Simple FM transmitter circuit with stable frequency

The working voltage of this circuit is 9V, and the working current is 2-6mA. The component parameters are shown in the figure. BG1 is 9018, BG2 is C1959 (it can also be 9018, but the power is very small. If it is D-40, the shooting distance can be extended to 1000 meters). L1 and L2 are 0.5mm enameled wires wound 4 and 3 turns on a 0.5 round rod. The working voltage can be increased to 12V, so the shooting distance can be increased, but the frequency will change. The whole circuit is best powered by batteries to achieve the best sound quality and frequency stability. When debugging, turn off the work of BG2 first, adjust the frequency you need, and finally turn on the BG2 circuit to adjust the power. The author of this circuit uses BG1--D40 and BG2--C1970, which has a good effect. The voltage is 12V, the working voltage of BG1 is 6V, and the distance is 3000 meters (directional experiment). If you want to use D-40, please note that the working voltage of D-40 is 6V! It is best to install this circuit in an iron box and add a fading reduction network at the input end. I wish you success!