What is Phase Shift and Target Identification in Metal Detectors

What is Phase Shift and Target Identification in Metal Detectors

Phase Shift and Target Identification (TID) are terms you come across early in your exploration of metal detecting technology.

Here we explain what these terms mean and describe how phase shift is related to target identification.

The basics of electricity tell us that running a current through a wire creates an electromagnetic field around that wire. If you move another wire through that field it induces current into that second wire. That effect is called electromagnetic force, or “emf.” Now it doesn’t matter if the wire moves through a stationary field or an alternating field moves through a stationary wire. The generation of emf works the same in both cases.

A detector runs a radio frequency current, anywhere from about 5-khz to 20-khz through its coil. This creates a moving field that expands and collapses many times each second. This is a moving field. A coin in the ground is like a tiny 1/2-inch piece of wire. The moving field from the coil induces a very small emf in the coin, called an eddy current, Figure 1.

electromagnetic fields with metal detector

Figure 1. The radio-frequency electromagnetic field from the detector coil generates an eddy current in the coin in the ground.

A Little Science for Metal Detecting – Target Identification

Now, here’s the trick. The physics of that current in the coin are such that it pushes back, in the opposite direction, against the current in the detector coil. This push-back, or echo, slows the current in the coil, but has no effect on the voltage. The result is that current in the detector coil becomes out of step with the voltage. This is called phase shift in electrical jargon. It means the current waveform lags behind the voltage waveform. See Figure 2.

phase shift metal detector

Figure 2. The eddy current in the coin pushes back on the field from the detector coil, causing a phase shift, where the current and voltage wave-forms become out of step.

What Causes Phase Shift on a Metal Detector

A highly conductive target, such as a silver dollar will create a large phase shift in the detector coil. A zinc penny will cause a smaller shift, and a rusty nail even less.

The push-back from the target also explains why you get mixed signals from asymmetrical targets. A long nail scanned in one direction will produce a different phase shift than if scanned at 90-degrees from the original coil swing.

These changes in the current/voltage phase shift are exceedingly small, so it takes a highly refined signal processing circuit to detect the differences.

For less expensive detectors, the phase shift scale is broken up into segments or categories, generally called notches. These notches can be turned on or off to either select or eliminate phase shift categories. If you want to look just for coins, you can turn off , or gray out, the notches for iron, foil, and pull-tabs.

The Fisher F22 has 10 such notches. The Garrett Ace 300 has 12 notches that span the entire phase shift scale. You can see the categories across the top in the first two face plates Figure 3. The more expensive Minelab Equinox has 50 notches and each one can be turned on or off. In Figure 3 you can see some of the notches are grayed out along the semi-circle of the phase shift scale. These are most likely programmed to eliminate junk iron, pull-tabs, and bottle caps.

Metal Detector Faceplate Fisher, Garrett and Minelab

Figure 3. Face plates for different detectors: the Fisher F22, the Garrett Ace 300, and the Minelab Equinox 600. Each shows the discrimination values that can be programmed on or off to eliminate unwanted targets.

Does Phase Shift and TID Cost More on a Metal Detector?

In a more expensive detector, the phase shift scale is more exquisitely defined, into many more specific readings called Visual Identification (VID) numbers. The engineering for this finer performance is what makes the detector more costly. The payoff, however, is that you have much more specific target identification. This allows you to distinguish between a zinc penny and a copper penny, or between a silver dime and a clad dime.

The VID scale numbers from any one manufacturer are generally different from other machines. Whichever detector you use, you soon become familiar with the numbers corresponding to specific coins or common junk items, such as pull-tabs. This speeds up your choices on which targets to dig.

I hope this answers your questions about discrimination. Good luck and happy hunting.

Vince Migliore_Author Metal Detecting Book

Vince Migliore is a writer and researcher. He has written numerous magazine articles on metal detecting and three books. His latest book is “The Art and Science of Metal Detecting,” available in paperback at Amazon.

Where to Metal Detect in Northern California (MAPS INCLUDED)

Where to Metal Detect in Northern California (MAPS INCLUDED)

California is a wonderful paradise for both metal detecting and scenic beauty. Here we explore some of the more exciting metal detecting sites in Northern California.

When I first came to California, it was on Highway 80 crossing from the Nevada border. That state line is near the summit of the Sierra mountains. The terrain ranged from snow-capped mountains to evergreens on the long, hilly descent into the farmlands of the Central Valley. Then, it was on to the San Francisco coast and the Pacific Ocean. In between there were farms, freeways, factories and floodplains all near the same roadway.

Gold was discovered here in 1849, creating a flood of new settlers, and sparking the dreams of adventure-seekers from all points east.
The only downside of California is that it’s a relatively new state. It doesn’t have the centuries of residents dropping earrings and pennies from their pockets that you see in the eastern states. Statehood came to California in 1850, one year after the Gold Rush.

Metal Detecting for GOLD in Northern California
Metal Detecting for GOLD in Northern California

On the other hand, Northern California probably makes up for the treasure trove deficit by featuring an almost ideal climate. People here love to jog, camp, and hike in the great outdoors, again, spreading their junk and jewelry as they glide by.

Legal Considerations for Metal Detecting in California

There’s an oddly depressing feeling the first time you look up from your detector and see a law-enforcement officer approaching. It happened to me. It’s not scary so much as embarrassing, as I was unaware of the local codes that prohibited me from detecting on what turned out to be police property.

No fines or citations, just a red face.

Before you dig anything up, be sure it’s legal to do so. In general, metal detecting is allowed in state parks but you cannot destroy plants in doing so. There are limits too on mineralogical, historic, and archaeological artifacts. You cannot dig up and remove fossils, minerals for commercial use, or remove a WWII firearm.

You cannot dig in Indian burial grounds. There is a complex mixture of regulations obscure enough to confound the most altruistic dirt-fisher. To find out more, check out the Metal Detecting Hobby Talk web site, for national regulations, and California laws.

Generally, it’s OK to search in National Forests and Federal Bureau of Land Management properties, but metal detecting is forbidden at national monuments. In California this includes the Giant Sequoia National Monument and the Fort Ord National Monument.

Read a little bit more about Metal Detecting on BLM land in this article. Can I Metal Detect on BLM Land?

A general rule is not to dig in manicured lawns. Metal detecting is allowed at almost all beaches. Most parks allow you to metal detect in sandy soil, weeded and undeveloped land and wooded areas, as long as you’re not destroying vegetation or wildlife.

We focus here on a few selected sites as samples of good prospecting areas for the metal detecting hobbyist. The fall into three somewhat broad and overlapping categories:

  • Beaches,
  • Trails, and
  • Forgotten cities.

Beaches and Trails in California for Metal Detecting

Beach detecting is really fun because it’s easy digging, generally quite productive, and you don’t have to worry about park rangers looking over your shoulder. There’s the added pleasure of sea breezes, open vistas, and relatively large search areas.

1. Seacliff Beach, Aptos, CA – Fun Metal Detecting!

If I could define one place that’s perfect for metal detecting Seacliff is it. A beautiful BUSY beach, convenient parking, lots to see and lots of sand for items to get lost in.

Seacliff Beach also has an RV park which makes it perfect for the traveling detectorist. Find a slot right on the beach and get out early and enjoy! Read more at the state park website. Website: https://www.parks.ca.gov/?page_id=543.

Seacliff Beach CA, for Metal Detecting
Seacliff Beach CA, for Metal Detecting
Image from Google Maps

Cautions for Metal Detecting at Seacliff:

  • Salty sand can play havoc with your ground balance. Be sure to adjust your detector according to the user manual.
  • This is not a sun-bathing beach. The weather is cold, as currents come down from Alaska on the west coast. Most beach activity is near the walkway.
  • The cliffs are very steep overlooking the beach. Use the stairs and roadways to descend to sea level. People have been killed from cliff collapses. See news story: https://www.wtoc.com/2019/08/03/killed-cliff-collapses-popular-california-beach/.
    The good news is that this is a very popular beach and is well attended. There is a huge RV parking lot on the west end that is about half a mile long and campers visit year-round. The beach continues to the east for about another mile and features an old WWI concrete ship that is quickly deteriorating in the surf.

Notes and Tips for Seacliff Beach:

You can avoid the park fee by driving to the corner of State Park Drive and Santa Cruz Avenue, just north of the park.

Next to the parking lot, which begins at that same corner, is a huge open field where you might want to detect also.

At the south-west corner of the parking lot is a very popular wooden staircase down to the beach. This vista point overlooks the shipwreck at the end of the pier. Well worth the walk!

2. Metal Detecting at Baker Beach, San Francisco, California

Baker Beach California for Metal Detecting
Baker Beach California for Metal Detecting
Image from Google Maps

This is a hugely popular beach and a great place to hunt, as it’s picturesque and close to the city of San Francisco. I’ve been there a few times and it’s usually filled with visitors. Tourists from all over the world tour this area and many choose this beach as their first view of the great Pacific Ocean.
About 400 billion gallons of water flow into and out of SF Bay every day, under the Golden Gate bridge.

Read about the park and plan your visit using the Golden Gate National Parks Conservancy webstite – LINK HERE

The tidal action and prevailing winds push all kinds of things onto this beach. (Link: https://sfenvironment.org/article/hydro/tidal-energy.)

Hunting tips:

Bring a long-handled sand scoop. It’s fine sand and the long handle will save you a lot of deep-knee bends. Read more about digging tools in this article: Metal Detecting Digging Tools a Complete Guide

Adjust your ground balance for the salty water.

It’s cold and windy out there. Currents in the Pacific come down from Alaska. Bring a windbreaker.

3. Stinson Beach, California – Super Popular makes for Great Metal Detecting

Stinson Beach is wildly popular with both tourists and the locals, and has been the playground for Hippies and Flower Children since the 1960s. Janis Joplin had her ashes scattered there in 1970. Just under and hour’s drive from San Francisco, it offers a whopping 2.4 miles of beautiful beach landscape.

Get to Stinson beach early, particularly on hot days. This beach is close to millions of folks and it seems like everyone wants to cool off. As a part of the National Park Service the beach and grounds are well maintained. Be sure to plan your trip before arriving, I’ve found the the Stinson Beach Website is a great resource.

I found some interesting facts on Wikipedia:

“Stinson Beach is about a 35-minute drive from the Golden Gate Bridge on California’s Highway 1. It is near important attractions such as Muir Woods National Monument, Muir Beach, and Mount Tamalpais. It has a long beach, and the cold water produces fog throughout the year.”

It’s a foggy and cool climate with lots to see and do. You can read some local news about the tidepools : https://baynature.org/article/a-tidepool-in-time/.

You need to have the RIGHT kinds of digging equipment for beaches. A METAL DETECTING SCOOP is essential. My most recent favorite is the Hand Held Garrett GAR1600970 (links to AMAZON to check out the prices and reviews)

4. American River – Sweeping for Gold

The American River near Auburn, California is rough-and-tumble country, with steep cliffs, a powerful river, and miles of hiking paths. The terrain is not suited for young children, but it is a great spot to metal detect.

Although the objective is to find coins and jewelry along the trails, there is at least the possibility of hunting for gold. It’s best to have a dedicated gold detector for this. Look for outcroppings of quartz rock in the hills and examine the eroded soil beneath these exposed areas.

With lots of gold history the American River and the town of Auburn can wet you appetite for GOLD.

Metal Detecting on the American River and surrounding area in California
The American River and town of Auburn have lots of history. Chases for Gold and lots of trails to metal detect on.

Don’t forget to stop and “smell the roses” so to speak along these trails. There are no roses to be seen, but the photo opportunities are spectacular. There are some trails that I recommend to metal detect on, the first two with plenty of hiker traffic.

  • Black Hole of Calcutta Trail.
  • Clementine Trail.
  • Quarry Trail.

For families with small children, I would suggest an alternative, such as the many camps that offer amateur gold panning. These sites may be a little more tame, but still offer excellent adventures for the adults.

  • Union Flat Campground, keeps the old time gold mining feel alive. Read more at the Recreation.gov website. https://www.recreation.gov/camping/campgrounds/234534
  • Marshall Gold Discovery State Historic Park, provide a first hand glimpse at panning for gold. With a metal detector your chances are better searching for gold jewelry. Plan a visit to the park using the States website – https://www.parks.ca.gov/?page_id=484
  • Malakoff Diggins State Park, learn about what hydraulic mining was in this 3000 acre park nestled in a pine forest. Metal detecting old tailing piles may actually kick-off a tone on your detector. Even more information can be found at https://www.parks.ca.gov/?page_id=494

5. Nevada City – Searching the Cascade Canal Trail

Cascade Trail CA for Metal Detecting
Cascade Trail CA for Metal Detecting – old trails get plenty of foot traffic

This is a particularly interesting trail. There’s not much chance of finding gold here, but the real treasure is an isolated walk in the woods that transports you into the heart of Mother Nature. It’s a canal that transports water from the mountain areas to the foothills of the Central Valley of California. See the web site link above for some come-hither photographs.

From the web page:

“This popular trail offers an almost level walk along a peaceful canal through a forest with many Douglas firs and dogwoods. At 3200′ elevation, it is a bit higher and cooler than many local trails. There are several places along the route where views open up briefly to more distant scenery.”

It’s in Gold Country, so there’s always a chance of finding some hidden treasure, but don’t count on it. Just to keep your imagination alive, though, here’s a story about finding stolen loot in Gold Country: News Link: https://www.sfgate.com/outdoors/article/Discovery-may-prompt-new-gold-rush-5281400.php.

6. Pioneer Trail at Hwy 20 – Remote Metal Detecting

This is an alternate trail you might want to consider. It’s not fully developed here because its very remote and probably too difficult for most detectorists. It’s located between Nevada City and Emigrant Gap in California, and marks an old wagon-train trail paralleling Highway 20. This trail might be good for relic hunting.

Note that this is a long trail, headed mostly down-hill. Plan accordingly, as the walk up hill will be a lot more strenuous at this high altitude.

The way I’ve planned my trip is to camp at the White Cloud Campground and plan for a full day of hiking the trail scanning along the way. Use a favorite tip of checking closely by benches and natural rest areas.

Forgotten Cities a FAVORITE Metal Detecting Spot

A great way to find the oldest neighborhoods in any city is to get a vintage map. You can find old maps for about any town on internet sites such as Ebay. Compare the old map to a modern one and you’ll have a good comparison to find the oldest parts of you city.

When I first moved to Folsom, California, I was disappointed to see how few coins I was finding. I got an old 1952 map and found out why. Up until that time Folsom was just a couple square miles in area. By the 1990s it had grown, tremendously, mostly to the south, where I was finding coins no earlier than 1980.

Using a Vintage Map for Metal Detecting
Using a Vintage Map for Metal Detecting

In the year 1900, Sacramento, likewise, had a population of only 30,000, confined mostly between A and X Streets, from the Sacramento River to 30th Street. Today it’s population is over half a million, and the oldest areas remain in that small square, with a few city blocks on the west side of the river, now part of West Sacramento. Figure 9 shows a map of the city from 1900, along with an image of one of the many streets with wide, grassy traffic dividers, good for metal detecting.

7. Old Sacramento / West Sacramento for Metal Detcting

There is a tourist section of town called Old Sac. Old Sacramento is a State Historic Park, so digging there is off limits. The surrounding areas, however, provide ample opportunities for metal detecting. See Figure 10.

Old Town Sacrament
Old Town Sacrament – History means lots of time for folks to drop something
Don’t tear up lawns!

Pristine lawns add glamour to the tourist area of Old Town Sacrament, but just a quarter mile away are undeveloped parks and walkways along old parts of the Sacramento River.

There are long stretches of waterfront that remain undeveloped and the west shore now has a little-used bicycle path. This area, being so old is ripe for finding relics and silver coins. The tourist center is off limits to detecting, but areas near by are waiting for your search.

8. Benicia – Old is Good for Metal Detecting

Benicia is one of the oldest cities in the San Francisco Bay Area, being just the third city to incorporate in the state of California. It was once the state capital, in 1853. Now it’s one of those communities you drive through while going somewhere else. Still, it has a rich history and dozens of great sites for the metal detector.

This is a good place to search for silver and old coins. There is lots of areas with hilly terrain and untouched nooks and crannies just waiting to be explored. See the list of target sites in Figure 12.

Map to Metal Detecting Spots in Benicia, CA
Map to Metal Detecting Spots in Benicia, CA

The weather there is often windy, as breezes from the ocean whip through a narrow break in the coastal range of mountains. This is a sleepy little town yet oddly fascinating.

The End – of this article but Keep Using Your Metal Detector

This has been just the briefest of samplings for metal detecting sites for Northern California. There’s plenty more to say, but we need to keep the articles brief for the sake of reader attention span! Ha, ha! But there are plenty of exciting areas to explore, which we hope to present in the future.

In the meantime, you can learn a lot and be inspired by checking out some the Metal Detecting forums and web sites on the internet.
Some samples:

  • Treasurenet: http://www.treasurenet.com/forums/forum.php
  • Metal Detecting Forum: https://metaldetectingforum.com/index.php
  • Metal Detecting Hobby Talk (Calif.) http://www.mdhtalk.org/cf/club.cfm?st=CA

Happy Hunting!

Vince Migliore_Author Metal Detecting Book

Vince Migliore is a writer and researcher. He has written numerous magazine articles on metal detecting and three books. His latest book is “The Art and Science of Metal Detecting,” available in paperback at Amazon.

How Deep Can Your Metal Detector Detect?

How Deep Can Your Metal Detector Detect?

Yep, most of metal detecting enthusiasts have heard this question dozens of times.
There are at least three different ways to answer it:

  • The quick, sloppy, just-being-neighborly response.
  • The technical, journeyman coin-shooter response, and
  • The practical explanation that gets to the heart of the matter, that is, how deep can I personally go with MY detector?
    Lets look at all three perspectives in turn.

The quick, answer to How Deep can a Metal Detector Detect?

The very easiest of answers is that the depth is about 80% to 100% of the diameter of the round coil you are using, or a little deeper for a D-D coil.

A slightly better estimate comes from reports of experienced dirt fishers. As a member of the Sacramento Valley Detecting Buffs, hunting with them about every weekend for several years, I’ve come up with rough estimate of coin retrievals and depths as summarized in Table 1.

We usually detected for about 3 hours, from 9:00 AM until about Noon. Then we’d lay out our coins and jewelry in front of each other and compare notes. A typical day would have twenty or so members, each displaying between a dozen and three dozen finds, mostly coins.

Experienced dirt-fishers with high-end detectors would generally have the highest counts, and beginners with $100 detectors would have the lowest. Similarly, the depths are deepest with the more advanced detectors. They would typically find money as deep as 9-inches. Although the expensive detectors can scan deeper, they still find treasure mostly in the top few inches of the soil. This is in California, after all, which is a relatively young state, so coins have not accumulated as much as in eastern states.

Table 1. Estimated depth based on detectorist reports.

Now, don’t go ballistic with this table. Conditions vary widely across the United States, by the experience of the dirt fisher, and by the equipment used, among other factors.

The Technical, Journeyman Response to How Deep do Metal Detectors Detect

For the thinking hobbyist the question of how deep you can find coins requires a more detailed look at the factors that affect performance. Some of these factors, like detector engineering, are beyond our control. Others may have fixes or work-arounds. All of them contribute to your understanding of the science of metal detecting, and that, in the end, serves to make you a better coin-shooter.

Baseline Factors for the Metal Detecting Depth

Metal Detector Engineering: Strength of Field, Circuit Design, Signal Processing

The upper limit of the search field of a detector is based on the strength of the radio frequency (RF) signal generated in the circuitry and the quality of the components, including the signal processing software. Manufacturers are constantly trying to balance the cost of the unit with consumer demanded features. This is why the higher priced detectors often work better. Generally, this is a fixed factor, except for your ability buy the next higher priced machine.

Power Supply of Metal Detector

Like the circuitry, the power supply is built in: you cannot change it. To work best you can keep the batteries fresh and recharged. Some detector models now have the option of a separate power pack that keeps the supply voltage at an optimum level for a longer period of time.

Metal Detecting Coil Size and Design

A larger coil size will penetrate deeper into the earth. Double-D, or D-D coils are better for deeper detecting. Many detectors models offer the ability to switch coils.

Detector type: VLF, Pulse-Induction, Two-Box

Many VLF Detectors now offer a choice of the radio frequency you can use. The lower frequencies generally penetrate deeper into the earth. Pulse Induction detectors usually penetrate deeper than the radio frequency models, but they suffer from sketchy target identification.

Pulse-Induction Detectors are superior in mineralized and salty environments. They are favored for beach detecting and even into the surf.
The only drawback of these detectors is that they are often poor at target identification. See: https://electronics.howstuffworks.com/gadgets/other-gadgets/metal-detector4.htm

The Two-Box Metal Detector is used to find very deep treasure. Think pirate trunks filled with gems and bullion buried on an island in the Pacific. Although they penetrate deep into the ground, they are not suited for small coin hunting. They are generally heavy and quite large.

These detectors are best employed when a treasure hunter has an approximate location to hunt in where a cache is known to exist (very rare). Normally two-box detectors would be far beyond the range of the hobbyist coin-shooter, but now some famous brands have stepped into the arena with specialized and add-on units for the hobbyist.

For more on two-box detectors see: https://www.kellycodetectors.com/catalog/library/best-two-box-deep-metal-detectors.

Environmental Factors Affect Metal Detector Depth

Soil Type

Hard-pan, heavy clay, and densely packed soils are harder for the detector signal to penetrate than loose, arable land. Similarly, ground containing large rocks, aggregate accretions, and intermittent strata can create chaos in the return signal, making both depth and target identification readings less reliable. See Figure 1.

Ionization and Mineralization

Certain minerals, especially salts, often interfere with the coil signal and will decrease effective depth. Water in salty terrain can create ionized particles which block the signal. Many minerals and ores, such as at quarries and in desert landscapes can create false readings and faulty target identification.

Be sure to adjust your ground balance in these areas. Many detectors compensate for mineralized soil by decreasing the signal strength or sensitivity, which in turn reduces the effective depth of your searching.

Electromagnetic Interference

Buried power lines, overhead power lines, and large utility transformers often muddle or even incapacitate your detector functions. Interference from other coin-shooters will do the same. Operating near a radio station will sometimes cause problems.

Air Test vs Ground Test metal Detecting
Figure 1 Air Test vs Ground Test – Junk metals, minerals, ionized particles all tend to scatter the radio signal, making depth measurement and target identification more difficult.

Figure 1. Air test versus ground test. Junk metals, minerals, ionized particles all tend to scatter the radio signal, making depth measurement and target identification more difficult.

Metal Detecting Target Factors

Metal detectors work by sending a radio signal through a coil. The electromagnetic field generated by the coil is transmitted into the ground. A metal object in the ground acts like a tiny radio antenna. Energy from the coil signal generates a minute current in the target, and the coil picks up that return signal, processes it, and tries to identify the target.
(Reference: https://www.minelab.com/knowledge-base/getting-started/how-metal-detectors-work.)

The return signal from the target is not very strong. It’s strength diminishes with distance, which is another way of saying depth. Any interference from other objects or ingredients in the soil will contaminate that return signal. This process works against both the ability to detect a coin and the ability to identify it.

Target Size and Orientation

The best orientation for maximum depth is horizontal to the land surface, and parallel to the surface of the coil. This position captures the most energy from the coil. Likewise, a larger coin, or larger metal object, will have a better response. A coin in the horizontal position receives the least energy and is most difficult to detect. See Figure 2.

Metal Detecting Target Orientation and Size
Metal Detecting Target Orientation and Size (FIGURE 2)

Figure 2. Return signal from the target to the receiving coil at different angles of orientation: A, parallel; B; askew at 30 degrees, C; on end.

Target Composition

If the target is a good conductor, such as copper or silver, the return signal will be strongest. Cheap, impure, and corroded metals will return a weaker response.

Metallic and Chemical Interference

Other metal objects near the coin, salts and ionizing chemicals, even ferrous rocks, will hinder the detection of the return signal. The most common culprits are nails, bottle caps, pull-tabs and metal garbage.

Metal Detecting Operator Factors

Swing Technique

Keep the coil close to the ground for maximum depth. It’s not a good idea to actually touch the dirt, as this will quickly sand-paper away the protective cover. Touching the grass is not as abrasive.

Use the pin-pointer feature on your detector if you have one. When you find a target, scan it again facing a different direction. For example, change a north-south scan to an east-west scan. Changes in the signal may indicate an oblong or tubular target.

Knowing Your Metal Detector

There’s very common saying in the detecting world. “RTFM!” It means Read the Manual. Not exactly sure what the ‘F’ stands for. (Wink!)

You have to know how to adjust the gain, the discrimination level, the notch filters, ground balance and related controls. This is one of the biggest factors in getting maximum depth out of your detecting. Not knowing, or not caring about these settings is the most common error among detectorists, and it’s the most easily corrected with just a little tinkering with your controls. The solution, again, is to read your user manual.

Detector depth is also related to your chosen goals. Relic hunting, or settings for “All Metal” mode with cranked up gain will get you pretty deep. Gold prospecting, with a higher radio frequency and a small coil will get you only a few inches deep. And there’s a vast range in between.

The Personal, Definitive Answer to Depth

In order to determine exactly how deep ANY metal detector can operate you would have to calculate each of the above listed factors, measure the percentage of loss by each of the variables, then multiply those losses by the ideal air-test depth measurement.

That, of course is impractical, if not impossible, for the average detectorist.
Instead, there are simple methods to determine exactly how deep YOUR metal detector operates.

Air Testing Your Metal Detector

  • Turn on your detector and prop it up against a wooden table or fence, away from any metal objects.
  • Lay out an 18-inch or 3-foot wooden or cloth ruler (nothing metallic) onto the table.
  • Cut a V-shaped notch into the side of a dowel or wooden stick, so that you can jam coins or objects into the notch and they will stay secure as you wave them under the coil.
  • Wave a series of objects directly perpendicular under the coil. The coins should be parallel with the base of the coil. See Figure 3. Suggested coins: zinc penny, copper penny, nickel, clad and silver dimes and quarters.
  • Measure the distance from the coil where you can just barely read the Target ID on your detector. Write down that distance onto a note-pad.

Field Testing Your Metal Detector

When you’re in the field and you find a relatively deep coin in your Target ID, write down the target and, if your detector displays it, the depth reading.
Dig for the coin without removing it. Once you locate it with your pin-pointer, measure the actual depth. Write that depth reading down next to the depth that was recorded by the detector. Is there much of a difference?
Repeat that for different coins and depths.

Field Research With Your Metal Detector

Remember that stick with the notch in it? (Air Test, above.) Use it to measure actual depth of your finds.

Take the stick and some test coins with you on a hunt.

When you’ve found something and you have deep hole, say 9-inches, then place the stick with a coin in the notch, and bury it with the loose dirt from the hole. Then scan it with your detector and record your readings. Repeat for each test coin.

Now you can measure the depth of each test coin in more realistic conditions. You will then have depth readings from three sources: the air test, the detector depth readings, and you own physical measurements from retrieved coins.

How Deep will a Metal Detector Go?
How Deep will a Metal Detector Go?

Figure 3. Depth calculations using an air test and measures in the field.

If the test coin is a quarter and you can easily detect it in the hole with dirt in it, then raise the coil up an inch at a time until the coin is just barely detectable. Add the height of the coil to the depth of the hole.

Now you will have a measure of depth for each coin in real-world conditions.

Of course, the loose soil in the measurements will not be as compact as the original conditions, but it will be a lot more accurate than the air test.

PRO TIP: Paint inch marks on your pin-pointer, or your digging too, so you can measure the depth in the field without carrying a ruler around with you.

Conclusions is Deeper Better Metal Detecting

So there you have it. You should now be able to rattle off the answer to the depth question for three different audiences.


  • For curious passers-by: “Oh, about the diameter of the coil.”
  • For the fellow dirt-fisher: “Well, it’s complicated. It’s mostly coil size, the quality of the detector, and conditions in the ground.” See Figure 4.
  • For your own satisfaction: “I did my own research and this machine goes reliably to 10 inches deep.”

I leave you with some helpful references. Happy hunting!

Where you Metal Detect also affects how deep your machine will go
Where you Metal Detect also affects how deep your machine will go


Typical depth-testing videos on YouTube:

Vince Migliore_Author Metal Detecting Book

Vince Migliore is a writer and researcher. He has written numerous magazine articles on metal detecting and three books. His latest book is “The Art and Science of Metal Detecting,” available in paperback at Amazon. Your can read more about Vince on his Biography Page

Finding Silver Coins With Metal Detecting

Finding Silver Coins With Metal Detecting

Wow! The thrill of finding silver – there’s nothing like it! It’s not just the monetary value, but silver in the ground often does not tarnish, so it pops out of the dirt in brilliant glory! Here’s how you can fine-tune your detecting skills to collect more silver for yourself.

The Sweet Sounds of Silver (Metal Detecting)

a) Detector Sounds – An Important Skill

Using your own ears to distinguish between detector sounds is a basic skill, but it deserves a second look when your goal is digging up silver.


  • Remember the classic “blub-uh-dub” sound you get from a soda can pull tab.
  • Compare that to the clear, steady “twang, twang, twang” you get from a copper penny.
  • The difference between the pull tab and the coin is about the same as the difference between a copper penny and silver.
  • Silver produces a louder, consistent signal, a rock-solid “zing, zing, zing!” (I know, my description of detector tones is not Pulitzer Prize winning material, but you get the idea.)

I suspect you already have these sound differences stored in your memory banks, but it’s valuable to focus your attention on their qualities as you set out to find silver.

b) Detector Settings – Getting it Right!

Just as your ears can learn to distinguish detector sounds and what they mean, your detector does exactly the same thing. Modern detectors accurately measure phase shift caused by the target, which helps determine the conductivity of the coin or jewelry.

Learn years worth of tips and techniques in my book – The Art and Science of Metal Detecting (Link to Amazon)

Silver is a pure element and an excellent conductor of electricity. It’s a better conductor than copper. This is what enables the robust sounds in your headphones described above. Figure 1 shows how electricity flows more easily through silver.

Learn more about setting the sensitivity and and discrimination in these articles: How to Set the Sensitivity on Your Metal Detector and What is Discrimination on a Metal Detector and How to Set it.

You can adjust the settings on your detector to alert you when you have a rich signal that indicates silver. More specifically, you can turn off the beeps that represent less precious metals. The relatively inexpensive ACE series of Garrett metal detector features notch filtering, where you can select to hear only the most promising targets.

Figure 1: Finding Silver with a Metal Detector
Figure 1: Finding Silver with a Metal Detector

Figure 1 Silver has one “loose” electron in its outermost ring. This makes electron flow easier. Impure metals impede the flow of electricity, so the detector signal is not as clear.

Settings on Metal Detector for Silver
Figure 2: Settings for Silver on Ace 300 and White

Figure 2 shows detector displays which enable you to select only the high-end phase-shift coins. The ACE 300 uses notch filters. The more expensive detectors use reference code numbers, or Target Identification (TID) numbers to indicate the coin. Fore example TID number of 18 is almost always a nickel, and a quarter registers at 79. You can see in Figure 2 the area of high value on the face-plate next to the word “silver”

In practice, I find it best to combine the above two methods. I usually set the detector to find the more valuable coins, eliminating nickels and zinc pennies. I then keep my ears open for the tell-tale zipping sound of the silver targets. This method is best because you will sometimes find a silver ring, which registers lower on the discrimination scale but still gives you that distinctive zipping sound of silver.

Figure 2. Face-plate images for the Garrett ACE 300 and White’s MX Sport showing settings for silver.

Metal Detector Quality

There’s no diplomatic way to say this: The expensive detectors are much better at finding silver coins and jewelry than the cheaper models. Sure, you can often find the valuable targets with a $100 detector, but for the dedicated dirt-fisher, the advanced engineering of the high-end machines are your best bet.

a) Discrimination Ability

The more advanced detector models have more robust signal processing features and better discrimination, which allows you to separate treasure from trash. The technology for this sport has advanced markedly in recent years, to where you can now measure not only phase-shift, but target conductivity, target identity, and depth of the coin.

I was on a 3-hour club sponsored hunt in a park using a relatively decent $500 detector. My buddy following behind me covered the same ground as I did and he came up with a silver quarter at 9 inches deep. This happened three times in the same day. He got two silver quarters and a silver dime in locations I had covered just minutes ahead of him. His machine was $1,200 model.

b) Signal Processing

The latest technology in detectors means that the newer, more powerful detectors add a host of features that help you find coins and jewelry in a more productive manner.


  • Precise notch filtering.
  • Coil frequency selection.
  • Run multiple frequencies at the same time.
  • Specific conductivity settings.

Lower frequency settings lets you find objects that are deeper in the soil, and the higher frequencies help find smaller objects.

c) Battery Voltage – More is Better

Likewise, be sure you buy batteries that are listed at 1.5 volts each. Some manufacturers have switched to selling batteries listed at 1.2 volts each, instead of the standard 1.5 volts.

TIP: Change your batteries frequently. This applies to all detecting modes, but it helps substantially in silver hunting. A detector that takes four AAA batteries at 1.5 volts each should register near the upper limit of 6.0 volts DC. If each battery drops to 1.1 volts, that is a loss of 27% in power output.

Metal Detector Coil Type for Silver

a) Metal Detector Coil Diameter

In general, the larger the coil the deeper you will be able to detect coins. Very large coils, however can be heavy and difficult to handle for long periods of time. The standard round coil will produce a magnetic field that is essentially bowl shaped. An elongated coil will produce a field that is shaped like an oval bowl.

b) DD Coil – Best for Silver Detecting?

Your best bet for silver fishing is the double-D (DD) coil. This arrangement is actually two coils whose fields interact in such a way as to produce flattened spade-like magnetic field. Figure 3 shows the shape of the coil field for a round coil versus a double-D.

Different Metal Detecting Coils for Silver Coins
Different Metal Detecting Coils for Silver Coins

The flatter, fan-shaped scan area of the double-D coil makes it easier to pinpoint the coin, and the field penetrates deeper into the soil. Conclusion: The DD coil works much better.

Figure 3. (Left) Field shape of a round coil, or a DD-coil seen from the side. (Right) Field shape of a DD-coil seen from the end. The flatter scan area goes deeper and makes it easier to pin-point the coin in the ground.

Best Locations for Finding Silver with a Metal Detector

Your hunting location is just as important as your detecting gear. Here are some tips for finding silver.

a) Old Maps – Great for Metal Detecting

Silver currency started disappearing from circulation in 1964, when the mint switched to silver plated coins. Knowing where people lived before that date will be a big help in scanning the most productive areas.


  • Get an old map of your town, one that was published say in 1950.
  • Compare that to a modern map. Do you see where the old parks were located? Where the fairgrounds once stood?
  • Choose the 1950 locations instead of the new housing development that went in just 10 years ago.
  • Focus on the main roads into and out of your town.
  • Choose locations in open areas in and near the older sections of the city.

You will have a much better chance of finding silver in the areas that were populated long ago.

b) People and Places – More Dropped Coins

Use your brain in selecting a place to hunt. Here’s an (oversimplified) example. I live in a town at the base of the foothills of the Sierra Nevada mountain range. The old covered wagon trails snake through a narrow pass that ends in a wide valley. Guess where the wagon train, and later millions of motorists, will take a break, stretch their legs and lean back against an old oak tree.

A few miles to the west of that pass is a small town which happens to be in gold country. The early Wells Fargo Bank had an assay office in town where they would exchange gold for hard cash. The town town council recently decided the old main street was too narrow for modern traffic. They pulled up the sidewalks for repaving the streets and walkways. Guess who was there with a metal detector for the two weeks between the sidewalk removal and the pouring of the new walkways?

Well, you might not have such ideal locations or opportunities where you live, but the mental process will be similar. Search in old areas where people often congregated.

Important Tips for Finding Silver While Metal Detecting

Silver coins are often worth more as collector items than simply the value of the silver. You can destroy much of that value by gouging a deep scratch on the surface when you retrieve it.

a) Hand-Held Probe – Pinpointer

Do yourself a favor and buy a hand-held probe. They make pinpointing and coin retrieval about twice as fast.

Metal Detecting Pinpointer
Metal Detecting Pinpointer

A complete guide to selecting a Pinpointer for Metal Detecting is HERE – What is a Pinpointer for Metal Detecting and Do I Need One?

b) Handle any Silver Finds with Care

When you find a potential silver target:

  1. Scan the target from one direction, say facing north.
  2. Scan again at 90 degrees, say facing west.
  3. You should now be able to pinpoint the exact coin location.
  4. If you have one on your detector, check the depth reading.
  5. If you have a hand-held probe, try to fine-tune the target area.
  6. Place your digging tool about 2 inches to the side of the target.
  7. Press the digger at least one inch deeper than the depth reading.
  8. Crank out the dirt slug and scan with your hand-held probe.
  9. Grab the coin from the edges without rubbing dirt across the surface.
  10. Let your face break out in a gleeful smile.

Most soil contains sand, or silica (silicon dioxide), often in the form of quartz, which is extremely hard and will easily scratch the softer silver. Even rubbing the dirt off with your fingers is enough to cause a scar. Best bet is to carry a small medicine container filled with soapy water. Drop the coin in there and wash it carefully when you get home.

c) Avoid Over-Fished Metal Detecting Sites

Many clubs have weekly events where dozens of detectorists descend on an urban park. These sites may be over-fished. They have been scoured many times for coins. Instead, focus on smaller parks, grassy areas near major travel routes, and open fields near the center of town.

Finding Silver with your Metal Detector

There’s an old saying: Treasure is where you find it. You can, however, increase your odds of success by applying some of the ideas discussed here. Good luck!


Vince Migliore is a writer and researcher. He has written numerous magazine articles on metal detecting and three books. His latest book is “The Art and Science of Metal Detecting,” available in paperback at Amazon.