FM Transmitter / Wireless Microphone 3 Transistors

This is yet another FM transmitter DIY kit for beginners and hobbyists. It is slightly different from our previous FM transmitters. It has 3 NPN transistors and the transmission range is around 50-100 meters.

• Current 5-15mA
• Working voltage DC 3-6V ** From experiments, it can be used with 9 volts.
  
• Transmission distance 5-50 meters
  
• Transmission frequency 88-108MHz, adjustable frequency by tuning at L4.
  
• Circuit board size 53*40mm
• The product is a kit. Customers must solder it themselves.
  
• Download Schematic

Rough operation of the circuit:

Q1 = acts as a pre-microphone, amplifying the audio signal from a condenser microphone to a suitable strength for use.
Q2 = generates a frequency and mixes FM waves.
Q3 = amplifies the transmission power (RF Power Amp) to a moderate strength for broadcasting.
C9, C10, L3 = Low pass filter, trapping frequencies higher than desired to ground.
JK1 = Jack receives audio signals from outside and is also a switch between the audio signal from outside and the internal microphone.