FM transmitter Circuit with 4 Transistors
This circuit delivers an FM modulated signal having an output power of about 500mW. The input microphone pre-amplifier is designed close to a pair of 2N3904 transistors (Q1/Q2), and audio gain is restricted by the 5k preset trimmer potensiometer (trimpot).
Some substitutes for the 2N3904 are: NTE123AP, 2N4401, BC547 (watch lead orientation), and so on