This wireless microphone that uses a charcoal microphone was found in an Argentine publication in 1973. It can be mounted with a BC548 and the charcoal microphone can be replaced by a small speaker. The coils for the medium wave range consist of 40 + 40 turns of wire 28 in a small ferrite rod. The antenna must be 50 cm to 120 cm and the range is a few meters, depending on the sensitivity of the receiver.
