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FAQS About Metal Detectors

How does a metal detector find metal?

Essentially, a metal detector detects metal through the transmission and reception of VLF) magnetic waves. Most of today's detectors operate

A magnetic wave is transmitted through the transmitter portion of the detector's searchcoil, which subsequently generates an invisible, intangible magnetic field that balloons outward into the surrounding medium, such as air, earth, clothing, water, etc.. The field size varies depending upon the size of the

When metal enters this magnetic field, it absorbs some of the field's energy. The remaining energy causes eddy currents to flow over the surface of the metal, creating a smaller, secondary magnetic field that also flows into the surrounding medium.

The receiver coil in conjunction with the detector's circuitry measures the field's power loss and detects the presence of the secondary field. Essentially, a metal detector "finds" metal by simultaneously interpreting these two effects and conveys the results via an audio and/or visual alarm.

All metals are classified according to their ability to conduct electricity. A metal is typically referred to as a good conductor (e.g., aluminum, gold, and silver) or a poor conductor (e.g., iron and stainless steel).

You can find out more information about the art of metal detecting, in Charles Garrett's book, Modern Metal Detectors.

What does a searchcoil do?

A searchcoil is the most vital part of a hobby detector. It is the device attached to the control housing, which "connects" the metal detector to the ground beneath it. It contains a transmitter and a receiver, which help the detector

Searchcoils are available in several shapes and sizes to meet a variety of hunting needs. Generally speaking, small searchcoils are designed to detect small shallowly buried objects, while large searchcoils are used to find large, deeply buried objects, such as relics and Caches. Coils can range in size from four to 12 1/2 inches in diameter. An all-purpose detector usually comes equipped with an eight- or nine-inch searchcoil that is practical for scanning parks, playgrounds, beaches and other popular coin-hunting locations.

A small searchcoil is often used in very trashy areas because its magnetic field penetrates a small area and therefore is less likely to pick up unwanted targets like trash. The Garrett four-inch Super Sniper is great for isolating

A large coil, whose magnetic field is wider and penetrates the ground more deeply, is best used in relatively clean areas, where there's little risk of good targets being masked by nearby pieces of junk metal. (Masking is a phenomenon that can occur while hunting in discriminate search mode instead of an all-metal or zero discrimination mode.)

Can I identify a detected object before I dig it up?

Unfortunately not 100% of the time. However, recent advances in microprocessor technology have enabled many metal detectors to avoid trash and to better retrieve and interpret information about a buried target.

Most microprocessor-driven detectors can be calibrated to include or exclude certain metals from detection via a user-adjustable discrimination (also referred to as elimination) mode. Metals are classified in a linear numerical scale according their ability to conduct electricity. At the low end of the scale are iron, foil and nickel, followed by nickel, aluminum and gold in the middle and gold, zinc and silver at the high end.

Typical discriminating detectors can determine to a relatively accurate degree, the target's conductivity and if it's a coin, can also determine its depth. But only Garrett's Power Master DSP-enhanced GTI detectors take target identification a step further by revealing the target's true size and true depth no matter

The GTI's unique ability to go beyond conductivity and retrieve information about any detected target, including trash, means that you know what the object is before you dig it up. Thanks to the GTI's easy-to-read Treasure Vision™ screen with graphic target imaging, a drink can is revealed it for what it really is - a can - NOT a quarter. And it doesn't matter whether the can is flattened or lying on its side, the GTI still identifies it as a can.

You can find out more information about the capabilities and limitations of metal detectors in the book, Modern Metal Detectors, by Charles Garrett.

At what depths can a detector find treasure?

It depends. Many factors can affect how deep a detector can detect, such as the condition of the soil, the material of a detected object and the quality of the detector itself. The size and surface area of a target also affects detection. For example, the larger a metal target, the easier and more deeply it can be detected. Therefore, it's impossible to predict with complete certainty how deep a specific detector can be expected to find something.

Generally speaking, a detector equipped with a standard-sized eight- or nine-inch searchcoil can be expected to detect:

Small jewelry (e.g., necklaces, thin gold rings) at 3 to 6 inches

Large jewelry (e.g., class ring) at 6 to 12 inches

Small coins (e.g., dime, penny) at 4 to 6 inches

Large coins: (e.g., quarter, silver dollar) at 6 to 12 inches

Mason jar lid at 9 to 16 inches

Coffee can at 1 to 2 feet

Cannonball, helmet, etc. at 2 to 3 feet

Using a searchcoil larger in diameter can also help a detector achieve greater depth. A 12 1/2" searchcoil produces a more extensive magnetic field that penetrates the ground more deeply to find objects at depths that a smaller size searchcoil can't reach.

How can I pinpoint a detected target?

Proper pinpointing enables you to recover a detected target quickly without damaging it or the ground above it.

First it is important to ensure you are applying the proper scanning techniques.

Slowly and methodically sweep the searchcoil from side to side, keeping it one to two inches above the surface. Overlap each sweep by advancing the searchcoil by about one quarter to one half of its diameter. Scanning in a straight line helps to keep the searchcoil level and the overlap sweeps uniform while reducing the likelihood of lifting the searchcoil after each sweep.

Listen for a peak in the audio sound. Hold the searchcoil one to two inches off the ground and slowly sweep it back and forth in an X pattern. Note where the sound becomes the loudest. The target should be located in the center of the imaginary X.

What do I need to know about batteries?

NiCads (nickel/cadmium) and nickel metal hydrides are rechargeable batteries that last between 8 and 12 hours and cost up to 10 dollars each. Alkalines are disposable batteries that last between 25 and 30 hours and cost about two dollars each.

Because extreme temperatures can drain battery power, it is recommended that you always carry a spare set of batteries. In cold weather, attaching the battery pack to your belt under your jacket can help keep batteries warm and dry.

Is overall depth compromised when searching with discrimination?

Yes. To achieve the greatest depths when searching for large, cache sized-objects, many professionals hunt in the All-Metal mode and use a large searchcoil.

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