How Do Metal Detectors Work?

Published by Jenna Anderson on 06/24/16

You can find coins, rings, jewelry, gold, relics, small buried caches and even deep treasures without knowing scientifically how a metal detector works. But to give you a better understanding, we created a video and simple illustrations to answer the question: How do metal detectors work.

How Do Metal Detectors Work: A Simple Explanation

Illustration ‘A’ shows a typical metal detector user. He has followed the instructions supplied by the manufacturer and has his metal detector turned on. After testing his detector on some surface targets (coins) to make sure it is working, he now starts searching for buried coins and treasures.

How Do Metal Detectors Work: A Simple Explanation

How Do Metal Detectors Work: A Simple Explanation

Notice the “red” signal pattern being transmitted from the metal detector coil into the ground. (Note: we have enlarged the illustration of the signal pattern for easier understanding). As long as the signal entering the ground does NOT come in contact with metal, there will be no audio signal, no flashing light, no vibration, nothing will happen.

Illustration ‘B’ shows what happens when the detector user’s metal detector search pattern comes in contact with metal objects, in this case both shallow and deep coins. When the search pattern touches metal it interrupts the transmitted signal and this interruption or disturbance of the search pattern will cause the metal detector to alert the detector user (you) with an audio signal, usually a distinct loud sound. In some cases flashing or blinking lights will accompany the audio signal.

Simple, isn’t it?

Kellyco Metal Detector Experts Have The Answers to Your Questions

Detector's Experts

Detector’s Experts

How Deep Will My Metal Detector Go?

What Treasures Could My Detector Find?

Can my Detector Work on Salt Water Beaches?

Can I Eliminate Junk Targets?

Are Different Size Metal Detector Coils Necessary?

If you want the answers to any of these questions,

Call Toll FREE 1-888-KELLYCO for an easy to understand answer from one of our Metal Detector Experts.

How Do Metal Detectors Work: More Complete Explanation

How Metal Detectors Work Reprinted with permission from Modern Metal Detectors

It is not necessary to understand the scientific principles of metal detection to use a detector. You can find gold nuggets, coins, rings, jewelry, caches or whatever you are searching for without knowing how a detector works. For better comprehension of what your detector is doing, however…to recognize why it just made that peculiar sound…to understand why it reacts the way it does to metals and minerals…it is necessary to learn how metal detectors work. Two examples illustrate this need. First, let’s say you are scanning in the field and get a detector signal. You dig down a foot and find nothing. You enlarge the hole and dig another foot and still don’t find anything. You might keep on digging to five or six feet before finally giving up. Yet, your signal persisted throughout all this digging! What went wrong? Was it your fault, or that of your detector? Was a target there? Well, yes there was a target though it may not necessarily have been a metal one. The response could have been due to some variation in mineral content.

For the second example, let’s say you are researching for a small kettle made of iron that is filled with gold coins. You know this iron kettle was left somewhere in a particular field under a large flat rock that had been placed on top of it. Unfortunately, however, there are at least one thousand large, heavy flat rocks lying in that field. The ground itself is highly mineralized and some of the large rocks themselves also contain a great amount of iron mineralization In these situations, knowing how your detector works, plus having an understanding of the various detectable minerals, will save you a great deal of effort. In the first instance, you will not dig at all, or perhaps no deeper than one foot, before you realize there is no metallic target in the ground. Unless you know something about iron minerals and their effect on metal detections, you will likely never find that iron kettle unless you decide to dig beneath every rock in that field. The “answers” to both these situations are presented elsewhere in this book.

Modern and All Purpose Metal Detectors, seek to present theory explanations that are simple with only very basic detector operating characteristics described.

All Purpose Metal Detector

All Purpose Metal Detector

This book was intended not to be a theoretical work but a home, field and classroom textbook to help metal detector users understand basic principles of their equipment. These principles are not difficult to understand. When you begin studying mineralization, target identification, field applications and other subjects, you will be rewarded by your study of this background material. You will understand what your detector is telling you…why you hear certain signals. You will become better able to determine if the object you have detected is one that you want to dig. Proper and highly efficient operation of a metal detector is not difficult. It does, however, require a certain amount of study, thought and field application.

Radio Transmission and Reception

You have operated one-half of a metal detector during most of your lifetime, perhaps without knowing it: the common radio. Metal Detection is achieved, basically, by the transmission and “reception” of a radio wave signal. The block diagram on the facing page illustrates the basic components of a typical metal detector. The battery is the power supply. The transmitter electronic oscillator at the extreme left of the diagram generates a signal. The transmitter signal current travels from the transmitter oscillator through a wire (cable of the metal detector coil), to the metal detector coil transmitter winding (antenna), and the transmitter antenna is a few turns of electrical wire, generally wound in a circular fashion.

As the current circulates in the transmitter antenna, an invisible electromagnetic field is generated that flows out into the air (or other surrounding medium, i.e.: air, wood, rock, earth materials, water, etc.) in all directions. If this electromagnetic field were visible, it would appear to be in the shape of a gigantic, three dimensional doughnut, with the transmitter antenna embedded in its center. Electromagnetic field theory states that field lines cannot cross one another. Consequently, they crowd together as they pass through the circular antenna, but they are not crowded on the outside. It is fortunate this crowding takes place, because the intensity (density) of the field lines is the very phenomenon that enables metal detection in the area adjacent to the metal detector coil to take place. In the drawing at the bottom of the next page note the area indicated as the two dimensional detection patterns. This is the site of maximum field crowding; it is here that metal detection occurs as a result of two major phenomena…eddy current generation and electromagnetic field distortion. (Note theMirror-image detection pattern above the metal detector coil.)

This electronic block diagram of a transmitter-receiver metal detector illustrates the basic components of a metal detector as they are pointed out in the description at left.

Eddy Currents Secondary Electromagnetic Field Generation

Whenever metal comes within the detection pattern, electromagnetic field lines penetrate the metal’s surface. Tiny circulating currents called “eddy currents” are caused to flow on the metal surface as illustrated in the figure on the facing page. The power or motivating force that causes eddy currents to flow comes from the electromagnetic field itself. Resulting power loss by this field (the power used up in generating the eddy currents) is sensed by the detector’s circuits. Also, eddy currents generate a secondary electromagnetic field that, in some cases, flows out into the surrounding medium. The portion of the secondary field that intersects the receiver winding, causes a detection signal to occur in that winding. Thus, the detector alerts the operator that metal has been detected.

As the transmitter current from the antenna generates the electromagnetic field, detection pattern (dotted lines) is the area within which metal detection occurs. Mirror-image pattern atop coil is not used.

Electromagnetic Field Distortion

Electromagnetic Field

Electromagnetic Field

The detection of non-conductive iron (ferrous) minerals takes place in a different manner. When iron mineral comes near and within the detection pattern, the electromagnetic field lines are redistributed, as shown in the figure on the following page. This redistribution upsets the “balance” of the transmitter and receiver windings in the metal detector coil, resulting in power being induced into the receiver winding. When this induced power is sensed by the detector circuits, the detector alerts its operator to the presence of the iron mineral. Iron mineral detection is a major problem for both manufacturers and users of metal detectors. Of course, the detector of iron mineral is welcomed by a gold hunter who is looking for black magnetic sand which can often signal the presence of placer metal. On the other hand, the treasure hunter, who is looking for coins & jewelry, relics, gold nuggets, etc., usually finds iron mineral detection a nuisance.

When any metal comes within the detection pattern of a metal detector coil, eddy currents flow over its surface, resulting in a loss of power in the electromagnetic field, which the detector’s circuits can sense.

When a target comes within the detection pattern, the metal detector coils windings become imbalanced at Point A and B, and electromagnetic field lines are redistributed as shown in this drawing.

Search Matrix

Any substance penetrated by the electromagnetic field is “illuminated.” Many elements and different combinations of minerals are within the soil, including moisture, iron and other minerals, some detectable and some not. Of course, it is hoped that the targets being sought are also present. A detector’s response at any given moment is caused by conductive metals and minerals and ferrous non-conductive minerals illuminated by its electromagnetic field as shown in the drawing below. One detector design criterion requires the elimination of responses from undesirable elements, permitting signals only from desirable objects. How this discrimination is accomplished depends on the type of detector.

This typical matrix beneath a metal detector coil illustrates how the electromagnetic field generated by the antenna in that metal detector coil illuminates every metal target in the area it reaches.

Electromagnetic Field Coupling

“Coupling” describes the penetration of the electromagnetic field into any object near the transmitter antenna. There is perfect coupling into some objects such as wood, fresh water, air, glass, and certain non-mineralized earth materials as shown in the drawing below. Coupling is inhibited, however, when the electromagnetic field attempts to penetrate iron mineralization, wetted salt, and other substances. This inhibiting of the electromagnetic field, as shown in the drawing on the facing page decreases the detection capability of the metal detector. Even though modern instruments can eliminate the effects of iron minerals, the electromagnetic field is still inhibited (distorted), which results in reduced detection capability and performance.

Salt Water and Beach Metal Detecting

Saltwater (wetted salt) has a disturbing effect upon the electromagnetic field because salt water is electrically conductive. In effect, salty ocean water “looks like” metal to some detectors! Fortunately, manufacturers are able to design detectors capable of “ignoring” saltwater.

Saltwater And Beach Metal Detecting

Saltwater And Beach Metal Detecting

This diagram of “perfect coupling” illustrates the general shape of a detection pattern that occurs when the electromagnetic field from a metal detector coil penetrates the earth or any other nearby object.

For tips on beach metal detecting, read this guide.

Depth of Detection

Numerous factors determine how deeply an object can be detected. The electromagnetic field generated by the metal detector coil transmitter antenna, flows out into the surrounding matrix, generating eddy currents on the surface of conductive substances. Any detectable target that sufficiently disturbs the field, is detected. Three factors determine whether the disturbance is sufficient for detection: electromagnetic field strength, target size and surface area.

Electromagnetic Field Strength

How far does the electromagnetic field that flows out into the surrounding matrix extend? Theoretically to infinity…but you can be certain it is extremely weak when it gets there! In fact, only a few feet away from the metal detector coil, the field is greatly reduced in strength. Several factors, including attenuation (absorption by the earth, matrix, materials, etc) and distance, reduce the field strength. When all things are considered, a detector may have several thousand times less detection capability at six feet then it does at one foot, so you can understand why detectors are limited in their depth detection capability.

Detection depth capability is inhibited in some elements such as iron mineralization and wetted salt where coupling is inhibited when the electromagnetic field attempts penetration.

Target Size

Targets can be detected better and more deeply simply because of their size. Larger targets are easier to detect because they produce more eddy currents. One object with twice the surface area of another, will produce a detection signal twice that of the smaller object but it will not necessarily be detected twice as far. By the same reasoning, the larger target will produce the same amplitude detection signal at a distance farther away from the bottom of the metal detector coil than the smaller target. Size is also an important factor in target discrimination, a metal detector characteristic discussed elsewhere in this book.

Any detected object has its own pattern, as shown above, with the detection pattern for the jar of coins being wider at the top and extending farther away from the metal detector coil’s bottom.

Surface Area Detection

Surface Area Detection

Surface Area Detection

Metal Detectors are, for the most part, surface area detectors. They are not metallic volume (mass) detectors. The larger the surface area of a metal target that is “looking at” the bottom of the metal detector coil, the better that target will be detected. The actual volume or mass of the target has very little to do with the most forms of detection. Prove this for yourself. Turn your detector on and tune it to threshold. With your hand, bring a large coin in towards the metal detector coil with the face of the coin “looking at” the bottom of the metal detector coil. Make a note of the distance at which the coin is first detected…say, eight inches.

Now, move the coin back and rotate it ninety degrees so that the edge of the coin “looks at” the bottom of the metal detector coil. When you bring the coin in toward the metal detector coil, you will see that the coin cannot be detected at eight inches. In fact, it probably will be detected only at a distance of four inches or less. Another proof of surface area detection is to measure at what distance a single coin can be detected. Then stack several coins on the backside of the test coin and check to see how far this stack of coins can be detected. You’ll find that the stack can be detected at only a slightly greater distance, illustrating that the increasing the volume of metal had very little effect on detection distance.

Fringe Area Detection

Fringe area detection is a phenomenon of detection, the understanding of which will result in your being able to discover metal targets to the maximum depth capability of any instrument. The detection pattern for a coin may extend, say, one foot below the metal detector coil. The detection pattern for a small jar of coins may extend, perhaps, two feet below the metal detector coil as illustrated in the drawing on the facing page. Within the area of the detection pattern, an unmistakable detector signal is produced.

This illustration shows the location and approximate proportional size of the fringe detection area in which faint target signals from around the outer edges of a normal detection pattern can be heard.

What about outside the detection pattern? Does detection take place? Yes, but the signals are too weak to be discerned by the operator except in the fringe area around the outer edges of the detection pattern as shown in the drawing above. A good set of headphones is a must, if you desire to hear fringe area signals. The next more important thing is training in the art of discerning the faint whispers of sound that occur in the fringe area. Skill in fringe area detection can be developed with practice, training, concentration and faith in your ability. Develop fringe area detection ability to a fine art and you are on your way to some great discoveries that many detector operators will miss. The ability to hear fringe area signals results in greatly improved metal detection efficiency and success.

You may be a metal detecting enthusiast, even an experienced detectorist, and yet you don’t know exactly how your detector works. Well, it isn’t magic! There is real science in how they work, and it’s information that may be helpful to you in your hunting. This post will explain, in general, how these machine work in simple terms. Of course, if you have a high-end or very specialized detector, there are much more detailed and intricate processes involved. The technology that is involved in metal detectors today can be very sophisticated and complicated, but the goal here is just to familiarize you with the basics of how metal detectors function.

Parts of a Metal Detector

Parts Of A Metal Detector

Parts Of A Metal Detector

In order to understand how metal detectors work, you first need to know what their key components are. Even though detectors look different, the way they work is typically the same, so they all have parts that function similarly.

The four key components are:

  • Shaft – This is the main part of the detector that all of the other parts connect to. It’s usually adjustable for the user’s comfort.
  • Stabilizer – This attachment is the part of the detector that makes it comfortable to use. Think of it as the armrest of the machine. It stabilizes the metal detector as you move it around.
  • Control Box – The control box is the brains of the machine. It contains the battery, device controls and settings, the microprocessor, readout, and speakers.
  • Search Coil – This is the bottom part of the detector that you swing over the ground. It’s an antenna that contains coils that are integral for the machine to be able to detect metal.

How Metal Detectors Work

While detectors can be complicated, the principle behind their function is fairly simple. Metal detectors transmit and then analyze a magnetic field as it is returned from the area that the signal was originally transmitted into (the ground).

There are two coils in the search head of the metal detector. One acts as a transmitter, and the other acts as a receiver. The first one transmits a magnetic field that is generated by electricity that moves through the coil. That magnetic field that is being transmitted will cause electricity to flow into metal objects that it comes into contact with. The second coil, the receiver, identifies the difference in the magnetic field that is created as the buried metal absorbs it and the electricity begins to flow through it.

When the change is detected, the second coil send the alert to the control box through the attached cable, and you hear the signal from the speakers or your headphones. The weaker the returning magnetic field, the weaker the alert.

That’s it in a nutshell. One coil sends, the other receives, detects changes and lets the control box know.

Final Thoughts

Now you understand the basics of how a metal detector works, and knowledge is essential to being successful with your detecting. Even the best equipment in the world will not do you much good if you don’t know how to use it. For a more detailed explanation of how metal detectors work, go here.

Best Metal Detector Information For New Owners

(How To Successfully Test Your Metal Detector)

The UPS truck had not even left the driveway before Jim was tearing open the shipping box containing his brand new metal detector. After watching episode upon episode of the many treasure-hunting reality shows as well as spending hours surfing the myriad of Internet sites that cater to today’s treasure hunters, Jim had convinced his wife that he needed a new hobby and a new metal detector was ordered. He was like a little kid at Christmas and just knew that the areas around his house contained all sorts of treasure just waiting for him to come by and recover it. He was glad that the detector came with batteries as that meant he could get out and start detecting for gold and coins and jewelry as soon as he pulled on his jacket. Waving to his wife, Jim grabbed his detector, jumped in his truck and drove over to the nearby park to begin what he knew would be an exciting and profitable hobby.

Turning it on, he started searching near the picnic tables figuring that would be an area loaded with coins but was confused by all of the beeps-&-chirps that his detector was producing.

Treasure Hunting

Treasure Hunting

The display was jumping from one end of the scale to the other as he swept the coil across the ground and Jim was not sure what it was trying to tell him lay beneath the surface of the ground. Thinking the area was cause, he moved to the grass surrounding the basketball courts and had the same experience. After more than an hour, Jim gave up in frustration and headed back to the truck… the only coin he had to show for his efforts was one he saw laying on the pavement in the parking lot just before he reached the truck! Totally dejected, Jim wondered how he was going to break the news to his wife that treasure hunting was a bust and he would be looking for some other hobby to fill his time.

I hate to say it but Jim’s initial experience is not unique and there have been many people that became interested in the hobby, bought equipment and just as quickly became disillusioned and sold what they had just acquired at a loss based on their initial experiences. Does anyone want to take a guess as to why Jim became so discouraged on his first trip into the field? If you said it was his lack of understanding of what the detector was telling him as he searched the park, you are 100% correct. All too often, people unpack their new equipment and head out in search of instant success only to find that frustration is about all that usually turns up. And before you think that this is limited to complete novices, it happens to those with years of experience under their belt almost as frequently. Treasure hunters that have been hunting for some time with a particular model and opt to switch brands based on new features or wanting to try searching for a different type of treasure can find themselves just as frustrated on their first few times out without the proper preparation.

Over the years I have often quoted Greg, a good friend and seasoned treasure hunter, on this subject. He frequently conducts training sessions for beginners and sums up the need to learn your detector this way. “How can you hope to be successful when you start detecting without knowing how to set your detector or what type of response to expect from the types of targets you are looking for or hoping to avoid? Going out searching for unknown targets with a detector you do not fully understand is a guaranteed recipe for frustration and failure. There are simply too many variables for you to be successful!” This is excellent advice for any brand of detector and for any type of treasure hunting you might be interested in trying your hand at.

Well where is this guide taking us? Well let’s start with what Jim did once his new metal detector arrived. He unpacked it and since they tend to go together only one way, he quickly assembled it and headed out the door leaving what might have been the most important item laying in the bottom of the box… the instruction manual. I know many of us subscribe to the philosophy of “When all else fails read the manual”; however, when it comes to equipment like metal detectors, that can often be the difference between success and frustration.

Proper Preparation

Proper Preparation

Even if you have experience with metal detectors, different manufacturers tend to use different terminology to describe features. Some models may have unique controls that if not adjusted properly, will produce erratic operation and as a result, frustration. All of this combines to leave one with the nagging question as to the soundness of the decision to purchase a particular piece of equipment. I can’t tell you how many times I have received a new detector and thought I knew everything there was to know about it only to find that the performance failed to meet my expectations… and then after looking through the manual and / or talking to someone that knew the unit, found that a slight adjustment made it perform at an entirely different level.

Place an Order with one of Kellyco’s Certified Metal Detector Experts!

OK, you’ve done your homework and narrowed down your choices for a new detector – what’s next? Place an order and hope for the best?Actually, unless you are basing your selection on input from a fellow treasure hunter in your area that is searching for the same types of targets you will be looking for (coins, relics, jewelry, etc.), you need to realize that every detector on the market will not perform equally under all conditions, in all areas and for all types of targets. Depending on what you are looking for and where you live, you may find that a detector that costs half of what you were planning on spending will actually perform better than your original choice for your application(s). The staff at Kellyco is well versed in the capabilities of everything they sell and combining that knowledge with talking with customers from across the country on a daily basis, know what works and what doesn’t in your area. A call to one of these factory trained and certified experts can help you avoid making an expensive mistake by ordering the wrong detector for your specific needs.

Make Sure to Read your Instruction Manual!

So you’ve made your selection and the big day as arrived… your new detector has just been left at the front door. Fight the urge to unpack it and head out to see what you can uncover! Once you have it assembled, set it aside and pull out the instruction manual. Skim through the pages on how to assemble it if that activity went well and focus on the section that covers each of the controls and what function they perform. Often there will be paragraphs that are highlighted, bolded, outlined or annotated with asterisks to let you know that they provide information the manufacturer feels is crucial to your success and these are typically marked that way based on repeat questions received from previous customers. Take the time to read through the information that has been provided as it will have a direct bearing on your overall success once you head out into the field.

With a basic understanding of the controls and how to adjust them, you are ready to move on to the next stage which is to conduct an air test.

Understanding The Controls

Understanding The Controls

This is simply a way to get familiar with the response various targets will produce as the search coil sweeps across them. You will find that real world conditions such as target depth, ground conditions and having multiple targets in close proximity to one another can and often will impact the response received; however, an air test will help you see the response produced by targets you are hoping to find (or avoid) as well as what effect changes to the individual controls will have on these responses.

Collect an Assortment of Targets!
Perform an Air Test – Make Note of Where Optimal Signals are Produced

Start by collecting an assortment of the types of targets you expect to come across in your searches and remember, the items will vary depending on what type of hunting you plan to focus on. Coin hunters will have a different set of test targets than a Civil War relic hunter or beach hunter will so be specific for what you plan on searching for. Don’t forget to include examples of the trash you can expect to come across so you can start to learn what not to dig and what settings will help you do that.

Lay the detector on a table with the coil away from any metal including heating ducts, braces in the table, nearby appliances or even items in your pockets or a belt. Remember that metal is detected both beneath andabove the coil. Turn your detector on and start passing various targets across the top of the coil at a normal sweep speed with the discrimination control set at “0”. Pass each target across the coil keeping them at least 4 inches away from the coil to ensure you are not overloading the circuitry and are receiving a consistent signal. The point of the air test is to listen the audio response and see how even subtle changes in settings affect the response which will prove to be invaluable when you head out in search of actual targets. Experiment with various adjustments and repeat the air tests to see how these changes alter the responses received. Change the Discrimination and Sensitivity controls among others that your specific model may have on it and make note of where the optimal signals are produced.

Once you’ve done some air testing to see how slight changes can impact the response to specific targets, it’s time to move on to the test garden phase. As we discussed earlier, changes in ground mineralization, moisture contact, depth and proximity to other targets (good or bad) can alter the response from specific targets and the only way to find out what that change will be is to check the response on known targets IN THE GROUND.

The basis for setting up a test garden is to provide you with an area where you can see how your detector responds to various targets buried at various depths in the type of ground that you will be searching in. You can also revisit the test garden throughout the year to see how changes in moisture content can affect the response each target produces. A good example of how moisture content can dictate what sites to focus on is tied to silver coins. Without going into a drawn-out technical discussion of detector circuitry, silver coins will produce a stronger signal when the ground is damp than when it is bone dry. Copper coins on the other hand are less affected by the moisture content making them easy to detect under a wide range of conditions. So if you have seen this phenomena in your test garden (you are getting less depth on silver coins when the ground is dry), start keeping track of sites that you have searched where Wheat cents and Indian Head pennies have turned up so that you can re-hunt them after periods of rain and pick up some of the deep silver that might have been missed previously due to the low moisture content.

Mark the Location of Targets in your Test Garden with Golf Tees!

You don’t need a large area to setup a test garden – even a 4 foot square plot can provide you with a wealth of information that will improve your success rate in the field.

Golf Tees

Golf Tees

Start out by scanning the area with the detector set at “0” discrimination to ensure there is no metal present which will produce more frustration and confusion than anything else. Now assemble the items you want to use for testing and again, what you use will depend on the type of treasure hunting you plan on doing. Remove a plug of dirt and carefully place the test item(s) into the hole. If you want to see how two targets close together react, put them in the same hole. Put the targets at different depths to see how deeper targets tend to react differently than those just under the surface. Shallow targets are easy to detect but the older, more valuable targets tend to produce mere whispers and are easily missed. This is the main reason there are still so many valuables waiting to be found despite countless people having searched sites for decades. Once you have placed each target in the hole and refilled it, mark the exact location with something such as a golf tee with a number written on the top with a permanent marker. Make sure you press them down so that they are not pulled out the first time a lawnmower comes through the area… and let me say that this is advice based on personal experience! After each tee is placed, make a list showing the number, what the target is and its depth so you know what you are checking whenever you use the test garden.

A comment I’ve heard from detectorists that live in apartments is that they are not able to make a test garden and I always remind them that very little “real estate” is required. If you are careful in removing the plug, there will typically be no sign of targets having been buried. All that will be visible – and that is only if someone is actually looking – will be the tops of 10 or so golf tees with numbers written on them.

An Old 14kt Gold Wedding Band that Turned Up From More than 9″ Deep in Mineralized Soil. Learning what Small, Deep Targets Sounded like in a Test Garden Played a Key Role in Being Able to Detect and Recover this Exceptional Artifact from the Early 1900’s. (Item was Recovered by the Author on Private Property with Permission from the Landowner)

If you stay in the area and can keep your test garden undisturbed, you will see that the longer the targets are buried, the stronger the response will be that they produce.

Old 14kt Gold Wedding Band

Old 14kt Gold Wedding Band

This will be especially noticeable on the deeper targets which many have only produced a faint signal when first buried. Over time the signal will improve as a result of what is known as the “Halo Effect” which makes the target seem bigger to the detector as the metal “leaches” into the surrounding soil. Some targets have a more pronounced halo than others due to their composition with items made of gold or silver leaching very little which tends to make them harder to detect. Check the responses after a period of rain to see how moisture content affects the signals. Conversely, if you have a drought, see what no moisture will do to signals in terms of limiting overall detection depth.

It is advisable to take a spin through your test garden if you get a new search coil, have not hunted in a while or if ground conditions have changed since you were last in the field. You may find that slight changes are required to get the desired level of performance. I always take any new detector, search coil or set of headphones through my test garden so that I am familiar with the response from known targets and as a result, tend to do better in less time when I am searching for actual targets under a wide range of conditions.

I almost hate to share this story but it demonstrates the point I am trying to make with this guide. I started metal detecting in the 1960’s and had nearly a decade of experience under my belt by the time the first detectors capable of ignoring mineralization made their appearance. My father and I were intrigued by the ads that were popping up in the treasure magazines and drove to a local dealer to see one of these new “wonder machines” in operation. A short demonstration was all it took to know we needed to get one of these and a week later, we returned and picked one up. The first site we visited was an old school near our house that we had hunted for years and had recovered literally 1,000’s of coins and other items during that time. My father was running one of our old detectors and I was using the new one hoping to start recovering the real old coins we knew had to be there. Well, my father’s detector had limited detection depth but did have rudimentary discrimination while my detector got amazing depth but lacked any discrimination. So while my father has digging coins at 4″ and ignoring most of the trash, I was digging targets at 10″ of which most were rusted nails and other trash. After an hour we compared targets and my 3 coins and a pile of trash could not hold a candle to my father’s pile of coins and a small gold ring. Frustration continued to build over the next hour or two and when he yelled over that he had just recovered a silver half dollar, I literally wrapped the new detector around a tree and snapped the shaft in two.

Old School

Old School

My father laughed and suggested we head home but it took a few days for me to cool off enough to head back out AFTER I took the time to test the detector on known targets and that preparation allowed me to ignore most of the trash the next time out with far different results… a handful of coins that dated back to the mid-1800’s! By the way, I still have that old detector in my collection and when I look at the welded spot on the shaft where my father repaired the damage caused by my frustration, I have to smile and remember that no matter how experienced I am, spending time with a new detector performing air tests and taking a spin through a test garden is essential if I want to unlock the true capabilities any detector has to offer.

Good luck in your searches and hopefully some of the techniques contained in this guide will help you find more and enjoy your time in the field in less time than simply heading out the door would have produced.

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