multipurpose FM transmitter circuit

Simple multipurpose FM transmitter circuit designed by using two NPN transistors and few easily available components. This circuit can be used as a voice transmitter or audio signal transmitter by adding Encoder and Decoder at receiver we can transmit digital data also.




This multipurpose FM transmitter circuit can be build on compact size PCB, and there is no signal interference due well placed filter capacitors. For experimental purpose here we used antenna without any signal booster circuit. If you want to transmit FM signal to long range then use proper antenna and signal booster circuit.

Circuit Diagram

Components Required

  1. Electret microphone Condenser = 1
  2. NPN Transistor BC547 = 2
  3. Trim Capacitor 60pF = 1
  4. Resistors 22KΩ, 1MΩ, 10KΩ, 43KΩ, 330Ω = each one
  5. Capacitors 22nF, 100nF, 1nF, 1μF, 27pF, 22nF = each one
  6. Inductor 0.1μH (22 swg copper wire) for L1
  7. Battery (3V – 5V)

Construction & Working

To construct this circuit start with Electret condenser microphone and apply bias through R1 Resistor, then connect output signal from mic to Q1 transistor base terminal through C1 and R2 elements, here the audio signal gets amplified and then output is applied to Q2 transistor base terminal through C2 capacitor and R4 bias Resistor.

Q2 transistor has Oscillator circuit here the audio signal is being modulated into FM (Frequency modulation) signal. Output signal from Q2 collector and tank circuit is connected to the Antenna. To make L1 we need 22 swg copper wire and make 5 to 6 turns in the diameter of normal pencil.

Notes:

  • Always use free FM band for your practice.
  • This circuit oscillates upto 100 MHz and you can tune and adjust oscillating frequency by varying Trim Capacitor.
  • FM receiver should have the tuning frequency range according to your transmitter circuit. (if your commercial FM receiver don’t have frequency range then you need to make FM receiver comply with transmitter frequency.




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