BFO "Beat Frequency Oscillator" metal detectors are about the most basic of all metal detector technologies, in fact one can build one of these type metal detectors with relative ease. Because of the simplicity of BFO metal detectors they are relatively cheap. One can easily purchase a BFO hobby type metal detector for $25 to about $200. Don't be fooled by the simplicity of this technology though BFO metal detectors are very useable and can work very well in certain applications.

What makes a BFO type metal detector tick?

A BFO type metal detector uses two coils that consist of tightly wrapped wire. One coil is large and is used at the search end of the metal detector, while the other coil is much smaller and is contained within the control box of the metal detector. Both coils in the metal detector are connected to an oscillator that produces thousands of electrical pulses per second. It is important to note that the frequencies being generated by these coils are offset from each other. The pulses must generate frequencies that are slightly different in order for the metal detector to work properly.

The pulses when traveling through these coils produce radio waves that are sent to the receiver of the metal detector to produce a reaction. Normally an audio series of tones. These tones indicate the differences between the two frequencies.

When the search end of the BFO metal detector is passed over a metal object, The coils in the metal detector displace a magnetic field that when passed over a metal object creates electrical currents that are referred to as "Eddie Currents". The eddie currents in the metal object then create a magnetic field in themselves which in turn send a signal back to the receiving unit on the metal detector. The metal detector then reacts in some way. Usually by sound.

As mentioned earlier, BFO metal detectors are generally simple and very inexpensive and can not compare to other metal detector technologies as far as accuracy and dependability go. VLF and PI metal detectors offer a greater degree of accuracy and performance, but are usually much more expensive.