What makes one brand of metal detector better suited for finding coins than another? Will the very same metal detector also be a good choice for finding gold? It all depends on the operating frequency of the metal detector.
Metal detector frequency explained
In electronics, we define frequency as the number of waves that pass a fixed point in a given unit of time. Frequency is measured in Hertz (Hz), Kilohertz (kHz), Megahertz (MHz), or Gigahertz (GHz). Generally speaking, very low frequency (VLF) metal detectors have operating frequencies between 3 kHz – 100 kHz. A metal detector that operates at a frequency of 10 kHz for example, is capable of transmitting and receiving 10,000 waves per second. And where are these waves going? Into the ground of course! And what are these waves doing? Looking for responses from conductive (metal) objects that are buried in the ground!
Lower frequencies, such as 4 kHz, have longer wavelengths which allows for deeper ground penetration. Higher frequencies, such as 18 kHz, have shorter wavelengths and therefore do not penetrate the ground as efficiently. There is also a relationship between frequency and conductivity. Lower frequencies are better when metal detecting for highly conductive targets such as large silver coins. Higher frequencies on the other hand are better when metal detecting for smaller targets and for gold which is a low conductor.
In case you were wondering; I was not voted most popular back in highschool! If you’re still awake, I’m going to go ahead and explain, in practical terms, why you wouldn’t just run out and buy a 4 kHz metal detector. It might seem like the obvious choice, given the information above, but there are reasons why metal detectors with low operating frequencies might not be ideal for use in all scenarios. For example, although metal detectors that operate at lower frequencies might work well for finding large silver coins, they will struggle with finding fine gold such as thin chains and rings. Metal detectors that operate at lower frequencies are also not well suited for finding small silver coins such as the US three cent silver (trime) and European hammered silver coins. Lastly, metal detectors with lower operating frequencies do not separate targets as well as metal detectors with higher operating frequencies do.
Metal detectors with operating frequencies of 18 kHz and higher are ideal for finding gold as well as relics and other smaller targets. Metal detectors with higher operating frequencies may not, however, be the best choice for finding smaller high conductors such as silver dimes. As you are beginning to see, no single metal detector, or operating frequency, is ideal for every scenario. Metal detecting is a hobby of tradeoffs. Fortunately however, when it comes to metal detecting operating frequencies there seems to be a sweet spot, at least as far as metal detecting in the United States is concerned.
In the United States, metal detectors with operating frequencies between 12 kHz and 15 kHz will provide the user with the most versatility. Metal detectors that operate between these frequencies will be best suited for coin shooting, but will also hold their own with regards to finding fine gold jewelry. You may have even heard metal detector enthusiasts referring to a particular brand of metal detector as being a “coin machine.” Now you know why! There is a technical reason why certain metal detectors such as the Garrett AT Pro, Fisher F75, and Whites MXT All Pro excel at finding coins.
So wait a minute… Do I need to purchase a separate metal detector for every operating frequency that I wish to use?
Back in the early days of metal detecting the answer would have been “Yes.” Nowadays however, we have the option to purchase multi frequency metal detectors. The XP Deus, for example, is capable of operating at 4 kHz, 8 kHz, 12 kHz, 18 kHz, and 25 kHz. An additional high frequency (HF) coil can be purchased for the XP Deus that will allow the user to operate the machine at even higher frequencies. The XP Deus allows the detectorist to select the frequency that is best suited for the type of target that they are hunting. There are also simultaneous multi frequency metal detectors that are capable of scanning the ground with multiple frequencies at once! The Minelab E-Trac and Minelab Equinox are examples of simultaneous multi frequency metal detectors.