Beat – frequency oscillation detectors
The BFO is a basic example of metal detector technology, which is a perfect starting point for understanding how metal detectors operate. It’s the best way to understand how metal detectors operate.
Two radio frequency oscillators are calibrated to the same frequency in a base frequency metal detector. One is the search oscillator, and the second is called the comparison oscillator. The outputs of the two oscillators are loaded into a mixer generating a signal that includes the components of the number and frequency of variations. This signal is passed through a low-pass filter that eliminates the harmonics. When the two oscillators are tuned to the same frequency, there is no pulse at the output. If the magnetic field of the search coil is disrupted by a metallic object, the frequency of the search oscillator gradually changes, and the detector generated an audio frequency signal.
Although once popular, professional metal detector makers will no longer produce BFO’s. It was easy and inexpensive and didn’t have precise and controlled mechanics like the PI or VLF detectors with modern technologies. There were attempts to introduce modern technologies such as discrimination and alternative versions in the 1970s, but the current and more innovative technology quickly overshadowed them. Beat-Frequency Oscillation developments are often added to low- quality toy type detectors and inexpensive portable devices.
The antique BFO detector is not just a piece of material but rather a fascination and a collector’s item.
Very low frequency detectors
The most powerful types of metal detectors (VLF) are dependent on the variety of materials used in them. They are detectors of very low frequencies, that is, IB (Induction Balance). The VLF detector incorporates two synchronized coils, in the same manner as all IB designs: the outer coil functions as a transmitter, alternating current to generate an electrically skewed magnetic field and the internal coil acting as receiver interpreting the secondary magnetic region generated by the conductor device. The magnetic field is enhanced to audio. The demodulators help to distinguish between object types.
Pulse induction metal detectors
The metal detectors for pulse induction (PI) give regular electric current pulses to the quest coil, generating a magnetic field. The coil emits a pulse to the ground, which gives the target point a replying vibration. A sample device monitors the pulse and transmits it to an integrator that produces an audio sound. The very low frequency/transmitter-receiver is surpassed by the pulse in areas where little garbage is dumped, on the saltwater beach, or mineral soil, as the conductive salts and mineralization can be ignored simultaneously when detecting. Pulse induction metal detectors can detect deep-grained artifacts, but they are susceptible to iron and can not discriminate against various metal types. This fault makes it particularly difficult to use on inland areas.