Description.
A very stable and simple FM transmitter circuit is given here. With a matching antenna, this transmitter can attain a range of around 200 meters. I assembled this transmitter few years and got very good results. Let us see how the circuit works.
A condenser microphone (K1) is used to pick the sound to be transmitted. Capacitor C1 is a DC decoupler and the sound signal is coupled to the base of Q1 which wired as a preamplifier.R2 and R3 are the biasing resistors of Q1. Amplified sound signal will be available at the collector of Q1 and it coupled to the emitter of transistor Q2 through the capacitor C4 and 1mH inductor L1. Capacitor C4 decouples the DC component from the preamplifier output. Q2 performs the job of oscillator and modulator. Inductor L2 and variable capacitor C5 forms the tank circuit necessary for creating oscillations. Capacitor C6 is the feedback capacitor. The modulated FM wave will be available at the collector of Q1 and it is transmitted using the antenna A1.
Circuit diagram.

200M FM transmitter circuit

Notes.

  • Assembling the circuit on a good PCB will give better results.
  • I used a 12V battery for powering the circuit. A 9V PP3 battery will also do the job.
  • A battery eliminator is also fine but it will induce noise.
  • Antenna A1 can be a 25cm long copper wire.
  • K1 is a condenser microphone.
  • C2 should be a Tantalum capacitor.
  • Variable capacitor C5 can be used to adjust the transmission frequency.
  • This simplified formula will help you in making inductors, L = (d²n²) / (18d+40l). Where L is the inductance of the coil in uH , d is the coil diameter in inches, l is the coil length in inches and n is the number of turns. Just try to make the inductor your self using this formaula. If you can’t, then comment here.I will give you the winding details.
Author

136 Comments

  1. hi jacky, thanks for the circuit, the problem with my case is i want to design a fm transmitter and a reciever in the 50 MHZ band since it is allowed for amateur radio users….can u help me on how to build those both and what r the components that i may require?

  2. Can I set the frequency into the UHF range with adjusting the inductor? (Something between 400 and 500MHz)

  3. can i send audio signal..with out noice through this??and can i have the receiver circuit for this fm transmitter….

  4. sir,hw can i make the inductor coils? pls.reply asap..

  5. hi sir, what is the power requirement of 200 meter fm transmitter? please i need it asap.. thanks sir..

  6. Gagandeep

    Can anyone plzz tell me the full value of 1uf tantalum cpapcitor means 1uf and how many volts? Thnx

  7. can i use a fixed capacitor of 30pf instead of the variable one so that i could get a fixed frequency of 91.9 MHz, which can be atleast heard over a radio. Please reply me as soon as possible. I am in the mid of my project assignment.

  8. i can’t understand L 1 and L 2. please answer me about this.

  9. sir, idoes’nt got the variable capacitor and other pf and nf capacitors,
    from our local area shop.what I do now, iam in india,kerala, malappuram,perinthalmanna (street)

    • Hi suhail, it is an intresting circuit, most of capacitors can be found in scrap radios like 10band world reciever, coil is 3 to 4 turns #22swg or take it from old fm radio. 1mH coil can get from old tv,vcr,dish reciever..etc.

  10. Ali Alavi

    Hi,I would like to learn youre exellent experiences in electronic design circuits. Thank you.Regards Ali

  11. SABYASACHI BANERJEE

    DEAR MR. JACKY,

    I am facing problems regarding the making of the inductors 0.1uH & 1mH specified in the circuit. Kindly please specify the details, i.e TURNS, LEGTH, DIAMETER & GUAGE OF WIRE. I have bought 24 AWG wire, is it okay??
    And also tell me that what range of frequency you had used in your circuit using the tank circuit comprising 0.1uH inductor & 3-10pF capacitor because I have theoretically calculated using the formula ” F = 1/(2*pi*sqrt(L*C))” that the range will be approx 159MHz(for 10pF) to 290MHz(for 3pF) which is beyond the range of commercial FM broadcast band i.e 88MHz to 108MHz.

    PLEASE REPLY ME AS SOON AS POSSIBLE TO SORT OUT MY PROBLEMS. ITS VERY URGENT.
    THANK YOU & GOOD NIGHT.

    SABYASACHI BANERJEE.

    • Seetharaman

      L2 should be 3 1/2 turns of 18SWG with an id of 8mm. Coil can be spread or compessed to achieve the broadcast band range. L1 can be standard 1mH choke or honey comb wound 250 turns of silk covered 28 gauge wire on a 3mm former. Since this type of winding will be difficult you can buy a standard one and use it. L2 can be easily wound.

    • ElectronicIsLife

      My problem is same with u, I wanted to comfirm about the frequency generated by the cap and inductor, by using a 3~10pf trim cap and the 0.1uH will generate 159mhz~290mhz, totally and clearly above the fm radio receiver broadcast band, should i use 3~10pF trim cap, or use a more capacitance trim cap? pls respond

      • Seetharaman

        add a 10 pf fixed capacitor in parallel with the variable capacitor to bring down the frequency to the required range.

      • Hi, just assemble the circuit and use any of 22,33,47 pf fixed cap and any guage wire between 28 to 20 swg is fine and strech or press the coil to get desired frequency, use variable cap to fine tune. A coupling cap is good for ANT.

  12. sir can u pls give me a ciruit for generating radio waves using simple circuits like oscillator and amplifiers at low cost. pls tell as soon as possible.

  13. I see your formula for calculating inductors, but how do you determine the size wire to use. Like #18 #24

  14. RAHULRAZ

    i m making many projects using this website circuits, All circuit is working nice, so need any help about 200m Fm X-ter, ,transistorized intercom, Em field detector,noise detector ..etc,then send ur req on fb >> solmate solution

  15. nice guy

    thx sir it’s work for me,but i replace the 2n3904 with 2n2222

  16. I tried this in Proteus but I don’t think its working. The o/p should be sinusoidal right? please help me

  17. anand gupta

    Please tell me that where the transmitted signal can be received either fm radio or another receiver circuit for testing and what will be the receiving frequency. Also tell me how we can make the inductor.

  18. Seetharam, where can i connect a crystal to in this circuit, i want a very stable frequency, please show me where to connect the crystal

    • Seetharaman

      Hi Rex between collector and base of Q2

      • sir, I think you are in kerala, as I know you can help me .iam in malappuram district, kerala .idoesnt got the pf and nf capacitors and also the trimmer capacitors what I do now .you know wich shop I got these components

  19. Can you give the no. of turns of the inductor L1 and L2.. please, thanks

  20. seetharaman

    Yes by tuning the tank circuit suitably you can get the signal in your FM radio in the 100MHz range

  21. the 200m fm transmitter at what MHz can it be received in a radio

  22. greetings,

    I built this circuit but i could not get any output from the oscillator.
    Is the value of c6 really 4.7pf? because when i bought the components, the said that there was no 4.7pf capacitor, so i just replaced it with a 4.7uf capacitor. And is L1 1mh or 1uh? thanks 🙂

    • podés usar un condensador de 8.2pF o 10pF

      You can use a capacitor of 8.2pF to 10pF

  23. Hey guys . I telling in the basis of i have first in eletronics and working in sony as eletronic expert.this site is cheating u. Ucan do this circiut but wOULD NOT WORK.U CAN DOUBTS. Ucan see the rivews .any get the output of the circiut . Every body’s are not working. As u want good working hobby circiuts . U can purchase “HOBBY ELETRONICS” books from shops .its is more better and good. Don’t spoil ur money and time.

  24. apple mind

    Hey guys in the internet so many web site providing hobbycirciut i listened and looked these circiut and it is wrong trust me . I telling in the basis of i have first in eletronics and working in sony as eletronic expert.this site is cheating u. Ucan do this circiut but wOULD NOT WORK.U CAN DOUBTS. Ucan see the rivews .any get the output of the circiut . Every body’s are not working. As u want good working hobby circiuts . U can purchase “HOBBY ELETRONICS” books from shops .its is more better and good. Don’t spoil ur money and time.

    • Seetharaman

      You can delete R4 and K1 and directly connect input to C1 and common ground

  25. I want coil details.Please send on my Id ‘Mdwxyz@Gmail.com’

  26. is any1 dere..plz yr help out.. fr designing dis ckt in orcad i need the values of transistor , diode, antenna and microphne..just lyk u had provided d values for resistance and capacitor..provide dese values too..!!!

  27. hey..dese components of dis transmitter..r so random..wil dese b easily available..!??

    • yeah these are easily available if not then contact me i ll give u hell of these components come to me then Khusbu lga k 😀

  28. Seetharaman sir, I have read all the comments and your respond.before that i bought all the components and made one inductor of 1mh…but…as you replied …to Shine that….L1 should be 1uH (not imH)20 turns of 20SWG (0.9mm dia wire)6mmID covering a length of 20mm…….i tried really hard to built 1 mh’s inductor…..what should i do…i’m using this as my lastyear diploma project..my collage’s project’s sir said to change the project if you are not able to find inductor in a week…and i really want to finish this one….
    jak.arm1o1@gamil.com
    would you plz help me out.

  29. Dayanand Mishra

    Sir, please give me winding details of inductors on my id

  30. sir, i cant get a stable frequency also cant get clear sound,it is too much noisy. what can i do?

  31. sir i assembled the FM Transmitter circuit its not working i cant find out the frequency

  32. Hi, what would happen if the input voltage was increased? Would a greater range be achieved? what would the maximum voltage for this circuit be?

    Thanks.

  33. Helo sir dis is shilpa
    Can u give d information abt inductor winding n antena designing
    Plzz msg to my no. 08125613393

  34. Saavithri

    we are connecting the circuit in breadboard and using 0.47 micro henry inductor in place of L2.
    what all changes we should make in the circuit for obtaining a freq between 88-108 MHz? And how to check the output?
    Plz reply as soon as possible…ITS VERY URGENT…
    Thank you

  35. Seetharaman

    Hi Shashank Solid Tantalum capacitors are close tolerance (+/- 5% or even better)type and of very low internal leakage current, hence most suitable for timer appliocations. As there is no inductance involed most suited for decoupling in high frequency circuits.

  36. Shashank

    Hi Seetharaman. Can we replace tantalum capacitor by any other type?

  37. Why don’t you just give the info of the inductors. geez!

  38. hi Seetharaman, can we replace Tantalum capacitor by any other type of capacitor?

  39. Seetharaman

    Hi Zain I have not tried, it should work whether it is audio or pulse train.

  40. Zain Uddin

    Hello Seetharaman,
    Can you tellme on thing if i want to use micro controller chip such as HT12 E/D
    will it work?
    i mean if its not audio signal but digital signal… such as 8 bits with 4
    or its only for audio signal ? thanks

  41. Seetharaman

    Hi Haniff Please see my Dec 23rd comment for frequency

  42. haniff adris

    what is frequency of this transmitter???

  43. Zain Uddin

    Hello Seetharaman,

    Can you tellme on thing if i want to use micro controller chip such as HT12 E/D

    will it work?

    i mean if its not audio signal but digital signal… such as 8 bits with 4

    or its only for audio signal ? thanks

  44. Seetharaman

    Hi By using the formula f= 1 / 2 pi (root [L X C])

  45. Ssembatya

    describe for m how i determine the transmission frequency, and the bandwidth i can use with capacitor C5.

  46. Hey. I got the answer from your circuit. The oscillator circuit with feedback condition did not work.
    I’ve removed c3 parallel with the R5.
    Thank you.

  47. gud evening seetharaman,can i use d c5 capacitor as fixed capacitor?and have i know between frequancy range in c5?

  48. hey seetharaman plz help me with my battery charger circuit using scr.
    i have left questions on that page.

  49. seetharaman

    Hi Shine L2 should be 6 turns of 18SWG (1.2mm dia wire)wire air cored ID of 6mm and winding covering a length of 12mm. L1 should be 1uH (not imH)20 turns of 20SWG (0.9mm dia wire)6mmID covering a length of 20mm.

  50. as i’m new in electronics i don’t know how to make a inductor. please tell me about this. in addition, what will i mean by SWG? and how many turn needed to make those inductor?

  51. Seetharaman

    Hi Akash the pins which are at 180deg is common that is Vcc and the middle one should get connected to Collector.

  52. i complete this design but i m not getting output at proper frequency wt can i do now?
    my variable capacitor has a 3 terminal which terminal i give to vcc ?

  53. Seetharaman

    Hi Munna the supply voltage 12 volts hence the capacitor w2orking voltage should be greater than that. can 16volt 25volt or even 40volt.
    Hi Robert wind L2 with 18SWG super enamelled copper wire with 6mm id and 4 turns, windings spaced at dia of wire. The oscillator center frequency will tune around 100MHz.

  54. I’m not able to make the inductor. I assembled all the parts in PCB accurately but it doesn’t work. What can i do. Please help me.

  55. There is no specific volt identified for the capacitors. I don’t understand capacitors of which volt i’ll use for making a FM transmitter. Please help me……

  56. There is no specific volt identified for the capacitors. I don’t understand capacitors of which volt i’ll use for making a FM transmitter. Please help me.

  57. Sir, I’m not able to make the inductors ………. can please tell me the exact no. of turns and the diameter of the inductors, especially of the 1mH one!

    Thank you.

  58. seetharaman

    Hi Mike Q1 is the audio amplifier. Q2 is the colpitts oscillator and the oscillator is modulated at the emitter(Q2)with audio and with the passive tank circuit the modulated RF signal is radiated.

  59. Thanks Seetharaman It’s a good idea but I’ve another question. Can you explain me why “Q2 performs the job of oscillator and modulator”? I thought that tank circuit is oscillator but Q1 is amplifire so how transistor can create oscillations?

  60. Seetharaman

    Hi Atul 3.9, 5.6 PF can be used here.
    Hi Mike you can add a 22PF fixed capacitor in parallel with the existing C5.

  61. I’d like to have a tramsmitter with a range about 100MHz so may I use 10-30pF variable capacitor to get lower frequencies?

  62. plz suggest me anthr capacitor instead of 4.7pf feedback capacitor of T2.

  63. seetharaman

    Hi Meleja yes with C5 you can set the frequency.

  64. Hi, what frequency does this work at?

    Thanks

  65. Nandagopal

    How find the length of a copper wire by using its weight and diameter…?

  66. Seetharaman

    Hi Gustav if it is readily available please use it. no need to test your patience in winding.

  67. Can I use inductors bought in a an electronic shop or do I have to make it at home?

  68. Emmanuel

    how do i calculate the frequency? i constructed it and it worked but i need to know how to calculate the frequency.

  69. can i change the value of variable capacitor and inductor to increase the range of frequency

  70. i would like to ask is air core inductor a compulsory components? can i use other type of inductor such as coloured-band inductor? i assembled this circuit and i didnt get any output from it. can anyone tell me how to troubleshoot the circuit?

  71. Pls. send me the winding details of the antenna for the 200M FM transmitter.

  72. i need project on fm transmitter having frequency 500Mhz

  73. Shijo Joseph

    Please help me to get the details of winding of inductance coil of .1uH and 1mH.

  74. Seetharaman

    Hi Tyler diode is decoupling audio and rf stage to minimise cross modulation. C8 is the supply decoupling capacitor it can be upto 100nF.

  75. What is the purpose of the diode, and c8 in this circuit diagram. I just finished building it and it works great!

  76. What is the purpose of the diode? Also what is actually doing the modulating here? I just built it and it works great!!!

  77. can you give printed circuit board (pcb) of this circuit? it is very urgent.

  78. can you give this circuit’s board design? please.
    (can it be 1,65 * 1,25 inches?)

  79. Seetharaman

    Hi Saad with the given inductor and variable capacitor it will tune between 160 and 300MHz.
    F = 1 / 2π √ L X C

  80. hi,how to make the inductor.wouldn’t the inductor will be available in the market,plz reply quickly,

  81. even i hav the same doubts whch these ppl hav., hw 2 find the freq. of tranmitter? tel me much about designin of inductors.,.

  82. ya…. its very interesting.. but at wat frequency i can receive my message..

  83. sir tell me about how many turns required for 1mH & 0.1uH Intductors for 200m fm Transmitteralso about the thickness of wire plssss its very urgent………….plsssss ?????????????????????????????

  84. What is the frequency range? I assume C5 is used to alter this?

  85. thank you . kheily khob bood.
    امیدوارم موفق باشید.

  86. How to calculate the frequency of this fm transmitter and how to make inductor coil of 0.1uH please suggest some methods to make inductor coils

  87. De 18 and 40 are they constants. How do i increase the output power of my transmitter

  88. Could you Plz tell the o/p frequency of the transmitter.
    i.e. at which frequency I could be able to get the signal in my FM Receiver.

    Plz Its URGENT.

  89. Hi, now i’m in Cambodia , some comnponent not easy to find but i want to buy online can u tell me where to buy (website)

  90. good one but i want that winding details….. can u please help me…..

  91. How to calculate the frequency of this fm transmitter and how to make inductor coil of 0.1uH please suggest some methods to make inductor coils