Adjusting Sensitivity. Fisher Research Labs F75 SPECIAL EDITION, F75SE

F75ltdBLK-MANUAL.qx6 3/31/14 2:01 PM Page 12

F75

SE

Comprehensive Operating Manual & Guide to Metal Detecting

Controls (continued)

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 button to reactive the user interface.

3. Press-and-Hold the MENU button to temporarily switch to the dE

(default) process, only when operating in the bP or

CL process.

The dE process will only be engaged while the button is depressed.

Releasing the button will return you to the process you were operating in.

When using any processes other than bP or CL , pressing-and-holding the button will have no effect.

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 motion All Metal Modes.

When in static All Metal Mode, pulling the trigger zeroes the audio threshold to the signal level currently preset. If the searchoil is up in the air away from metal, this maneuver corrects for threshold drift due to temperature changes.

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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. FASTGRAB™ can be used at any time during operation.

Comprehensive Operating Manual & Guide to Metal Detecting

F75

SE

Search Techniques (continued)

HOT ROCKS

A hot rock is a rock which causes the metal detector to sound off because the rock contains iron minerals. They come in two basic types.

Negative hot rocks

(also called cold rocks) are usually magnetite or contain magnetite, and give a negative response because their ground balance value is a higher number than the soil they are found in. They tend to be dark in color, usually black, and usually heavy. In some cases they will have rust stains. They are usually attracted to a magnet, and for this reason gold prospectors always carry a magnet—the ultimate ferrous/nonferrous discriminator. In Motion All Metal Mode, negative hot rocks produce a boing sound rather than the zip sound of a metallic target; recognize the difference and you will learn to ignore them.

Positive hot rocks are iron-bearing rocks which have been oxidized by natural weathering processes so that their Ground Balance number is a number lower than the soil they are found in. They are often small, right on the surface, sound just like 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 is a large concentration of them, the discriminator may not quiet them all. In that case, you can revert to the rule of thumb -- “don’t dig nonrepeatable signals”.

Using the sensitivity control

When the

F75 is first turned on, the Sensitivity is at a medium setting appropriate for most coinshooting. For relic hunting or gold prospecting, higher Sensitivity settings are usually preferred.

In the event of detection of electrical interference from electrical power lines, electrical or electronic appliances, or another metal detector, it is usually necessary to reduce the

Sensitivity setting to achieve quiet operation. Alternatively, use the Frequency Shift feature described earlier in this manual.

If, while searching, you are constantly getting signals from which you cannot recover metal targets, you may be detecting small or deep targets which are not recoverable using the methods at hand. So, you may do better if you reduce the Sensitivity setting.

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