Fisher Labs F75 User Manual

32
SEARCH TECHNIQUES (continued)
Tips on ground balancing
When the F75 first turns on, the ground balance setting is preset to 90. This will give a
positive response on nearly all soils. If you search in the Discrimination mode, you will
probably not have to balance to the ground. If you switch to All Metal mode, ground
balancing will probably be necessary.
You must find a spot of ground which is free of metal to accurately balance to the ground.
Before you attempt to Ground Balance, sweep back and forth to see if any metal target is
present. Locate what seems to be a clear area and then Ground Balance. Ground
Balancing may be done automatically by pushing the trigger, or manually if you are in All
Metal mode. After you have ground balanced, sweep back and forth to see if there is little
or no audible response to the soil. This is best done either in All Metal mode, or in
Discrimination mode with discrimination set to zero. Alternatively, use the PinPoint
trigger to check the spot. If there is little or no response, ground balancing was successful.
If there is still substantial response, there may have been metal present where you
attempted to ground balance, so find another promising spot and try again. If you cannot
find a spot to successfully ground balance, it is time to give up. Reset the ground setting to
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
balancing procedure to accommodate changing soil conditions.
When you ground balance, the numerical Ground Setting will momentarily appear on the
LCD screen. In general, sandy or gravelly soils will tend to read in the 75-95 range, light
colored loams and clays will tend to read in the 50-80 range, and red clays will tend to read
in the 35-55 range. To express it in other terms, the more highly weathered, oxidized, or
finely grained the soil is, the lower the numeric reading will be.
The Fe
3
O
4
bar graph indicates how much iron mineralization is present. For it to work, the
searchcoil must remain in motion. The most accurate readings will be achieved by
pumping the coil as you do when ground balancing. The higher the mineralization, the
greater the necessity to ground balance the detector for the best depth performance.
If you are searching for relics, you can make a map of the soil of the site. Make a grid of
the site. Then collect data. Ground Balance to document mineral type; view mineral
amount on the Fe
3
O
4
bar graph. Then plot the data on the site map and draw isolines. In
this way you may be able to locate areas which have been dug, backfilled, or subjected to
fire. This information in turn helps to reveal the history of the site.

Fisher Labs F75 Specifications

General

Brand	Fisher Labs
Model	F75
Category	Metal Detector
Language	English

Summary

Specifications

Quick Start Guide

Assembly Instructions

Mechanicals

Batteries

Details on battery types, life, and installation for the F75 detector.

Arm Rest Adjustment

Explains the adjustable width and position of the arm rest for user comfort and stability.

Introduction to the Fisher F75

High Performance Features

Highlights the F75's capabilities in sensitivity, ground balancing, and target identification for various uses.

User Comfort Design

Focuses on the detector's lightweight design, adjustable arm rest, and ergonomic grip for user comfort.

Easy-to-Use Interface

Describes the LCD display's menu system, target ID, battery condition, and mineralisation information.

Reset Functionality

Provides step-by-step instructions on how to reset the F75's microprocessor settings to factory defaults.

Controls Overview

On-Off & Volume Knob

Details the function of the knob for powering on/off and controlling audio volume for speaker and headphones.

Menu Pushbutton

Explains how to use the red button to navigate menu selections and recall settings.

Settings Knob

Describes how to use the knob to change settings and select operating modes.

Trigger Switch

Explains the trigger's function for PinPoint and FASTGRAB automatic ground balancing activation.

The Menu System

Ground Balancing

Automatic Ground Balancing (FASTGRAB)

Outlines the steps for using the FASTGRAB feature to automatically balance the detector to ground conditions.

Manual Ground Balancing

Explains when manual ground balancing is preferred and the general process involved.

Performing Manual Ground Balancing

Provides step-by-step instructions for manually adjusting the ground balance setting to eliminate ground signals.

Positive and Negative Response

Explains how incorrect ground balance settings cause positive or negative mineral responses.

Motion All Metal Mode

Threshold Adjustment

Explains how to adjust the audio threshold for optimal detection of weak signals and noise reduction.

Sensitivity Control

Describes the function of sensitivity for signal gain and its adjustment based on environmental noise levels.

Static All Metal Mode

Threshold Adjustment

Explains how to adjust the audio threshold, noting it may drift and require retuning.

Sensitivity Control

Advises setting sensitivity high for depth, reducing it if chatter is too high.

Discrimination Mode

Discrimination Level Setting

Details how to adjust the discrimination level to eliminate unwanted targets, with instructions on setting the value.

Notch Feature

Explains the NOTCH feature for including or excluding specific target ranges, detailing how to set and program notches.

Number of Tones (# Of Tones)

Describes how to select the number of audio tones, outlining different selections for target identification.

Process Number Selection

Explains the Process Number selection for audio discrimination methods to suit different search conditions and preferences.

PinPoint Feature

How to Pinpoint Target

Provides step-by-step instructions on how to accurately pinpoint a target's location using the PinPoint feature.

Ground Pick-Up Explanation

Explains ground pick-up in PinPoint mode and recommends prior ground balancing to eliminate it.

LCD Visual Display

Numeric Target ID (2-digits)

Presents a table of common objects and their typical 2-digit target identification numbers on the LCD.

Probable Target ID Zones

Explains how the LCD display categorizes signals into probable target ID zones based on metal object characteristics.

Depth Indicator

Explains how the numerical display and bar graph indicate the estimated depth of a detected object.

Fe3O4 Bar Graph (Magnetite)

Explains the bar graph that displays magnetic mineralization factor and its influence on detection depth.

Advisory Messages

Lists advisory messages displayed on the LCD, such as OVERLOAD, RAISE COIL, and PUMP COIL TO GB.

Frequency Shifting

Capabilities and Limitations

Detection Depth

States the detection depth for coins and large objects under various conditions.

Target Identification Accuracy

Explains how the F75 identifies probable metal types, noting factors affecting accuracy.

Ground Balancing Importance

Discusses achieving maximum depth via ground balancing and its importance in different modes and conditions.

Discrimination Features

Defines discrimination as ignoring metal objects and highlights the F75's features for customization.

Steel Bottle Caps & Flat Iron Trash

Offers methods to minimize digging steel bottle caps and flat iron trash by using specific processes and sweep techniques.

Search Techniques

Pinpointing with the Trigger Switch

Explains how to use the trigger switch to pinpoint target location after detection, emphasizing prior ground balancing.

Sweeping Searchcoil Technique

Instructs to keep the searchcoil in motion parallel to the ground for target detection and accurate ID.

Estimating Target Size, Depth, and Shape

Details techniques for differentiating target size, depth, and shape, especially for aluminum cans versus coins.

False Signals and Chatter Causes

Identifies five major causes of false signals and chatter, including electrical interference, and suggests solutions.

Ground Minerals and Effects

Describes how conductive mineral salts and altered soil minerals affect detection and ground balance, offering strategies to manage them.

Hot Rocks Identification

Differentiates between negative and positive hot rocks, explaining how they affect detector response and how to identify them.

Tips on Ground Balancing

Provides practical advice on finding a metal-free spot, performing ground balancing, and interpreting ground settings.

Detecting Activities

Coinshooting Guidelines

Details coinshooting locations, typical targets, discrimination use, and etiquette in public places.

Relic Hunting Basics

Describes relic hunting targets, the importance of depth sensitivity, and managing iron trash.

Gold Prospecting Areas

Identifies areas for gold prospecting in the US and the importance of finding gold where it is known to be present.

Cache Hunting Strategies

Explains cache hunting, research methods, ownership issues, and recommended search modes.

Shallow Water Hunting

Covers searching in shallow water, coil waterproofing, beach hunting etiquette, and dealing with water conductivity.

Salt Water Hunting Measures

Provides measures to silence salt water response while retaining sensitivity for searching in or over salt water.

How Metal Detectors Work

Explains the VLF Induction Balance technology used by most hobby metal detectors, including coil function and signal analysis.

5-Year Limited Warranty