When I was just starting out, it took me forever to understand the difference between a Very Low Frequency and a Pulse induction metal Detector. So, you can imagine my frustration when I learned that even within these classifications there are different operating frequencies that metal detectors use. However, I have since learned how this information can help me improve my searching ability, and I am writing this article to tell you what I wish I would have known when I was new to the hobby.
Which Frequency is Best for Metal Detecting?
The best frequency for metal detecting is somewhere in the range of 5 kHz to 15 kHz. This range is where most general-purpose metal detectors are tuned too, and also the easiest to manage for beginners. Nevertheless, you can always get more specialized detectors once you have mastered the basics.
How does Frequency affect Metal Detectors?
The operating frequency of a metal detector refers to the number of electromagnetic waves (measured in Kilo-Hertz per second or kHz per second) that the metal detectors coil is able produce in a set amount of time, generally per second of operation. A metal detectors frequency can range anywhere from 1.5 kHz per second to a whopping 100 kHz per second. However, to be fair most metal detectors operate in-between the frequencies of 5 kHz per second and 25 kHz per second. This means that a standard metal detector is capable of sending between 5,000 and 25,000 electromagnetic waves into the ground every second.
So, how does the operating frequency actually affect the metal detector? Well, in general this depends on a few factors. These factors include, but are not limited to: conductivity of the metal, size of the target, depth of the target, and even the level of soil mineralization. As a general rule, lower frequencies have longer wavelengths and penetrate the ground deeper than higher frequencies. That being said, higher frequencies have greater signal strength and will result in a more sensitive metal detector. Moreover, the more conductive a metal is the lower the frequency should be for your metal detector and vice-versa.
This all still may be confusing so here is an easy to read chart for various scenarios and metals…
|Targeted Treasure||Best Frequency||Metal Detector Brand|
|Silver/Copper/Brass||3 kHz – 7 kHz||Garrett Ace 150 operating at a frequency of 6.5 kHz|
|GOLD||14 kHz +||Garrett AT Gold with an operating frequency of 18 kHz|
|Iron/Ferrous Metals||10 kHz +||White’s Goldmaster GMT operating at a frequency of 48 kHz|
|Zinc/Cobalt/Stainless||9-10 kHz||Fisher Labs F75|
|Nickle/Aluminum||4 kHz – 8 kHz||Garrett AT Pro|
|Small Objects||7 kHz and Less||Minelab X-calibur 2 operating at a frequency of 1.5 to 25.5 kHz|
|Large Objects||7 kHz and Above||Minelab Xterra 305 operating at a frequency of 7 kHz and 18.5 kHz|
Multi-Frequency Metal Detectors vs Single Frequency Detectors?
Most metal detectors are single frequency detectors. This means that they operate at one frequency and only that frequency. These are typically, either at or below 10 kHz per second or above 30 kHz per second. The former is good at ground penetration and finding highly conductive targets. The latter is better at finding smaller low-conductivity targets, but also struggles with ground penetration.
However, there is a small percentage of newer machines which can actually detects at two or more frequencies at the same time. These metal detectors are known as simultaneous multi-frequency detectors. Like I said this could be happening at the same time, or possibly at an imperceptibly fast interchanging pattern.
These detectors are just as reliable as single frequency detectors, but obviously more capable due to their improved range of detection. The only downside is that these machines can sometimes be difficult to use, and they definitely cost more than the average metal detector. However, if you are somewhat skilled and money is not a huge issue, this new technology is definitely better (as long as the manufacturing quality remains unchanged) and worth the investment.
Some of the newer simultaneous multi-frequency detectors can even detect a greater number of frequencies than ever before. Previously, the standard was either one frequency or three frequencies (aka Selectable Three Frequency). But, a new technology called Full Band Spectrum can detect up to 28 total frequencies all at once. This ensures you detect any number of targets regardless of size, composition, or depth.
Best Frequency for Finding Coins?
Coins are generally closer to the surface and of a higher conductivity, this means that the best frequency’s for searching for coins are anywhere from 10 kHz and below. That isn’t to say that some rare gold or silver coins won’t benefit from higher frequency detectors due to their specific composition.
Best Frequency for Finding Jewelry?
Although jewelry is often marketed as gold or silver, or even platinum, the reality is that these are often alloyed with other metals that have higher conductivity so a midrange frequency detector is acceptable for looking for jewelry. Somewhere from 10 kHz and Above should do just fine.
Best Frequency for Gold Prospecting?
Gold is mostly only found is small pieces, and of course in remote areas such as western Australia. However, if it is gold you are after then you will need a machine that is 14 kHz and above. The higher the better as gold has a very low conductivity so it will be difficult to detect otherwise.
How does Ground Mineralization Affect Frequency?
Due to the effect that ground mineralization can have on the normal processes of a metal detector it makes sense that it would also affect the frequency you should be using for detection. First thing first however, no matter the frequency you should be using a Pulse Induction metal detector if possible as it won’t be affected by the mineralization. That said, a lower frequency is most likely the best option for a highly mineralized area. The higher the frequency is the more it will be affected by the ground’s composition and even temperature fluctuations.
Following this logic, when you are treasure hunting at the beach, especially a saltwater beach, it is best to use lower frequency Pulse Induction metal detectors. The moisture in the sand, along with the salt and any other number of minerals, can cause false signals that effect high frequency machines and Very Low Frequency machines the most.
How does Search Coil Size Affect Frequency?
The larger a search coil is, generally, the lower the frequency which it produces will be. Furthermore, the smaller a search coil is, generally, the higher the frequency it produces will be.
This means that as a general rule large search coils are good at ground penetration but it will be lacking in sensitivity. Also, this means that as a general rule the smaller a search coils is the worse ground penetration it will have, but the better sensitivity is will have as well.
How a Metal Detector Creates an Electromagnetic Field?
A metal detector creates an electromagnetic field by sending electrical energy through a coiled piece of copper. The various specifications of this process affect the frequency which is produced but the general process is the same no matter what the operating frequency is. An electromagnetic field is produced by the interaction of an electrical field and a magnetic field. These two fields have to be at the same frequency, and also at an opposing direction. This can be seen in the graphic below…
The effect of these two fields coming together is an electromagnetic field which can affect metallic objects in the ground and therefore can be detected by the metal detector.
The Best Frequency for Metal Detectors: Revisited
At the beginning of this article I said that the best frequency for metal detectors is 5 kHz – 15 kHz. While this is true for general purpose metal detectors, hopefully I have given you the information to determine which frequency is the best for your specific use case. I say this because, now that I have explained metal detector frequencies, it is clear that 5 kHz – 15 kHz is not always the best range to have when metal detecting.
For example, if you are searching for gold you need a metal detector which is operating at a frequency that is at least 14 kHz but preferably as high as is possible. The reason for this is that gold is often only found is small pieces. Furthermore, gold is not very conductive. Both of these factors contribute to the reason why a high frequency metal detector is the best for searching for gold.
Moreover, if you are searching for silver then it is preferable to have a metal detector which is tuned to have the lowest frequency possible. A metal detector capable of transmitting frequencies around 3 kHz in fact. Of course, putting this use case squarely out of the range of my original recommendation. But, silver is highly conductive (the most conductive metal in fact) and so it is necessary to use a lower frequency detector to find targets of this kind.
Further judgement calls can also lead you to decide that my recommendation is not the best for your specific case. If you know that what you are looking for is very deep in the ground then the lowest frequency possible is the best frequency to use. Somewhere 5 kHz and below. Inversely, if you know what you are looking for is near the surface, it is possible that a higher frequency would be better. Somewhere 10 kHz and above.
Looking for a versatile Metal Detector with a wide range of Frequencies? The GARRETT AT PRO is a solid choice with a proven track record.
Even further, if you know the area which you will be searching in is either highly mineralized or moist or both, a lower frequency Pulse Induction metal detector may be the best option for your search. But, then of course if this is not a possibility then a Very Low Frequency metal detector which has an operating frequency of somewhere around 6 kHz and below is the best option. The discrimination features which are possible with Very Low Frequency metal detectors can further assist you in removing the effects of ground mineralization as well.
So, the moral of this story, or rather the conclusion of this article, is that for an experienced metal detector there is no one best operating frequency to use all of the time. There is however a best operating frequency to use in any specific scenario. The challenge is knowing what works best and when. However, there is no need to fret, from the information in this article you have all of the knowledge you need to have a good understanding of metal detector frequencies and use cases for those frequencies.