This simple FM Transmitter is very powerful (mean its not simple one..! but its easy to make..). You can transmit FM signals up to 5km radius circle area using this Transmitter. I recommend to use 12V battery for supplying power. If you wish to use 12V AC-DC adapter you may want to make a very smooth DC out put using stabilizer, unless it will generate low frequency hum when listening to FM radio out put. For making L1 coil use 18SWG copper wire (about 1mm diameter) and make 7 turns(see figure 2). Use 75Ω TV cable's middle wire for antenna, It should be 2meters long(see figure 3).
Making the coil(use 18SWG copper wire or around to it)>>
Antenna(Use this cable for best results, otherwise you can use any type of copper wire(at least 2meters long))>>
Transistor pin identification>>