Metal Detecting FAQ and Tips
This Metal Detecting FAQ and Tips guide provides helpful information and insights on everything from choosing the right metal detector and accessories, to understanding how to interpret signals and properly use your equipment.
Where are Minelab Metal Detectors made?
Minelab Metal Detectors are designed in Australia and made in Malaysia.
Are most metal detectors basically the same?
Metal detectors are like cars: They have many different technologies, features, and performance characteristics that revolve around their intended use. There are five basic types of metal detectors:
- General Purpose: Coin/Relic/Treasure
- Gold Prospecting
- Underwater and Salt Beach
- Cache Hunting/Deep Searching
- Industrial and Security
Some metal detectors are designed specifically for one type of searching. For example, Gold Prospecting detectors are designed to be extremely sensitive to small pieces of gold. General Purpose models are typically not designed to detect metals as small as a grain of rice but do offer far superior trash metal rejection compared to prospecting models.
When purchasing a metal detector, it is important to consider what type of metal detecting you will do most often and prioritize according to your typical use.
How deep do metal detectors detect metals?
This is the most frequently asked question and unfortunately the most difficult to answer! Most General Purpose models are factory equipped to search for coin and jewelry sized metals at depths of 8 to 12+ inches, depending on metal size and alloy. To significantly and consistently detect beyond 12 inches requires larger accessory search coils, and/or to give up attempts to eliminate trash metals. The 15" search coil responding to all metal alloys can detect larger metal items (coin jars) at depths up to four feet. However, sensitivity to single coins is greater with smaller search coils. White's TM 808 can detect 55-gallon drums at 16 feet and car-sized metals at 20 feet. However, it is not likely to respond to individual coins or pieces of jewelry.
Detection depth varies with many factors:
- The size, shape, exact metal alloy, and orientation of the object in the ground. Objects with greater surface area can be detected at greater depths. For example a coin lying flat exposes a greater surface area than a coin lying on its side and will be detected at a greater depth.
- The size of the search coil. Search coils come in a wide range of sizes and shapes, including 4", 6", 8", 9.5", 12" and 15". There are also differences in the configuration of the coils inside the search coil producing different shape search patterns. The larger the search coil, the deeper it can detect larger metal items. However, it is more difficult to use in trashy areas with less depth to find small metal items. Smaller search coils provide better separation in high-trash environments and better sensitivity to small metals.
- Soil conditions and the amount of minerals in the soil. The higher the soil mineralization (i.e. the presence of magnetic and/or conductive properties) the more difficult it is for a metal detector to cancel the interference these soils produce. Detection depth is reduced in severe grounds. Depth may increase or decrease with subtle changes in the soil conditions, more noticeably with the entry level models. Soil mineralization varies widely around the country and around the world.
- The experience and skill of the operator. There's no substitute for experience. Knowing how to operate your detector and understanding the signals will significantly increase detection depth.
- The metal detector used and the selection of settings, particularly All Metal or Discrimination.
What types of things will a metal detector help me find?
All metallic objects. Example: gold, silver, iron, nickel, copper, brass, aluminum, tin, lead, bronze. Metal detectors will not detect nonmetal items such as gemstones, diamonds, pearls, bone, paper, or stone figures.
What is discrimination?
Discrimination is the ability of a metal detector to tell the difference between different types or alloys of metals. This allows you to selectively dig up only those types of metals likely to be of interest to you. There are audio (speaker/headphone) types of discriminators and visual (meter, LCD) types. Most higher-end models have both types. The idea is to increase the odds in favor of digging valuables, and decrease the odds of digging trash.
Can a detector be set only to respond to gold?
No. There are too many variables with exact alloys and sizes to pin it down tightly enough to dig only one type of metal. For example, a large piece of gold may read high on a display or audio discrimination scale and a small piece of gold may read low on that same scale. Gold with some copper, silver, or platinum within its natural alloy will indicate differently. And other metals with similar electrical characteristics may read identically. Lead and aluminum are the most difficult common trash metals to eliminate. Even with the most sophisticated detectors available, expect to dig some trash. But a good discriminator increases the odds in your favor.
What is operating frequency?
Frequency in a metal detector is referred to in kHz (kilohertz, or 1,000 Hertz). Frequency is the number of times the signal is transmitted and received by the detector every second. For example a metal detector operating at 6 kHz will transmit and received 6,000 times per second; and at 50 kHz, this occurs 50,000 times per second.
As a rule, lower frequency detectors offer better sensitivity to copper and silver and better overall detection depth and trash rejection. Most general purpose models operate at lower frequencies.
Higher frequency detectors are more sensitive to small metals and natural gold. However, they have difficulties with discrimination against nonferrous (not-of-iron) metals. They’re sensitivity to small metals makes them tedious to use around trashy areas. Most gold prospecting detectors operate at higher frequencies.
Are there any good places left to hunt?
Nobody gets it all. Just because an area has been hunted before doesn't mean a person with patience and a modern detector can't still find the "good stuff" just about anywhere. Research can still turn up places which may never have been searched. Seasonal changes such as storms, frost heaves, and erosion can also renew areas — particularly beaches where the surf is a constant source of new targets.
What will target ID displays or meters do for me?
Many models have displays that indicate the likely identification of the metal detected. This is in addition to the audio discriminator. Once an audio signal of interest is heard, the display will give a second, independent, opinion about whether the target is a good target, or trash. You dig less trash with an ID display.
ID displays are a very accurate measure of a target's "electrical phase." Unfortunately, many different metals have the same electrical phase. The Target ID will increase your odds of digging good alloys and decrease your odds of digging trash alloys. If, in a given area, a particular indication consistently turns out to be trash, such indications in that area are likely to continue to be trash and can be ignored.
I want to go metal detecting with friends and family. Will multiple detectors interfere with each other?
Yes. Like models operating on the same frequency will interfere with each other if operated within 100 feet. To search with a partner nearby, at least one of the instruments requires the frequency shifting feature.
The standard equipment search coil is ideal for all-around searching. A person may want to use a smaller search coil for extreme trash (lots of close-together targets). A person may want to use a larger size for increased depth. Larger search coils, such as 15" loops, are recommended for larger targets (jars of coins) at extreme depths. Remember, with a 15" search coil, sensitivity to coin-sized targets decreases.
What about a carrying case for my metal detector?
For everyday use, the gun style detector bags are recommended. The detector and accessories can be installed and removed easily, without taking the detector apart. Shock-proof cases are intended for more serious storage and travel.
Do I need headphones?
Headphones will increase battery life, increase privacy, and increase your ability to hear signals clearly against background noise. They offer benefits even to those with excellent hearing. Crisp sound is typically more important than wide frequency specifications. In most cases, higher impedance headphones (100 ohms) offer crisper sounds.
What about rechargeable batteries?
Rechargeable batteries will save you money if you use your metal detector often, at least once or twice a week. If you use your metal detector once a month, rechargeable batteries will not likely save you money. Rechargeable batteries do offer the same metal detection performance — most models use a voltage-regulated system.
Where can I use a metal detector?
You must have permission to search both private and public property from the owner or person in charge of managing the property. In most cases you can locate the owner, or available permit system, through City Hall or the county seat.
If the area is city owned, contact the Parks and Recreation Department. If it is a State or Federal Park, contact the superintendent or grounds keeper. Known and marked historical sites, historical parks, and historical monuments are typically off limits to all metal detecting.
Start with your own yard. Valuables can be found anywhere people have congregated, gathered, lived, sat, walked, played, camped, picnicked, traveled, or fought. Any place inhabited before 1965 is likely to have the older styles of collectible coins.
How do I recover the target once I decide to dig it up?
Care must be taken to use the appropriate digging tool for the terrain, and not to leave unsightly excavations or holes. There are hundreds of digging tools designed to minimize the impact on grass and vegetation, and avoid damaging the items found. Sand scoops are all that is needed in some areas. In others, a hand gardening trowel or spade. Challenging ground conditions may require more sophisticated tools.
Some areas may have rules on the type and size of digging tools allowed. Make yourself aware of these rules. Respect the laws and restrictions in your area — unsightly holes left unfilled are dangerous to people and livestock, and are detrimental to the continued use of detectors.
What is sweep speed?
All modern detectors require some movement (sweep) of the search coil in order to respond to metals. If the search coil is swept too slowly, metals do not respond, or do not respond at as great of depths. Every model has an ideal search coil sweep speed, usually between two and four seconds per pass. Experimenting to find the ideal search coil sweep speed allows optimum detector performance.
A first time user typically has to practice to find their comfortable search coil sweep technique. Seeing others with good search coil sweep habits is a big aid in learning. Practice makes perfect. The desire is to sweep the search coil evenly with the ground in smooth even swings. Overlap each pass by at least 50%, always keeping the search coil in motion. Recognizing where the beep is on each pass and shortening the passes to zero in on the location (pinpoint) takes some practice as well.
What about after-market devices that claim to add depth to my detector? Do they work?
A well-designed metal detector has all the usable detection depth (gain) built into standard features. The only way to significantly increase depth is to maximize the standard features or use a larger search coil. There are many aftermarket devices that can make it easier to hear the metal detector, giving the impression of greater depth. Their degree of success depends on the individual's hearing abilities.
I want to go nugget shooting once a year, beach combing once a year, and the rest of the time I want to go hunting for coins and relics. What model of instrument should I be looking at?
A General Purpose detector would give you the best all-around performance. Only when beach or prospecting consumes the majority of your search time would it be wise to look at a model specifically for that purpose. Although prospecting or beach models offer increased performance for their purpose, they are not as effective as a General Purpose models for coin and relic hunting.
How Often Should I Clean Out My Skidplate?
Dirt, dust and moisture can be trapped inside the skidplate leading to false signals and poor performance. To maintain peak performance of your metal detector, it is recommended to clean out the skidplate quite regularly.
Can Metal Detectors Tell What A Target Is Likely To Be Before I Dig It Up?
Yes, metal detectors have the ability to ‘discriminate’ between different types of targets. The discrimination feature on most metal detectors measure two target properties, ferrous properties and conductive properties.
Ferrous properties refer to how much iron is in a target and therefore how strongly it’s attracted to a magnet. Ferrous targets tend to be trash, so can be discriminated/masked out based on their ferrous properties alone by the detector. Conductive properties refer to how well a target conducts electrical current and therefore responds to a metal detector’s magnetic field. Trash like nails and foil have different conductive properties to valuable targets like coins and rings. In this case the metal detector can make a judgement as to whether the target is trash based on conductivity.
The process for configuring the discrimination settings and the method used to indicate treasure or trash varies across the range of metal detectors.
How Do Different Coils Affect The Performance Of A Metal Detector?
Size
The size of a search coil can influence the detection depth or sensitivity of a metal detector. The larger the coil, the deeper it detects, but will have less sensitivity to small targets. Conversely the smaller the search coil’s diameter, the more sensitive it becomes but looses detection depth.
Smaller coils are lighter, easier to control and may be chosen for their ability to negotiate difficult terrain or undergrowth. They are also an advantage in areas of high trash.
Shape
The most common coil shapes are conventional solid round coils, elliptical-shaped coils and the open web coils. The main reason for the change in shape is to conform to a physical requirement, i.e. an elliptical coil can be pushed around bushes or between rocks easier than a round coil and open web coils move through water easier and are lighter. Conventional round coils are often more stable and perform better and are particularly popular for gold prospecting.
Configuration
The three most common types of coil windings are Concentric, Double-D, and Monoloop. The difference between these coil types is the pattern the wire is wound within the search coil.
Concentric coil
A Concentric coil has an inner circle and an outer circle wire winding. Its search pattern is cone-shaped and can be useful for accurately pinpointing a target. Concentric coils tend to be noisier in highly mineralized ground and require more overlap of sweep for thorough ground coverage.
Double-D coil
Double-D coils are the preferred coils for most detecting. They give a blade or chisel-shaped signal that covers the ground more uniformly and once an operator becomes accustomed to the signal, pinpointing can be very accurate. Double-D coils are also preferred for their superior ground balancing ability.
Monoloop coil
Monoloop coils have one winding of wire around the circumference of the coil, which is used to both transmit and receive. The signal pattern of the Monoloop coil is cone-shaped, requiring more overlapping. In extremely heavily mineralized grounds they can be more difficult to ground balance, however, they tend to provide slightly better depth than the Double-D coils.
What Are The Recommended Impedance Values Of Headphones For Each Detector?
Headphone specifications are not really critical in a metal detector as their audio circuitry does not produce Hi-Fi quality sound. e.g. most detectors frequency output range is only circa 75 -1200Hz
Metal Detector audio circuits will drive most headphones from 16 - 100 + ohms.
Audio optimization is also very subjective as everybody hears differently.
We endeavor not to confuse our customers with unnecessary technical specs because in reality there is no honest way to determine what headphones are best for you other than to try them.
If you have a detector with adjustable audio tones, we would also recommend you spend some time to ensure the detection tones are optimized for your hearing needs.
How Often Should I Send My Detector Back For A Service?
Only if it becomes faulty.
How Often Should I Ground Balance, Where Should I Ground Balance?
On some detectors, you don’t need to ground balance at all. On others, users new to detecting are recommended to use the Ground Balance Tracking function.
In Tracking, the detector will automatically ground balance for you and remain in balance even if the ground minerals vary. On manual ground balance detectors, you need to ground balance at the start of every hunt, and re-balance periodically as required. Always ground balance on clean ground, away from metal objects.
Why Can’t My Detector Detect A Gold Chain?
Gold chains are very difficult to detect, particularly very fine chains. Each link of a chain can be very small and the detector sees each link as a separate target, so it can easily be missed. You are more likely to detect the actual clasp or any pendants that may still be on the chain as these are much larger than the individual chain links. High-frequency detectors, will often pick up fine chains better than most coin detectors.
Why Does My Detector Pick Up Some Coke?
Coke is carbon and as such can be quite conductive, just like a coin.
I Would Like To Extend My Coil Cable, Can This Be Done?
No, cable characteristics are matched to coil windings at manufacture, so extending the cable will reduce the performance of the coil.
Can You Recommend A Good Coil For Trashy Ground?
Smaller coils are better for trashy sites, as they reduce the instances of detecting multiple targets at once. Concentric coils are generally better than Double-D coils for this same reason.
Check the coil selection guide to find the most suitable coil for your detecting needs.
Why Does My Detector Pick Up Signals In The Air?
Metal detectors pick up electromagnetic signals from underground metal objects. Similar signals can also be received through the air from other electromagnetic sources, such as power lines, radio transmitters, generators, etc.
How Will I Know If The Ground Is Mineralized?
If your detector is noisy when you are detecting, but goes quiet when you stop sweeping the coil, then it is receiving signals from the mineralized ground. Perform a ground balance and continue detecting.
Is It Possible To Miss Good Targets With Preset Discrimination Patterns?
The only guaranteed way to get every possible good target is to use no discrimination. However, digging every target can waste lots of time. Discrimination patterns are always a compromise between digging most good targets and ignoring most junk targets.
Sometimes I Dig What Seems To Be A Good Target And Then Cannot Find Any Metal, Why?
This can be caused by a number of reasons:
- Sometimes rusty objects get broken up during the digging process
- Metal objects can leach trace elements into the surrounding soil
- Some rocks can sound like targets
- Some targets get ‘lost’ or reburied during the digging process
Why Do I Sometimes Get A Signal At The End Of My Swing?
Usually because you are lifting the coil at the end of your swing. Always sweep slow, low and level for the entire swing.