200M FM Transmitter

jacky March 4, 2010 132 Comments

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.
Comments
  • yimer
    April 13, 2015

    i need long range FM transmitter details.

  • yimer
    April 13, 2015

    hello, it is good a person who enjoy it.

  • yash
    April 6, 2015

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

  • Eman
    November 25, 2014

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

  • Gagandeep
    November 15, 2014

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

  • ankit
    July 19, 2014

    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.

  • harshit
    May 15, 2014

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

  • May 10, 2014

    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)

    • Rajesh
      June 23, 2014

      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.

  • Ali Alavi
    April 23, 2014

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

  • SABYASACHI BANERJEE
    April 11, 2014

    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
      April 24, 2014

      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
      May 18, 2014

      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
        May 20, 2014

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

      • Rajesh
        June 23, 2014

        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.

  • Khushi
    March 10, 2014

    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.

  • mark
    December 20, 2013

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

  • RAHULRAZ
    November 24, 2013

    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

  • nice guy
    November 23, 2013

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

  • Akash
    November 14, 2013

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

  • nikhil
    October 27, 2013

    i just want the details of the inductor.

  • anand gupta
    September 16, 2013

    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.

  • Rex
    September 11, 2013

    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
      September 19, 2013

      Hi Rex between collector and base of Q2

      • May 10, 2014

        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

  • Reyrey
    August 28, 2013

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

  • seetharaman
    August 23, 2013

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

  • prince
    August 20, 2013

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

  • clyffe
    July 24, 2013

    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 🙂

    • agustin
      February 21, 2014

      podés usar un condensador de 8.2pF o 10pF

      You can use a capacitor of 8.2pF to 10pF

  • July 9, 2013

    send the detail of inductor coil in 200m fm transmitter circuit

  • June 1, 2013

    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.

  • apple mind
    June 1, 2013

    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.

  • Rafn
    April 22, 2013

    Could I have a mini jack input on this?

    • Seetharaman
      April 23, 2013

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

  • Fahad
    April 8, 2013

    how can i make an inductor of 0.1uH

  • MD
    February 24, 2013

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

    • Anguyo Emmanuel
      April 1, 2013

      Send me the winding details

  • aanya
    February 10, 2013

    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..!!!

  • aanya
    January 25, 2013

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

    • June 4, 2013

      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 😀

  • jak
    January 24, 2013

    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.

  • December 31, 2012

    how CE amplifier can works as a mixer

  • December 31, 2012

    how amplifier can perform modulation

  • akash
    November 29, 2012

    sir pls provide me details of “L”

  • Dayanand Mishra
    October 24, 2012

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

  • akshay
    October 5, 2012

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

  • muheen
    September 12, 2012

    sir i assembled the FM Transmitter circuit its not working i cant find out the frequency
    please mail it back to me muheenbasha2011@gmail.com

  • muheen
    September 12, 2012

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

  • Jack
    August 31, 2012

    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.

  • Shilpa
    August 15, 2012

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

  • Saavithri
    August 7, 2012

    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

  • Lijo joseph
    July 13, 2012

    Please give the winding details

  • Seetharaman
    July 3, 2012

    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.

  • Shashank
    June 30, 2012

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

  • toby
    June 28, 2012

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

  • shash
    June 27, 2012

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

  • Seetharaman
    June 23, 2012

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

  • Zain Uddin
    June 22, 2012

    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

  • Seetharaman
    June 22, 2012

    Hi Haniff Please see my Dec 23rd comment for frequency

  • haniff adris
    June 22, 2012

    what is frequency of this transmitter???

  • Zain Uddin
    June 19, 2012

    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

  • Seetharaman
    June 5, 2012

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

  • Ssembatya
    June 3, 2012

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

  • saeed
    May 11, 2012

    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.

  • May 6, 2012

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

  • May 3, 2012

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

  • seetharaman
    May 2, 2012

    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.

  • May 2, 2012

    Sir L1 L2 winding pls sms this no 9633823272

  • ashok
    April 24, 2012

    how the copper wire used as antenna?

  • munna
    April 24, 2012

    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?

  • Seetharaman
    April 22, 2012

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

  • akash
    April 21, 2012

    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 ?

  • March 29, 2012

    Sir please i dont understand , please sir can you picture or video it for me ? To see it … My email sir … Mugabi103@yahoo.com. Thank you .SIR

  • Seetharaman
    March 26, 2012

    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.

  • March 25, 2012

    Sir please help me the tips and how i can tune it 88 -108 email. Mugabi103@yahoo.com THANK YOU .

  • February 5, 2012

    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.

  • February 3, 2012

    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……

  • February 3, 2012

    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.

  • Rex
    January 20, 2012

    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.

  • seetharaman
    January 5, 2012

    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.

  • mike
    January 4, 2012

    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?

  • Seetharaman
    January 3, 2012

    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.

  • mike
    December 31, 2011

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

  • Atul
    December 26, 2011

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

  • seetharaman
    December 24, 2011

    Hi Meleja yes with C5 you can set the frequency.

  • mcleja
    December 24, 2011

    How is the frequency set? Is it set via C5?

  • seetharaman
    December 23, 2011

    Hi Meleja between 150 and 300MHz.

  • mcleja
    December 22, 2011

    Hi, what frequency does this work at?

    Thanks

  • Nandagopal
    December 19, 2011

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

  • Seetharaman
    December 12, 2011

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

  • nanirex1
    December 12, 2011

    please tell me the winding detials.

  • Gustav
    December 12, 2011

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

  • November 29, 2011

    dear,send many circuits diagram for project related

  • November 28, 2011

    what is the output frequency

  • November 26, 2011

    Pls send the details of L in the circuit the winding detail
    And antenna details

    Thanks

  • Emmanuel
    September 13, 2011

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

  • buiad
    June 30, 2011

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

  • kevo
    June 19, 2011

    please send me IR transmitter and receiver

  • Gary
    April 13, 2011

    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?

  • Romeo
    March 16, 2011

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

  • abc
    February 26, 2011

    i need project on fm transmitter having frequency 500Mhz

  • jady burg
    February 24, 2011

    Winding details:http://www.circuitstoday.com/how-to-make-an-air-core-inductor
    You can find requency by frequency counter device
    Or use the formula
    F = 1 / 2π √ L X C

  • February 6, 2011

    please tell coil turns details

  • Shijo Joseph
    December 22, 2010

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

  • Seetharaman
    December 7, 2010

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

  • Tyler
    December 5, 2010

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

  • Tyler
    December 4, 2010

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

  • MET
    November 21, 2010

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

  • paresh
    November 16, 2010

    here what friquancy

  • chandu
    November 15, 2010

    how to calculate transmitter frequency

  • Seetharaman
    November 14, 2010
  • met
    November 13, 2010

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

  • Seetharaman
    October 2, 2010

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

  • saad
    October 2, 2010

    operating frequency?

  • saad
    October 1, 2010

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

  • shravan
    September 22, 2010

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

  • nandini
    August 10, 2010

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

  • June 26, 2010

    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 ?????????????????????????????

  • June 21, 2010

    sir can i make that inductor L3 by my own pls suggest….

  • Elliot
    June 9, 2010

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

  • hamed
    March 21, 2010

    thank you . kheily khob bood.
    امیدوارم موفق باشید.

  • Dinesh
    March 19, 2010

    How to create inductors?

  • hardik
    March 17, 2010

    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

  • gideon
    March 12, 2010

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

  • Ashish
    March 11, 2010

    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.

  • tong
    February 27, 2010

    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)

  • guna
    February 27, 2010

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

  • suraj
    February 18, 2010

    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

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