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Sunday, October 19 2014

All metal detectors, regardless of brand or model, are susceptible to electrical interference. The high sensitivity of today's metal detectors combined with numerous sources of electromagnetic interference in our environment means you are likely to encounter electromagnetic interference  at some point while out detecting. In general, the most sensitive models and brands tend to be affected more than lower-end models. Since you're likely to experience this, it's important to learn a little about electrical interference and its "symptoms" so that you don't unnecesarily send in your machine for repairs, and so you don't give up and leave a good hunt site too soon.

Examples of interference include overhead and/or underground electric power lines, thunderstorms, electrical fences, electric motors, and VLF-UHF wireless communication systems such as cell phones, Bluetooth, Wi-Fi, etc. These common sources can cause a machine to "chatter" spontaneously, lose sensitivity for no apparent reason, or to cause "wobble" in the audio. What you might experience will depend on what model of detector you are using, the operating mode it's in at the time, and the source of the interference. It's interesting to note that small searchcoils usually pick up less electrical interference than larger coils, and concentrics usually pick up less electrical interference than a DD.

All detectors are equipped with a sensitivity control (sometimes called gain or threshold). The primary reason detectors provide sensitivity control is so that users can reduce sensitivity in order to eliminate response to electrical interference. You might be hesitant to reduce sensitivity out of fear of losing depth, but don't be. The sensitivity control really is your first line of defense against electrical interference, so use it. Many mid-range and high-end detectors also have a "frequency shifting" control. This can be used to reduce or eliminate certain kinds of interference such as power lines, but it won't be effective against other types such an thunderstorms. Consult the user manual for your particular model for more information.

Many detectors have both a Discrimination Mode and an All Metal Mode (often called Autotune Mode) which has a slower, smoother response than Discrimination. Electrical interference is often more controllable in the All Metal Mode than in Discrimination Mode. In the latter, you'll often find that although the machine may seem chattery if the searchcoil is not in motion, once you start to sweep, the signal from the ground will suppress the electrical interference chatter except for a random pop or click noise. When doing "air testing" indoors, you may find that changing the orientation of the coil makes a big difference in electrical interference pickup.

metal detectingIf you carry a cell phone or other high-tech gadget with you out in the field, try turning it off (all the way off -- not just airport mode) and see if that solves the problem. When hunting near overhead power lines, you may get the best results right under the lines; the worst results occur about a 30 to 45 degree angle away. Many sources of interference are intermittent, so through trial and error you might find that a particular time of day or day of the week is makes it more or less difficult to detect. Power lines are usually quietest late at night and on early weekend mornings.

If you're experiencing a "noisy detector" but electrical interference is NOT the problem, then the culprit could be a defective searchcoil or its cable or connector. In many cases, a defective coil is intermittent, which can be determined by giving it a solid whack with your hand. If whacking it fixes the problem briefly, then you know for sure electrical interference is not a factor. Dirt or water in the coil cover or scuff could also cause problems. If you use a cover to protect your coil from abrasion, remove it periodically and clean it. Dirt and water can move around while you're sweeping, causing false signals. And although rare, a noisy detector could be caused by an internal calibration which has drifted over time. It is very uncommon in today's detectors, but if you have a very old machine, it's worth getting it checked out.

Keep in mind that on most metal detectors, especially high performance models, the sensitivity can be adjusted high enough to "work into the noise." This is not a defect, rather an intentional design feature. Experienced detectorists striving for maximum depth often adjust the machine to "work into the noise" and then they listen "through the noise" for the sound of real targets.  In general, if you experience a noisy detector, first determine if electrical interference could be the cause and use the advice listed above to overcome it. If you verify that the problem is not from electrical interference or improper use of your machine, by all means send it back to the factory for repairs.

Posted by: Denise AT 03:47 pm   |  Permalink   |  0 Comments  |  Email

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