Low-cost FM transmitter circuit powered by two transistors

Here is a simple and low-cost FM transmitter powered by two transistors. The circuit can be adjusted to operate in the 87-108MHz range with a range of 20 or 30 meters. This circuit is powered by a 9V power supply, and the quality is better when using a regulated power supply.

Coil L1 consists of 7 turns with a tuning plug on a 1/4 inch plastic former. Adjust the tuning block to tune the transmitter. The actual range of this prototype is adjusted from 70MHz to around 120MHz. The antenna is a few inches of wire. Wires longer than 2 feet may dampen the oscillations, preventing the circuit from working.

Although the RF circuit is best built on a PCB, you can use a veroboard, keeping all leads short and breaking the tracks at appropriate points.

Last but not least, don't hold the circuit in your hands and try to talk. The body capacitance is equivalent to a 200pF capacitor in parallel to ground, damping all oscillations.