Different types of metal detectors
If you have already started to take an interest in metal detecting, then there is a good chance that you will have researched in magazines or online by watching YouTube videos or posts on social media. Glancing at these, you may have been bewildered by the apparently staggering number of different machines that are currently available on the market.
Unless you have already acquired a metal detector, you will probably be wondering at this point which machine is most suitable for you. To help in making this decision you need to ask your- self the following:
1. How much am I willing to spend?
2. How much time will I devote to using my new detector?
3. Where will I be detecting – field or beach?
4. How good am I at adapting to new technology?
5. Do I need a lightweight and/or compact machine?
Choosing your first metal detector can be very confusing.
There have been many people who have jumped straight in at the deep end and purchased very sophisticated and expensive machines, only to find that they don’t understand how to use them. Consequently, they either get sold or end up gathering dust in a cupboard having never had a sniff of a bit of silver. Most people starting out in the hobby purchase a low to mid-range detector for two to three hundred pounds. With experience gained, they will then tend to add either an additional coil to the machine or upgrade to a more expensive model with increased features performance. If you’re unlikely to spend much time out in the fields then an expensive machine may not be a good investment. Saying that, of course there have been occasions when fortunate prospectors have ventured out for the first or second time and found something worth more than the machine they have just purchased! This happened to me (Dave Stuckey). After having purchased my first machine in 1976 at a staggering cost of £80, I took it out for its first trial and within minutes I found a solid gold pocket watch. The scrap value of the gold more than covered the cost of the detector.
To explain the differences between the different types of metal detectors available it is necessary to go a little into their history and development. (If some of the terms used are unfamiliar, a glossary is included in The Beginners Guide to Metal Detecting). The first types of hobby metal detectors to become readily available in Britain in the late 1960s were BFO (Beat Frequency Oscillation) models. These were very basic and thus cheap and easy to produce….and buy. Most had two basic controls: on/off-volume and tune. Tune consisted of setting the detector to a faint ticking noise that could be heard continually from the speaker (or headphones). When a target was located this tick- ing noise would increase in frequency. They had single coil open search heads, which made pin- pointing a find difficult. Depth was seldom more than a few inches. They had no discrimination and would pick up nails, silver paper and ring pulls as well as wanted targets such as coins. They were also subject to drift and needed retuning every few minutes (or sometimes less!). Despite the primitive nature of these machines, fields, com- mons and other sites were ‘virgin territory’ and some good finds were made by their users. Several American detector manufacturers produced more advanced models of BFOs in the 1970s, but other designs eventually overtook these early machines. To my knowledge none are available new today although some may still be found at car boot sales or in junk shops. However, they are more of a curiosity and collector’s item than a usable piece of equipment.
The next model to become available in Britain in the early 1970s (although already established in the USA) worked on the IB/TR (Induction Balance/ Transmit Receive) principle. These had two balanced coils in their search-head and would signal when a metal object disrupted their electromagnetic search field. Depth and pinpointing were a lot better than on earlier models. Although at first, they did not have variable discrimination, some would naturally reject small pieces of iron or tiny fragments of silver paper. Most models, again, had two controls: on/off-volume and tune. Tuning consisted of adjusting the control so that just a faint noise could be heard. When a target was located this would increase in volume. How- ever, the problem of drift and the need for manual retuning remained. The problem was partially overcome with the development of push-button auto-retuning. This new control was a button that was held down while the detector was being tuned to threshold and then released. If the detector drifted from its pre-selected threshold point, all that was necessary was to push the button to bring it back to threshold.
Variable discrimination, which appeared at around this time, was another technological advance. Detectors of this type were usually referred to as: ‘TR/Discriminators’. Here a rotary control could be used to set the detector’s reject level to unwanted junk targets. However, the use of discrimination brought three disadvantages: it increased the detector’s susceptibility to mineralised ground, it caused loss of depth, and it meant that wanted targets were sometimes rejected alongside unwanted ones.
The next development, in the mid-1970s, was the VLF/TR (Very Low Frequency/Transmit Receive). Detectors of this type had, in effect, two separate circuits. One circuit, the VLF was less prone to mineralisation and could provide good depth. However, it was all metal and could not reject junk items. The TR side could discriminate but had less depth. Thus, searching was carried out in VLF mode, and once a target was located the detector was switched to TR to establish if it was junk or a wanted find. The problem with this system was the need to switch back and forth between the two modes.The invention that overcame this was meter discrimination. In detectors of this type both circuits were working at once, the VLF all-metal side controlling the audio while the TR discrimination side worked the meter. Thus, all registered targets came through on audio, but the meter needle swung left for junk, right for wanted tar- gets. Further developments included variable discrimination on the TR side, and an overlay of tone on the VLF side (low for junk, high for wanted targets). On some models of this type of detector it is possible to select meter or tone discrimination, or both. Such detectors are still in production today and have proved very effective in the hands of their adherents, particularly on finding good targets amongst high levels of junk contamination.
Most beginner detectors today are single frequency VLF ‘motion’ type machines. These machines first made an appearance in the late 1970s to early 1980s. Such detectors can over- come ground effect while discriminating at the same time by means of continually and automatically auto-tuning. At first the sweep speed had to be very fast, but further developments slowed this down to normal. To register a target with a motion detector, the search head must be in movement. If the search head is held stationary over a target, the auto-tune circuitry will simply cancel it out. However, many motion detectors have an all- metal, non-motion mode for pinpointing – even without this, pinpointing can be achieved quite easily as the coil movement required to register a target can be very slow.
A Selection of Current Metal Detectors
During the mid to late 1980s computing technology began to be incorporated into metal detectors. In the same way that it is possible to program a PC, it became possible to program certain detectors with a host of variables by means of an LCD screen and touch pad controls. These detectors came with basic ‘factory pre-set’ pro- grams, or you could devise and store a program that you had developed yourself to cope with the conditions of a particular site. Some detectorists took readily to this new technology while others stuck to the simple ‘switch on and go’ machines. Recent developments have made metal detectors like mobile phones. You now could update certain detectors’ software via the internet if/when the manufacturer provides it. This has enabled some machines that may have been problematic in certain conditions to now be fixed due to a ‘tweak’ to the machine’s software. Also, this can include adding many more additional features like adjustments of the machine’s tones, extending the battery life along with additional programs and settings.
Easy to visualise interfaces and features (including graphical charts to help identify the target) has driven a growth in people creating their own detecting programs. You will find many articles and videos in magazines and on YouTube and other social media on the best program for your detector to find a hoard! However, tempting it might be when you acquire your first machine to enter these programs straight away and hope to find your dream treasure, it is highly recommended that you first get to know each and every defined program your machine comes with along with the tones, numbers and graphical displays.
A traditional control box on the CSCOPE metal detector launched in 2012 and the 2024 Minelab Manticore screen.
Many mistakes have been made with people not only confusing themselves with a ‘special’ set- ting they have added but also not using the right program for the land conditions they are detecting on. Thousands of hours and lots of money have been invested by manufactures in providing a specific program that suits a machine best for example ‘Field’ or ‘Beach’. Once you are confident with your machine and you can almost know what you are going to dig from the tone and/or the ID numbers on your screen, that’s the time to have a play with defining your own program or switching to another one you have been itching to try. The biggest change to detectors in recent years has been the introduction of ‘Mutli-Frequency’. This uses not one single frequency like the traditional VLF machines, but multiple frequencies at the same time. Detectors now offering this can automatically adjust the frequency of the electromagnetic waves emitted by the coil as well as calculating the ground conditions, thereby optimising its detecting capabilities. For example, low frequencies are better for detecting large metal objects at greater depths, while high frequencies are better for detecting smaller objects at shallower depths. By emitting multiple frequencies simultaneously, a multi-frequency metal detector can increase your chances of detecting items of different sizes, types and depths. This technology has enabled machines to work extremely well compared to traditional VLF (single frequency) machines on wet sand on beaches with ‘Beach’ mode, while many machines these days are also fully submersible to many meters. There is now a broader spectrum of makes and models to choose from than ever, but ensure you stick to a well-known brand from a renowned metal detecting dealer. Many copies of well-known detectors have been made over the years and are often seen on online auction sites marketing over exaggerated depths and features. These are of inferior quality and need to be avoided. This also applies to pin pointers used to aid the detection of your targets in the hole you have just dug.
At the end of the day, the main differences in more expensive / high-end detectors is they have faster processors which are able to calculate targets quicker and more effectively. The more expensive machines are also more durable, normally waterproof and have better features like wireless audio, better ergonomics, are more compact and lighter. This makes them suitable for a wide range of applications, from beach and water detecting, searching for hoards or gold nug- gets in the Australian outback or just popping the machine in your backpack and detecting in the field for a few hours or day. Overall, while these models may come at a higher price point, they are often well worth the investment for those who are serious about metal detecting and want the best possible performance and features. However, you need not rule out the traditional single frequency VLF (Very Low Frequency) metal detectors that use just one or more frequencies (which must be manually changed) i.e. 5, 10 and 15kHz – these are still a very popular choice and offer some benefits over multi-frequency machines. They are a lot simpler in design and easier to operate with fewer settings and are more user friendly, especially for beginners. They are also less expensive if you are on a tight budget. Some single frequency machines can often detect at greater depths as well and can be more specialised in finding specific metals i.e. silver or gold. Let’s not forget that many great finds have been found with these machines over the years!
The Garrett Axiom pulse induction metal detector.
One other type of detector technology which is also available but less popular is PI (Pulse Induction) which were first available to the hobby market in Britain in the 1970s. PI detectors put out a very strong electromagnetic field that energises metal objects buried in the ground and creates eddy currents around them. This makes such targets easier to detect. The system is virtually free from ground effect and Pulse detectors can be capable of above-average depths. However, PI detectors are sensitive to iron, and many have no ability to discriminate against this or other types of metal. This makes them difficult – or often impossible – to use on inland sites. Battery drain is also often higher than with normal detectors. Apart from the detectors mentioned above, there are also more specialised machines designed specifically for underwater detecting and hoard hunting on a larger and much deeper scale. Large hoard hunting machines used by archaeologists and prospectors are very powerful and expensive machines. These tend to be a mini-PC with screen or laptop connected with a large search head either connected to a detector style machine or using a moveable bed with wheels. These and are designed to look for large targets, such as pots of coins buried at great depths or even caves. They are, generally, less efficient at locating smaller targets nearer the surface and are used by archaeologists to map the ground when carrying out surveys. Many can give you a live 3D view of the ground below as well as recording the survey to be played back later. Another benefit over the years is built in rechargeable batteries and the ability to plug in USB power banks to your detector and head- phones. This enables you to detect for longer (especially good when camping or away from a power source). Long gone are the days of having to keep spare batteries in your bag as a backup.
A final consideration often forgotten is that of weight and ergonomics. If you become addicted to the hobby like so many have, you may be holding your machine for up to eight hours a day and even more, which can be physically exhausting. Ergonomics was often overlooked in the past, but now with 3D computer modelling, manufacturers can measure the balance, angles and fit of new machines. However, if you can ‘try before you buy’ from a friend, club or by visiting a dealer, it is highly recommended to get the real feel for a machine.
This article is an exert from our popular ‘Beginners Guide To Metal Detecting’ updated in 2023 and provides a wide range information for those interested in starting out or new to the hobby.