This transmitter uses a 741 operational amplifier in modulation. The microphone can be any type and an antenna of 10 to 20 cm can be connected to the collector of transistor L1 has 4 turns of wire 22 to 26 in the form of 1 cm without core and the trimmer is common. The circuit can be powered by voltages from 6 to 9V and its range is in the order of a few tens of meters.
