This is a long range stable FM transmitter circuit. The circuit is using a LM2950 5V voltage regulator IC comes in TO 92 transistor package, which will provide a stable 5V to the oscillator till the 9V battery runs down to 5.5 volts, due to which the oscillator becomes frequency stable. The circuit is using two
transistors, transistor Q1 is working as an oscillator and Q2 is working as an RF amplifier and also separating the oscillator from the antenna due to which the circuit becomes more frequency stable. Coil L1 and L2 are air cored coils equal to 10 turns of 1mm enameled wire close wound on a 3mm form. The frequency of the transmitter can be adjusted with trimmer C4. The maximum output power can be achieved by adjusting the trimmer C5. A field strength meter or RF power meter will be required to set the transmitter on the maximum output power. Use 30 inch wire antenna for maximum range. Keep all the components as near as possible in the circuit. The maximum range of the circuit will be 2 KM or more in the open area.
Note: This circuit is for educational purpose only.