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.
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: