Simple FM Transmitter with BC549

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This is simple FM transmitter for FM broadcast band in 88-108 MHz. BC 549 is small signal transistor for wide applications, but usually for AF. You can build simple FM transmitter with one BC549 transistor and several other component parts. Simple FM transmitter with only one transistor is often called “bug”. This project is suitable for beginners in radio amateur, education, or hobbies. As an antenna you can connect 150cm of copper wire. 

The input can be replaced with any sound source, like ipod, Mp4 player, laptop, or TV. Transistor circuit outputs 1-5 mW RF signal that can travel around 30 meters, due to limited power supply voltage, limited modulation, very loose coupling with the Antenna. The Antenna has to be connected either directly to the tank circuit or via a small capacitor. The Antenna now forms part of the tuning circuit. If you approach the antenna, the frequency of the oscillator may shift slightly. This effect is called “Frequency Pulling”. The frequency of operation shifts as the battery runs down. This effect is called “Frequency Pushing”. The internal capacitance of the transistor also changes with the temperature of the transistor. The tuning capacitor also changes values slightly with temperature. So one experiences a slow frequency drift till the transmitter reaches thermal equilibrium with it’s surroundings.