Understanding FM transmitter circuit


Posted on Feb 7, 2014

Wireless FM Transmitter. The site has some explanation on how the circuit works, however I`m not sure about a few things, including the electret mic & how the frequency modulation takes place. The electret microphone has a current of 200uA which changes by +- 3 uA depending on sound waves. This sets the voltage across R1 to 2V and the voltage acro


Understanding FM transmitter circuit
Click here to download the full size of the above Circuit.

ss the mic to 4 volts. As the sound hits the mic the current through R1 increases slightly reducing the voltage across the mic. Is that what is happening This changing voltage is passed on by the coupling cap, C1 to the base of the transistor, which is biased by R2 & R3 to approx 2V. The voltage across R4 with no signal on the mic will be Vb - 0. 7 (drop across vbe), 1. 3 volts. As the voltage at b changes R4 will change by the same amount. This change in voltage is seen at the base of the tank circuit. And the signals voltage is increased/decreased. Isn`t this what happens in AM As wouldn`t the capacitance need to change in order to get Frequency modulation And if it was amplitude modulation occuring in the FM spectrum, then how would a radio receiver be able to demodulate the signal At this point I`m not sure what is happening at the capacitor C3, what is that doing Is it holding CE at a fixed voltage And is it along with capacitor C2 considered a bypass capacitor Or do bypass capacitors need to be connected to ground




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Radio Wave Alarm
    10 Watt Power Amplifier (TDA2030)
    Sound Level Indicator LM3915
    Low-frequency-oscillator
    Proximity Alarm I Circuit
    Making a Line Sensor using IR Receiver
    300w power amplifier circuit with 2n773
    Motorcycle Alarm PCB
    2-to-1 Multiplexer
    Infrared Detector Circuit with PID20
    NTSC Video Using the 68HC908QY4
    ASTABLE MULTIVIBRATOR USING OP AMP
    pll circuit



    Top