Hobbies And Interests
VLF Technology
Very low frequency detectors use a two-coil transmitter/receiver system where one coil -- the larger one -- transmits an electromagnetic current perpendicular to the coil into the ground. The magnetic field continually -- thousands of times per second -- pushes down and is pulled back up from the alternating frequency of the coil. The second coil -- smaller, inner one -- is the receiver or antenna and when the EM field of the larger coil interacts with conductive materials in the ground, the disturbance in the EM field is picked up by the receiver. It sends a signal to the processing unit on the detector as a beeping signal. The various beeps then, depending on the quality of the detector, tell you the size, depth and type of material. VLF detectors with phase-shifting technology can distinguish between various types of metals though analyzing the reactivity of the object to the EM field disturbance.
PI Technology
Pulse induction technology detects metal through a series of electromagnetic pulses from the coils of the detector. PI detectors are not as common as VLF detectors but no less efficient. PI detectors have from one to three coils working together to send signals at a high rate of oscillation into the ground. It essentially creates an echo when the EM pulse hits a metal object, reflects the signal back and is collected through the integrator circuit -- similar to how sonar works in bats. PI detectors will outshine VLF detectors in areas of highly mineralized soil or salt such as beaches, because their control circuitry can ignore such barriers. PI detectors are most popular for deep searching since the signal transmits much deeper than VLF or beat rrequency oscillator detectors and also for beachcombers since the lack of large iron deposits, which PI detectors have problems with, are not common.
BFO Technology
Beat frequency oscillator detectors are the simplest type. BFO technology is also the oldest. It uses two separate radio frequency oscillators with frequencies close to each other but not exactly the same. The search oscillator is near the ground, while the reference oscillator is in the control unit of the detector. An EM current is created between the two oscillators and is pulsed into the ground as radio waves. The simplicity of the detection circuits made it possible for amateurs to make their own BFO detectors at home or buy them for very low costs. The technology is still used in the 21st century because it is much cheaper to manufacture than the more advanced VLF and PI circuitry but does not have the level of control and accuracy that the other modes of detection provide.