How to make an FM transmitter

By Sagar Sapkota -
299220

After getting several comments from young electronic students , I am rewriting this article to make the FM transmitter making process more clear.

This tutorial is for making simplest FM transmitter using one transistor. You can make this project with less components and it is an easy and simple project for beginners.

Before you proceed, please see the schematic given below. In the schematic, you will see the components required for making an FM transmitter.The transmission range of this circuit is approximately 10-20 meters.

The schematic of FM transmitter is given below:

You need the following components for this experiment:

1. Q1- Transistor- 2N3904

2. Capacitors- 4.7pF, 20pF, 0.001uF, 22nF.

Note: 0.001uF has code 102 and 22nF has code 223.

3. Variable capacitor: VC1. It is also called trimmer capacitor. You can buy one from your local store. The capacitance range should be 0-100pF or 10-100pF. If you cannot get one, try to get a trimmer capacitor that has minimum capacitance of 20pF. You can also get such capacitor from your broken radio, but you may need assistance in getting that out from your radio.

4. Resistors- 4.7 kilo Ohm, 470 Ohm

5. Condensor/ Electret Microphone

On your electret microphone, you will see that on one of the pins, there is solder pad connected to the case of microphone. Remember that pin is always negative.

6. Inductor- 0.1uF.

6-7 turns using 26 SWG wire.

You need to scrap the ends of inductor, otherwise, the inductor won’t work. Check the video given below to know how to make an inductor.

Or you can also use another inductor.

0.1uH

Learn to make an inductor for FM transmitter

7. Antenna: Use 15cm to 1 meter long wire for antenna. If you have a long antenna, the signal transmission will be better.

The following picture shows the components used for making FM transmitter. You can simply follow the steps shown below.

On the image shown below, you can notice that I have not used a trimmer/variable capacitor. I have used a fixed 20pF capacitor instead. So, if you don’t have a variable capacitor, you can use a fixed capacitor also.

Insert transistor, resistors and capacitors on breadboard. You can see the values of the components on the previous picture.

Then insert electret microphone.

NOTE: terminal touching the casing is -ve

Use 15cm long antenna. You can use a normal wire for antenna.


Then, with a non-conductive tool, adjust the capacitor for the clearest reception, rotate it till the receiver receives a sound from the microphone of transmitter. Use the following formula for determining the frequency.

Set your FM receiver for a clear, blank station.


Best of luck 🙂

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FM transmitter imagesBUILDCIRCUIT HAS RELEASED A NEW DIY FM TRANSMITTER KIT. PLEASE CLICK HERE TO KNOW MORE ABOUT THE KIT.

 

FM TRANSMITTER DIY KIT (16)

try this also

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165 COMMENTS

  3. i cant found VC1 which is available in schematic diagram but not in BREADBOARD….and i also can’t see a ANTENNA clearly…

    • Hi, I used 20pF(right below the inductor) in place of variable capacitor. Please use any ceramic capacitor between 1-100pF. For antenna(the green wire standing erect), you can use 5-10cm normal copper wire. best of luck.

  4. can u please tell me what is the frequency i sould tune in my receiver…..?
    i made nearly three circuits…nd came to ur circuit…which is using 2n 3904..
    can i replace bc 547 in that place(Q1)…? plz reply i am preparing my self for mini project..

      • thanks for replying…ur really a great helper..bcoz in other blogs i can find simply many ckts but no reply..about trouble shooting…
        sorry for other question…whats the range of this transmitter…?
        actually i constructed the ckt in three different circuits available in internet..but all of them failed..
        in receiver i can hear ..popping sound when i made to hit the mic with screw driver..but voice is not transmitting
        is there any tips for troubleshoot…any suggestions for ckt…

        • the range of the transmitter depends upon the length of the antenna. In your case, it should be around 10cm only.
          Troubleshooting:
          a. Did you scrap the ends of inductor? if you don’t scrap, it doesn’t work.
          b. Keep wires of microphone short. If they are long, that introduces extra inductance and the frequency changes. Therefore, keep it short.
          c. Follow the instructions given on the page carefully.
          d. change the value of VC1- variable capacitor, you may keep 20pF, 22pF, 33pF, keep on trying…
          e. In place of R1- 470, try with 330 Ohm resistor also.
          f. In place of C2- 4.7pF, insert 100pF, or 20pF or some other nearest value capacitor. but it should be in pF only.
          g. Check this video: how to make inductor: http://www.youtube.com/watch?feature=player_embedded&v=UcRY_bqTTfw
          h. Check this video: how to connect electret mircophone: http://www.buildcircuit.com/how-to-use-electret-microphone/

          Remember that this kind of radio projects don’t work in the first attempt, you have to make several hit and trails, best of luck.

          • ok..thanks for troubleshooting tips….any way i am using readily available inductor…
            i am going to college and use ur trouble shoot tips and post the result after that testing….

          • i have doubt about antenna..to use whether 15cm or 10metres..i am in middle of my mini project..

          • I am sorry, my mistake, it is 10cm. Not 10m, it is obvious that 10meters is too long for such a small transmitter. Did you make the length of electret microphone very short? It should be short. And do you have an extra electret microphone? sometimes, while soldering, the microphone breaks down. So, always keep extra components. I will try to make the circuit again today (just for you) and let you know if there is any problem.

          • sir ..plz how to use trimmer capacitor…..VC1 ….it is having three terminals….by the way i am also connecting right now…is it possible to contact u in another way..bcoz its taking long time ..to contact u sir plz…

  5. sir …i tried on my bread board..i made changes as u said sir..it worked..but only i can hear popping sound…in ur previous reply u said that antenna height is 10metres…!. but u have used 15 cm only that to copper wire…i have used whip antenna like the antenna used in pocket fm radios…plz reply sir i am waiting …

  6. Hey I like the circuit and am wondering if I could integrate it with my own project. I would like to control a servo for my home made RC car. If I were to put a potentiometer in place of the mic would the signal that I receive allow me to control the speed of a motor or a servo.

    Thanks

  7. i am doing fm transmitter.
    the transmitted output can be seen by mobile fm receiver.but i am not gettin the exact voice .
    please tell me the exact freaquncy.

  8. can you tell me the exact range of transmition.
    how far can plase the reasever.
    can i use cell phone as receiver.

  9. Hello,
    Great job,i have personally implemented its working propely. How can the range of frequencies be extended to say over 10meters or so,using the same circuit design with little modifications?
    Regards.

    Kaguai George.

  10. Hello,
    Great job,i have personally implemented its working propely. How can the range of frequencies be extended to say over 10meters or so,using the same circuit design with little modifications?
    Regards.

    Kaguai K George.

  12. can a wire serves as an antenna in fm transmitter…..if yes., which wire should be should be used as an antenna and how much long it should be?

  13. i want to make a project whih transfer electriity using wirless antenna…not using coil…..is this possible…

  15. hi…..friend…….i used 2 transistors bc547, bf494 instead of 2N3904 , but i am confused with the transistor terminals .emitter , base , collector……please say me whether it is ebc , ceb , ceb? For both bc547 , bf497

  16. can you explain how can we check a remote control usind transmitter and receiver i.e.,when a button is pressed on the remote,by seeing at the receiver end ,we should able to say which button is pressed??

  19. I m nt gettin the 22nf capacitor. Wht can i us instead of that??? And i have got 0.001uf capacitor of code 103 instead of 102. Will it work??????

  25. Please reply ! 🙁 need help …

    What can i use instead of a Variable capacitor ?
    i cant find one …. also what if i use 0.1 H Inductor instead of Copper coil. i cant find the said wire as well ! :(((

  26. I tried with microphone. I tried with jack wire. i didn’t find 4.7 pF and used 20 pf. I have something that has writen on it u4.7 not 4.7u is the same ting no ?
    I used 1.2 uF it may be the problem?
    I tried reciving fm sound with phone and radio. Didn’t work I tried every frequency.
    Even I tried to calculate the frequency but I don’t know the exact valu of L …
    Maybe you can tell me in what range of values (80-90 90-100) the correct frequency may be.
    Thx in advice.

  27. sir……….i couldn’t find 0.1uh inductor nor 26swg wire in my city instead 1uh is available.will the circuit still work if i use 1uh…………reply ASAP

    • the LC is the oscillator its self, a.k.a. tank circuit, it operates on a resonance frequency given by the formula. btw, i would suggest getting a frequency counter from ebay, its pretty cheap. so you can tune your fm receiver at that frequency, and you dont have to get a variable cap for that.

      or you could just vary the length of your inductor to tune your transmitter.
      looking at this formula:

      L = [(d^2)(n^2)] / [18d + 40l]

      L – in uH (inductor)
      d – in inches (coil diameter)
      l – coil length in inches
      n – number of turns

      ive been building transmitter for about 10years now. fm/pm/am/fsk/psk/etc.

  35. Sir Good Day.. Can I ask how far this transmitter can transmit signal??how many meters?If i wanted to extend its range of transmission, what should I adjust or what should i change?

    This is my first time here..Please reply sir..Thank You!!

  40. Sir, I want to send music as my modulated signal. I am actually doing this for the first time. Can I use a female 3.5mm jack and connect it to an audio source? Please help me…

  44. sir,what receiver can i use? in this there is no receiver circuit..
    the receiver circuit should be tuned to the same frequency know… so can u post the receiver circuit….please….

  58. Hi, I think this would be nice for a personal project but I have a question, Can i use an earphone jack instead of a microphone so that i can transmit the signal from an mp3 player (like an iphone) to the radio? If not, can I still use this design but only changing a few thing in order to make it work with a jack instead of a microphone?

    • Yes you can, just connect every line from your earphone jack microphone to the microphone entrance circuit or even you can use your small speaker as a microphone if you prefer. Just remember the circuit is not stereo and you have to join the line A with B from your mp3 player or other device speaker lines you want to use as source of sound with the positive line in the entrance of your circuit.

  64. Switch on the transmiter , We have to get a reciever to acepts the signel. Give some sound to microphone. Switch on receiver (any fm radio). Now we can her the sound in receiver.

  65. sir i am very new to this field and i bought a new multimeter dt830d but i am not sure whether it is working so how can i test it. i havve all the above components to make a transmittor

  66. instead of wirewound inductor you made and as shown in description instead of wirewound inductor can i use a fixed 0.1uh inductor will the circuit work. and also tell me any circuit modification to increase the range. or any other circuit.

  78. Hi, this design has some little problems! 1st the resistor for bias mic is to low it should be 47k for 9volt supply.
    C2 must be 10p couse 4.7 is to low and T2 get some problem in turning on. and must important thing is that mic shouldn’t connect directly to base use 22nf capacitor to bipos it.

  85. I am a Communication Engineering student from Ethiopia. Your project seems smart. but what if I want the capacity to be raised to 1000m?

    • Hey Melaku, i think you first need a powerful battery plus you need to adjust the length of the antenna and look for a transistor with great amplification factor.

      ain’t sure coz am a computer eng. student too but hope that the best i can say.

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  95. So my group and I decided to try to modify this project a little, by replacing the microphone with a male headphone jack, we didn’t have a new one but I used one from an old pair of headphones. It didn’t seem to be working, but when we set it near the radio we were using as a test, after removing the jack because we were not getting a signal, we began to pick up other radio signals while varying the 0-100 uF capacitor. Does anyone have an idea of why it is doing this?

  100. Thanks man,, is there any way of making a good antena,bcoz without antena my transmitter was giving 10 meters range,,with antena range was increasing but causing noise

  102. From the formula above, if I use capacitor 20pF and inductor 0.1µH, that mean I will get frequency 112.60 MHZ, is right? Thanks.

  108. Wow, FM Transmitter :D, great..
    is it work well.., with that thing?
    if can’t sound maybe on calibrating freq, tuning transistor to 88-108Mhz RF
    the inductance is ok, nothing usefull with that, need 3mm long to create tuning form.

    Result, Not Work.. 😀 haha

  111. I have a question about the formula.
    I know L is inductance, but I want to to which capacitor value to use for C.
    I am not able to find the frequency.

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