Signal_PCB
This PCB contains the circuitry to apply the DC polarising signal to the sensor and to detect and amplifier the return AC signal. The IC's have had their numbers removed in a (poor) attempt to hide the operation of the unit. The IC near the centre of the PCB seems to be an NE5534 op-amp the other 2 ICs are a quad op-amp and a dual op-amp,
The switch ('Area Tune' control) switches capacitors in parallel with the sensor coil to resonate it at the approximate frequency of the return signal.
Signal_PCB
This PCB contains the circuitry to apply the DC polarising signal to the sensor and to detect and amplifier the return AC signal. The IC's have had their numbers removed in a (poor) attempt to hide the operation of the unit. The IC near the centre of the PCB seems to be an NE5534 op-amp the other 2 ICs are a quad op-amp and a dual op-amp,
The switch ('Area Tune' control) switches capacitors in parallel with the sensor coil to resonate it at the approximate frequency of the return signal.