4 Transistor 500mW FM Transmitter Circuit
This is a pretty simple radio transmitter circuit that uses 4 transmitters and broadcasts on the FM band at approximately 100 MHz. The output power is approximately 500mW (0.5 Watts).
As shown, the audio input is a microphone, which uses 2 x 2N3904 as the microphone audio preamplifier. The audio/mic input level is adjustable by means of a 5k preset / potentiometer.
The circuit uses a Colpitts oscillator for frequency generation, which is free running and operates at the fundamental frequency i.e. no complex frequency multiplication or control. The frequency tuning component of the circuit consists of 2 5pF (picoFarad) capacitors and a single 10uH (micro-Henry) inductor. These components can be modified if a change in frequency is required - perhaps even replaced with variable capacitors (if you're up to the challenge).
An output RF amplifier takes the frequency produced by the Colpitts oscillator and amplifier to somewhere around the 500mW (0.5 Watt) range - so this is the approximate output power of this FM transmitter. You are advised that since this transmitter operates at the fundamental frequency, and because there is no output filter, there is likely to be some frequency drift and harmonics/spurious emissions.
- Fm Transmitter Circuit
- Fm Transmitter Circuits
- 500mw Fm Transmitter
- 4 Transistor Fm Transmitter
- 500 Mw Fm Transmitter