A nice and very useful project i stumbled over a time ago is this circuit, which is commonly credited to Japanese multimedia artist Tetsuo Kogawa. It takes audio input through a 1/4″ phono jack and, constructed as shown, without the optional antenna connections, will broadcast an FM radio signal about 30 feet.
This circuit is the standard model of Mr. Kogawa’s simplest FM transmitter, which is slightly more complex than his most basic design in that it includes a trim capacitor to adjust the transmitting frequency. It can be powered by a 9V battery and uses a hand-turned copper coil.
The circuit is extraordinarily simple and could be built on an experimental panel. Just follow these Make instruction to build your own FM transmitter: