A cheap wireless microphone circuit

Recently, a wireless microphone is sold on the market, priced between 10 and 20 yuan. The microphone is tuned in the 88-108MHz FM band, with a transmitting distance of about 30 meters. It can be received by any FM radio, and the received sound is clear and pleasant, without clutter interference, and has no impact on local FM radio stations. Based on the actual machine, I drew its circuit diagram for the reference of the majority of electronic enthusiasts. How the circuit works. The sound is coupled to the base of the triode through the microphone through the high and low frequency resistance-capacitance filters composed of R1, C1; R2, C2. Due to the positive feedback amplification effect of the triode, the high-frequency signal of the high-frequency oscillator composed of L1 and C3 is equivalently fed back to the base of the triode through C4. The two signals are mixed together by the transistor to form a high-frequency FM carrier (88~108MHz), which is transmitted to the antenna via C6, and the antenna emits FM signals to the surrounding space. Fine-tuning the gap of L1 coil can change the frequency value of FM frequency modulation wave. When in use, the FM receiving frequency can be selected arbitrarily between 88 and 108MHz. Selection of component L1. Use ∮0.6mm enameled wire to wrap 4 times around the core of an ordinary ballpoint pen. Use C9018 high-frequency low-power tube for the transistor. Other components can be marked according to the parameters in the picture.