FM microphone circuit with voltage regulator circuit composed of LM7806 - Power Circuit - Circuit Diagram

Second, the selection of components MIC selects high sensitivity electret microphone, VT1 is 9013H, β ≥ 125. VT2 is 2N3866; β≥90, L1, L2 are 密 0.71mm enameled wire on the ordinary ballpoint pen core respectively around 4匝 and 10匝, C4, C5, C6 using ceramic capacitors, error ± 5%. The three-terminal regulator uses the LM7806 power supply, with a 9V battery, and the board can be self-made.
Third, the assembly and debugging circuit assembly is relatively simple, as long as the components are not damaged, one can be successful. After the circuit is soldered, the antenna is soldered up. The antenna is equipped with a 0.5-meter radio antenna. When debugging, the microphone is placed at the sound source, and then the person leaves the microphone 5 to 6 meters away. Turn on the FM radio and adjust the knob. The turbid harmonics are received, and the spacing of the oscillating coil L1 can be adjusted by the driver. When the L1 pitch is large, the frequency is increased, and vice versa, and the sound received is not a harmonic.
If you want to increase the transmission power, you can change the length of the transmitting antenna, or replace the VT2 transmitting tube with a 34D50 triode, and replace the R4 resistor with 4.7kΩ. The emission distance can be increased by about 100 meters.