this is a mini fm transmitter. this can transmit audio signals to a radius of upto 30 meters. and its frequency could be found in the auto tune feature of fm recievers or smartphone fm.

Step 1: Materials and Tools-

electrical components needed-
transistor bc548
electret mic
capacitor 1 uf
capasitor 10 pf
capasitor 33 pf
resistor 4.7 k ohms
330 ohms
9v battery and its cap
an antena
inductor 9 turns

material and tools-
soldering iron
soldering wire
nipper
wet sponge
multimeter
etc

extra -
solder fume extractor

Step 2: Circuit Diagram -

Step 3: Lets Begin!!!

(SORRY FOR THE LACK OF PHOTOS )
now take your transistor and solder its base to possitive terminal of the electret mic then there solder a 4.7 k ohm resistor and possitive terminal of the 1uf capasitor to that same junction now solder any terminal of the 33 pf capasitor to the 4.7 k ohm resistor and the other end of the capasitor to the collector of the transisitor solder the ends of the inductor the 33pf capasitor and other to the collector of the transisitor now solder the wire of the antena to the collector of the transisitor now solder possitive terminal of the 10 pf capasitor to the collector of the transisitor and its negative terminal to the emitter of the transistor,now solder the other end of the 1 uf capasitor to the negative terminal of the electret mic solder a 330 ohm resistor to the collector of the transisitor and the other end of the resistor to the negative terminal of the electret mic and finally solder the negative terminal of the battery cap to the negative terminal of the electret mic.

Step 4: Final Testing!!!

now make sure that the antena is not touching any metal object, the switch on your smartphone fm and choose auto tune when the transmitter is on and when you find it
then congratulations!!! you've made it.