controlled specifications, they can be accurately identified. Identification of pull-tabs and foil is less consistent because these kinds of targets come in wide variety. 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, and zinc pennies, which read moderately high because of their size and shape. Although nails and other iron and steel objects will usually give low readings, ring-shaped pieces of iron (for instance steel washers and harness rings) will usually produce medium to high readings. Flat pieces of iron or steel, such as can lids, will occasionally do the same.
Most targets can be identified accurately in air to a distance of about 10 inches. The minerals in many soils will cause identification to be less accurate. In most soils, effective target identification can be had to a depth of at least 8 inches.
REQUIREMENT FOR MOTION: PINPOINT FEATURE
As with other modern metal detectors, the F75’s searchcoil must be kept in motion in order to both detect and identify targets. The All Metal modes are more forgiving of sweep speed variation than is the Discrimination mode.
The trigger-activated PinPoint feature continues to detect metal if searchcoil motion stops over the target. The PinPoint feature is used primarily to pinpoint the exact location of a target so that it can be retrieved with a minimum of digging, and does not provide target identification.
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Comprehensive Operating Manual & Guide to Metal Detecting
Motion All Metal Mode
The Motion All Metal mode is more sensitive and offers better feel than the Discrimination mode, and is used to find all metal objects present in the ground. The searchcoil must be in motion for objects to be detected. This is a single filter search mode similar to the “fast autotune”, “SAT”, or “P4” modes found in other detectors you might already be familiar with.
F75
THRESHOLD: Adjustable from -9 to +9. For maximum ability to hear the weakest signals, adjust this background noise level high enough so that it is barely audible while the detector is in use in the field. To eliminate the weakest signals, adjust into the negative region, which will allow the machine to run silently if the Sensitivity is not set too high.
The threshold level changes slightly with each detent step on the SETTINGS knob. Each number on the numeric readout corresponds to five steps.
AUDIO PITCH This control allows you to change the range of frequencies that you hear.
Values range from -9 to 9; 0 is default. Negative numbers lower the frequency of the tone you hear; positive numbers raise the frequency. This feature is intended to make the tone more pleasant to your ear; choose your personal preference. Users who have suffered some hearing loss, (including the natural loss of ability to detect high and low frequencies with age) may find this control helpful.
SENSITIVITY This controls the 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 preference. However, if you cannot hear at least some noise, the smallest or deepest objects will not be detected.
The sensitivity system has two stages, 1-29 (low gain), and 30-99 (high gain). As you decrease sensitivity and cross the transition from 30 to 29, you may notice that the background noise increases. Despite this increase as you decrease sensitivity to the lower setting, 29, the sensitivity is in fact lower under 30, and the machine is less susceptible to overload from large targets, ground minerals, and salt water. 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.
MANUAL GROUND BALANCE
Manual Ground Balance can only be performed while in an All Metal mode, but the resultant setting will carry over if you change into Discrimination mode. See the previous section on
Ground Balancing for instructions on how to use this feature.
We suggest that you manually ground balance using only the MOTION All Metal Mode. The result will be more accurate than when using STAT All Metal Mode.
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