Micro wireless FM microphone circuit diagram

As shown in the figure is a miniature wireless FM microphone circuit. The circuit uses very few components, only 4, to form a miniature wireless FM microphone. The working frequency is relatively stable, the transmission distance is greater than 10 meters, and when powered by 1.5V, the current Less than 0.5mA, such energy-saving microphones are rare, and the distance can reach 30 meters when powered by 3V. It can lead from one end of the corridor to the other, a full 20 meters away, realizing the FM dream of a group of us enthusiasts.

The circuit is as shown in the figure. BG, L and the junction capacitance of the triode form a high-frequency oscillation circuit. The junction capacitance of the triode is about 2~3P. To make the frequency fall within the FM range, the coil should be wound 7 times around a 5mm diameter core, and the condenser microphone will receive the call. The vibration of the time modulates the high-frequency signal to produce frequency deviation, achieving frequency modulation . The emission distance is related to the working current of the emission tube. The resistance should not be too large or too small. It should be between 300 and 500 ohms, and the power should be less than 1 milliwatt.

When choosing BG, the fT of the tube must be greater than 300MHz. If 2SC3358 high-frequency tube is used, the frequency will be more stable and the distance will be longer. The inductor L is divided into two coils to be wound, but the winding direction must be the same. L1 is wound with 4 turns of 0.5mm diameter enameled wire on a 5mm diameter frame, and L2 is wound with 3 turns. The antenna can use a 10cm long soft wire. Touching the antenna during use will affect the frequency change. It is very stable when used in a fixed location.

This circuit can be installed in the cap of a small bottle of Rumo, or in a pen case. The battery should be A13 or smaller, but be careful to add a switch when using a small-capacity battery.