This circuit is used with high impedance microphones, such as ceramic or crystal capsules. The circuit is from a 1989 publication but can be fitted with a BF494 transistor. The coil consists of 4 turns of 24 or 26 AWG wire in a 1 cm form without core. The antenna can be 10 to 30 cm long and the range can reach a few hundred meters. Capacitors must be ceramic.
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