Medium power FM transmitter circuit

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Description.
This is the circuit diagram of a moderate power FM transmitter circuit employing two transistors.The voice signals picked by the microphone will be amplified by the transistor Q1.The second transistor is wired as an oscillator operating in the FM band.The output of T1 is given to the base of T2.T2 performs the modulation also.The tank circuit comprising of components L1 and C6 determines the frequency of the signal, and can be varied by adjusting C6.The capacitor C7 couples the FM signal to the antenna.

Circuit diagram with Parts list.

fm-transmitter-circuit

Notes.

  • You can assemble the circuit on a general purpose PCB.
  • The circuit can be powered from a9V PP3 battery.
  • The Antenna A1 can be a 1M long wire.
  • The inductor L1 can be made by making 6 turns of 0.8mm enameled copper wire on a 5.5mm diameter/4.5mm length plastic former.
  • With a matching antenna and proper tuning this transmitter can have range upto 100meters.
Show Comments

75 thoughts on “Medium power FM transmitter circuit

    • Seetharaman

      Hi Amit It has to be ceramic or it can be solid tantalum bead type. not wound tubular capacitors, which has inductive component also buit in.

      Reply
  1. Tabat

    What type of crystal oscillator can I use to replace the tank circuit with? Pls I need a reply with the frequency.

    Reply
  2. naser

    hi. if I use mp3 player out put for this circuit (change Mic with audio in) what I do? can I connect player out to c1 directly?
    with tanks Naser Khiavi

    Reply
    • Seetharaman

      Remove R1 and C1 and feed direct to C2 and common. Adjust MP3 volume for clear sound from the FM monitoring receiver.

      Reply
  3. aiya

    is c1 elctrolitic? cn I have c6 fixed? well that would mean the frequency to be fixed too right?

    please reply asap

    Reply
          • Azeem

            i’ve implemented the circuit. But i’m having problems with the frequency of transmission. It is probably the inductor that i didn’t get well. Please can you explain the oscillator stage of the circuit for me. Also is c7 and that 5pf part of the tank circuit?

          • Azeem

            i got the frequency. However it does not transmit voice signals. If i tap the mic, i can hear it. Also At different frequencies by varying c6. But if i speak, i don’t hear it. If i play mp3, i don’t here it also. I used a condenser electret mic. Please help me. I’ve already submited the proposal for this project in school. I can’t drop it.

          • Seetharaman

            Hi Azeem check polarity of capcitor C2 and try by reducing C4 to .002uF.(2k2 pf or 2200pF) it should solve the problem.

          • Seetharaman

            In the notes the winding details of L1 is given you try it it should solve your problem.

  4. DavidCheng

    Will the circuit work if I change C7 to some other value (i.e. 2.2pF or 22pF)? I probably won’t be able to get 0.022pF capacitor

    Reply
  5. Amit Sharma

    Sir
    Medium power FM transmitter circuit

    in which shop available in mumbai
    because i want to the buy. this circuits

    Reply
  6. Chintan

    i am unable to see any oscillations on the collector of Q2.
    What can be the reason?
    I have not connected microphone yet.

    Reply
  7. supath mohile

    please can u describe that on which frequency this medium power FM transmitter circuit will be work.???

    Reply
  8. NO name

    i think all ground are connected.,correct??
    but i confuse what is the voltage of ceramic cap. it is 50V??
    and electrolytic cap is 16V??

    Reply
  9. seetharaman

    Hi Ashnuka place order through net and get it or please drop the project, without ceramic capacitors it will not work.

    Reply
  10. munna

    I understand everything of this diagram except capacitors. I don’t understand which volt of capacitor i’ll use….?

    Reply
  11. Alex

    Hello, I understand everything on the schematic except for “M1″. Can anyone tell me what component this represents?

    Thanks.

    Reply
  12. tang

    hi i tried to simulate the ckt in multisim 11 in the op i got voltage of nanovolt it s correct??????
    and also i want a formula for calculating the frequency

    Reply
  13. ResR

    I want to ask is the 0,022pF correct value? I can’t find any capacitor with that value available in Estonia.

    Reply
  14. seetharaman

    Hi Prudhvi you can use anything between 18 to 22SWG super enameled copper wire. Q1 is the mic amplifier and modulator. Q2 is the oscillator and power amplifier.

    Reply
  15. prudhvi

    complete discription about this circuit………..plz send me…..its urgent plzzzzzzzzzz……….

    Reply
  16. prudhvi

    can u give me the gaze value for 0.156uhenry inductor?????
    it is very urgent plzzzzzzzzzz………..

    Reply
  17. ADN

    hey guys I construct the circuit but i want to now the frequency at the output to receive the signal!!
    please reply as soon as possible

    Reply
  18. Rickson

    That bit above that said:

    1uF = 1000000F
    1nF = 1000000000F

    is wrong.

    1 uF is 0.000 001 Farads
    1 nF is 0.000 000 001 Farads.

    A Farad is a very large unit of Capacitance

    Reply
  19. seetharaman

    Hi Pecanins any standard FM radio will receive the signal. Tune to a frequency where there is no broadcast signal, adjust capacitor C6 till you get the acoustic feed back through mic. now your transmitter is ready.

    Reply
  20. seetharaman

    Hi Saad the best receiver with 1watt audio output to speaker operation from 2 to 12 volt DC is sony CXA1619

    Reply
  21. seetharaman

    yes telescopic antenna can be used dimension = wavelength / 4 (wavelength in metres = 300000 / frequency)

    Reply
  22. saad

    hello sir i want the the circuit for the receiver of the above circuit and want to know the operating range.and also how could i increase it.thanks

    Reply
  23. seetharaman

    Hi writting in 3 digit is similar to color code. Brown black brown is 101 That is 10 X 10¹ 100PF, Brown-green-brown that is 15 X 10¹ 150PF, brown black orange 103, 10 X 10³ 10000PF or 10nF or 0.01µF. First two digits are indicated in then the third digit is the mutiplier. You can represent only preferred E12 values in decade series 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82. 159PF is not possible in 3 digit system.

    Reply
  24. badr-ess

    can you tell me please about the capacitors? is it o.047MIC 47NF ? and what’s value of 0.5MIC ;0.2MIC and (on nano farad nF) and the value of 0.022PF. thanks a lot

    Reply

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