Comparison Minelab X-Terra 505 vs Garrett THD

General device type. The purpose and features of functioning directly depend on this.

— Metal detector. This category includes metal detectors of traditional design — devices designed to search for metal objects in the ground or under water (see "Purpose") in vast areas. Such devices in most cases have a characteristic design — with a long rod, at one end of which there is a handle, at the other — a coil. The accuracy of metal detectors in most cases is rather low — about 20 – 30 cm, they make it relatively easy to find the desired objects over a large area, however, to determine the exact location, most likely, you will have to dig the ground manually or use a pinpointer (see below).

— Pinpointer. This name is applied to high-precision metal detectors that look like characteristic "rods" or "blades". They allow you to locate a metal object with an accuracy of 1 – 2 cm; but the range of the pinpointer and coverage are very small. There are two main types of such devices. The first one is ground/underwater pinpointers (see "Intended use"). They are designed to be used in conjunction with classic metal detectors (see above): first, the approximate location of the desired object is determined using the metal detector, and then a pinpointer is used for a more accurate search. At the same time, many pinpointers of this type can even be used as improvised probes for tearing the ground. The second variety is inspection models; fo...r more details about them, see "Appointment".

- Ground. Metal detectors designed to find metal objects buried in the ground - from coins and other historical artifacts to pipelines and caches. They can have different characteristics and scope of application - from the simplest models, suitable only for collecting scrap metal, to powerful professional devices capable of searching even at a depth of a couple of meters. The coil can be protected from moisture (see below), but ground metal detectors are not designed for complete immersion in water.

- Underwater. Metal detectors, designed, as the name suggests, to search for objects under water - primarily at the bottom of reservoirs. Their main features are due to optimization for the environment: a sealed waterproof case (in most cases, with the ability to submerge the entire body to a depth of several meters), the ability to work with wet salty soils, and a weight distribution designed for ease of use under water. Also, such models are usually equipped with waterproof headphones. Note that buying such a device for land use is hardly justified: holding an underwater metal detector in the air is not as convenient as a regular ground detector, and the expensive moisture protection of the case loses all its meaning.

- Inspector. Devices designed to conduct searches and search for metal objects on the human body, under clothing. They are used by law enfo...rcement agencies, security services at airports, train stations, security agencies, etc. Note that in this case we are not talking about stationary “frames”, but only about hand-held detectors. Almost all of them belong to pinpointers (see “Type”) and have a fairly compact size. Thanks to this, the device can be used as a portable device for express inspections, constantly carried with you along with other equipment. However, such a detector can also be useful at a stationary checkpoint, in addition to the frame - it helps to determine exactly where on the body the object that “disturbed” the frame is located.

— For mine clearance. Highly specialized metal detectors for detecting mines or other explosive objects left by the echo of wars and hostilities. Such devices do not need to separate finds by type of metal. Their main purpose is to search for large projectiles, but there are other types of devices for solving specific problems (for example, detecting plastid with a fuse). Small pieces of hardware are usually ignored by such metal detectors. Mine clearance detectors are rarely found in common use, and they are incredibly expensive. Devices for this purpose are heavy and inconvenient, but durable and resistant to weather conditions. They are aimed at professional use by the military and rescue workers.

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 characteristics of the installed coil determine the operating frequency of the metal detector. See "Detection frequency" for more details.

The size of the standard coil (frame) of the metal detector. Theoretically, the larger it is, the deeper the device is able to “see” and the more space it captures in one pass, but the worse it is suitable for searching for small objects and the lower the accuracy with which it localizes them. At the same time, these characteristics depend on so many other factors that in fact, the size of the coil itself affects them very little.

Note that for coils (frames) of an elliptical shape, only one size can be indicated — along the length.

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 number of individual operating frequencies at which the metal detector can operate. For more on the frequencies themselves, see "Detection Frequency" below; here we note that the more options ( 3 frequencies and more) are provided in the design, the wider the capabilities of the metal detector, the easier it is to adjust it to the specifics of the objects being searched and the environment. However, most models have one frequency.