Long Range FM Transmitter

How to make a long range FM transmitter at low cost

Description

The use of transmitters which have a more powerful output than the ‘flea-power’ are sometimes required when there are many obstacles in the path of the surveillance transmitter and monitoring station receiver, or the distance between them is too far so as to make a low powered device feasible. Whereas a typical micro transmitter will produce an RF power in the order of just a few milliwatts, i.e. a few thousandths of a watt, the VHF-FM transmitter described has a power output of between around a half and 2 watts, depending on the power source, which may be anywhere between 6 volts and 30 volts d.c. The battery or batteries should be of the alkaline high power type, since the current drain will be found to be relatively higher when compared to microtransmitter current drain. The power output of this device is somewhat proportional to the current drain and so therefore both may be decreased by altering the value of R6 to a higher resistance, or a variable resistor with a value of around 1k may be introduced in series with the existing R6, so as to give a variable power output. The variable resistormust not be a wirewound device because this would act as an inductor which will cause feedback problems.The audio input to the power oscillator, which incidentally is formed by TR2 and associated components, is derived from a piezoelectric microphone which drives the simple audio frequency amplifier TR1. The input of the audio amplifier is controlled by the gain pot R1, which selects the correct amount of voltage that is generated by the piezoelectric microphone, then connects this signal to the base of audio amplifier TR1 via C7. It may be found that there is insufficient housing space for a bulky piezoelectric microphone, so with a slight modification to the circuit, it is possible to employ an electret microphone insert as shown. Since the RF field that is generated by this transmitter is relatively large, the problem of RF feedback may very well be encountered. This may be overcome by placing the transmitter inside a metal enclosure, keeping all internal wiring as short as possible and the aerial wire.

Component listing for 1 watt transmitter

Resistors Semiconductors R1 = 27k TR1 = BC547 R2 = 330k TR2 = 2N2219 fitted with heat sink R3 = 5k6 MIC = piezoelectric microphone R4, 5 = 10k R6 = 100R

L = 6 turns 22 gauge enameled wire wound on 3⁄16″ former

Capacitors

C1, 2, 3 = 330 pF C4 = 2–10 pF trimmer C5 = 4p7 C6 = 1 nF

C7,C8 = 40uF/25V Electrolytic

Circuit diagram for Long range FM Transmitter

Long range fm transmitter circuitWe have some other Radio Transmitter circuits of your interest;listed below:

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4. Versatile FM Transmitter

5. FM Adapter Circuit for Car Stereo

Show Comments

125 thoughts on “Long Range FM Transmitter

  1. Jay Jongko

    The piezoelectric mic needs a supply voltage to operate. In this circuit, in my opinion, we need to add a resistor connected from the + of mic to the 12volts supply in order to complete the entire operation.
    Btw, thanks for this useful circuit. and indeed, I used it as a reference for my own project.

    Reply
  2. JAmes white

    Thanks for the circuit diagram. The transistor use in the diagram like 2219 is not in my country how can I get some from you.pls reply me as soon as possible I needs your friendship. Thanks I am from Liberia west Africa.

    Reply
  3. Harsh Verma

    Use 2n3904 transistor in place of TR1 and remove r1 and place + terminal of mic to the base of TR1 and also use 100 pf variable capacitor to get clear sound. And also you can use bly81 or blx65 in place of TR2.

    Reply
  4. Daudi Sulemaani

    Teacher, radio propagation principle says – if electricity is vibrated in a wire at 10kHz and above, those Radio Waves created will are continuous and will be picked even behind hills, why then FM follow line-of-sight yet MW,SW,LW won’t? Thank you. From Ugamda.

    Reply
    • Seetharaman

      High RF frequencies travel in straight line. to receive the signal line of sight is important. since earth is curved during favorable conditions it can reach 60 to 150kms depends on power and height of transmitting and receiving antenna. AM signals in MW band are transmitted through ground wave hence they can reach longer distance During nights they can travel 1000s of kms. you may get lots of distant stations during nights in your MW AM radio.

      Reply
  5. Albert

    I have a question that at which frequency i should tune my radio to hear from it tell me please i want to use my small mobile radio to hear that it is working.

    Reply
  6. Rajib saha

    Have you solved Mr. Avdi?
    This is a feedback capacitor which has been connected between Emitter to collector to keep oscillating the tank circuit (Coil and Capacitor). You can use any disk capacitor between 4.7pf to 10 pf as a feed back capacitor.
    You are Lucky because you are from Texas, you can buy BH1417 stereo FM IC and 7.68 crystal to make very very perfect radio. It is very simple. But I am far from America or Europe, so I never found this IC and crystal.
    Regards

    Reply
  7. ALITUHA PATRICK

    TRY TO SEND ME ATLEAST DIAGRAMS OF 300WATTS AND ABOVE; SIMPLIFIED,AND EASY TO BUILD THANKS AND MORE ESPECIALLY RF CONTROL SECTION[RF PRE-AMPLIFIER SECHMATIC DIAGRAM]AND THEN MAIN OUTPUT SECTION

    Reply
  8. barathi

    sir, i want the clear explanation of signal transmission in communication oriented circuits. and i am waiting your favorable replay . thanking you

    Reply
  9. Raj

    Have you solved Mr. Avdi?
    This is a feedback capacitor which has been connected between Emitter to collector to keep oscillating the tank circuit (Coil and Capacitor). You can use any disk capacitor between 4.7pf to 10 pf as a feed back capacitor.
    You are Lucky because you are from Texas, you can buy BH1417 stereo FM IC and 7.68 crystal to make very very perfect radio. It is very simple. But I am far from America or Europe, so I never found this IC and crystal.
    Regards

    Reply
  10. KALPESH CHHABHAIYA

    HELLO FRIENDS,
    I MAID THIS PROJECT SUCCESSFULLY. WITH PROPER FREQUENCY AND STRENGTH.IF YOU WANT HELP THEN CONTACT ME ON kpkpkalpesh@gmail.com or at 08866792042…… i will surly help you to bring out you from the problem :)

    Reply
  11. Munib Ali

    I am student Of Electrical Engineering Sir Tell me About Which Antena I used This transmitter and
    2nd tell me About Its Case

    Reply
  12. gaurav tomar

    sir, i am a student of electronics and communication engg. i want to established a low power 1-2 km. fm transmission station in my college campus. I am authorized by my faculty to working on this project. they will arrange for license of Fm. so please give me appropriate guideline for this through mail @ grvt@live.com

    Reply
  13. Fitsum

    I need fm transmitter am from Ethiopia and want to transmitte some info to my vilag farmers. I have been trying to mack fm transmitter befor two times i fell to mack it real
    If you have 100% workig project, you can mack my Drem true.
    Send me at city35@yahoo.com

    Reply
  14. seetharaman

    Hi Simon you can use 1/2 wave length dipole for directional radiation and for omni-directional radiation 1/4 wave length whip antenna (telescopic antenna of suitable length can be used)

    Reply
  15. THIYAGARAJAN

    hi everybody,
    I need the steps to make my own fm transmitter so
    if intrested means someone can help me

    Reply
  16. pujan

    It’s really great experience to work on above fm trasmitter circuit diagram. it’s having quite good frequency range…..

    Reply
  17. Bogus Dude

    C8 listed after C3 SHOULD NOT be their
    The correct C8 is listed after C7

    C5 can also be a: 47pF
    C6 can also be a: 0.001uF

    R1 27k– is that correct?

    TR1 can be substituted with a 2N3904

    L – a 3/16″ drill bit will work fine for this

    Reply
  18. Alone

    Hi Master
    I need a 10km range fm 88-108 mhz transmitter please send me some detail or much better if you can provide the circuit diagram and the component list please just mail it to me at kmuin@yahoo.com thanks and more power.

    From Alone
    Johore Bahru Malaysia

    Reply
  19. ziddik

    did anyone try this circuit? I want build it and also i have build a 100 meter range transmitter with only one bc547 transistor n it works perfectly with high clarity sound output!! If any1 want the diagram just mail me

    FROM ZIDDIK

    TIRUR,MALAPPURAM DT,KERALA-INDIA

    Reply
  20. Programming

    Hi there, You’ve done an excellent job. I’ll certainly digg it and personally suggest to my friends. I am confident they will be benefited from this web site.

    Reply
  21. Krishna

    Hi, I am looking for a 15v 1.5Amph smps circuit diagram and googled a lot and end-up with nothing. If any kind heart can help me on this, i will be very much thankful. Thank you verymuch in advance..

    Reply
  22. Avdi

    HI i buy 2 FMtransmitter kit 1[KIT32] and 1[K18V2] but after i insatal all parts on bord , nothing no workin i install parts on bord 100% good,,but i think maybe they sale wrong parst or damaged alectronickit,now i m buildin one nother with 2Transistor2N2222,,,but i can t find ceramic disc 4p7,,so can sameone help me,,what i can use inplace 4p7, i have ceramic disc 5,i have 10,,i have 18,27,33,68.102,103Z,104Z.. but 4p7 no have no wher stores,,frys electric radishack no have,,, I M FROM TEXAS USA

    Reply
  23. Sumeet

    Can you tell me if there any circuit for generating Train Horn like sound and which can be implemented on My Bike.
    Input Voltage Supply Should be 12VDC.
    Thank You.

    Reply
  24. Seetharaman

    Hi Sanjay this transmitter itself can be used with dipole antenna to achieve 2kms.
    Hi Ravi what is the frequency of operation you require, AM or FM omni or uni directional.

    Reply
  25. ravi ranjan

    hiii……
    i m a btech 3rd year electronics and communication engineering student..
    i want to make a radio station at our college for our tech fest only..
    will u elp me with the circuit by sending it 2 me…
    i need a transmitter of nearly 2km range..

    thanks..
    waiting 4 your prompt reply..

    Reply
  26. seetharaman

    Hi Favas you can tune this transmitter in frequency range of Band I, Band II and Band III (between 50 to 250MHz)

    Reply
  27. seetharaman

    Hi Favas sorry for this long silence. this transmitter will operate in VHF say 65 to 200MHz. Since we have with us broadcast band receivers operating from 88 to 108MHz. we can use them to monitor by tuning our transmitter to this frequecy range.

    Reply
  28. Seetharaman

    Mr. Kulla you make a small variable trimmer yourself. Take 0.2mm insulated wire 2″ length each. connect one to one end of the coil and the other to other end of the coil. now twist them closely tightly (like twin twisted plastic wire-not electrically connecting them). Now you can expand compress the coil ‘L’ to acheive the required frequency.

    Reply
  29. KILLUA

    i see… thank you so much.! this really helps… can i ask another question? can i substitute the trimmer capacitor with another kind of capacitor (as in electrolytic or mylar).. the local electonics stores here dont have trimmers..

    Reply
  30. kiLLua

    hi.. i hope the admin would read my comment.. im a neophyte when it comes to electronic circuits, but i just want to ask this question. the r1, which is 27kohms, has only two ends right? so why it is that there are three components connected to it? 2nd question, what does a piezoelectric microphone do? piezoelectric means electricity by means of putting pressure on a thing..

    pls answer me, i need to be guided.. thanks.

    Reply
    • admin

      reply to kiLLua
      R1 is a potentiometer and it has three terminals (two end terminals and a wiper terminal).

      Piezoelectric microphone will produce an output voltage according to the sound waves falling on it. It converts the vibrations caused by the sound waves into a proportional electrical signal.

      Reply
  31. NILOY

    Hi i’m a daily reader of circuits today, and i’m in love with ur site, many many thanks for ur hard work and for such wonderful and useful circuits

    But anyone tried this circuit and is it a success?

    Reply
  32. Manoj kumar

    Hi there,i am a daily reader of your site,circuitstoday.I just want to know,what is the distance covered by using the above LONG RANGE FM TRANSMITTER.Plz reply me or better mail me!Thanking you.

    Reply
    • admin

      At full supply voltage it will cover up to around 2Km. For maximum performance you need a good power supply , matching antenna, correct inductors and a very efficient PCB.

      Reply
  33. myokoko (myanmar)

    I live in Myanmar.The transmisson licenses aren’t tight here.I want a FM Transmitter with a
    wattage of up to 4-watts to transmitter as an
    amateur.Could you help with this?Thanks!

    Reply
  34. myokoko (myanmar)

    I live in Myanmsr.The transmisson licenses aren’t tight here.I want a FM Transmitter with a
    wattage of up to 4-watts to transmitter as an
    amateur.Could you help with this.Thanks!

    Reply
  35. sunny

    Sunny : What should be the value of C7 and C8?
    I think they are disconnected terminals ,right?

    Author:Thanks for pointing the error.I have added the values of C7&C8 in the parts list.Please check.

    Reply
  36. khasru

    Khasru:can i use it for radio transmission.

    Reply: You are from India.I figured that from your name.Sorry my friend,you can’t use it for radio transmission. Any sort of radio transmission without proper licence is punishable in India and of course in most of the countries.For educational or study purpose you can make radio transmitters,thats quite OK.But continuous transmission over long ranges will invite trouble.If police came to pick up your transmission in their wireless or any body files a complaint against you ,that will be trouble.If you are regularly transmitting,they can easily track the source.

    Reply

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