Surely many of you are fond of books and films about adventures. Take, for example, the famous Indiana Jones, whose name has become almost a household name. Romance of adventure, mystery, mysticism, treasures - all this has attracted, attracts and will almost certainly attract thousands of people at all times. But if in works of art the search for values looks very exciting, then in reality it requires persistent and painstaking work. Modern technologies can make it a little easier. And to be more precise – metal detectors, which will be discussed in this article.
First, let's figure out what kind of device this is. A metal detector is a device that allows you to detect metal in a neutral or slightly conductive environment. These environments can be different, but the models from our rating are used, as a rule, for searching in the soil. This, coupled with advances in electronics that made it possible to create a compact and lightweight device, made metal detectors popular among treasure hunters. Moreover, both among amateurs and among professionals.
And here it is worth understanding that a metal detector is a device for which design and beauty are not important. It is, first of all, a complex tool for performing a specific task, and therefore regular updates and improvements to the technique are needed for better determination of metals. Ideally, to choose a device specifically for your needs, you need to thoroughly understand terms such as “metal discriminator”, “pinpoint”, “detection depth” and many others. We will move on to the rating, where we will consider models divided into categories depending on cost. This is much easier for beginners, and the functionality directly depends on the price of the device.
The first category is addressed to the most inexperienced treasure hunters, for whom the chosen metal detector will be the first, and therefore it is very important to choose a model that will not empty your wallet - hence the conditional price limit of 20 thousand rubles. Of course, you may decide that it’s better to pay an additional 10 thousand and get a device at a higher level, but such a decision is only partly reasonable. Firstly, it is far from a fact that treasure hunting will captivate you enough to spend large sums on it. Yes, if you have been going out with your friends on searches for several years now, the answer is obvious, but in all other cases it is worth moderating your ardor. Secondly, more expensive models have more functionality, which is very difficult for a beginner to master. Therefore, even a significant advantage on paper over a budget model may turn out to be absolutely useless in the hands of an inexperienced search engine. In general, if you know exactly what you need, scroll to the next category. For beginners, we advise you to familiarize yourself with the rating of the best inexpensive metal detectors.
Light weight
Country: Australia
Average price: 7490 rub.
Rating (2019): 4.5
Treasure hunting enthusiasts highly praise the inexpensive metal detector from Minelab. With a detection frequency of 7.8 kHz and a 20 cm coil, it increases the accuracy of detecting non-ferrous and ferrous metals. There is moisture protection, which allows you to continue searching for coins in water at a depth of up to 15 cm. Reviews often mention the light weight, only 1 kg, and the compactness of the device, which is ideal for long searches and hiking trips.
The metal detector is powered by four AA batteries. There is a sensitivity setting and two search modes. The first one looks for all metals, the second one ignores garbage. But in such a simple model, gradation does not guarantee a 100 percent result. However, Go-Find 11 can rightfully be considered the best budget option for a first metal detector.
The best model for land and water
A country: USA (manufactured in China)
Average price: 16,900 rub.
Rating (2019): 4.5
This is the brainchild of an American-Chinese brand that creates universal metal detectors. The model belongs to professional equipment, despite its modest price. The equipment allows you to immediately start searching for metal both on land and in conditions of high humidity: Deteknix Quest Q20 can be immersed in water to a depth of three meters.
The device uses an operating frequency of 9 kHz and searches for both small objects (coins, rings) and large metal products. The metal detector penetrates the soil to a depth of 80 centimeters. The display shows the discrimination level and VDI number. There are three automatic search programs, automatic and manual adjustment of soil type to reduce the influence of soil characteristics on signal quality. A bonus is a flashlight and a rubberized handle with adjustment. Judging by the reviews, this is the best inexpensive universal metal detector.
Best Selling
Country: USA
Average price: 18,350 rub.
Rating (2019): 4.5
Fisher can be called a pioneer in the world of metal detectors. The first model appeared back in 1931, and was, of course, far from today's technology. At the moment, the company’s assortment also includes models for beginners. F22 is just one of them. The main feature of the device is its very high operating speed, which is useful when searching in a heavily polluted area. Thanks to the fast response, it is easier for the user to distinguish between several closely spaced elements. Also highlighted is a protected control unit with touch keys, which is not afraid of water and dirt. Otherwise, this is a fairly ordinary, but well-made metal detector.
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Popular
Country: USA
Average price: 17,650 rub.
Rating (2019): 4.7
This metal detector from Garett has gained such high popularity among domestic treasure hunters that it even has an affectionate nickname - “Aska”. The model gained such fame thanks to a good combination of characteristics, cost, build quality and reliability. The latter is far from unimportant, because the device operates not in greenhouses, but in field conditions. It is also worth noting that the controls are as simple as possible, which even a person completely unfamiliar with metal detectors can handle. In general, all these advantages are typical for other Garett models, and therefore the entire range of this American company can be recommended for purchase.
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The cheapest
Country: USA
Average price: 6450 rub.
Rating (2019): 4.8
Metal detectorfrom America conquered the Russian market with its low price and high search accuracy. Buyers often note in reviews that this budget employee is not inferior to expensive and advertised onesmetal detectors– finds metals at a depth of up to 80 cm. The round coil is waterproof, so it can easily search for ferrous and non-ferrous metals in water up to a depth of 15 cm.
The battery is crown. The frame is made of plastic and metal. It is adjustable in length from 114 to 135 cm and weighs 1.35 kg. There are three search modes: all metals, DISC, TONE. The first mode is for search absolutely any metals, including gold , the second - to ignore metal debris, the third - to more effectively search for non-ferrous metals.
Metal detectors of this group can hardly be called devices for beginners. Yes, they are still not very difficult to learn, but they already have significantly expanded functionality, which, if it does not increase the detection area and depth, then certainly makes metal recognition more convenient and accurate. According to the possibilities, the price, of course, also increases. It does not differ so much from devices in the budget segment, but it is difficult to call it affordable.
In general, metal detectors in the mid-price segment can be addressed to people who are serious about taking up their hobby. For such users, searching for valuables is not yet work, but it is no longer just a pleasant pastime a couple of times a month. It is also worth noting that devices from this category can be safely purchased by people who, over time, are going to devote even more time and effort to searching, because the functionality is not very critically different from premium models, and therefore such metal detectors are purchased for many years. You can look at the best models in our rating.
Manual and automatic ground balancing
A country: USA (manufactured in China)
Average price: 26,690 rub.
Rating (2019): 4.6
Another metal detector produced by Deteknix has rightfully earned a place in our top. The design of the device differs from most other models - the handle with the control unit can be moved and mounted on a straight three-piece rod in a way that is convenient for you. Detection frequency – 13 kHz. Powered by a built-in Li-Pol battery with a capacity of 2000 mAh. There are both automatic and manual ground leveling, which is the best solution for a metal detector.
There are six search modes. You can increase the response to non-ferrous metals, which is very convenient when searching in a littered area. The voice acting changes depending on the setting. Searches for both the smallest objects made of ferrous metal and more expensive items made of non-ferrous metal.
Small Target Detection
Country: USA
Average price: 25950 rub.
Rating (2019): 4.6
A good metal detector in the middle price segment. A distinctive feature of this model from its counterparts is the presence of Iron Audio. This function sounds ferrous metals and non-ferrous metals in different tones so that they can be immediately distinguished without starting excavation. Iron Audio works even when the discrimination sleeper is turned off.
With a detection rate of 10 kHz, the ACE 400i detects even the smallest targets. But the higher the detection frequency, the shallower the depth. There are five modes for searching for coins, jewelry, all metals including gold, relics; and manual setting, in which the set parameters are remembered for subsequent use. This model definitely deserves the attention of potential buyers.
Wide functionality
Country: USA
Average price: 25,900 rub.
Rating (2019): 4.6
Fisher is part of top best manufacturers metal detectors. And this model is another masterpiece. Although beginners will have to tinker with learning manual ground balance, it is worth the time spent.Metal detectorrefers to professional equipment and, in addition to its standard functions, can analyze the soil and show the degree of its mineralization, as well as accurately localize the location of the buried object.
The maximum detection depth is 110 meters. The 10-inch elliptical coil has high sensitivity to small targets and is waterproof, allowing you to searchcoins and jewelryin shallow water. Operating frequency – 7.8 kHz. The small weight of 1.3 kg prevents your hand from getting tired from long searches.
Best price
Country: USA
Average price: 23,300 rub.
Rating (2019): 4.6
Ace 350 is the closest relative of the popular ICQ in Russia - the 250th model. Like the younger model, this device has an excellent price-quality ratio. Yes, the functionality lags a little behind the leader in the rating, but you will also have to pay significantly less for Garett. The main feature of the Ace 350 is its versatility - the model is capable of working in ancient times, for treasure hunting, for beach searching, and for military archeology. In general, an excellent model for a wide range of search engines for little money.
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Buyers' choice
Country: Australia
Average price: RUB 30,476.
Rating (2019): 4.7
And again we turn to the line of semi-professional metal detectors from the famous Minelab. The 705th model is the top model in the X-terra line, and therefore has the most extensive functionality and the most advanced technologies. Here you have a larger number of frequencies, ground balancing, and a “DD” coil. Yes, even the lower rod is made of carbon - that’s where the technology is! What’s even more surprising is that it’s combined with the same clear pentagram-shaped interface that even the least experienced searcher can figure out. Finally, the cost - with such characteristics it is quite low.
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Finally, we get to premium devices. Beginners will no longer buy these, if only because of their high (over 30 thousand rubles) cost. The number of functions in this category is the largest, but mastering them all will be quite difficult even for an experienced search engine, not to mention beginners. Everything in these devices is aimed at finding the desired object as accurately and quickly as possible. Of course, they won’t do the work for you, but they will certainly make it as easy as possible. In order not to delay, let's move on to the rating of the best professional metal detectors.
Maximum depth of metals
Country: USA
Average price: 54,250 rub.
Rating (2019): 4.5
A unique deep metal detector from the manufacturer Fisher. This model is chosen by those who are tired of occasionally finding coins at a depth of 10 cm and are ready to explore the bowels of the earth in search of treasure. The search depth for large objects reaches 6 meters. The metal detector simply ignores small targets. Searches for both local and extended objects.
Soil mineralization is a common problem when searching for metals, but Gemini 3 has special settings that can help overcome this difficulty. Power is supplied from 1.5 V AA batteries that hold a charge for up to 45 hours. The detection frequency is 81.9 kHz and weighs only 2.8 kg. Ground balancing is manual. Suitable for gold prospecting.
Best for Finding Gold
Country: Australia
Average price: RUB 554,990.
Rating (2019): 4.5
The Australian brand has created the ideal metal detector for gold miners, which deservedly made it into our top best models. The innovative ZVT gold prospecting system will allow you to find gold at depths that are inaccessible to others. At the same time, the “seven thousandth” is adjusted to the maximum sensitivity of gold, so you can easily detect valuable objects even where other metal detectors have passed through more than once.
In addition, the manufacturer pleased with the possibility of precise ground balancing. The model copes perfectly even with “complex” mineralized soil, balancing indicators for accurate search in super-heavy soils. The model is also equipped with a noise immunity function - more than two hundred noise reduction channels provide a smooth search without atmospheric noise. Well, the icing on the cake was the waterproof reel (withstands immersion up to one meter) and the waterproof case, which allows you not to interrupt the search during the rain.
Good price
Country: USA
Average price: RUB 37,999.
Rating (2019): 4.5
No matter how strange it may sound, the top-end metal detector from Fisher has the lowest cost among professional-class devices. Moreover, the price does not in any way impair the capabilities of the device. Yes, there are no cutting-edge materials or secret proprietary technologies here. This is simply a high-end metal detector that does its job very well. There are also many manual settings and increased speed.
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Best Detection Depth
Country Russia
Average price: 50,000 rub.
Rating (2019): 4.7
Metal detection is one of the few areas in which domestic equipment seriously competes with famous global brands. Many reputable search engines call Signum “legendary”. And there are, of course, many reasons for this. In short, the MFT 7272M offers the user simply limitless possibilities for fine-tuning each individual parameter. It is also worth noting excellent selectivity - for example, this model is able to distinguish a beer cap from a coin.
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The most technologically advanced
Country: France
Average price: 50,999 rub.
Rating (2019): 4.9
The name of the metal detector is more than telling: lat. Deus is translated as "God". In this model, the manufacturer has assembled the most advanced technologies at the moment. Moreover, these innovations are useful not only for directly searching for objects, but also add basic convenience. Just look at the lack of wires. Yes, yes, the coil, electronic unit and headphones are connected “over the air” here. Of course, this solution also has an unpleasant side - the need to constantly charge all elements. But the lightness (only 970 grams) and convenience more than compensate for this small drawback. Of course, in addition to this, the device has other features.
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1080 564 Search with a Garrett ACE 250 metal detector http://site/wp-content/uploads/2015/05/DSC_0003-1600x836.jpg 21.05.2015 28.02.2019
The writing of the article was preceded by the purchase of an inexpensive (for the price of the housing and cable) faulty NEL Tornado coil. First I found out whether the generator part was working in it. To do this, I downloaded a spectrum analyzer from the Internet specan22, which successfully installed under Windows 7 (×64) and compared the operation of two NEL Tornado coils (working and faulty). Later I found out that this program works well under Windows 10.
A small INTRODUCTORY
1. How to measure frequency? — We need to make a simple probe. sensor/probe/probe damaged the cat, made a new one:
Any wire for the coil - I used a single core from a “twisted pair”, then wrapped the finished coil with white electrical tape. Any silicon diodes, I installed KD522. For those who are not very experienced, I inform you that the capacitor is marked with the number 104 (this is 0.1 µF). A 10 kOhm resistor is needed for reliable operation of a computer sound card - if there is a resistor, the card believes that a microphone is connected to its input. At the output there is a jack connector with a cable from some headphones (the cable has a splice, which is shown at the top of the picture - do not pay attention, there a thin black cable goes into a thicker light cable, which just ends with a 3.5 mm connector). The coil and other radio components are placed on a square piece of cardboard, all parts and soldering are additionally fixed with PVA glue. Below, in the pictures, this probe is shown a couple more times.
2. The actual measurement
The output of this probe/probe is a 3.5 jack connector that plugs into the microphone input of your computer. On my computer, I plugged the JACK into some input, and the computer immediately offered the choice of using this connector either as an output to speakers, or as a linear output for a bass amplifier, or as a microphone input - I chose the latter. (Be sure to turn off the webcam first, because it is occupied by the computer’s audio channel), then you must activate the program downloaded from the Internet specan22, then the sensor/probe is placed directly on the coil and the “Start” button in the program window is pressed. (Yes, the coil itself must be connected to a working MD, because the probe/probe picks up the signal from the coil). By moving the probe along the surface of the coil, we achieve the greatest return, i.e. the highest amplitude on the computer screen (at the same time we find out on which side of the DD coil the transmitting part is located) and use the PrintScreen key to take screenshots.
So, back to my purchased faulty NEL Tornado reel. As I mentioned, I also have a working NEL Tornado of the earliest generation. Let's compare:
The frequency response (amplitude-frequency response) graphs cannot be distinguished, although the top one was taken from a working coil, and the bottom one from a faulty one. On the body of the faulty coil there are 2 cracks in the area of the Rx winding - I draw two conclusions for myself: since the Tx winding works and “produces” the required frequency and amplitude, then: either the Rx winding is broken, or there is a problem in the cable. While I was remembering where I had a small diamond cutter lying around to begin work on repairing the coil, I took graphs of frequencies and amplitudes from the rest of my coils.
Measuring the frequency of native MONO coils from ACE 250:
Frequency response of the native coil ACE 250 6.5x9″
Frequency response of the native coil ACE 250 9x12″
Above is the frequency response of 5x5.8″.
You should pay attention not only to the frequency (almost 11 kHz), but also to how the high quality factor Q affects the amplitude (Peak Level) of a given coil, and the scale is in decibels. I counted 15 dB of difference with the original ACE 250 9x12″ coil, i.e. the voltage of the ACE 250 circuit generator, which develops in resonance and is applied to the generator winding Tx of my homemade coil, is more than 5 times higher than the voltage that is obtained in the native ASI coil!
That's all for now. The article will be updated, and now it will be useful for me for internal transitions.
The frequency determination method is suitable for any coils and any MD. My simple probe, wound on three fingers (I’m not kidding), determines the frequency very accurately, the amplitude relatively, i.e. in comparison with other coils or MD. Personally, I would like to look at the comb of the MineLab spectrum, the owners - whoever repeats it, please sign up.
PS. The dead NEL TORNADO coil ended up in a “long box” - an autopsy showed damage to half of the veins in the receiving part of the Rx - I don’t even know when I’ll repair it, especially since the other day I bought from friends an almost new “blonde” of the latest generation with protection and its operation satisfied.
— — — — — — — — — — —
Over the past couple of years I have bought several coils for my ACE.
Among the purchases there is a coil from ACE 350 (now there is a probe for measuring the frequency response on the coil):
Here is the frequency response of the coil from ACE 350:
Frequency - 6.72 kHz. What does this mean? - yes, that Garrett cares about its customers. For example, on the Garrett ACE 350 MD, for which this coil is, so to speak, “native”, it will operate at a frequency of 8.25 kHz. And on my ACE, the same coil showed 6.72 kHz. There is end-to-end compatibility of coils for the ACE model range. Therefore, if you can buy an inexpensive used reel for the ACE 250 (offers are a dime a dozen on the sites of diggers), and want to use it on the ACE 350, then you are welcome. In addition, all your coils from the ACE 250 can be used not only with the ACE 350 and ACE-EURO, but also with the recently appeared ACE 300 and ACE 400. However, I personally am satisfied with the ACE 250 for now. Someday I will publish the frequency response of all my factory coils, I have already done this work and all my sensors/coils showed similar frequencies - 6.5-7.0 kHz, i.e., the passport ones for the ACE 250.
Let's once again confirm an important conclusion, especially concerning owners of new versions of Garrett ACE - there are still few coils/sensors “specifically for these devices”, sellers are taking advantage of the situation and raising prices for new versions of “ACE”, but now you don’t care, because you are armed with information (and the information is this: the resonance frequency is set by a pair of radio components: inductance L and capacitor C, “L” is your coil/sensor, and “C” is located on the device board and therefore it does not matter for which model the coil was made, it will still reach the correct operating parameters with exactly the “head” to which it is connected), so take inexpensive coils (or you can use used ones from trusted sellers) for ACE 150, 250 and feel free to install them on your ACE 200, 300, 350 , EURO, 400 and AT Pro (and only the latter will require re-soldering the connector; you’ll find how on the Internet).
Let's add another frequency response, this time it will be “NEL Tornado” of the latest modification:
— — — — — — — — — — —
The idea came up to change the frequency of the large NEL Attack coil.
1. Put the probe on the coil
and got the frequency “before”:
I laid out the capacitors on the table.
Then I disassembled the connector (it was decently assembled, the connector has gold-plated contacts, I didn’t like the solid filling of the connector with some kind of wax-like compound - the compound does not contribute to high Q (quality factor), air is better). Then I brought out two wires from pins 1, 4 and soldered the smallest capacitor 0.047 µF. I got this frequency response:
You can notice a tiny shift in frequency towards its decrease, we continue the experiment.
2. We change the capacitor to 0.1 µF, here is the frequency response:
It’s already warmer, the frequency has dropped below 6 kHz.
3. In addition to the 0.1 µF, I solder a 0.047 µF capacitor, the picture on the connector is something like this (in this case there are 2 x 0.1):
With this 0.15 µF capacitor, the frequency response turned out like this:
4. It was not possible to move below this frequency: I set it to 0.2 µF - it doesn’t work, with the blue capacitor at 0.18 µF the ACE 250 generator also did not start, just in case I threw up the air conditioner at 0.33 - it did not work.
Conclusions from this experiment. You can lower the frequency. The result was 5.73 kHz (it was 6.78 kHz). But the trouble is that the amplitude fell, by an estimated 5 dB (see graphs), so the “air range” dropped by a dime of the USSR and the Bellton disappeared. (Waving a stainless steel kitchen knife over the reel - there is a Bellton). Since the efficiency of the coil had decreased, I returned everything back, unsoldered the capacitors (there were two in parallel), but left the green wires, since the experiments will continue... (They called me on a trip through the fields, so I urgently turned off).
On the same day I went out into the field, the reel so far looks like this:
What is this all for? Large coils should operate at a lower frequency, this is indicated by the theory of metal detecting. It is also known from the literature that the optimal frequency for searching for copper and silver coins (and treasures) is 3.5 kHz. To get a frequency shift of more than 1 kHz, in my case I will have to go into the ICQ block and increase the positive connection on the generator there, we’ll leave that for later. I have several “aseks”, one can be optimized for deep search, at the cost of changing the scheme (let’s repeat about the feedback depth, let’s also add ground balance, and increase in coefficient. the gain at the first op-amp, now there is exactly 1000 times, or 2 thousand or 5 thousand is possible, although before that you will need to “define the coil/coils” (more on this below).
“Coil definition” as a concept (my term). There will be a separate article, but now briefly. The coils are made by different manufacturers and there is a variation in the balance, I haven’t really measured it, but I admit that hundreds of millivolts are possible. And so, suppose that you have an unbalance of only 10 mV on the coil, now multiply by the coefficient. amplification of the input microcircuit, now I will give a diagram of the input part of the ACE 250:
The ratio of R16 to R15 is 1000 - this is the coefficient. op-amp gain. (The Rx coil is connected to pins 3, 4 of the connector).
So, multiplying 0.01 V by 1000 you get 10 V, and the power supply for this microcircuit is 2 x 4 V - it will simply choke and jump along the output from power to power at the frequency of the generator, this does not work.
“Coil definition” (any, from any manufacturer) is carrying out work to compensate for coil imbalance. My experiments with reel for gold(and there, on the high-quality generator coil Tx, the amplitude accelerated to a hundred volts, see frequency response above) made it possible to obtain 0.000 V on the output coil Rx.
How to identify a finished factory coil? To do this, you need to go out into an open field and place the coil through a gap (let it serve as a cutting board) on the soil that you most often encounter in your search practice. Next, the coil/sensor should be connected to the MD through a home-made intermediate connector-spacer, such that the output signal from the Rx coil can be removed from it (without feeding it inside the “ASI”) and the output from the Rx coil can be connected to a Chinese tester that can measure variable voltage. Then remove the side cutters and stored scraps of copper, aluminum and steel wires from your pocket, and placing these scraps on the upper surface of the sensor, thereby shifting the phase on the output coil. Having selected the type of metal and the point on the sensor/coil, you should achieve/measure zero and three decimal places of alternating voltage. Then fix the piece of wire on the surface of the sensor. All. From now on, it makes sense to increase the coefficient. amplification on the input chip by increasing resistance R16. But it should be added ground balance, it’s not difficult - you’ll find it on the Internet.
...Like this: I started for health, ended for peace and bombarded the poor reader with graphs and diagrams - I need to write a separate article...
Updated 10/31/2018Various models of metal detectors use one or more operating frequencies when searching. This is due to their scope of application and engineering solutions. The range of frequencies used in modern devices is from 1 kHz to 30 MHz.
The operating frequency of a metal detector is directly related to detection depth, object size and metal discrimination. This is explained by the physics of propagation of electromagnetic waves. At the same time, the operating frequency of metal detectors determines their discrimination capabilities...
When using low frequencies, the detection depth of objects increases, but sensitivity to small targets near the ground surface decreases. Regarding the target metal type, a low detector frequency increases the detector's sensitivity to silver and copper, but decreases it to gold and nickel.
When using high frequencies, the opposite happens. The detection depth of objects is reduced, and sensitivity to small targets near the ground surface, gold and nickel increases.
There are four operating frequency ranges for universal and specialized metal detectors:
There are also multi-frequency or multi-frequency metal detectors, which operate simultaneously on several frequencies (4 frequencies, 17, 28 and more). This allows you to solve search problems at various levels simultaneously, for example, searching for large objects at low frequencies and searching for small colored targets (coins, rings) at higher frequencies.
Related tags: metal detector frequency, operating frequency range, optimal metal detector frequency, metal detector frequency detection depth, metal detector operating frequency, vlf, Very Low Frequency
Single frequency or multi frequency metal detector
Recently, many new models have appeared on the market, which are already far from the analog detectors of the early nineties, but can they be considered real multi-frequency metal detectors?
The operation of the metal detector is based on the principles of electromagnetism, which make it possible to detect various objects in both air and non-air (soil, water, etc.) environments that are struck by electromagnetic waves emanating from the metal detector coil. Each frequency is responsible for its own size of the object (from a millimeter to several centimeters) and the depth to which it can “work.” Thus, the same frequency can work completely differently in different areas.
A significant part of single-frequency metal detectors are initially configured to search for coins, either small objects like Soviet kopecks, or large objects (badges, medals, Arab dirhams or Old Russian hryvnias).
If the metal detector is tuned to a high frequency, that is, approximately 14-18 kilohertz, then it will be able to “catch” objects up to approximately one or two millimeters in diameter. Meanwhile, such a high frequency causes the ground to absorb the signal, which leads to a decrease in search depth but greater selectivity.
Low-frequency metal detectors (tuned to a wavelength of 1-4 kHz) have difficulty detecting small objects, while operating at a decent depth. Moreover, the lower the frequency of the device, the greater the depth it “sees” metals.
Moreover, the effectiveness of a particular frequency depends on the contamination and mineralization of the soil. If, say, a high frequency works well in clean soils, then with an increase in the proportion of debris (or mineralization) in the soil, the result will no longer be so high.
The situation is somewhat different with multi-frequency metal detectors. Most of these models allow you to catch almost thirty frequencies, from one and a half to one hundred kilohertz, by varying which you can combine the advantages of low-frequency and high-frequency devices. Working with a multi-frequency detector practically replaces a whole squad of search engines with metal detectors tuned to different frequencies. If you want to search for small objects but still reach deep, this is very convenient.
The use of several frequencies made it possible to correct the situation with the effectiveness of searches in littered soil. Helping to practically neutralize the effect of mineralization, they search for both small and large objects, without regard to the composition of the soil. Some technologies also allow you to search in several frequencies at once, which creates great convenience. In order to determine whether your metal detector can handle this, you should pay attention to the letters FBS (in the Explorer series) in the technical specifications. This abbreviation is translated into Russian as “full spectrum of frequencies” - the ability to search in several frequencies at once.
Unfortunately, there are not many such powerful devices at good prices in Russia yet. There are often multi-frequency devices on the market that operate on two or three frequencies, separately or at once. An example of such a metal detector would be Whites Spectra v3i. 
Multi-frequency metal detector Whites Spectra v3i - the display shows indicators for three operating frequencies at once.
It all depends on your financial capabilities and the intended search objects.
Single-frequency metal detectors, being tailored to a single frequency, can show very good results. At the same time, however, with the slightest change in the mineralization or contamination of the soil under which these frequencies are imprisoned, the result will not change for the better. Therefore, it is necessary to think through and calculate how clean the soil is of impurities. This means that success in finding real treasures will depend, among other things, on your analytical skills.
Then – search depth. By choosing a single-frequency metal detector with a high frequency, you will no longer be able to search for objects in the deep layers of the soil so effectively. Consequently, you will have to look for places where there have been no seekers, archaeologists, etc. before you. – in this case, objects can be found in the upper soil layers. And, conversely, low-frequency metal detectors can be used in popular search areas to “get” small coins there.
Multi-frequency ones seem to have solid advantages in this regard, but efficiency suffers. Not being “tailored” to one or a couple of frequencies, they are usually poorly tuned, and therefore do not give, say, at a frequency of three kilohertz the same result as a single-frequency metal detector geared to three kilohertz. Prices for multi-frequency metal detectors in Russia are still high, but this is more justified than carrying several single-frequency devices with you when searching.
An intermediate option can be metal detectors in which you can change the operating frequency by replacing the coil. (example minelab x-terra 705 or Aka Sorex Pro)
Or the innovation of Russian engineers, a multi-frequency metal detector aka signum pro With coil in which it is possible to change the operating frequency.
Therefore, the choice depends on your preferences, financial capabilities and the characteristics of the area in which you are going to search.
