And, of course, a simple radio can locate buried metal, even only as receiver, but in radar mode can be detected at more distance and depth. Here "radar mode" doesn't mean radar frequency, mean transmission and reception of RF. Also you can use only transmitter in wich you inserted modulation, this modulation creates in a receiver (wich acts no as detector, just for register changes in TX) a kind of phase shift. The buried metal changes the state of phase shift and voilĂ*! The same with IR beam and radio as monitor for register change in phase shift. "Radar mode" is very old:
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