You can transmit your speech or audio to an FM radio located more than 100 meters away using this Mini FM transmitter circuit. It is handy and pocket sized ,using only one transistor and a few other easily available components. Try it. I have made it successfully.
It is easy to assemble the whole circuit in a small piece of common PCB. Coil used in the circuit is a 5mm diameter air core coil made up of 4 turns of 22 SWG enameled copper wire. The coil can be wound around a ball pen to get 5mm diameter. Transistor can be any general purpose NPN transistors like BC547, BC 548 or BC549.Use a small 22P button trimmer. MIC used in the circuit is the small condenser mic used in tape recorder. Use a 12 volt mini battery to make the circuit too compact.
Align the windings of the coil and adjust trimmer to get maximum range. If a 100 cm plastic wire is used as antenna, range of the circuit can be as high as 100 meters.