Double (DD) and Mono coils - pros and cons. The difference between mono and DD (DD) coils - an educational program for diggers Which coil is better - mono or DD

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Today we’ll talk about coils for metal detectors, dd - coils. As you know, they come in 2 types - regular, round and elliptical. What exactly is the difference between these two coils, let's try to figure it out. Or is it still better to have both coils in the search engine’s arsenal at once? Using the example of a small 6" sniper coil and an ellipse.

The first difference between an ellipse and a round dd-coil is its lightness. The coil mounts, and this is a minus, are slightly smaller than those of a standard 10" dd coil. As experienced searchers say, it is better to search with an ellipse in heavily littered areas; with such a coil there are many times more finds. It is worth noting that, according to the principle of its operation, the ellipse coil is similar on the so-called sniper, a small DD coil measuring 6 inches. But the ellipse is much larger. It is more versatile, it can also be used to search in the field (with a sniper you will be crazy to walk in the field), at the same time, the ellipse has proven itself to be excellent in littered areas. Besides all These advantages of the ellipse can also be noted in the ease of use where there are bushes, branches, the coil is narrow and it is very convenient to stick it between the bushes.The penetration depth is many times greater than that of a sniper coil.

But if, nevertheless, the area is very littered with debris, then when searching there is no equal to the sniper, a round 6" coil. It is convenient for it to work even in other people’s holes, as a rule, the holes are larger in size than the coil itself, so you just stick the coil in someone else’s hole and you break through the walls, but again you lose in the depths, sniper hits too shallow. Although it is not intended for deep holes, but for searching on the surface.

One of the disadvantages of the ellipse is the coil mount. It takes a very long time to assemble, so digging professionals recommend immediately purchasing a separate lower rod, attaching the ellipse and not removing it anymore. When installing on a metal detector, simply replace the lower rod.

Well, another significant disadvantage of the ellipse is moisture intolerance. After just half an hour of work on wet grass, the reel begins to fill with glitchy trills. So keep in mind that you can cure it by strengthening the tightness of the bottom and edges.

The strong sensitivity of the ellipse also causes a lot of trouble, especially in the spring, when it hits dry stems of grass and burdock, the coil also begins to sing and fill.

So, to summarize everything, the ellipse is a coil that occupies a middle position among standard 10" round and 6" sniper coils. That is, if you decide to walk along a regular field, then your choice is a standard 10" dd coil; if the field is heavily littered, then ellipse. If you walk around one place where there is a lot of metal trash, but the place is promising, then use a sniper. Something like this. Of course, everyone decides for themselves where and what to go with, but extra information will not be superfluous. By the way, new ones came out recently

The search coil is the most important part of the metal detector, and knowing its structure and operating principle will help you make your choice. Such knowledge will allow you to fully use the inherent advantages of a certain type of coil and minimize its disadvantages.
The search coil consists of transmitting and receiving antennas housed in one housing. There are two main types: mono and DD. Let's consider their features.
The mono search coil is also called coplanar concentric. This name was given to it because of the special location and shape of the antennas. The transmitting and receiving antennas of a round or ellipse shape in a coplanar concentric coil are located one inside the other and lie in the same plane. Most often, mono coils are used to search for jewelry, relics and coins, as they allow you to quickly detect small objects. This property is due to the location of the sensitive zone - it is located directly in the center of the search coil. Mono coils also have excellent discrimination, which allows you to effectively exclude ferrous metal objects from the search.
DD coils got their name due to the location of the transmitting and receiving antennas - their configuration resembles two letters “D” written in Latin. Search coils of this type are not affected by mineralized soils, therefore they are successfully used to search for gold of various fractions and conduct searches in places with complex geological conditions.
The third type of search coil is the coaxial coil, in which two receiving antennas surround one receiving antenna: this configuration requires a special manufacturing method. Coaxial coils are small in size - from five to twelve centimeters - and are used for searching in places with limited space: attics, basements, near foundations. These search coils have received the nickname “sniper” from search engines, since they allow you to determine the location of a valuable find with impeccable accuracy, even in heavily littered areas. The detection depth of coaxial coils is small, but they have the ability to recognize objects close to each other. Also, search engines highly value the stability of the operation of coaxial search coils in places replete with electromagnetic interference - the design of coils of this type allows one to ignore such influence.
By far, mono and DD coils are the most common types of search coils. So which one should you choose?
Among the advantages of a mono coil, one should note the high accuracy in determining the location of the target - the so-called pinpoint. Possessing high sensitivity, mono coils allow searching at significant depths. If you want to increase the capture area, choose an ellipse-shaped mono coil. Also in favor of choosing this type of search coil is its lightness and low cost.
The disadvantages of mono coils include increased sensitivity to “hot stones”, exposure to soil with a high level of mineralization and a small volume of scanned space.
DD coils are attractive due to their large coverage area and significant detection depth in soils of any complexity.
Among the disadvantages, the most significant are the more imperfect discrimination of objects located near the earth's surface compared to mono coils, and the possibility of false alarms at the border of the scanned area. It is worth noting that DD coils are one of the most expensive search coils.
Thus, each of the coils under consideration is good in certain conditions, and the choice should depend on the goals that the treasure hunter sets for himself. Mono coils are best used to search for relatively deep-lying objects in areas with neutral or slightly mineralized soil. DD coils are ideal for searching for small items - jewelry, small nuggets - even where the level of mineralization does not allow other types of search coils to work.

The first step is to understand the classification of coils, their purpose and the features of the device itself. The main difference between DD and Mono coils is the signal shape, which seriously affects the quality and direction of the search. But when changing it, the coil model and the device model must be compatible. Otherwise, serious interference may occur or the control unit may be damaged. You should not try on a hobbyist’s reel on your device if you are not sure of the compatibility of the devices. After all, the ability to replace the coil was made to make the metal detector cheaper to maintain, thanks to replacing only part of the device, or to allow targeted searches, by using special coils.

Classification by coil types.

Until recently, it was mono coils that came with the metal detector. They have a cone-shaped signal, which is better suited for spot searching or searching in contaminated areas. However, this type of signal covers a small amount of ground, and the swing for each step should overlap the previous one by about half. So at a depth of 10 centimeters, the diameter of the beam with a 9-inch coil is reduced by half, and at a depth of 20 centimeters it will be only 3-5 centimeters. Mono coils are best used after detecting a cluster of targets. This will reduce the area of ​​the cop and get a clearer picture of the alleged subject.
With the advent of DoubleD coils, search efficiency has increased several times, and the latest metal detectors are supplied with this type of coil. They got their name because of the mirror arrangement of the receiving and transmitting loops, reminiscent of two inverted letters “D”. The signal in the DD coils has the shape of a cylinder, which makes it possible to uniformly scan the area under the coil. This type of coil is ideal for highly mineralized soils and scanning large areas. But the difference between DD and mono coils is not the only criterion for improving your results.

The influence of coil size on search.

An effective instrument search must also take into account the size of the coil, which can vary from 4 to 20 inches (if necessary, coils up to two times larger can be found). Small diameter reels are popularly called “snipers”. The small size of the coils allows not only to scan areas in hard-to-reach places, but also to minimize the influence of soil mineralization. By searching at standard frequencies using a “sniper”, you can detect even the smallest objects and achieve an accurate determination of the material of nearby objects. The disadvantages of such coils include the high swing frequency of the device and the shallow search depth.

More versatile are medium coils ranging from 8 to 12 inches, capable of detecting a variety of targets. Coils larger than 13 inches in diameter are better suited for deep searches for large objects, but they often miss smaller objects. This is due to the need to analyze a large volume of soil and equate small objects to the earthen background. In addition, the weight of a large coil can exceed 1 kg, which will become a significant factor during many hours of searching.

Search direction depending on the coil frequency (kHz).

Having delved into the selection of coils in more detail, it is imperative to pay attention to their frequency. The frequency of operation is directly related to the quality and strength of the response from various targets. Amateur devices are most often capable of operating at a single frequency, but professional models with differentiated search frequencies can also be found on sale. The most optimal frequency is 6-7.5 kHz, which allows you to search for medium coins. It is suitable for most metal detectors. Coils with a frequency of 13 to 50 kHz are often used to search for small objects, jewelry and even gold nuggets. But the use of high frequencies significantly reduces the search depth due to the attenuation of electromagnetic wave oscillations. If the goal is to search for a large object at a depth of up to 1 meter, then you should pay attention to devices with an operating frequency of 3-4 kHz.

Coil shapes.

In addition to the technical component, the coils also differ in their shape. They can be rectangular, elliptical, round, or butterfly-shaped. If you take into account the fact that for each step the coil swings from side to side, then the length, not the width of the coil, will be more important. The number of swings depends on the length. Therefore, the elliptical shape is considered the most convenient, which greatly facilitates balancing of the coil. The round shape has now practically lost its relevance and is quite rare.

Comrades, especially those who are just starting to search with a metal detector, you will find more interesting tips in. I am a digger myself and collect everything useful there.

Is it necessary to upgrade the metal detector, can it be done at home and is it worth doing?
The topic is very large, there is practically no information, since device manufacturers do not publish the circuit design of the devices.
I'll try to figure this issue out too. Foreign colleagues, like us, have been trying to modernize devices for a long time, I suggest you familiarize yourself with their achievements and choose the optimal solution for yourself.

Question that came by email:
I have a Garrett ACE 250 and I see that some sellers offer this metal detector with a DD coil. But on the official Garrett website I found out that this reel is not for the Garrett ACE series. The ACE series only has two coils, 6.5x9" Proformance (standard) and 9x12" Proformance, but they are "concentric".
What's the difference between concentric and DD coils? And is it possible to put DD on the ACE 250?

I will try to answer your question: a concentric search coil (mono) is equipped with a large transmitting coil and a small receiving coil, the centers of which are located on the same axis in the same plane. These coils are much easier to manufacture, and the symmetry of their shape helps to minimize electrical interference that occurs during operation and changes in temperature conditions. In addition, they provide better discrimination for shallow targets. In such a coil, the search volume has the shape of an inverted truncated cone.
The figure clearly shows the working area of ​​such coils.
A DD coil is two D-shaped coils connected by their bases. The search volume of these coils is a parallelepiped, only about 5 cm wide, but the length of the entire coil, respectively. The search depth is the same in the center of the coil and at the edges. With such a search volume, the risk of missing a signal is minimized.

The figure clearly shows the working area of ​​such coils.

There is more detail in another article about which coils are “better” under various search conditions.
On one of the Italian sites I came across measurements of coils for the ACE series. I made a technical translation into Russian and here is the result:

1. Nature of the wire (usually copper)
2. Its diameter
3. Coil diameter
4. Number of turns
Items 3 and 4 will give us the inductance value L (i.e. the characteristic of the coil), elements 1 and 2, the resistance value (in Ohms), and if we know the operating frequency of this device, we can even calculate the impedance values ​​(in Ohms) .
However, we must admit that manufacturers never give this kind of information, they simply indicate the frequency of operation.

Let's take measurements:
A digital multimeter is useless because it can only measure current and we need a device called RLC bridge, a professional instrument to accurately measure resistance, capacitance and inductance.
Knowing the measurement results, we can adapt coils from different manufacturers to the metal detector without burning the device. Our goal is not to create a new coil for the ACE-250, but to test which Garrett coils can adapt to this device without any problems. And also find out the result of the metal detector using different coils.

Measurement results:
ACE reel standard 17x23 cm (6.5x9" Proformance)
The ACE Proformance coil connector consists of 5 pins.
1 - 4: (L = 2.48 MH and R = 60.1 ohm)
2 - 3: (L = 1.68 MH and R = 36.9 ohms)

We also accurately measure ACE 23x30cm (9x12" Proformance) coil
1 - 4: L = 2.44 MH and R = 55.6 ohms
2 - 3: L = 1.45 MH and R = 34.7 Ohm
You should be aware that industrial coil manufacturing tolerances can be as high as 10% or more.
Therefore, we take the average result.

We measure a 10x14"" Proformance DD coil:
1 - 4: L = 2.49 MH and R = 55.3 ohms
2 - 3: L = 27.5 MH and R = 398.7 Ohm
Although the 10x14" coil was originally intended for GTA and the coils have different designs, the measurement characteristics perfectly match our request. We install the DD coil on the metal detector and do the first tests in the air, the result is positive, the discrimination works!!

DD coil 24x36cm for Garrett ACE series, field test results:
There are false signals (isolated cases), temporary instability.

Soil test results:

Conclusion: 1. The DD coil can be installed on the ACE 250/150 metal detector. 2. The ability to increase search volume without losing depth. 3. There is instability in the device with the DD coil. 4. 9x12" coil is not inferior to DD.

*In Ukraine, they began producing NEL coils for the ACE 250 and other models of metal detectors. The results can please the most avid treasure hunter - the depth was almost doubled!

Ordinary people, which includes me, divide metal detector coils into 2 types - Mono and DD. Metal detector manufacturers are cutting thinner…

Why does the DD coil have this designation? Do you know the difference between Mono and Concentric coils? And if you do not have a pulse metal detector, then what you call a mono coil is more correctly considered concentric. Let's look at the difference between search coils and how this affects practical search.

Mini educational program... A metal detector coil most often consists of 2 components - a transmitting loop (Transmit Coil, TX) and a receiving loop (Receive Coil, RX). The first generates an electromagnetic field, the second monitors changes in this field (when a metal object gets under the coil, the field is deformed, these distortions give the metal detector a reason to tell you “dig!”).

If the transmitting loop is larger, the generated field will also be larger. Hence the dependence of the coil size and detection depth. A small nuance, high mineralization of the soil can introduce interference into the field, and this is part of the search environment.

Concentric coil

A concentric coil is most often what we call a Mono coil (for example on the Garrett ACE 250). But just a mono coil is a type of Concentric.

The peculiarity of a concentric coil is that the transmitting and receiving loops are spaced as far apart as possible. This allows you to create a symmetrical field (hence the accuracy of the pipoint), slightly better separation of adjacent finds with one sweep (from the conical shape of the field).

Concentric coils are designed to cover the full range of existing finds. Logical positioning - universal coils. They are susceptible to the influence of high mineralization of the soil; when increased, the coil loses depth.

Mono coil

The classic understanding of a Mono coil implies that it is used on a pulsed metal detector (most modern detectors are not pulsed). Mono coil is a type of Concentric (remember the terms, we will apply pressure on the field with our brain).

The peculiarity of a mono coil is that the receiving and transmitting loops are located next to each other. Has the same properties as the concentric one, including the influence of the soil.

Imaging coils

Also a type of concentric coil. By the way, some metal detector sellers claim that this is a DD coil. We know everything ourselves, and politely correct))

The peculiarity of the coil is that it has an additional receiving loop. This allows the metal detector to more accurately determine the intended find. For example, in assessing the size of a find before digging it up.

Garrett claims that only they have this type of coil (GTI series of detectors), and no other metal detector in the world can boast of this.

DD coils

Do you know why DD is called DD? Because the transmitting and receiving loops are shaped like the Latin letter “D” and are mirrored.

The features of DD coils are significant. Designed for color purposes, good sensitivity for small finds. Unlike Concentric coils with a cone-shaped field, DD coils have a “flat bucket” type field (same visibility at any depth, but pinpoint accuracy suffers). DD coils are also less susceptible to high mineralization, and in such an environment they do not lose detection depth.

According to the shape of the coils

Let me add how metal detector coils differ in shape. There are ellipsoidal and round. Ellipse coil better “separates” targets that are located close to each other (in theory, in practice this is imperceptible). Ellipsoidal coils have higher pinpoint mode accuracy (in practice, it’s a stretch to say that this exists), plus a little less weight (doubtful).

Round reel has more depth compared to an ellipse. This is difficult to verify in practice - you need to test the same coil of different shapes on the same model of metal detector. But if you compare different manufacturers, it always turns out that the round one actually adds 1-2 centimeters to the coin.

In his, he indicated the type declared by the manufacturer. If the type is not specified, it means that no explicit confirmation could be found.