There actually isn’t much to these tbh, oscillator, mixer and pcb antennas. To use these in an application you would have to still process the analog waveform

There actually isn’t much to these tbh, oscillator, mixer and pcb antennas. To use these in an application you would have to still process the analog waveform coming out. Fortunately the frequency is very low (audio range) allowing for all manner of inexpensive detection/measurement circuits.