Comparison Minelab Go-Find 20 vs Fisher F75 LTD

A method used by a metal detector to find items. Describes both the general scheme of the signal and how it is processed.

— VLF. Abbreviation for "very low frequency". As the name implies, these metal detectors operate at relatively low electromagnetic frequencies (less than 20 kHz). They use the “transmitter-receiver” operation scheme: one winding transmits the search signal, the other receives it. The transmitting and receiving windings are located in the same plane, in a concentric pattern or DD (see Coil Type). This technology allows you to create relatively inexpensive devices with good ground balance, minimal sensitivity to false alarms and a high degree of accuracy in metal recognition. Of the shortcomings, it is worth noting the rather high cost of production (coils require precision tuning), as well as the relatively small working depth of such metal detectors.

— VFLEX. A variation of the VLF technology described above, developed by Minelab. The key principles of operation in such metal detectors are the same, however, the control unit in them receives not an analogue, but a digital signal. This has a positive effect on the quality of its processing, but significantly increases the price of the devices themselves.

— R.F. This principle involves the use of high frequencies and the presence of two coils — a receiver and a transmitter — sep...arated by a certain distance (usually several tens of centimeters) and located perpendicular to one another. Such a scheme provides a greater depth of detection, but does not allow you to search for small objects and determine the type of metal. Therefore, it is mainly used in "deep" metal detectors.

— P.I. Abbreviation for "pulse induction" — "pulse induction". In such devices, one coil is provided, "mono" (see "Type of coil"), which plays the role of both a receiver and a transmitter. The coil emits signals in separate pulses, and in between them it works as a receiver, "listening" to the response signal from the ground. Such a scheme allows you to effectively search for objects even in an environment unfavorable for electromagnetic pulses — in particular, highly mineralized soils and in salt water. The latter makes PI instruments extremely useful for marine archeology, both underwater and on wet, salty sand beaches. On the other hand, qualitative discrimination in such models is not available.

— OR. A method based on the so-called breakdown of resonance. The coil in such metal detectors is part of an oscillatory circuit, to which a signal is supplied from the generator with a frequency close to the resonant frequency of the circuit. When a metal object enters the field created by the coil, the characteristics of its inductance and, accordingly, the resonant frequency of the entire circuit change. Based on the change in resonance characteristics, the control unit determines not only the presence of metallic objects, but also, to some extent, their composition. OR-devices are simple in design and inexpensive, since they do not require precision settings; at the same time, the depth of detection and the reliability of operation in them are low, and mineralized or wet soil further worsen the performance. Therefore, this method has not received wide popularity; it is used mainly in entry-level devices.

— ZVT. Minelab's proprietary technology, developed primarily for searching for gold treasures and nuggets. The abbreviation stands for "zero voltage transmission", the principle of operation is described as "the creation of ultra-constant high-power magnetic fields of opposite polarity." Due to this, according to the manufacturer, the efficiency and depth of gold detection are significantly increased, as well as the resistance to interference is improved and it becomes possible to work even on soils with very high levels of mineralization. However, ZVT-metal detectors are quite expensive, and the possibility of working with other metals, except for gold, is usually not mentioned in the description of such devices.

The design of the coil(s) of the metal detector.

— Concentric. The name of this type is due to the fact that such a coil includes two separate windings — receiving and transmitting — one of which is located inside the other. It is used in metal detectors that use the principles of VLF and VLFEX (see above). The field from a concentric coil has a small width, which determined both its advantages and disadvantages: on the one hand, due to this, it is possible to determine the location of an individual find with high accuracy, on the other hand, it takes a lot of time and effort to carefully examine vast areas. This shortcoming can be partly compensated for by the elliptical shape (see below). Also note that concentric models are quite sensitive to mineralized soils.

— Mono. The simplest type of coil, having only one winding. This option is used in PI, OR and RF devices, and in the latter case, two mono-coils must be installed. The main advantages and disadvantages of this type are similar to those described above concentric.

— D.D. Also known as Double-D. Such coils have a pair of windings in the form of the letters D, turned in different directions and arranged closely so that they form a circle or an ellipse. In terms of application, DDs are similar to the concentric coils described above, but they differ in the shape of the generated field: it is a narrow plane directed along th...e line of contact of the windings. This makes it possible to cover a fairly wide band in one pass, and also reduces the sensitivity to interference from mineralized soils. Among the shortcomings, compared with concentric ones, it is worth noting the high cost and lower accuracy in the localization of individual finds (however, the latter can be compensated by the skills and experience of the operator).

— Super-D. Coils of a specific design, consisting of three windings — a central one, which plays the role of a transmitter, and two external ones, working for reception. They were developed specifically for ZVT metal detectors (see "The principle of operation"), taking into account the features of their work.

The shape of the coil (frame) of the metal detector.

— Round. The traditional form used in almost all types of ground and underwater metal detectors (see "Type"); the only exceptions are models that work according to the RF method (see "Operating principle"). When using concentric coils (see "Coil Type"), this option allows you to create a conical field, which is convenient for pinpointing the location of the find, but reduces the covered area and makes it difficult to search over a large area; models with DD coils do not have this drawback.

— Elliptical. The shape in the form of a longitudinally elongated ellipse allows you to somewhat "stretch" the field created by the metal detector in length. This is especially true for coils of the concentric type — however, such an expansion somewhat reduces the positioning accuracy of individual finds. But in coils of the DD type, where the accuracy is by definition low, the choice between round and elliptical shape is most often not fundamental.

— Rectangular. A specific form used in RF or PI instruments. For technical reasons, it is considered optimal for such devices, but it is practically not found in other types of metal detectors.

— Butterfly. Another option used in DD coils along with the ellipse (see above). In fact, it consists of two elliptical windings..., partially combined and resembling butterfly wings in shape — hence the name. This option is typical mainly for large-sized DD coils; with a large width, it is considered more optimal than an ellipse.

The number of coils provided in the scope of delivery of the metal detector.

Emitter-coils are used in metal detectors with all operating principles (see above), except for RF (frames are more justified for them). Also note that, unlike the frames, such emitters are installed only one at a time, and even a paired DD type emitter (see "Coil type") is considered one coil. So if there are several coils in the kit, this means that they are interchangeable. Such a complete set is convenient in that it allows you to choose a working nozzle depending on the specifics of the situation. For example, for the initial search, you can use a large coil, with low accuracy and wide coverage; and having found something interesting, you can put a "sniper" attachment and determine the exact location of the find. However, the features of such a configuration may be different, interchangeable coils may have a specialization in metals, soil types, etc., and it's ok to clarify their features separately before buying.

Also note that some models may not be equipped with coils at all. On the one hand, this means additional efforts to select and purchase these parts, on the other hand, it allows you to choose them yourself according to your own requirements, without relying on the manufacturer's decisions. This option is useful for advanced "treasure hunters".

The operating frequency (or frequency range) of the metal detector. This is one of the most important parameters when choosing a device, because the optimal frequency for different cases will be different — depending on the size and material of the items being searched, the characteristics of the soil and other factors. Detailed recommendations on the choice of frequency for each specific situation can be found in special sources; And already on the basis of this information, it is worth choosing a specific model.

Note that the actual frequency at which the metal detector will operate also depends on the installed coil — they are usually made for a specific frequency. Therefore, to use the full capabilities of the device with the ability to adjust this parameter, you may need replaceable coils.

The greatest depth at which a metal detector is guaranteed to be able to detect a metal object. Note that this parameter is most often quite approximate, moreover, somewhat conditional. This is due to the fact that it is usually indicated for an perfect environment (low-mineralized soil, a fairly large object, the material of which optimally matches the frequency of detection of the coil, etc.), and even for such conditions it is difficult to derive an absolutely accurate value. Therefore, in fact, the detection depth is highly dependent on a number of additional factors (from soil characteristics to user skills) and can be significantly less than indicated in the characteristics. Nevertheless, the claimed depth describes the capabilities of the metal detector quite well, and it is quite possible to compare different models with each other.

Note that a large depth not only increases the cost of the device, but can also adversely affect its ability to detect small objects.

The deepest depth at which a metal detector is capable of detecting small coins and other objects of similar size. Many users buy a device with the intention of “hunting” for metal trifles, so manufacturers often indicate this parameter separately in the specifications. Due to the small size of the coins, their detection depth is usually much less than the total maximum detection depth (see above).

The number of individual discrimination programs provided in the design of the metal detector. In this case, discrimination means filtering the detected objects using a discriminator (see above) so that the device does not work on unwanted objects such as pieces of foil, bottle caps, etc. You can also configure such a filter completely manually, but this may require special knowledge and create difficulties for inexperienced users. To avoid this, some models may have preset programs instead of manual settings. Thanks to such programs, the user just needs to select from the list what type of objects the metal detector should react to, and all the necessary settings will be set by the device's electronics.

Ground balancing method provided in the design of the metal detector. By itself, such balancing is a setting of work parameters for the characteristics of a particular soil — after all, depending on its mineralization, humidity, etc. The soil affects the search signal in different ways, and the device electronics must take this effect into account for high-quality processing of such a signal. Due to the correct balancing, the detection of the desired objects is ensured and at the same time the probability of false positives is minimized; and it can be done in the following ways:

— Automatic. The most convenient type of balancing that does not require the user to manually adjust the device. Usually, tuning requires some time to move the coil up and down above the ground until the automation sets the necessary parameters. There are two types of auto tuning: preset and tracking. The first option involves balancing the metal detector for a specific type of soil before starting work, after which the device uses the same parameters until the next setting. Such a scheme is inexpensive and can be used even in fairly simple models, but it is not very reliable: even a small change in the type of soil under the coil leads to a decrease in the effective detection depth and an increase in the probability of false positives. Follow-up balancing does not have this disadvantage: devices with this function constantly monitor the characteristics of t...he soil and make the necessary corrections to the operating parameters right in the process of operation. This increases the efficiency of the search, however, the price of such devices is very high.

— Manual. As the name implies, with such balancing, the necessary parameters must be set by the user himself. This option is considered the most reliable, because. even the most advanced automatic systems do not always work perfectly; And yes, this setup is cheap. On the other hand, it requires certain skills from the operator and may not be suitable for inexperienced users.

— Manual / automatic. A variant that combines both types of balancing described above; in such models, the user can choose the way of setting as they wish.