This direct detection circuit was found in a 1986 documentation. The output is of low power, but it excites a speaker. The coil is formed by 30 + 70 turns of wire 26 or 28 in a ferrite rod and the antenna consists of a piece of wire from 3 to 10 meters. The power can be done by batteries or source. The resistor in series with the speaker can be 47 ohms.
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