Metal Detectors ∞ Headphones ∞ Sand Scoops ∞ Gold Pans ∞ Coil  ∞ Chargers

How a metal detector works:

Metal detectors work due to the fact that metal is conductive. Metal detectors create an electro-magnetic field, which penetrates the ground. When the search coil senses a change in this field (caused by a metal object) it sends a signal back to the control box which then alerts the operator. Metal detectors react to the surface area of the objects, not their mass, therefore the larger the object, the deeper it can be detected.

Operating Frequencies and sensitivity:

Measured in kilo Hertz (kHz) the frequency is the number of times a signal is transmitted into the ground and received back, per second. The lower the frequency used by a detector, the deeper it can normally penetrate. At low frequencies however, the sensitivity to small targets is sometimes reduced. The higher the frequency, the higher the sensitivity to small targets, but it may not penetrate as deeply. In general, gold detectors operate at higher frequencies (to find small nuggets) while coin and treasure detectors work at lower frequencies for deeper penetration (the exception to this is MPS type detectors that are sensitive and deep-seeking simultaneously).

Difficult Soil:

Soil contains naturally occurring salts and minerals, which are known as mineralization. Areas of highly mineralized soil are generally known as difficult soils. Sandy or loam soils are low in minerals and are usually very easy to detect. Most detectors have a control called ‘ground balance’ which is used to compensate for the areas where mineralization varies. Here, the operator must repeatedly re-balance their detector unless their machine features Automatic Ground Tracking (AGT) technology, which will continuously and automatically adjust the detector for ground balance.

Quiet Ground:

Quiet ground does not contain minerals. It is neutral and generally loam to sandy in consistency. Ground balancing a metal detector is much easier in these conditions.

Discrimination:         

Discrimination refers to the ability of the metal detector to estimate the type of metal a target is made of. Discrimination gives you the ability to ignore unwanted objects like iron, steel, pull-tabs etc. while detecting for valuable items made from metals like silver, gold, brass or copper.

Coils:

The coil sends an electro-magnetic field into the ground and receives a response that is interpreted by the control box. The size of the coil can affect the depth a target can be detected, or the sensitivity to that target. Coils may have different search patterns, depending on how they are made. There are two coil types; Double-D and Monoloop which give the greatest detection coverage, depth and highest level of overall performance. By changing the size or design of coil, the detector can become more versatile for changing conditions.

Depth:

This refers to the distance that the metal detector can penetrate and detect metal objects into the ground. This can be influenced by the frequency the metal detector is operating on (low frequency tends to give better depth than high frequency and vice-versa), how sophisticated it’ circuitry is and how well it will cope with highly mineralized soil. Often some metal detectors produce extraordinary depths in air but are disappointing when used in the field. Some detectors with BBS & FBS (broad band spectrum/ full band spectrum) technology scans in multiple frequencies to give depth and sensitivity. If gold prospecting in mineralized soils, the MPS (multi-period sensing) technology which pulses in different frequencies and band widths are the most versatile of all.

Sensitivity:

This is also determined by the frequency of the detector. Depth on larger targets often suffers when a detector is only searching in high frequency. The higher the sensitivity setting, the smaller amount of signal a target needs to produce to have the detector give an audio signal. A very small or very deep target will not produce the amount of signal that a large or shallow target will. By increasing the sensitivity, the detector will give an audio signal to the smaller and deeper targets.

Discrimination:     

This is the function some metal detectors have that enables the operator to determine what type of metal has been detected before digging it up. This is a great time saver for treasure hunters with some discrimination systems being highly accurate. Notch discrimination enables the operator to cancel out some unwanted metals without canceling out everything below the level of discrimination being used. Discrimination is not advised when using the metal detector to search for gold nuggets, as the impurities in gold and the concentrated minerals in the soil around the nugget will confuse the discriminator and may produce a false reading. For this reason a lot of metal detectors manufactured specifically for gold prospecting have limited discrimination ability.

Ground Balance:

For gold prospecting, this is probably the most important function on the metal detector and often the only one that is overlooked when comparing capabilities of each metal detector. Ground balancing is setting the metal detector so that it can compensate for the effect the minerals in the ground have on the machine. This allows it to scan the ground and only give a signal when it passes over a metal object. If this is not done properly the metal detector will produce false noises from the ground itself and you will find it very difficult to tell the difference between ground noise and a metal target.

All metal detectors come with ground balance of some sort, some can be manually adjusted, some are factory pre-set and some are true automatic. The metal detectors with automatic ground balance excel in highly mineralized soil areas, as their ability to test the ground and compensate every few seconds make them so much easier to use and more efficient.