There are two BC547 in the circuit. The one on the left is acting as an
audio frequency amplifier....
"First amplification stage: this is a standard self-biasing common emitter
amplifier. The 22nF capacitor isolates the microphone from the base voltage
of the transistor and only allows alternating current (AC) signals to pass.."
http://en.wikipedia.org/wiki/Common_emitter
The second one on the right is acting as a Radio Frequency
Amplifier/oscillator....
"The tank (LC) circuit: every FM transmitter needs an oscillator to generate
the radio Frequency (RF) carrier waves. The tank (LC) circuit, the BC547 and
the feedback 5pF capacitor are the oscillator in the Cadre. An input signal
is not needed to sustain the oscillation. The feedback signal makes the
base-emitter current of the transistor vary at the resonant frequency. This
causes the emitter-collector current to vary at the same frequency. This
signal fed to the aerial and radiated as radio waves. The 27pF coupling
capacitor on the aerial is to minimise the effect of the aerial capacitance
on the LC circuit. The name 'tank' circuit comes from the ability of the LC
circuit to store energy for oscillations. In a pure LC circuit (one with no
resistance) energy cannot be lost. (In an AC network only the resistive
elements will dissipate electrical energy. The purely reactive elements, the
C and the L simply store energy to be returned to the system later.) Note
that the tank circuit does not oscillate just by having a DC potential put
across it. Positive feedback must be provided. (Look up Hartley and Colpitts
oscillators in a reference book for more details.) "
http://en.wikipedia.org/wiki/LC_circuit
http://en.wikipedia.org/wiki/Colpitts_oscillator
Something like a BC107 should be a suitable alternative (case maybe
different).
It's already quite simple.
