This could be the simplest FM transmitter circuit you can find on the internet. Only using a single transistor and few passive components, this transmitter can deliver signals up to 50 meters. The transistor Q1 serves as the modulator as well as oscillator. Capacitor C2 and inductor L1 forms the necessary tank circuit for making oscillation. The voice to be transmitted is coupled to the base of Q1 using an electret microphone. The FM signal available at the collector of Q1 is radiated using the antenna.
- Use a 3V battery for powering the circuit.
- The circuit can be assembled on a Vero board.
- Coil L1 can be made by making 5 turns of 24AWG wire on a 1cm plastic former.
- Adjustments in the transmission frequency can be made by compressing or relaxing the coil.
- Antenna can be a 25cm long 18AWG wire.