This 2-transistor circuit is used with high impedance microphones, such as ceramic or crystal capsules. The circuit is from a 1989 publication but can be assembled with a BF494 transistor for Q2 and BC548 for Q1. The coil consists of 7 turns of 24 or 26 AWG wire on a 0.5 cm form (adjustable core). The antenna can be 10 to 30 cm long and the range can reach a few tens of meters. Capacitors must be ceramic.
