Fisher Lab's F-75
By Andy Sabisch
From page 11 of the October issue of Lost Treasure magazine.
Copyright © 2007, 2007 Lost Treasure, Inc.
--------------------------------------------------------------------------------
Fisher Research’s F-75
Fisher Research Laboratory is, as their corporate tagline states, “The oldest name in the metal detecting industry,” having been founded by Dr. Gerhard Fisher in 1931. Over the decades, Fisher’s engineers led the industry with many innovations that have stood the test of time and found their way into even other brands of detectors. While the business landscape changed, and the Fisher company was acquired by First Texas in 2006, the Fisher commitment to producing first-rate equipment for the most demanding detectorists has not, and it was with this mission statement that the engineering team of the relocated company set out to develop a new detector that would be of a caliber others would be measured against. The result is the F-75, named to commemorate 75 years of production under the Fisher moniker. Having personally used Fisher detectors for more than three decades, I was looking forward to giving the new F-75 a try.
Features
The F-75 was developed to be a professional-grade detector designed for a wide range of applications, including coinshooting, beach hunting, relic hunting and even gold prospecting. While lead engineers Dave Johnson and John Gardiner worked to “push-the-envelope” in terms of in-field performance, they kept focused on the need to keep the unit’s weight manageable and the adjustments simple enough that a novice could be successful with it straight out of the box.
The effort that went into the design of the F-75 becomes immediately apparent when unpacking it. Its ergonomic shape places the two primary controls within easy reach and the display is large and well laid-out. The weight also is worth noting, in that the total weight – with batteries - is about 3.5 pounds. For someone looking for a high performance detector without the weight, the F-75 is definitely a pack-leader in that respect!
Despite the F-75’s versatility, it is controlled through one pushbutton and one knob on the control housing, a trigger toggle switch above the handgrip, and an ON/OFF/VOLUME knob under the armrest. A common complaint from users of high-end detectors has always been the complexity of making adjustments, often requiring scrolling through layers of options on the menu screen and then trying to remember how to get back to a specific option if additional adjustments are required. Well, the Fisher engineers listened to the end-users and made ease-of-use a priority second only to setting a new standard of performance and sensitivity.
Due to the space limitations of this print-version of the report, I will not go into great detail on each of the F-75’s features, but more detail is available in the report on-line at Lost Treasure’s website (
www.losttreasure.com).
The F-75 operates at 13 kHz which was selected based on the combination of detection depth, target ID accuracy, and sensitivity to the type of targets today’s treasure hunter typically searches for. There are three separate search modes combined with an all-metal, non-motion pinpoint circuit which provides users with an option to handle virtually any application or condition. The search modes are Static All-Metal, Motion All-Metal and Motion Discrimination. Each of these search modes offer different functions which can be adjusted using the push-button and knob on the face of the control housing. In the Discrimination mode, the options include Sensitivity, Discrimination & Notch Levels, Tones (type of audio response produced for specific targets), and Processes (how the F-75 processes target signals and produces audio signals). In the All-Metal modes, the options include Threshold, Audio Pitch, Sensitivity, and Manual Ground Balance. To make an adjustment to any of these options, simply press the MENU pushbutton until the option you want to adjust is highlighted and use the knob to make the desired change. A nice feature of the F-75’s menuing system is that it will remember the last option you adjusted, so if you are trying to “fine-tune” one, when you press the MENU pushbutton, it will immediately go back to the option you had been adjusting, rather than starting at the top of the menu screen.
The toggle switch serves a dual function. When pulled back, it switches the detector into a non-motion, all-metal pinpoint mode and changes the display to indicate target depth in inches. Pushing the toggle switch forwards activates the automatic ground balance circuit, which is described below.
Proper ground balance is essential on any detector in order to achieve maximum detection depth and target ID accuracy; however, on many detectors, finding the proper setting can be somewhat of a challenge and many detectorists tend to avoid machines that offer manual ground balancing for that reason. The F-75 offers two methods of ground balancing – fully automatic (called FASTGRAB) and, if needed, a full-range manual mode. Another key aspect of the F-75 is that the ground balance adjustments apply to both All-Metal and the Discriminate search modes, so maximum performance is obtained in virtually any ground and in any search mode. To use the FASTGRAB option, simply push the toggle forward and pump the coil up and down a few times until a consistent value is displayed on the screen. When the circuitry has selected a ground-balance setting, the numeric value displayed on the LCD screen will provide information on the type of ground mineralization present. The on-line report contains some tips on how this can be used to survey a site. In severe ground, such as black sand beaches or alkali ground, manual ground balancing may be required, but even that process is easier than on many other detectors.
The LCD screen provides a wealth of information. In the center is a large numerical value that corresponds to either the target’s ID - ranging from “0” (iron) to “100” (silver) when in one of the three search modes, or depth when the Pinpoint mode has been selected. Along the top of the screen are segments that provide the probable ID of detected targets and they will correspond to the target ID values displayed on the screen. A point worth noting is that Target ID information is provided in all three search modes which greatly enhances the ability of relic hunters and prospectors to pull “keepers” from areas that might otherwise be too frustrating to hunt with a straight all-metal detector. A 3-segment depth indicator is located on the far left side of the screen and, while not as accurate as the depth reading in Pinpoint, it does provide a relative indication of target depth when in one of the search modes. Another unique feature of the F-75 is the Target Confidence Indicator, which lets you know how sure the detector is of the target’s ID which can help increase the number of good targets you recover.
The F-75 also displays a relative value of magnetite or magnetic mineralization present which can adversely affect target ID accuracy. Having this piece of information allows you to better interpret what the F-75 is telling you as ground conditions change. A final comment on the display screen is that it is backlit using an always-on low-drain LED, so the F-75 can be used in low or no-light conditions – a real plus for hunting beaches or similar sites when the temperatures drop or the crowds have left.
Target ID is provided through both audio and visual indications. In the Discrimination mode, there are eight different options available that determine the audio response of the F-75 to various targets, as well as four “processes” that further define how the F-75 responds to specific objects based on their content or surrounding ground conditions. This flexibility allows the F-75 to be adjusted to fit your personal preferences as well as different conditions you might come across in the field, such as certain types of trash you wish to eliminate or particular targets you wish to pick out from dozens of others.
Two other features worth mentioning are the frequency shifter and Notch Discrimination. If electrical interference from power lines or other detectors causes erratic operation, one of seven slightly different frequencies can be selected through the use of the trigger and Menu touchpad. The F-75’s Notch Discrimination circuit is useful when you want to reject a specific type of target when running at a low discrimination level, or if you want to accept a specific type target when running at a high-level of discrimination. Both of these options are well covered in the manual and simply expand on the F-75’s versatility under a wide range of conditions and applications.
The F-75’s search coil is an 11”x7” Double-D which, surprisingly, is an excellent all-purpose coil. Being a Double-D, it covers a full 11” swath with each sweep, yet is sensitive enough to detect even tiny targets such as gold nuggets, small relics or jewelry at impressive depths.
The F-75 is powered by only four AA batteries in the battery compartment beneath the arm cuff and, considering the performance and features it offers, its battery life is quite surprising – 35 hours on alkalines! Battery strength is always displayed on the LCD screen. A ½” stereo headphone jack is conveniently located at the rear of the armrest.
Field Test
With higher-end detectors, I tend not to take time when conducting a field test to search areas where the majority of targets are recently lost, as it does not provide a true test of the detector’s capabilities. If possible, I try to search sites that have been well hunted, where targets are known to be deep, or where concentrations of trash give any detector a real workout.
The first site was one that dated back to the Revolutionary War and has been hunted by many detectorists for the past 30 years. Opting to use the motion All-Metal search mode for maximum detection depth, and to avoid any possible target masking that can occur when using higher discrimination levels, I quickly switched to the All-Metal mode and ground balanced the F-75 using the FASTGRAB circuit. Targets were more plentiful than I had expected based on the number of hunters that had preceded me, and I spent a good deal of my time at the site on my knees digging, which is always a good sign. Virtually every target was 6” or deeper, and even those that approached double-digits in depth produced clear signals (although the target ID accuracy and confidence did drop-off as one would expect). One V-nickel, two Indian Head cents, several smaller brass artifacts and a bridle bit were uncovered from just a small portion of this multi-acre site.
The next site was a field that had seen church picnics and other activities for more than 100 years. As the ground in the open areas was fairly dry from lack of rain, I focused on the portion covered by trees. Selecting the Discrimination mode, I started with the it set at preset (10), which left the circuit in the non- high gain mode. Based on the potential of finding an Indian Head, I selected the 4H Tone option. Bumping the Sensitivity up to “75” and ground balancing the F-75 using the FASTGRAB circuit, I started searching.
The first few signals were clearly trash, based on the erratic target ID values and the low confidence factor displayed and turned out to be just that. Approaching a large tree, a solid “72” appeared, accompanied by a consistent audio response and four bars on the Confidence scale. The Medium depth bar was illuminated and this was confirmed when 7” was displayed in the Pinpoint mode. Removing a deep plug, I saw the unmistakable glint of silver in the bottom of the plug...a 1906 Barber dime that had been at a 45-degree angle at close to 7” came to light! Over the next two hours I recovered 19 more coins from similar depths that included five Wheat cents, two Mercury dimes and a silver quarter that lost a battle with a lawnmower years ago (and was now a half-quarter). In one section, older rusted bottle caps caused some frustration; however, switching to the BC or bottle cap process mode, which makes the F-75 produce an audio signal that distinguishes bottle caps from targets that register in the same area, quickly solved that problem and allowed me to pull a few “keepers” from an area I would otherwise have given up on. Additional field test results are available in the on-line version of this report.
Summary
The F-75 most assuredly sets a new standard in terms of performance, versatility and ease of use that will stand for some time. Despite the wide range of adjustments possible, the F-75 is quite simple to set-up and can handle virtually any application and environment it might be used in. Despite only being available for a few months, a number of impressive finds have been reported from users worldwide. There are a few “quirks” with the F-75 that require some tweaking that is not really covered in the current manual, such as deactivating the high-gain circuit to reduce electrical interference, and using positive ground balance to reduce ground “chatter.” However, your local dealer can explain those techniques to you first-hand and, hopefully, this information will be incorporated into future revisions of the manual.
The F-75 lists for $1,095 and comes with a 5-year warranty. Factory options include control housing and battery compartment weather covers, a coil cover and a hand-held pinpointer probe. For more information about the F-75, the company behind the detector, or to find a local dealer, contact the factory at (915) 225-0333 or visit their website at
http://www.FisherLab.com, and be sure to mention you read about the new F-75 in Lost Treasure Magazine!
