Do-it-yourself search coil dd. Double (DD) and Mono coils - pros and cons
When I was just starting to dig the old days, I had a standard, full-time search coil from my old Minelab x terra 34 - 9 inches, mono. The finds came across by themselves, sometimes even very good ones, but after a while I began to feel that the mono coil was still rather weak for searching for coins in the fields, this is where we search most often with my comrades. And for the next search season, I bought an additional coil for quickly knocking out large areas, DD with a frequency of 7.5 kHz, coil size 10.5″. For those who don't know, this is a stock coil that comes with the cooler x terra 505 and 705 models.
What is the difference between dd and mono coil? Firstly, the volume of the tested ground in DD is larger, because it hits the ground in the same way, without narrowing the scanned beam. It turns out, something like a blade. The mono coil, on the other hand, does not hit so deeply, and even its beam narrows downwards. It turns out that at a depth of at least 10 cm, the diameter of the beam will be not 9 ″, but 2 times less. That is why it is very difficult to find anything at a depth of more than 20 cm with a mono coil. at this depth, the beam narrows to 3-5 cm in diameter. But DD hits evenly, its beam is cylindrical. Accordingly, the volume of the earth is larger and the depth is also greater.
Secondly, double coils go better on mineralized soil, better cope with mineralization, do not bug like mono.
On the other hand, mono perfectly center the target, with such a coil you will not dig large holes, it is enough to dig the target from 4 sides, it will not run away from the edges of the hole, as in the case of a DD coil. So for searching in garbage areas, a mono coil, standard and inexpensive, is better suited. Depth is not its main trump card, the main thing is the accuracy of the readings, so when searching for a beach, it fits one hundred percent.
However, there are also small DD coils, their size is very small, 6″ or slightly larger. They are also great for the beach, especially if the beach is sea, there will be strong mineralization, and DD copes with this perfectly. Well, the small size will allow you to clearly and accurately knock out the territory, there will be finds and you will dig less garbage.
For searching in large areas - fields, for example, a double coil will allow you to comb the area much faster, identify places where coins come across, which means it will be effective. if there is a lot of garbage on the field, then you can put a mono coil, however, the speed of surveying the site will drop. Set mono when you have already found a place of accumulation of coins, there you can already thoroughly finish off the place with a mono coil. Although DD will also cope, especially if the coins come across at a depth. The general conclusions are that mono is for debris and a clear centering of targets, and DD is for most other cases. Incidentally, the largest number positive feedback got a coil Nel Tornado, it has a signal amplifier and can be installed on budget metal detectors, the increase in depth will be very noticeable.
Below we will talk about coils for metal detectors. What are they, why do we need small ones, why do we need large ones?
In addition, we touch on the scope of coils.
DD and Mono Coil Metal Detectors
The mono coil of a metal detector consists of 2 concentric circles - one is smaller, the other is larger. Look at the photo:The signal under this coil propagates in the form of a cone. (Later we will show a picture of this signal)
The DD-coil (or DoubleD) resembles two inverted English letters D. That is why it is called so. And in appearance it is a circle or an ellipse with a longitudinal spoke. Look at the photo: 
The signal of such a coil propagates along the longitudinal spoke and has a wider shape than that of the Mono coil.
Compare the two coil signals:
Of course, this figure shows the difference schematically. The signal from the DD coil goes wider. But the Mono coil hits, as a rule, deeper.
DD metal detector coils are recommended for use in heavily mineralized fields.
Recently, all manufacturers prefer to install coils on their DoubleD metal detectors.
It should be noted that DD coils are more expensive to manufacture than Mono. This affects their price.
Look at another picture. In our opinion, the difference between a DD and a Mono coil is more correctly shown here.
The green area is the coverage area of the DD coil. It can be seen that in one direction she loses to Mono, in the other she wins. The truth is not as big as in the first picture. IN reality not very big. But at depths where the Mono coil can barely reach, coverage with DD is wider.
Why do we need different sizes of coils
As a rule, the manufacturer installs a standard 9"-10" search coil on their metal detectors.This is considered medium. With this reel you can walk on most of the fields.
But if there is a lot of metal debris, then you have to install a coil of a smaller diameter. Usually 6".
This is required because several targets fall under the large coil at the same time: colored and black nails. The metal detector in this case gives a black signal. Or, at best, obscure.
Reducing the coil diameter avoids this situation.
If we have a small density of debris, then we can increase the search depth by taking a coil of a larger diameter. In addition, when searching, we will reduce the number of missing targets. (see picture above)
Coil shape
Coils for metal detectors are round and elliptical. Elliptical coils are more difficult to manufacture. But they give some advantages when searching.Elliptical coils allow you to walk on rather littered fields with a larger longitudinal size. Those. I provide a greater depth of search.
Also, these coils have more coverage.
Coil Applicability
Coils can only work with the metal detector for which they are intended. Those. if the coil was designed to work with a certain Garrett metal detector, then it will not work with a metal detector from another manufacturer (for example, Minelab).There are several reasons for this:
- mismatch between the characteristics of mine detectors (for example, the Garrett ACE-250 metal detector operates at a frequency of 6.5 kHz, and the Fisher F75 at a frequency of 13 kHz. Of course, their coils are not interchangeable.)
- mismatch of connectors (All manufacturers install their connectors on the coil. That is, different diameters, with a different number of pins, and the wiring in the connector is different)
- if you need coils for an AKA metal detector, then you need to look in the AKA coils section
- if you need coils for a Garrett metal detector, then you need to look in the section for Garrett
- coils for metal detectors 705, you need to look in the Minelab coil section
Examples of such manufacturers:
- Coiltek
- Detech
Coil prices
The price for a metal detector coil ranges from $100 to $300. On average, a reel costs $140.The coil itself is considered a consumable and requires replacement after a while. As a rule, the period of its operation is 3-4 years. But maybe more (depending on how carefully you treat it).
But in order to extend its service life, coil protection is used, which protects it from mechanical damage (from below and from the side).
Among novice treasure hunters and just lovers from time to time to wander with a metal detector, you can often hear disputes about which coil (sensor) is better. What can you hear in these disputes, people operate with knowledge in physics, and someone even begins to build some hypotheses.
I am not a physicist, and to be honest, for all the time I have been fascinated by this hobby (and this is not one, not two years) I have not tried to delve into the physics of the ongoing processes. By and large, the user does not need to know all the subtleties, it is enough to understand some of the basics and nuances.Of course, if you are passionate about electronics, if it is fundamentally important for you to know how a DD coil works, how the soil affects the emission and signal perception, then, of course, you can set up various tests and take measurements, because passion is passion.
An ordinary digger is a person who works with maps, walks a lot, loves nature, studies the history of his region. For him, a metal detector is just an additional tool, thanks to which he finds answers to his questions and assumptions. And if we talk about coils, then we can say with confidence that all the coils that are on the market are good! It can also be said that MONO coils are no worse than DD coils, and vice versa. Just different types coils are designed for different search conditions.
Map analysis is one of the foundations of a real search engine
About the advantages of MONO and DD coils
So, if you have a huge field in front of you, and you need to quickly walk through it in order to find out whether the place is worthy of attention or not, then preference in this case can be given to a DD coil of a larger diameter. This type of coil radiates in a rectangle, and at depth the beam does not narrow and is approximately equal to the width of the coil itself.
In other words, for a unit of time with such a coil you explore a larger piece of land, the probability of missing something will be minimal. But, if the field is littered (metal debris), or, then you will have to dig with such a coil, since it will snatch nearby signals.
The beam of MONO coils narrows into a cone as it moves away from the surface of the coil, that is, at a certain depth, the coil will scan only a small area (the apex of the triangle). Such a coil needs to be driven more carefully, the step of the searcher will be slower, and you need to make a deeper overlap of the coil on the previous pass (max).
Mono coil: general view
But this type of coils has its advantages: they very accurately show where the target is, it is more convenient to work with them in the "garbage". And if they lose a little in depth (and not on all soils, a lot depends on the search conditions and purpose), but they allow you to explore the place in more detail.
In general, ideally, the treasure hunter should have experience with both types of coils in order to draw a conclusion for himself which coil is more convenient for him. Indeed, in littered areas, you can safely work with a DD coil, you just need to change the standard coil to a smaller coil.
The general principle of operation of the DD coil
So, as you can see, although the coils differ in the scanning method, all this has little effect on the quality of the search in skillful hands. There are searchers who will never change their DD to MONO, there are also those who are used to working with MONO, they dig holes less, they like this kind of search.
MONO and DD: taste selection
Many search engines in a new place start working with a DD coil, and if the place is promising, mentally or in other ways divide it into sectors and explore with the help of MONO coils. Although, all this could be done with one coil of any type - this is a matter of taste.
You can talk about the fact that coils of one type are somewhat lighter than their counterparts of another category, but we did not specifically weigh them, and the difference of several grams (comparison of coils of the same diameter) is not fundamental. Regarding the “noisiness” of the coils, we can say this: “If you conduct the search wisely and do not knock the coil on the bricks, everything will be fine. If you hit the walls with a coil, phantoms will be on any coil.
What else can be said about coils? Probably, it should be added that the searcher should have at least two coils in the arsenal: a smaller and a larger diameter. Well, do not forget about. Otherwise, a lot depends on luck, luck and understanding of what and how you are doing.
Have you protected your coil?
Your Alexander Maksimchuk!
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Ordinary people, to whom I also belong, divide metal detector coils into 2 types - Mono and DD. Metal detector manufacturers cut thinner...
Why does a 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. We 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, then the generated field will also be larger. Hence the dependence of the size of the coil and the depth of detection. A small nuance, high mineralization of the ground can interfere with the field, and this is part of the search environment.
Concentric Coil
The concentric coil is what we most often refer to as a Mono coil (eg on the Garrett ACE 250). But just a mono coil is a kind of Concentric.
A feature of the 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), a little better separation of nearby finds with one wire (from the cone shape of the field).
Concentric coils are designed to cover the full range of existing finds. Logical positioning - universal coils. Subject to the influence of high mineralization of the soil, with an increase, the coil loses in depth.
Mono coil
The classical understanding of the Mono coil means that it is used on a pulsed metal detector (most modern detectors are not pulsed). Mono coil, this is a kind of Concentric (we remember the terms, we will put pressure on the field with the brain).
The peculiarity of a mono coil is that the receiving and transmitting loops are located side by side. It has the same properties as the concentric, including the influence of the soil.
Imaging Coils
Also a kind of concentric coil. By the way, some metal detector sellers claim that this is a DD coil. We all know 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 the find, before digging it out.
Garrett claims that only they have this type of coils (GTI series of detectors), and no other metal detector in the world can boast of this.
Coils DD
Do you know why DD is called DD? Because, the transmitting and receiving loops are in the shape of the Latin letter "D", and are mirrored.
The features of the DD coil are significant. Designed for non-ferrous targets, good sensitivity to small finds. Unlike Concentric coils with a cone-shaped field, DD coils have a “flat bucket” field (the same visibility at any depth, but pinpoint accuracy suffers). Also, DD coils are less affected by high mineralization, and in such an environment they do not lose detection depth.
In the form of coils
I will add how metal detector coils differ in shape. There are ellipsoid and round. Coil Ellipse better "separates" targets that are close to each other (in theory, in practice this is imperceptible). Ellipsoidal coils have a higher accuracy of the pinpoint mode (in practice, it can be a stretch to say that it is), plus a little less weight (doubtful).
Round coil has more depth than an ellipse. It is difficult to verify this in practice - you need to try the same coil of a different shape, try it on the same model of a metal detector. But if we compare different manufacturers, it always turned out that the round one on the coin really adds 1-2 centimeters.
In his own, he indicated the type that the manufacturer claims. If the type is not specified, then it could not find an explicit confirmation.
Hello everyone on the pro blog.
Today we will talk about coils for metal detectors, dd - coils. As you know, they come in 2 types - regular, round and in the form of an ellipse. What is the actual 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. On 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. Coil mounts, and this is a minus, are slightly smaller than those of a standard 10 "dd coil. As experienced search engines say, it is better to search with an ellipse in heavily littered areas, there are many times more finds with such a coil. It is worth noting that, according to the principle of its operation, the ellipse coil is similar on the so-called sniper, a small 6" DD coil. But the ellipse is much larger. It is more versatile, it can be searched for in the field (with a sniper you will go crazy walking in the field), at the same time, the ellipse has proven itself well in trashy areas. Besides all Of these advantages, the ellipse can also be noted for 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 the sniper coil.
But if, nevertheless, the litteriness of the site is very strong, then when searching, there is no equal to a sniper, a round 6 "coil. It is convenient for her to work even in other people's pits, as a rule, the pits are larger in size than the coil itself, so just stick the coil into someone else's hole and you break through the walls, but again you lose in the depths, sniper rifle hits too hard. Although it is not intended for deep holes, but for searching on the surface.
Of the minuses of the ellipse, the coil mount can be noted. It takes a very long time to assemble, so detecting professionals recommend immediately buying a separate lower shaft, attaching an ellipse and not shooting again. When installing on a metal detector, simply replace the lower stem.
Well, another significant minus of the ellipse is moisture intolerance. After half an hour of work on wet grass, the coil begins to flood with buggy trills. So keep in mind, 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 spring, when it hits dry grass stalks, the burdock coil also starts to sing and flood.
So, to sum it all up, the ellipse is a coil that occupies a middle position among standard 10" round and 6" snipers. That is, if you decide to walk on 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 debris, but the place is promising, then a sniper. Something like this. Of course, everyone decides for himself where and with what to go, but extra information will not be superfluous. By the way, a new one just came out.
