2 km FM transmitter

Description.
With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The transistor Q1 and Q2 forms a classic high sensitive preamplifier stage. The audio signal to be transmitted is coupled to the base of Q1 through capacitor C2. R1, R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier stage comprising of Q1 and Q2. Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier.C9 and L1 forms the tank circuit which is essential for creating oscillations. Inductor L2 couples the FM signal to the antenna.

Circuit diagram.

2km Fm transmitter
Notes.

  • Assemble the circuit on a good quality PCB.
  • The circuit can be powered from anything between 9 to 24V DC.
  • Inductor L3 can be a VK220J type RFC.
  • For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter plastic former. On the same core make 2 turns of 1 mm enamelled copper wire close to L1 and that will be L2.
  • Frequency can be adjusted by varying C9.
  • R9 can be used to adjust the gain.
  • For optimum performance, value of C8 must be also adjusted.
  • Using a battery for powering the circuit will reduce noise.

Show Comments

421 thoughts on “2 km FM transmitter

  1. John from Holland

    Dear Seetharaman, I built this circuit first on a breadboard for testing and it just worked fine. So I assembled it on a piece of general purpose PCB, and it performed just better. For the RF choke I used a choke inductor of 220 uH, I don’t know how to call it officialy, but it looks like an electrolytic capacitor with radial wiring (leads out of the bottom).
    For antenna I used a car whip antanna of approximately 1 m (app. 3 ft 4 inch).

    I didn’t dare to power this circuit up because of the relatively big transmitting distance (I don’t want law enforcement on my doorstep because I try to learn how radio works:P). But thankfully it performs below the stated 2 km in my assembly. I measured the amount of needed curent and it turned out to be 115 mA, with a lab powersupply of 13.8 V, therefore I rate the power P=13.8*0.115=1.6 W. Note that this isn’t the transmitting power but the power that is needed to operate, transmitting power depends on the type of antenna (please refer to the literature on RF electronics for the complete details)
    Because Q3 (a good old metal case 2N2219 tor) gets bloody hot, I just bought myself a 4 cm fan which is to be installed after my schoolday.

    I’d like to thank Seetharaman for his nice circuit, it works fine and it’s easy for people who built multiple circuits before this (like myself). If you are an absolute beginner, skip this project, get familiar with transistors in simpler applications, then return an build this amazing circuit.

    Kind regards,
    John

    Reply
  2. Eng Mahmoud

    Dear All
    I have made this circuit before and it work well to 70 m
    but in analysing the circuit how Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier?
    the third stage is only bandPass amplifier first order
    i ,d like to discuss this point

    Reply
  3. Tesfaye

    Hello everybody!
    I am Social Science graduate of Business Management. but i have special interest to build simple FM transmitter at home. but as i told you i do not have the basic knowledge. but i tried to read so many websites about how to build simple FM radio transmitter and i got some hints but not the basic one.

    I got difficulties to get answers related to the following questions.

    1, How can i know the voltage of parts used in any homemade FM transmitter? How can i get the exact voltage of parts used in any homemade FM transmitter? I mean how can i determine the voltage of parts used in any homemade FM transmitter? Is there any calculation used/applied to get the voltage of parts used.

    (For example, what are the voltage of each parts used in the above FM transmitter?)

    PLEASE, PLEASE, PLEASE give me some hint??? Waiting your response soon, very soon!!!

    Reply
    • Neftali Loya

      Hello Tesfae:
      This 2KM FM Transmitter works on low voltage; thus, all of its associated components will do too. However, I am providing you with some hints in this scenario: All the resistors within the schematic will be required to dissipate less than 1/2 Watt, so you should buy at least 1/2 Watt power dissipation resistors; If you plan to plug your transmitter to a +24 VDC source, then you should use 36 VDC rated electrolytic capacitors (C1 and C4), otherwise, 24 VDC rated will do; C3 and C5, being Mylar or Polystyrene capacitors, they should be rated at 50 VDC which is a standard voltage value for these types of components; C6 and C7 “MUST BE CERAMIC CAPACITORS”… I insist… Ceramic Capacitors, and as such, they are normally rated between 500 VDC to 1 KV; last, but not least, we have C8 and C9… variable capacitors come in all shapes and forms, so their final voltage rating will be a function of your preferences. If you buy air- capacitors like the ones furnished in old radios, they can withstand several hundred volts between their plates, if you buy printed-circuit-board-mountable capacitors, they are often times rated at 50 VDC, so as you can see, the standard voltage rating for these components will have you covered. This is a fun project to build and it works just great; nevertheless, you should take into account that temperature changes will make the transmitter´s central frequency to drift back and forth. These variations in your transmitter´s central frequency will create annoying hissing noises in your FM receiver and chances are that you will lose fragments of information every now and then. If you plan to power this unit on batteries alone, you will experience frequency drifting as the batteries begin to become depleted. If you plan to power this transmitter on a fixed power supply, chances are that you will end up changing the transmitter´s output capacitance and your final transmission frequency will need some fine tuning. If this is your case (powering the transmitter from a fixed power supply), and before even striving to use C8 and C9 as your tuning devices, consider widening or stretching L1, L2 and/or L3 coils first, of course, affecting one piece at a time. Although this is a trial-and-error approach, without an RF meter or spectrum analyzer, your ears, an FM receiver, and your fingertips are all you got to succeed in making this extraordinary FM transmitter work. May I wish you the best of lucks and the best of funs while working on this amazing project… enjoy yourself to the bones!

      Reply
  4. Achala Athukorala

    Does this circuit do actual FM transmission (Frequency Modulated Transmission) or else does it just amplify the amplitude of the input signal? I don’t see how it can do frequency modulation as it doesn’t have a carrier signal. Forgive me if I’m wrong.

    Reply
    • Neftali Loya

      It is an actual FM Transmitter! Q3, along with its associated components, comprise the transmitter´s oscillation stage. Then, the sound frequencies coming from Q1 (voltage amplification) and Q2 (current source and impedance isolation) through R9 and C5, are algebraically added to the transmitter´s central frequency. The circuit works outstandingly well for a transmitter this size and caliber!

      Reply
  5. utshab

    Which is correct process for designing L3?
    Seetharaman
    April 3, 2014 at 2:27 am
    L1 and L2 will be with 18SWG super enameled copper wire and for L3 use 28 SWG 250 turns on 6mm former 5mm width honeycomb winding.
    or
    seetharaman
    August 23, 2013 at 4:12 am

    Hi Naren you can use any RH Choke in this place. you can wind around 24 turns of 22swg enemelled copper close wound on 6mm dia self supporting, without any core material(air core)you can wind on a pencil slideout and use.

    Reply
    • Neftali Loya

      You can calculate its size according to the transmitter´s wavelength. Let us say that for instance your transmitter’s central frequency if 91.5 MHz (you can find this on the FM receiver you plan to use to receive whatever information you are transmitting with this device), Calculate its wavelength in meters.

      a) Convert MHz to s¯1: 91.5 MHz = 91.5 x 106 s¯1 = 9.15 x 107 s¯1
      b) Use the formula λν = c: (x) (9.15 x 107 s¯1) = 3.00 x 108 m/s, then x = 3.28 m

      3.28 meters would be the perfect antenna size for this frequency; however, any multiple and submultiple of 3.28 will also work perfectly (6.56m, 1.64m, 82cm, 41cm, 20.5cm, and even a 10.25cm-long antenna would work just fine). For practical reasons a too-large or too-short antenna should be discarded, and maybe a 20.5cm long antenna will work just fine for you (believe it or not, it will work), but remember that only 20.5cm equals to 20.5cm. If you use a 20cm long antenna instead, it will not work as well as the original measured at 20.5cm because of a radio frequency transmission phenomena known as “Band Reject”. Remember that you are transmitting through this antenna, and if your antenna is shorter or larger than the transmitter´s frequency wavelength, it will not only transmit but receive radio frequency signals coming from itself. These “received” signals coming from within, will interfere with the signal you are striving to transmit and you will not transmit 100% of the energy generated by the output transistor (in this case Q3).

      Reply
    • gajendra

      c1, can ground directly through a resistane they can absorb the ultrtas noise or ripples which are produs=ced by the feedback or other electro,agnetic wave present in the sarroundins….

      Reply
  6. Arumugam

    Sir i completed the circuit..and I have problem when i am going to touch inductor (L1) with my hands at the time i get the output with clear sound…when i released my hands i get only noisy output…..pls pls help me to get clear sound..

    Reply
    • Neftali Loya

      Just open or close the winding loops! One loop at a time! Pull loops togheter (make the spring shorter in length) or pull them apart (make the spring larger).

      Reply
  7. Msala

    Hi Seetharaman
    Could you please email me the detailed design, as in how you arrived at each of the component values. Thanks

    Reply
  8. naresh.ece

    I have finished every thing in the circuit except inductor L3,any one please tell me how to create L3.THEN I can finish my project.

    Reply
    • Neftali Loya

      Any choke will do. L3 is used only as a filter so radio frequency waves coming from Q3 do not reach the preamplifying transistors. Use the coil of a 24 Volt relay and it will work just fine! Best of luck with your project!

      Reply
  9. Victor

    Hi Seetharaman,
    Unfortunately, my project is unsuccessful as I can not get to work, no matter what I do. I’ve done my best, so I’ve decided to finish it up now.

    Reply
  10. Victor

    Hi Seetharaman,
    I did some research and came across this:

    Carbon film
    A carbon film is deposited on an insulating substrate, and a helix cut in it to create a long,
    narrow resistive path. Varying shapes, coupled with the resistivity of amorphous carbon can
    provide a variety of resistances. Carbon film resistors are available in a power rating range of
    0.125 W to 3 W at 70 °C. Resistances available range from 1 Ohm to 10 MegOhm. The
    carbon film resistor has an operating temperature range of -55 °C to 155 °C. Maximum
    working voltages from 200 to 600 Volt DC. Due to the spiral cut nature of the resistance
    element Carbon Film Resistors are not suitable for use in radio frequency circuits as they
    exhibit high internal inductance.

    http://www.philipstorr.id.au/radio/technical/Resistors.pdf

    Just thought you would like to know.

    Reply
  11. Sabin

    i have searched L3(VK220J type RFC) for more than 2 months in many shop but i didnt found.. i think its very rear, can you suggest me that where i can find it.. or can we make it by simply turning piece of wire like L1 and L2.. plz give me best advice anyone.

    Reply
    • Victor

      Seetharaman
      April 3, 2014 at 2:27 am
      L1 and L2 will be with 18SWG super enameled copper wire and for L3 use 28 SWG 250 turns on 6mm former 5mm width honeycomb winding.

      Reply
  12. victor

    Hi Seetharaman,
    Ive put in the proper transistor, but now R12 is smoking and burning. Ive tried 0.5 and 1 watt resistors but they still burn. How many watts is R12 supposed to dissipate?

    Reply
    • Seetharaman

      Hi Victor it should be 5 watt carbon / 100 ohms 2 watt carbon 2nos in parallel or non inductive wire wound 5 watts resistance, for 24volts operation of the circuit. for 9 volt operation it should be 1/2 watt.

      Reply
  13. Victor

    I think I’ve gotten hold of some 2N2219A trasistors in the TO-5 case from ebay.
    http://www.ebay.com.au/itm/4x-2N2219A-NPN-Transistor-/400645038617?pt=AU_B_I_Electrical_Test_Equipment&hash=item5d484e2219&_uhb=1
    Just one question about them- will they need to be attached to any heat sink, or are they fine on their own?
    Also I’m starting to get worried about my other transistors as they are all replacements. However, they both stay completely cool. Could you please tell me if they are fine?
    BC549 replaced the BC109
    http://www.jaycar.com.au/productView.asp?ID=ZT2156
    BC557 replaced the BC177
    http://www.jaycar.com.au/productView.asp?ID=ZT2164
    Sorry for being so much trouble, and thank you in advance.

    Reply
  14. Victor

    Hi, I’ve have made the circuit but it is not working and I have a suspicion that its either the transistor or the variable capacitors.

    For Q3, I couldn’t find the exact transistor, so I switched the 2N2219 for the BC337 NPN Transistor. Problem is, it gets so hot that I can’t touch it, though it doesn’t smoke or burn or anything. Do you think there is a problem here?

    Also, where did you buy capacitors for C8 and C9? If you bought it online could you please give me the link? The ones I bought are so dodgy.

    PS: I’m doing my major project for the HSC and this is very important for me.
    Thank you in advance.

    Reply
  15. Physics guy

    I rebuild this circuit. Very high power output, medium sound quality, super sensitive amplifier and less parts: I like it! Tip: Use cooling for Q3 (someting like a small metall strip,… Dipol antenna works best for this!

    Reply
  16. ASHIQ HUSSAIN

    hello sir what type of antena should be used for this circuit please send a mail, images of this antena with detail

    Reply
    • Physics guy

      Hi there! Im not the admin here, but I guess U can use a dipole antenna for frequency around 100MHz. Take a long pipe of wood/ plasic. Cut two copper wires with a lenght around 75cm. Then attach them to the pipe, so all in all the lenght should be 150cm. Solder the inner ends to a coaxial cable, one to the coat, and one to the core. Then solder a antenna plug,… to the other ends. It should look like this: ~| (~=cable; |= stick with copper wire) If you need more info, google “dipole antenna”

      Reply
  17. Narayan

    Hi- Are there any altranative transitor can be used for 2N2219. Can I use BF494 as the susbstitue – thanks

    Reply
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    Reply
  19. suman

    sir, i am doing electrical and electronics engineering last year.
    plz give the swg number of l1, l2 ,l3???
    thanx.
    i have made the rest of the circuit except inductance. plz help me.

    Reply
    • Seetharaman

      L1 and L2 will be with 18SWG super enameled copper wire and for L3 use 28 SWG 250 turns on 6mm former 5mm width honeycomb winding.

      Reply
  20. Suprovo

    Hello Sir, is this circuit has really more than 1 km range with good quality sound and very low noise?i tried many different 2km FM transmitter circuit on internet but all of those can not go even 150 meter and also full of noise.so i am afraid.PLEASE HELP ME TO INFORM ME ABOUT THIS CIRCUIT…

    Reply
  21. Gaju jayebhaye

    Hell sir, how making the 2km fm transmiter and this circut in whiche components are used , they components availebal in which city on shope plz list of components and designe the circuit send the data in pdf format

    Reply
  22. Shane

    Hello Sir, I have gone through the Long Range FM Transmitter project also.
    I want to know whether this one or the long range one works better.

    Reply
    • Ashiq bhat

      yes it really 100% works it depends upon the circuit designer if he/she design it well it will work well

      Reply
    • seetharaman

      Hi Naren you can use any RH Choke in this place. you can wind around 24 turns of 22swg enemelled copper close wound on 6mm dia self supporting, without any core material(air core)you can wind on a pencil slideout and use.

      Reply
  23. laxman rawat

    SIR I AM LAXMAN I WANT MAKE A 2KM FM TRANSMITTER . I HAVE SEEN THE CIRCUIT BUT I AM NOT UNDERSTAND WHAT IS L3 THIS IS A COIL AND WHAT IS C9 40PF AND C815PF .THESE ARE PRE SET THIS IS AVALIABLE IN MARKET AND WHAT IS CALL IN MARKET .

    Reply
    • shubham

      go get a life…if you don’t know about capacitor and coil how u will develop these things…get thorough knowledge on capacitor and inductor then start doing FM-transmitter

      Reply
    • Manish h

      Actually Laxma,C9 and C8 are the Variable capacitors which you can buy in electric stores….Difficult to find in Local Markets But sure you can buy that online..

      Reply
  24. Raphael Muhoro

    Hae its me again,is there something i can do to the circuit to increase that radius.And also i would like to knw the approximate cost of making the whole circuit.Thank you

    Reply
  25. sushil

    Seetharaman sir, I have made L1 L2 couple inductor bt my circuit does not give any output. would u plz upload the photo of this couple inductor?

    Reply
  26. sushil

    would u plz explain abt L3 inductor?
    is it aircore?
    inductance value=???uH
    no. of turn=???
    coil diameter =???

    abt L1 & L2 ?
    is it aircore?
    wht distance should be between L1 & L2?
    no.of turn =???

    Reply
    • Seetharaman

      Hi Sushil see the notes it is clearly given how to wind L1 & L2. for rf choke L3 you can use any RF choke from market in 100 to 500uH range.

      Reply
      • sushil

        wht is plastic former? is it hollow tube or solid tube? can I use marker pen which is hollow tube? why L3 is used here? what does it do? what happened if I remove this L3 part?

        Reply
        • Seetharaman

          Hi Sushil you can use any hollow tube even pvc electric conduit. marker pen etc etc without any metal in them. L3 is an RF choke it is a must.

          Reply
          • masthan

            hi this is masthan. pls help me what is the triangular symbol enclosed in a circle in receiver circuit. and the symbol of 4.7uf left to it? will you explain pls…..

  27. lukesh

    hi sir im using part is
    15uf place in 22uf
    0.033uf in 333
    0.022 in 203
    0.47uf in 474
    1000pf in 102
    40pf in 39pf
    and vk 220j in 2 torn 1mm copper wire

    other is on the your droing list bot i can not proved -ve triminnal plz send me solution. this is right or not right please healp me.

    Reply
    • Seetharaman

      The negative of the supply should be connected to common line shown as connected to ground. All your components are ok except choke. See my earlier comment.
      (Hi venkatesh it is an rf choke to prevent rf entering the audio amp stage through power supply. any choke around 200 to 500uH will do. it is normally aircored with 200 to 300 turns honey comb winding to 5mm width with an ID of 6 to 10mm.)

      Reply
  28. sushil

    can I used fixed capacitor c8 & c9 bcoz I donot found trimmer capacitor. how can I increase range of this transmitter?

    Reply
    • Seetharaman

      Hi Sushil you can try 5.6PF for C8 and 22PF for C9. To get the right frequency you may compress or expand the tank coil L1. (that is increasing / decreasing the gap between winding)

      Reply
  29. ricco yabes

    Hi can you explain how L1 will couple the signal to L2. It wasnt quite clear, can u send a video or picture on how to make the coils and their connection. Thanks

    Reply
  30. mj

    hello sir,could u please tell me which electronic componemt is used to generate frequency like remote controlled cars,fm transmitters,nd what we have to do to increase the frequency range

    Reply
  31. sushil

    what is c8 & c9? is it gang capacitor. I have gang capacitor bt it has 4 terminal. how to use it, i don’t know.

    Reply
    • Seetharaman

      No, they are individual trimming capacitors. C8 for making the circuit to oscillate. C9 is for tuning to the required frequency of transmission.

      Reply
  32. Mercle

    and can i reduce the transistor number by using LM386 or any thing else ??
    is there any smd LM’s

    Reply
  33. salut

    you can send me the simulation of this transmitter in isis or workbensh or pspice
    thank you in advance

    Reply
  34. SONIA BHATIA

    Pls tell me how to connect the antenna to the coil?
    As antenna has only one terminal..would the other end of the coil l2 end up in the ground?
    PLS REPLY!

    Reply
  35. Rafn

    Would also love full details of all components. You have many great schematics but should also have full detail lists with them

    Reply
  36. sam

    sir i want to find out the values of all componant. . Can u give me releted formule for this .and tecnique how to find that. . Plz reply me its imp for me

    Reply
  37. BetaRajab

    hi i am BetaRajab,
    i appreciate the circuit..i really like the range
    my problem is i cant find some of the components to finish my projects.
    these are..
    capacitors- 1000pF,0.033uF,0.022uF,15uF,40pF(trimmer)
    transistor-2N2219..
    also the type of antenna to be used.

    can you help with the voltages of each component..and if possible the equivalent components of each mentioned above in case i cant find them in my area..

    PLEASE HELP!!

    Reply
  38. Tarek

    Hello seethamaran, can you please tell me why the antenna has two connections to the circuit and wether the “ground” indications mean directly to the negative line. Thanks.

    Reply
  39. Salami AZEEZ Adeyemi (S'Baz - Propose Engineer)

    I have successfully made the transmitter and I want to say a big thank you to you….. I now want another help from you in making a long distance (above 3km in distance)…. Please help me send the detail to my e-mail address…. salami_azeez0619@yahoo.com …… Please

    Reply
    • Andrew

      The reason they are adjustable is because according to tolerance differences in ALL of the components you will need to fine tune these two to get the frequency you want. The best way to get the frequency you want is to attach an easily identifiable audio source and set your receiver to the desired frequency. Adjust c9 until you start receiving.

      Reply
  40. Crazy Guy

    Hello Sirz, I am crazy guy. I cannot get range to neighboring village of Kazadh-Bhi-Srinivas. What capacitor needs to make 4.9 TeraHertz frequency?

    Please explain all electrical concepts of life and universe. Also, please to post schematic of 50″ LCD TV with 3D effex.

    Reply
  41. Appah Evans

    PLEASE IAM ELECTRONIC MAN AND I WANT TODO ANOTHER ELECTRONIC SCHOOL IN OUTSIDE COUNTRY . HES OF IAM FROM POOR FAMILY AND I NEED A COMPANY TO HELP ME AFTER ERITREAN I WILL WORK FOR THE COMPANY.

    Reply
  42. deepak champati

    iwant to make a small radio station, that 1 transmit the song and 50 reciver can recive the song. can any one help me

    Reply
  43. mazhar f.sathliya

    mazhar
    Hi Sir ….
    My rikavayamenta f. M the transmitter and 2 from
    5 km’s and Anne F.M phikvensi. radio
    The phikvensi should be separate from …
    Do you have a circuit that I receive phikvensi of the person
    I’m just so it can be heard …
    About 500 to 700 homes in the
    I speak only of which can be heard in the house …
    mazhar f sathliya-gujarat-dahod-+919227100786

    Reply
  44. imunna

    I need a 25watt fm transmitter. Can anyone give me a ready made fm transmitter. I’ll pay for it, just i want to buy a fm transmitter of 25 watt. I’m from bangladesh. My phone number:+8801719974170, email: imtiaz2580@yahoo.com
    please help me.

    Reply
  45. fausitine

    first of all i would like to thanx 4 ua various circuit that help us to learn more electronic knowledges.
    i expect to build about 50m fm transmitter of few components, kindly help please,,,,,,,,,,,
    by faustine from Dar es salaam Institute of Technology (DIT)

    Reply
  46. shah alam

    hy…..
    i can not found bc177 have it any exchange transistor. if any 1 know it please send me information please pls…….

    Reply
  47. Seetharaman

    Hi ad tune an FM receiver to 89MHz. Adjust C9 trimmer to get the carrier ine the receiver. (use nonmagnetic screw driver for adjustment best is an ebonite rod)

    Reply
  48. Yakubu Bano jnr.

    I want to construct the 2km fm transmitter as my project, but i want to change one of the BJT with either of the other transistors, how can i do that?

    Reply

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