Cordless FM Mike, Color : Black

Cordless FM Mike can effectively achieve 10-20mtr receptions from transmitters. You can listen your sound in any FM radio (Receiver) by tuning radio frequency in between 88 to 108 MHz. This FM circuit uses a medium power VHF oscillator built around BC547 transistor. The BC series transistors frequency is 200-250MHz.These can oscillate well in VHF range.
Audio is picked up from the room by an condenser microphone and transmit by T1. 10K resistor (R1) supplies the bias voltage for the microphone. A varicap based circuit is used for good quality frequency modulation. Operational frequency can be altered by adjusting spacing of coil L1. L1,C4 from LC circuit to produce oscillations. Coil L1 consists of 20 SWG wire, space wound air core. Antenna tap is taken at one turn from bottom end. By using 7cms wire arial, range up to 10 meters may be expected. The range can be extended by using a multi-element ground plane antenna. Output power of the transmitter can be raised by lowering value of resistor R5 connected between emitter of transistor T1 and ground to, say 27 to 39 ohms.