FM Transmitter Circuit Diagram (Single Transistor Wireless Microphone)

The following wireless microphone uses a single transistor with additional passive components. It only needs a single cell 1.5volt battery, and can work on 1.2V rechargeable battery. Here is the schematic :

Single Transistor Wireless Microphone

Single Transistor Wireless Microphone CIrcuit diagram

Transmission range is between 30-50m radius, depends on the surrounding path and obstacles. Any transistor with high frequency bandwidth and low base-emitter will do : 2N2222A, PN2222A, BC109B, C, BFxxx series, and also theĀ  BC238 is suitable. The critical part is the inductance. It should be handmade. Using AWG24 enameled copper wire and make 2-4 loose turns with diameter around 4-5mm. Try to receive the signal around 90 MHz. To fix the coil, use a glue to fix it, this is to avoid mechanical deformation which could change its inductance value.

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