BFO Metal Detectors (Beat Frequency Oscillator)

Metal detecting can be fun, exciting and lucrative! But before you start metal detecting you will want to know the different types of metal detectors and their applications.

So, what are the different types of metal detectors? There are 3 main types of metal detectors.

Beat-Frequency Oscillation (BFO)
Very Low-Frequency (VLF)
Pulse Induction (PI)

In this article, We will explain Beat-Frequency Oscillation (BFO) in detail and you will learn if it would be the best to use for certain metals and environments. Once you are done reading this article you will have a clear understanding ofBeat-Frequency Oscillation (BFO) and what circumstances to use each one in.

BFO Metal Detectors is one of the most rudimentary metal detection systems. It’s processed by six analog circuits, one digital circuit, and several basic components. The inductor coil’s capacitance, variable by the metal detected, serves as the “input”. The headphone jack is the “output”, with potentiometers determining tune and volume. This report will demonstrate the process of building the BFO metal detector, applications of learning development, and the extent of which this circuit can be used.

It is the simplest (and oldest) type of metal detector technology and is a good starting point for learning how metal detectors work. The basic beat-frequency metal detector employs two radio frequency oscillators which are tuned near the same frequency. The first is called the search oscillator and the other is called the reference oscillator.

The outputs of the two oscillators are fed into a mixer which produces a signal that contains the sum and difference frequency components. This signal is feed to a low-pass filter removing the harmonics. As long as the two oscillators are tuned to the same frequency, the output will have no signal.

When a metallic object disturbs the magnetic field of the search coil, the frequency of the search oscillator shifts slightly and the detector will produce a signal in the audio frequency range.

Although once popular, BFO’s are no longer being made by professional metal detector manufacturers. They are simple and inexpensive, but do not offer the accuracy and control of modern PI or VLF detectors. Attempts have been made to add new features such as discrimination and more advanced models were produced in the 1970s, but they were soon replaced by recent, more sophisticated technology.

BFO Metal Detectors are still used in cheap hand-held devices and in low quality, toy type detectors. The vintage BFO detector is more of a curiosity and collector’s item than a usable piece of equipment.

In BFO metal detectors use two oscillators that are configured on the same frequency. In this case, the frequency of the reference generator unchanged. The coil circuit of the measuring oscillator is at the same time search or measuring coil.

When the search coil excited by an electromagnetic field appears metal object, the frequency of the measuring oscillator is changed. Signal the modified frequency is fed to the mixer where it is mixed with the reference signal frequency. As a result, the output of the mixer is allocated a signal with a beat frequency, which is supplied to the display unit.

As an indicator of the detectors on the beat is usually used acoustic devices, however, there are designs with a needle and led indicators. When using acoustic indicators the change in the sign of the beats is quite simple to determine the kind of metal, color or black, is made the object located in the zone of action of the device.

It should be noted that the beat frequency in the BFO detectors lies in the low-frequency range, closer to the lower limit of sound perception the human ear. This allows to considerably simplify the design of the unit indication, since the beat frequency of the measurement, search engine) and auxiliary (reference) generator can be analyzed by ear. However the sensitivity of the detectors, operating on the principle of beating leaves a lot to be desired. However, the characteristics of these devices are completely satisfied unassuming users.

Which Type of Metal Detector is Right For You?

In our opinion unless you are going to do some underwater metal detecting or want to find pure gold I would go with the very low-frequency metal detectors. VLF’s do a much better job at deciphering between metals and they are priced cheaper.

But on the other hand, if you are in search of mainly gold then there are many pulse induction detectors specifically designed for gold detection. And if you want to detect gold underwater then you definitely want to get a pulse induction metal detector.

It all comes down to what types of metal you want to detect for, your experience in metal detecting, what terrain you are detecting in and at what price point you can afford for a metal detector.

I hope this article helped you understand the difference between metal detectors and hopefully you will be able to make an informed decision of what type of metal detector you want to get.

If you have any questions or comments please leave them in the comments section below. I would love to hear from you.