FM = Frequency Modulation. The FM circuit works on the principle of creating changes in the center frequency according to the change of the audio signal input amplitude.

FM Transmitter circuit can operate in the range of 80-120 MHz. Different frequencies can also be tried by adjusting the C in the LC circuit connected to the collector.

PC-Laptop audio output can be connected to the audio input terminal.

The circuit works efficiently up to a distance of 100-150 meters.

Although the regulated capacitor is drawn in the LC tank circuit in the circuit diagram, a 5pF capacitor is used with the L=400uH coil.

L=400 nH, C=5pF in the LC circuit. FM receiver receives the audio signal clearly at 107.7 MHz on the radio.