Here the simple and low cost FM transmitter circuit. The frequency range of this FM transmitter should be about 89MHz ? 109MHz. Output power is about 9mW at 9V.

Components List:

Resistors:
R1, R6        : 12K
R2, R4        : 100K
R3            : 22K
R5            : 1K
R7            : 100R

Capacitors:
C1            : 10uF/25V
C2            : 22n
C3            : 10n
C4            : 3n3
C5            : 2p7
C6            : 22p 
C7            : 100uF/16V
Trimmer       : 0-30pF tuning capacitor

Mic           : ECM-60P

Transistors:
Q1            : BC338
Q2            : BC548B

The battery supply rails have been well tied together with respect to radio frequencies (C1, C2 and C7.) The tracks are also thicker. This makes the circuit a single “solid” block eliminating RF currents in different parts of the circuit. This also means the battery no longer has RF on it which makes the whole unit a lot more frequency stable. A battery is perfect choice.

Download the complete explanation of this FM Transmitter (include circuit diagram, component list, the circuit’s work) in PDF format:
[wpdm_file id=42]

Source: kitrus.com