Fisher Gold Bug Pro
By Chris Gholson
From Page 23
February, 2011 issue of Lost Treasure

Field Testing the Fisher Gold Bug Pro While Alexander Graham Bell may have been the first to experiment with metal detection devices, it is usually Dr. Gerhard R. Fisher that is credited as being the father of the metal detector. During the 1920’s, Dr. Fisher was working as a research engineer in Los Angeles, California. His work and recent patent on aircraft radio detection finders attracted not only the attention of other scientists, like Dr. Albert Einstein, but the military as well.In the 1930’s, he was hired by the U.S. Navy to install a radio detection finder aboard one of their dirigibles, the USS Macon. He continued his research and eventually concluded that a portable electronic instrument could be developed using the same principle to detect small, buried objects.In 1931, he founded Fisher Research Laboratory in a garage behind his home in Palo Alto, California. With the help of four employees, he began producing the very first patented metal detector; the "Metallascope." In comparison to today’s modern metal detectors the M-Scope was a monstrous device consisting of two large, flat wooden boxes containing simple copper coils, five vacuum tubes and a few assorted components. Despite its less than user-friendly size, the M-Scope soon became the accepted standard in metal detection equipment across the world.Over the years, the number of detectors Fisher produced began to grow and so did the size of their factory. In 1987, they set the gold industry abuzz with the release of their now legendary Gold Bug. The 19.17 kHz “Bug” gained tremendous popularity among nugget hunters and quickly dominated the goldfields.Several years later, the Bug was once again modified and released as the Gold Bug II. This version operated at 71 kHz and was openly embraced by the prospecting community as well. It continued to be Fisher's most popular gold machine and remained unchanged until 2010 when the Bug got its biggest facelift ever.Some of the changes include the addition of a 3" x 2" display, a reduction in the size of the control box, improved ground balancing system, touchpad controls, a 5" round DD water-proof search coil, and a unique discrimination system. This newest version has been dubbed the Gold Bug Pro.Although the "Pro" can be used for coin and relic detecting, the sole focus of my field test report was to determine its ability to find gold nuggets. The testing was conducted in central Arizonaover the course of several days. Numerous sites were visited, all of which contained varying levels of ground mineralization and hot rocks. While I must admit that no large nuggets were found, I did unearth several nice pieces and the overall results were impressive.As far as the number of controls goes, Fisher has kept them to a minimum. On the main control panel there are just two knobs and three touchpad controls. The POWER knob is used to turn the unit both On/Off and to adjust the level of Gain. The MODE knob is used to both adjust the level of Threshold and to either activate the All Metal or DISC modes. The center touchpad control labeled GG is used to adjust the detector's ground balance, and also to activate Pinpoint. The two touchpad buttons below are labeled with a plus and minus sign. These controls are used to manually adjust the ground balance, and to increase or decrease the discrimination level. The display itself also provides a variety of data about a target's identity and ground conditions.The POWER knob is an important control because it sets the level of Gain. All detectorists want to run their Gain as high as possible, simply because it increases both sensitivity and depth penetration. Unfortunately, in many areas this is not always possible due to high levels of ground mineralization and electromagnetic interference (EMI). In these places an elevated Gain will cause the detector to become unstable, background noise will be amplified, and overall performance will suffer.A higher Gain is always more desirable, but not if Threshold stability is sacrificed. Therefore, the operator must choose an appropriate level based on the ground conditions and amount of interference present. I would recommend starting in the 12 o'clockposition first. Then, if the Threshold is stable, slowly increase the Gain. When the Threshold begins to "chatter," slowly back it off it until it settles down. The Threshold, which is controlled by the MODE knob, adjusts the continuous background hum heard while the detector is on. The purpose of the Threshold is to provide your ears with a steady reference point making it easier to identify weak responses, which are often small or deeply buried targets. The level of Threshold a person chooses is largely personal preference. For myself, I chose to run it between 8-10. There is no Threshold when operating in discrimination mode. The discrimination system found on the Pro is surprisingly good for a machine priced well below $1,000. It allows the operator to weed out certain types of targets by either "blanking" the signal completely, or by giving off different audio tones. Adjustments to the discrimination level are done via the plus and minus touchpad controls. The range of discrimination is from 0-80. At higher DISC numbers the Pro becomes more selective on which targets it allows to be heard. Lower numbers are more forgiving and a greater number of targets will be found.When a target is detected an audio signal will be generated. Low pitch signals typically represent ferrous objects, while high pitch signals typically represent non-ferrous objects. The Pro also provides a 2-digit Target ID number in the center of the display, and three segments will simultaneously appear above the arc at the top of the screen.For example, if the coil passes over a non-ferrous target (like a lead bullet), a high pitch tone will be heard, a Target ID of 52 will appear in the screen, and three segments will illuminate between the 50 and 60 on the arc. If the coil passes over a ferrous target (like a rusty nail), a low pitch tone will be heard, a Target ID of 22 will appear in the screen, and three segments will illuminate between the 20 and 30 on the arc. Although the Target ID numbers can vary slightly with each sweep of the coil, the system is fairly reliable and provides the operator with both audio and visual data.    I will be the first to say that discrimination has real value, especially when hunting coins in a trashy local park. However, when looking for gold I have always preferred to hunt in the All Metal mode. This means that all metallic objects will be heard, but it ensures that the machine is operating at peak sensitivity and no targets will be missed. I did, however, find the discrimination mode extremely useful for double-checking the identity of suspicious targets.If I came upon a target that I was unsure about, I would simply turn the MODE knob fully counter-clockwise and set the DISC number around 41. No discrimination system on any metal detector is 100% accurate, but, after much testing, I found the Pro's discriminator to be right more often than wrong.If a person opts to run in the DISC mode, I would recommend running the lowest level of discrimination that a particular area will allow. This will help prevent very small, or deep, nuggets from being overlooked. If the site is very trashy, better results may be obtained by running the DISC at 41 or higher.In order to combat naturally occurring minerals in the soil, the Pro has a new feature called Ground Grab. It is simple to use and takes the guesswork out of ground balancing. The procedure is accomplished by pressing down the GG touchpad while pumping the search coil over the ground. When very little change is heard in the Threshold while moving the coil towards and away from the ground, the detector is said to be ground balanced. The Ground Balance Number (GND BAL) will appear in the bottom right of the display.I should also mention that the Pro can be ground balanced manually using the plus and minus touchpad controls. The process is nearly identical except that the plus or minus touchpads are pressed while raising and lowering the coil. These two controls can also be used to fine-tune the balance after using the Ground Grab.Soil conditions will change as you move around in the field, so it is important to monitor the ground balance. This can be done by periodically raising and lowering the coil over the soil. If a large variation is heard in the Threshold, the process above will need to be repeated. The operator can also watch the GND PHASE value in the middle of the display. This number represents the Ground Phase and is an indication of the type of minerals in the soil. If the GND BALand GND PHASE numbers differ by a great deal, it would be a good idea to re-ground balance.The Ground Grab feature does not work while in DISC mode, therefore the operator must first ground balance in the All Metal mode, then switch into DISC. If the GG touchpad is pressed while in DISC mode it will activate the pinpoint function.   I tested the Pro on two different nugget patches and found gold at both. The first area (Site #1) was a dry wash where I had detected nuggets in the past. It had a substantial amount of exposed bedrock showing along its length and seemed the ideal place to test out the Pro's sensitivity. The ground conditions at Site #1 proved more problematic than Site #2. The desert wash was full of black sand and lots of heavy, dark colored hot rocks. The bedrock was easy enough to balance out, but, as soon as I swung over where the sand and gravel had accumulated, I needed to readjust the balance. This really wasn't that much of a surprise, as this wash had been difficult to work with previous machines as well.My solution was to reduce Gain closer to 10 o'clockand elevate the coil slightly above the ground. I knew I was losing some depth and sensitivity, but it was better than listening to the constant moans and groans of the ground mineralization. After a short time I had also memorized the distinctive "boing" sound of the hot rocks and was able to quickly deal with them. This usually entailed kicking them aside with my boot or simply tossing them off into the bushes.Site #1 produced quite a collection of targets for me, both ferrous and non-ferrous. My finds included tacks, lead bullets, BB's, rusty scrap, nails, bits of wire, and several spent shotgun shells. The best targets came from deep within the bedrock cracks. These were the yellow targets I was hoping to find.The first nugget of the day was a real shock. I had expected another piece of lead or a BB; instead I spotted the distinctive glint of gold between two folds in the bedrock. It was only a small half-grammer, but it set the pace for what was to be an exciting day. By late afternoon, Site #1 had yielded approximately 30 targets, six of which were gold.The supplied 5" round DD coil worked splendidly on the exposed bedrock. Its small size allowed me to negotiate the bedrock cracks, in between boulders, and amongst thick brush. The sensitivity was impressive, and I soon learned that it had no trouble locating nuggets as small as 1/10th of a gram. Of course, when running a smaller coil there is a loss of depth penetration and ground coverage. Fortunately, Fisher also offers an optional 11" waterproof DD. This coil provides enhanced depth and coverage without a substantial increase in weight. At less than one pound, it can be swung for hours on end with very little fatigue.The standard 5" DD is best suited for working shallow ground, exposed bedrock, and around old mine dumps. If more depth penetration is needed, or a large area must be covered quickly, the 11" DD would be a much wiser choice.The ground was deeper at Site #2, so I opted to use the 11" DD. I only recovered one nugget from this location, but it proved to be the largest piece found during the field test. While wading through some very nasty Manzanita brush, I came upon a little clearing that was covered in quartz float and tiny black rocks. It looked good and was one of the few places on the hillside that wasn't covered in brush, so I hunted it thoroughly.I received one signal in the clearing, which I initially thought was a hot rock. When I kicked it out of the way and the signal remained I became more optimistic. By the time I hit the five-inch mark, the signal was really screaming at me. I scooped the dirt from the hole and quickly pinpointed it in the pile. I felt a tiny surge of adrenaline rush through me when I spotted a shiny 3-grammer in my hand!What I enjoyed most about the Pro was its ease of use. If the goal of the techs at Fisher was to create a user-friendly detector, then they definitely succeeded. It is one of the simpler machines on the market to run. I would imagine that even if a person had zero detecting experience, it would only take them a matter of hours to get a handle on the Pro.Operating at 19 kHz, the Pro is not quite as sensitive as the Gold Bug II, however, I was okay with this shift back towards a lower frequency. I found it to handle the ground mineralization and hot rocks better, and it would not pick up my hand. This may seem a strange thing to mention, but it is important for folks like myself that pinpoint targets using their hands. The Gold Bug II would often "false" when I waved my hand over the coil - not so with the Pro. Even though it is operating at a lower frequency, it is entirely capable of "sniffing" out the tiniest of nuggets.  If I could make any changes to the Pro it would be the following. I would ask for an adjustable Threshold while in DISC mode. Silent search is okay for working trashy sites, or when seeking out shallow targets, but when it comes to finding really deep gold, a slight variation in the Threshold is all that will sometimes be heard. Without that constant background hum, I find it much more difficult to pick out those faint whispers that often indicate a large nugget at depth.It would also be nice if the Ground Grab feature worked while in DISC mode. This would save a person from having to flip back into All Metal, ground balance, and then back into DISC. Other than this, I had no major complaints.In closing, I will say that the Pro has not disappointed me, actually quite the opposite. It's incredibly lightweight, easy to use, and super sensitive to the tiny bits. I was really glad to see the engineers didn't simply move around the controls, add some fancy graphics and push it as a new model. The detector is completely redesigned with computerized controls, new ground balance system, LCD screen, and a sweet little 5" DD coil that is perfect for chasing bedrock.It comes with a 5-Year Warranty, and what makes it even more appealing is the price tag. With an MSRP of only $699, this is one of the most affordable gold machines around. If you happen to be in the market for a new detector, the Pro is definitely worth considering.  If you would like to learn more about the Gold Bug Pro, visit the manufacturer's website at, or call 800-685-5050. For additional information on metal detecting for gold, visit the author's website at

Small nuggets detected using the new 5" waterproof DD coil.
A closer look at the Gold Bug Pro's main control panel.
A lovely 3-gram Arizona nugget found during the field test.
A full view of the Fisher Gold Bug Pro, shown with optional 11" DD search coil.

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