Build a 4 Transistor FM Transmitter Circuit Diagram. This 4 Transistor FM Transmitter Circuit Diagram provides an FM modulated signal with an output power of
around 500mW. The input microphone pre-amp is built around a couple of
2N3904 transistors (Q1/Q2), and audio gain is limited by the 5k preset
trim potentiometer.
The oscillator is a colpitt stage, frequency of
oscillation governed by the tank circuit made from two 5pF ceramic
capacitors and the L2 inductor. The output stage operates as a 'Class D'
amplifier, no direct bias is applied but the RF signal developed across
the 3.9uH inductor is sufficient to drive this stage. The emitter
resistor and 1k base resistor prevent instability and thermal runaway in
this stage.
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