Mini FM Transmitter

The circuit is the simplest with very few components. It can be used as a children's toy or carried around. It consists of a NAND gate IC1 (74Ls13), a microphone MIC1, and four resistors and capacitors.

The bias voltage required for the electret microphone is supplied by the power supply through R1. The microphone signal is sent to the ⑤ pin of IC1, and the FM signal is output through the ⑥ pin and transmitted into the air by the antenna. C2 improves the sensitivity of the circuit. C1 is the decoupling capacitor of the power supply, which can suppress any peak pulse interference. The antenna can use an ordinary short wire.

The transmitting frequency is about 100MHz (third harmonic), working in the VHF FM band, and the FM wave can be received by an ordinary radio. The coverage range of the transmitting signal can reach 20 meters.

The circuit is very sensitive and can sometimes give positive feedback (especially when held in the hand). As long as the transmitter is placed in the right place, it will work fine.