Metal Detecting for Fun and Profit

[Lori Dee]

Metal Detecting Basics

I have been metal detecting for decades. When I was a teenager, my dad, an electronics engineer who worked for NASA, built a metal detector in our garage from kit parts. With my background in Electronics and experience as an Electronics Instructor, my goal here is to provide some basics for our members who may be interested in this hobby.

Metal detectors work by taking advantage of certain electrical principles.

Ampere's law states that a changing electric field produces a magnetic field.  This is how electromagnets work and is the underlying principle for making electric motors turn.

Faraday's law states that a changing magnetic field produces an electric field. This is how electric generators work. A magnet is turned inside a coil of wire to produce electricity.

A generator uses Faraday's Law to generate electricity. That electricity travels through a wire, and that electricity generates a magnetic field around the wire. This happens with any conductor and is not limited to wires. Conductors are not just metals. Metals are the best conductors, but other minerals, like salt, also conduct electricity. The difference is that non-metals are either poor conductors or are insulators that have near-zero conductivity.

The metal detector transmitter coil sends a magnetic field into the soil. That magnetic field produces a very small electrical current and thus a tiny magnetic field in any conductors in the soil. The metal detector's receive coil detects these tiny magnetic fields and transmits the data to the control box for analysis. The signals are so weak that they must first be amplified before they can be analyzed.

In the earliest models of metal detectors, the signal was converted to an audio signal. It was up to the operator to know what these sounds indicated and how to interpret them. Modern-day detectors still produce an audio signal, so I will cover how that works.

The sound produced has several distinct qualities that vary according to the target detected.

Targets are first separated into ferrous (iron) and non-ferrous. This is an easy task because iron is a great conductor, therefore producing a stronger magnetic field, and iron can be magnetized, so it holds the magnetic field longer. Non-ferrous targets can still be great conductors, like aluminum, gold, and silver, but they are not magnetic and do not hold the magnetic field.

The soil itself produces a signal as well, due to soil conditions such as moisture content, salinity (salt content), and composition (iron particles). Since the soil covers a larger area, the audio signal produces a slight buzz or hissing sound in the background. As the detector moves over the soil, a target produces an anomaly with a sound that is louder than the background noise.

The target sounds produced may vary by detector manufacturer, but generally sound like a bloop, blip, bleep, or buzz sound.  The volume of the sound indicates the size of the target. Larger targets sound louder, while tiny targets may be barely audible above the background noise. The pitch of the sound (bloop, blip, or bleep) indicates the type of metal detected. The clarity of the sound indicates the clarity of the signal received. A coin has well-defined edges and a distinct shape, so it will have a clear, crisp sound. A wad of aluminum foil will have a more buzzing sound.

The best way to learn what these sounds mean is to practice with a detector. Many dealerships that sell metal detectors will allow you to rent one. That allows you to test drive various brands and models to find what you like before making a purchase. Many detector manufacturers set up test grounds with various soil types (sand, clay), density (gravel, rocks), and composition (high mineral content, iron, saltwater).

I set up a "coin garden" in my backyard that I would use for practice. Set up an area for use and use the metal detector to find, then remove, all metallic objects in that area. At certain locations, I would place various coins (penny, nickel, dime, quarter, half-dollar) as well as some junk items like a nail or screw, pull-tab, aluminum foil, bottle cap, key, etc. Allow several inches between targets so your coil does not detect more than one at a time.

As I would pass the coil over the target, I would try to remember what that target sounded like. After a long winter, it was a great way to remind myself what the detector was telling me. I would then test my knowledge by detecting another part of the yard and attempting to identify the target before digging it up. The key to remember is that your detector cannot lie to you; it is a machine. It is up to you to understand what it is saying.

With the advances of technology, modern detectors can analyze the data in much more detail and present the information as audio signals and visual displays. The visual displays will tell you approximately how deep your target is, as well as the most likely metal type. They provide a Target ID number to help narrow down what your specific target might be. (More on Target IDs later) They provide circuitry for ground-balancing, which helps remove the background noise produced by the soil, resulting in a more accurate signal for processing. They have a Discrimination circuit to block out iron targets, like nails. Some even have a "Notch" function so you can teach the detector what targets you wish to ignore, like bottle caps and pull tabs.

Detectors have become even more specialized, with circuits designed to specifically detect certain types of targets. My first two metal detectors were Bounty Hunter brand. The Bounty Hunter Pioneer 505 was an excellent machine, and I used it for almost twenty years. They work very well for coin-shooting and relic hunting. Every trip was successful in bringing home at least ten coins and occasionally a piece of jewelry or a metal toy.

With my interest being primarily gold prospecting, I invested in more specialized machines. I have a Garrett AT Gold Pro, which is designed to detect small gold nuggets, and I also have a Falcon MD-20 handheld detector for locating gold veins in rock or gold content in rock samples. I will explain more about those machines later.

Feel free to ask questions about this section. I will add more content to this thread later.

[Northern Star Girl]

@Lori Dee

Dear Lori:
Thank You for posting your very informative treatise about the designs and
operational details of metal detectors and your metal detecting endeavors.

I will be following this topic as you add more postings.
HUGS, Danielle

[Pema]

Lori, I think this is a great idea, and I eagerly await future installments in the series. Thank you for doing this. You've already sparked a desire in me to get a metal detector, so I hope you'll discuss the different brands and types at some point.

[Maid Marion]

I have a metal detector and haven't used it much.  Need to sweep my front yard for lost snowblower parts!

[Devlyn]

Lori, I thought you preferred looking for metal through the sights? 

Hugs, Devlyn

[Lori Dee]

Lori, I thought you preferred looking for metal through the sights? 

Hugs, Devlyn

I do, but the ammo is so danged expensive! 

[Lori Dee]

Next Up: Where to Go?

If you are thinking of where to go metal detecting, these are places where I have always had success.

1. Your own yard. Think about it. Unless you built the place, chances are someone lived there before you. They may have dropped coins, keys, or jewelry. If they had children, there may be old metal toys to be found.

In my yard in Illinois, I found a bronze commemorative medal that was given out at an unveiling ceremony for the local Soldiers & Sailors Memorial. At the memorial, there were two bronze statues made by a famous sculptor. The medal I had showed the statues and a brief bio of the sculptor.

I also found a rare Army Branch insignia. I recognized it as Army, but nothing else. After much research, I learned that it was for the Transportation Corps. It turns out that there was a brief period of only a few years when the Army Transportation Corps transitioned from horse-drawn wagons to trucks. This insignia was from that period, which gave it a specific time period when it was in use. It was soon replaced by a new insignia.

I sold both pieces to collectors on eBay for $40 each.

2. The Beach! People are always losing things in the sand at the beach. Sunscreen makes rings slip off easily. Jewelry gets dropped and lost quickly. And that is not counting the wedding/engagement rings that get tossed in a fit of anger. My grandfather had boxes of stuff he found at the beach. Everything from diamond rings to knives, keys, earrings, and even two pistols.

3. Picnic areas and campgrounds. When you have a lot of people gathered, drinking, playing games, or just relaxing against a tree, things fall out of their pockets.

4. Public Parks. Same as #3 above.

5. Parking lots. When people are walking to and from their vehicles, they take their keys out of their pockets, and sometimes other stuff gets pulled with it. Check the edges of parking lots and along the edges of sidewalks.

My dad has had great success at local high school parking lots after school is out. During the school year, students are rushing to and from their vehicles, dropping things along the way. In winter, the lots get plowed and everything gets pushed into a giant ice pile at the edge of the lot. When the ice thaws, there is a pile of trash underneath. He once found a $20 bill stuck in the ice. He didn't need the metal detector for that find.

6. Sporting areas. Soccer, baseball, and football fields. Under the grandstand bleachers at the fairgrounds. It is not the players, but the audience that loses the most. Look at where the spectators stand or sit.

I once found a silver toe ring near a soccer field. Somebody was probably changing socks and dropped it right there on the sidelines.

I combine these tips when I am looking for an area to hunt. The City Park is a good place, but even better is near the parking lot. Look for the most likely travel path that people will take. In areas that I am not familiar with, I will just watch people walking and see where they go, how they get there, and what they do.

In Rapid City, at Founders Park, there are from three to five food trucks parked in the parking lot almost every day. That is a lot of money changing hands and being dropped in the grass along the curb.

I hope these tips will give you some ideas of where to go hunting in your area. I have more tips that I will share soon.

Good luck!

[Lori Dee]

Target Identification circuitry analyzes the target's conductivity and mass. The result is presented on a visual display. The simpler machines may just have a scale that runs from Iron > Foil > Silver.

Newer machines also present a Target ID number to more precisely locate the target on this scale.



Visual Display Panel of the Garrett AT Gold metal detector.



Metals have varying degrees of conductivity. Magnetic targets will hold the magnetic field (eddy currents) longer over time. A target with a higher mass will have a higher eddy current.



"Conductivity, coupled with mass, can give dramatically varying results.

Example: A 1/5 oz. lead fishing sinker will ID as a low foil reading, whereas a 5 oz. lead sinker is identified as a higher zinc penny reading. Reason: The level of conductivity remains the same (lead 7), but the volume of conductivity is much greater, hence a larger eddy current is attained by the heavier sinker, giving a higher detected reading.

The opposite holds true, comparing a piece of thin copper foil the diameter of a penny, vs an actual copper penny. Both items are highly conductive, but the copper foil will ID as foil because it lacks the mass of a penny.

A nickel has a larger mass when compared to a penny and can be detected at a
greater distance, but because the conductivity is substantially lower, the ID reading on the nickel is also lower." (~ Fisher Intelligence by Thomas J. Dankowski.)

How is this helpful?

The metal content of U.S. coins has changed dramatically over the years. A penny has not been made of 100% copper since before 1857. Before 1866, a nickel was made out of 100% silver.  Quarters were 100% silver before 1965.

The modern coins (1965 – present) are referred to as "clad".  Pennies are now copper-plated zinc. Nickels are now 25% nickel and 75% copper. Obviously, this will affect where the target is displayed on the Target ID screen.



Notice that the modern (1965+) dime, quarter, and half-dollar metal content. They are the same! How does the detector know which it is? By the mass (size). And if you look up at the top image, you can see that the larger coins have higher Target IDs and the nickel scores lower than a dime or penny (even though it is larger) because it has a different metal content.

Each brand, model, and individual machine will give different Target ID numbers, so it is important to practice with your machine and learn what these numbers mean. The scales shown for visual displays are a good general indicator, but your numbers might differ just a little and be in the same range. I keep a notebook with me and jot down the ID of any new targets I encounter.

My Target ID List




Now for the fun stuff. Some of my finds.



Let's see what you have found.

[KathyLauren]

No discussion of metal-detecting is complete without a mention of the charming British TV series "The Detectorists".  It only lasted three seasons, but it was delightful to watch.  We watched it on either Acorn or Britbox, don't remember which.

The series follows two detectorists and their interactions as friends, as well as their interactions with their families, fellow club members and rival detectorist clubs.  The writing and acting are superb.

[We now return you to the regularly-scheduled program.]

[Lori Dee]

No discussion of metal-detecting is complete without a mention of the charming British TV series "The Detectorists".  It only lasted three seasons, but it was delightful to watch.  We watched it on either Acorn or Britbox, don't remember which.

We had a similar TV show here in the U.S. called "Diggers". It was on National Geographic's channel. It was fun to watch.

It was somewhat misleading because sometimes they would claim they were going to search for artifacts on historic battlegrounds. That is not allowed. Historic sites, National Monuments, and State Parks do not allow metal detecting. In Yellowstone National Park, you can't even bring a detector into the park. It will be confiscated.

The way the TV show got around the rules is that the sites where they were detecting were not "historic battlegrounds" but places (private property) where historic battles occurred nearby. As long as you have permission from the property owner, it is fine.

Basic rules of metal detecting:

1. Always get permission to be on private land. Written permission is not as easily revoked as verbal permission. (Hint).
2. Always fill any holes you make in the ground.
3. Take any trash you find with you. Leave the area cleaner than you found it.

Many private property owners will permit detecting on their land because they are curious about what you might find. It is a common courtesy to let them see what you found afterward and perhaps allow them to pick something they would like to keep.

Many detectorists advertise their services as "Location Specialists" to assist people in locating lost items. I never charged a fee to do this. My offer is that I get to keep anything I find that is not what I am searching for. So if you have me searching for a lost ring and I find a Rolex, the watch is mine. 

[Devlyn]

I'm waiting for the chapter on magnet fishing.  🙂

Hugs, Devlyn

[Lori Dee]

@Devlyn

Magnet Fishing!

Well, no. I have watched videos of it being done, but I have no experience in that "sport".    But it makes a great segue into my next post.

@Pema asked about recommendations or suggestions for brands or models. There are many to choose from, so it will depend on what you are hunting.

The main difference in the type of machine is in targeting specific types of targets. Machines have two modes: one is All-Metal Mode and the other is Discrimination Mode. In this case, Discrimination is a good thing. 

In All-Metal Mode (as the name suggests), the machine is set to detect all metals. Discrimination Mode locks out iron (ferrous) targets, like nails, fencing, staples, and other annoyances. This allows you to only hear non-ferrous targets. The machine then identifies the target based on metal content, shape, and size.

Coins have a specific shape and size, so the machine can easily pick these out of the "noise". The gray area is in the "foil" midrange. In this range are targets that have a definite shape and size, but are trash items, like pull tabs and bottle caps. Many detectorists will ignore targets in this range, preferring to focus on targets in the Silver range.

By doing so, they miss a lot of targets. In a previous post, I showed that a nickel coin falls in this range. It is not silver and is a similar size and shape to a bottle cap. This is where practice makes perfect. I have detected in city parks that were well-hunted by others and found plenty of nickels, some even older than I am.

By listening carefully to the sound of the target, you can tell the difference. I dug up a lot of trash learning this. A nickel has clean edges, whereas a bottle cap has rough edges. A coin has a crisper sound, whereas the bottlecap sound has a buzz to it.

A gold machine, like I use, is specifically designed for use in high-iron soils. Instead of primarily operating in Discrimination Mode, they operate in All-Metal Mode. Goldfields typically have a lot of mineralization, so the soil will have a high content of iron, manganese, copper, etc. By using different frequencies than the standard detector, the circuitry works better at identifying tiny targets like small gold flakes. It doesn't remove the iron signals, but amplifies the gold target so it can be heard above the background noise. It does have an Iron Discrimination setting, so you can hear if your target is iron. That setting allows you to set the level of discrimination so that large iron targets like nails are ignored, but subtle iron in the soil is still heard.

For coin shooting and relic hunting, iron is usually a nuisance and can be filtered out without affecting your ability to find good targets.

The next thing to consider is weight. Swinging a heavy machine on your arm for a few hours takes its toll on your back. Modern machines use lightweight materials, and there are "suspenders" that you can get as an accessory to take some of the weight off your arm.

Speaking of accessories, some things that are nice to have but not mandatory.

A coil cover is a plastic piece that fits over the bottom of the detector coils to protect them from scrapes against rocks and gravel. They are cheap and worthwhile to protect your investment.

A handheld pinpointer probe is very handy. It is a small all-metal detector that helps you locate your target in the hole you just dug. Can you do without it? Yes. But you will be glad to have one. I have had three. I lost two somewhere, so now I attach it with a lanyard so I don't walk off without it.

A plastic garden trowel for digging your targets with. Plastic will not interfere with your detector, and you can use the pinpointer probe on the soil as you dig it out of the hole.

Last, an apron. You will be digging in mud and getting dirty. (That's half the fun!) You will want an apron that has pockets. One pocket is for the trash you dig and will take with you. The other pocket is for "the good stuff". I have one from Garrett that has a main pocket where I store spare batteries and a snack, plus a zippered pocket for the "really good stuff", as well as a holster for my pinpointer probe. You don't need to get fancy. Go to a hardware or home builders' supply store and look in the carpentry/roofing area for a nail apron. Sometimes you can get them for free; at most, they will be a couple of dollars.

If you want to look at the various brands and models of detectors, check out metaldetectors.com. I have purchased from them, and they are trustworthy. Top brands like Fisher, Garrett, and Minelab will command a higher price. But you get what you pay for. My dad has two White's machines, which are good, but I heard that White's has gone out of business. Between COVID, Chinese knock-offs, and difficulty stocking parts, they just gave up. The machines can still be found in stock in many places, just understand that warranty or repair issues might be limited.

I suggest that anyone thinking about buying a machine look for a local dealer. There, you can see the machine, feel how heavy it is, ask questions, and get an idea of what you are looking for. Many dealerships will even let you rent a machine and show you how to use it. Then, when you have an idea of what brand/model you are interested in, go online and look for the best price.

If you just want to dive right in, check out the Bounty Hunter Pioneer 505. I got my first one decades ago at Walmart. It is a great beginner's machine. I accidentally left it in a garage when moving out of state, so I bought another. They are not too expensive, and I used it for close to twenty years before giving it to my friend when I upgraded to my gold machine.

The nice thing about going cheap to start with is to make sure that this is a hobby you enjoy. As you become more experienced, you may decide, like I did, that you want to upgrade to a nicer machine. If it turns out that it is not your thing, you can give the machine to a kid or grandkid and let them have fun with it. You won't be out a lot of money just "trying it out".

[ChrissyRyan]

Very comprehensive.  I was wondering if I found an old metal detector for sale, perhaps made by Radio Shack, if it would still detect metals well.

[Lori Dee]

Very comprehensive.  I was wondering if I found an old metal detector for sale, perhaps made by Radio Shack, if it would still detect metals well.

Yes! It will do the job. Those were the type made for finding coins and relics. Depending on how old it is, it may not have a visual display, so you would need to practice a lot to learn what all of the different sounds mean. It may not have Discrimination Mode or Ground Balancing, but they still work. If it doesn't have a manual, I can search around online and find one to help you get it set up.

[ChrissyRyan]

Yes! It will do the job. Those were the type made for finding coins and relics. Depending on how old it is, it may not have a visual display, so you would need to practice a lot to learn what all of the different sounds mean. It may not have Discrimination Mode or Ground Balancing, but they still work. If it doesn't have a manual, I can search around online and find one to help you get it set up.

Thanks.  I hope they do not point to old water pipes and other useless items!
I suppose you found some junk or useless things.

Do these detectors find things under wet sand?

[Lori Dee]

They will detect any metal; all metal detectors will. That is why learning what the sounds mean and what the visual display tells you, so you can decide what it might be. It will detect buried cable, which is why utility companies use them to mark where the cables and gas lines are underground.

They will also pick up iron rebar in sidewalks and driveways. There is no point in detecting on top of concrete since you can't dig it up.

The most interesting thing I detected (I knew what and where it was) is the titanium plate and screws in my neck, where my vertebrae are fused. I wasn't sure if it could, but it did!

Wet sand can be helpful. The moisture in the ground adds to the conductivity of the soil, making some targets easier to find. Sometimes it throws off the detector readings on how deep it is, but if you can detect it, you can dig it. Detectors only detect about 12 - 18 inches down into the soil. Wet sand might help with a little more depth.

Some of the best finds that my grandfather had he found in the surf at the beach. He would go at low tide and sweep the wet sand close to the water. Most detector coils are waterproof, so you can detect in shallow water.

My gold machine is completely waterproof except for the headphones. So I could detect in water chest deep. But then how would I dig up the target? 😀