FAQs

The depth at which you can detect targets varies based on the machine you're using and a lot of other factors. Here are some things that can affect detection depth:

• The soil's conductive properties. If the soil is heavily mineralized, it can reduce the penetration depth of your detector. You can ground balance your detector (some detectors do this automatically) to account for soil mineralization. For detectors with automatic ground balancing, it may help to decrease sensitivity and/or increase discrimination. (Find out more about Ground Balancing.)
• Target's time underground. Chemicals in the soil can cause metal to corrode; different metals decay at different speeds. As metal corrodes it rusts, releasing that rust into the soil. When that happens, the soil around the target becomes more conductive, making the target appear bigger than it actually is.
• Target size. The larger the target is, the easier it is to detect, and the deeper a sensor can detect it.
• Target shape and position. Ring, loop, flat, or dish-shaped objects lying horizontally are easiest to detect. Anything shaped like a rod, especially if it's placed vertically, is hard to detect.

That depends on what you're trying to do! Different coil sizes have different strengths. Many users find it helpful to have more than one coil size on hand for varying conditions.

• A small coil is lightweight and can be ideal for long searches. It's also better for picking out targets in high-trash areas.
• A standard coil is about 8"; this is considered an all-purpose coil. This popular coil size does well in most conditions.
• A large coil is ideal for low-mineralization, low-trash areas. It can cover more ground and penetrate 5 - 15% deeper.
• An elliptical coil makes it easier to get into nooks and crannies.

When you use discrimination, you're telling your metal detector to ignore small amounts of metals. Hunters often use discrimination in high-trash areas, or where there is soil with high mineral content.

When discrimination is turned off, the detector registers everything within the detectable range. Increasing discrimination lets your detector ignore small bits of metallic trash and ground mineralization. As you raise the discrimination level, your detector will ignore larger objects, like small nails and can tabs; it will also ignore some good targets, like nickels or gold rings.

It's a good idea to learn where to set discrimination on your machine for specific targets. To do this, scatter a variety of objects on the ground. Set your detector at its lowest discrimination setting, and scan each object. Gradually increase discrimination, and note the point at which your detector starts ignoring each object.

Sensitivity is an important tool – don't just set it to maximum and ignore it! You should adjust your sensitivity based on the conditions in which you're hunting.

It's generally a good idea to lower sensitivity around radio stations and power transformers, and in areas with heavy ground mineralization. Lowering sensitivity may reduce your detection depth, but it can prevent trouble with false signals or "chatter."

A good set of headphones can help maximize your number of good finds. They dampen outside noise from wind, traffic, waves, etc.; and they make it easier to hear the audio target signal. And because your detector can produce a quieter audio tone, using headphones saves you battery life.

False signals are a response from your detector to something other than a metal object. This happens most often in areas with naturally occurring iron oxides, like magnetite or hematite. The "black sand" common to areas with placer gold deposits is made mostly of magnetite.

You can ground balance your detector to help eliminate false signals. In some areas, mineralization changes abruptly, and you may need to adjust ground balance as you move; other areas may be so mineralized that adjusting sensitivity becomes necessary. (Find out more about Ground Balancing.)

The Fisher Gemini-3 is specifically designed for large, deep targets like caches (deliberately buried treasure) or buried pipes. Keep in mind that this two-box deep detector type is limited to larger objects at least the size of a cantaloupe.

Fisher tries to keep close tabs on this issue. The company is not aware of any reports of a hobby-type metal detector interfering with a pacemaker or other electronic medical device, or having any other adverse health effect.

A hobby metal detector's electromagnetic field is many times weaker than electromagnetic radio waves from a broadcast transmitter, a CB radio, or a cell phone, and weaker than the fields of walk-through security detectors like the ones found in airports.

Government agencies have spent a lot of time researching this issue because hundreds of millions of people are exposed to the electromagnetic fields in walk-through detectors every year. Over the years, there have been no more than a handful of reports of small malfunctions resulting in no lasting harm. However, because there is never a 100% guarantee of safety, companies that use walk-through detectors commonly post notices that people with implanted electronic medical devices may be hand-searched instead of walking through the detector.

Manufacturers design pacemakers to resist electromagnetic interference. Pacemakers and most other electronic medical devices are subject to FDA approval and stringent reliability and safety standards. However, Fisher has no control over pacemaker manufacture, and therefore cannot guarantee their performance.

A hobby-type metal detector's magnetic field is concentrated to within a few inches of the search coil. Even if you brought that magnetic field up close to an electronic medical device, the device would most likely continue to work properly. Even if there were a temporary malfunction, the device would most likely self-correct and resume normal operation once the search coil was removed. Still, obviously, common sense tells us that no matter how safe it is likely to be, we should not put a metal detector search coil directly next to an electronic medical device.