AM Transmitter circuit

admin November 27, 2018 89 Comments

Simple AM Transmitter

Transmitters are devices that are capable of transmitting audio as radio waves from an audio device. There are two types of transmitters; FM & AM. We have many posts on FM transmitters, so we decided to make one on AM transmitter.

AM transmitters create radio waves using Amplitude Modulation (that’s why AM). That means only the amplitude of the waves gets changed but the frequency remains the same. In this case, the frequency of career frequencies falls within a predefined range called Carrier Frequency. The carrier frequency changes from country to country.


Here is the circuit diagram of a simple AM transmitter circuit that can transmit your audio to your backyard. This circuit is designed with limited power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs. You will love this!.

The circuit has two parts, an audio amplifier and a radio frequency oscillator. The oscillator is built around Q1 (BC109) and related components. The tank circuit with inductance L1 and capacitance VC1 is tunable in the range of 500kHz to 1600KHz. These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit.

C2, the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again. The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground.

Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistanceR5.

AM Transmitter Circuit Diagram with Parts List 

Am Transmitter Circuit

Am Transmitter Circuit Diagram


  • The transmission frequency can be adjusted using the variable capacitance C3.
  • Use a 200uH inductor for the L1 in the tank circuit.
  • Power the circuit using a 9V battery for noise free operation.
  • Use a 30 cm long insulated Copper wire as the antenna.

We have more Radio Transmitter Circuits that you may like to take a visit;

1. Long Range FM Transmitter

2. Single Chip FM Transmitter

3. Simple FM Transmitter

4. FM Tracking Transmitter

5. FM Telephone Bug

  • August 15, 2014

    I just simulated the circuit using Multism 12.0 and there was no clear Amplitude Modulation . The circuit may not be working at all .

  • vks
    June 20, 2014

    sir please provide a am transceiver circuit plzzzz

  • Rex
    August 1, 2013

    Please i need the Receiver circuit for this transmitter

  • ajay
    March 7, 2013

    sir what is cond mic in the circuit

    • Rafiq Rana
      November 19, 2014

      Cond Mic >>> Condenser Microphone

  • Philippe
    February 24, 2013

    My simulation of this circuit don’t work… Did someone succeed in doing it ?

  • December 4, 2012

    sir,could u plz tell me what is the necessity of c1…how is it related withot c1 wat will happen

    • A.D.
      March 23, 2013

      C1 is decoupling capacitor. Before feeding any signal to transistor base, the signal is decoupled so as to remove any noise present in it, if any. The circuit may not function effectively without C1, if noise dominates the signal. In that case, it will be a directly coupled circuit. Though, capacitor coupled circuit is always preferred.

  • November 29, 2012

    That is one slick item.

  • sharvari
    May 19, 2012

    this circuit works real nicely.however its range is very small.sir could you explain how the dsb-fc generation actually happens in this circuit??

  • May 18, 2012

    hi,,,i have implemented its circuit but there is something i dont understand about ,,how i will check my output ,,??? what actually the output should be ,,,i m using L1 =220uH can it affects my circuit ???
    if u have the calculations plz share it with me ,,??
    what should be the value of Beta for both of the transistors ..plz answer my questions because i am doing it as my semester project …

  • seetharaman
    April 30, 2012

    Hi Shavari you are correct. the corrections should be “The oscillator is built around Q2”; “Q2 is provided with the regenerative feedback”; ” base and collector of Q2 to opposite ends”; “re of Q2(BC 109)”,

  • sharvari
    April 27, 2012

    sir please explain the working of the there a mix up int the explanation?it is written that Q1 is the oscillator and Q2 as the amplifier??

  • Sid
    April 12, 2012

    This ckt is nt working i hav used 220 microhenry insted of 200microhenry. . .is this right?
    Plz help m

  • eldoz
    March 1, 2012

    which type antenna that i want to use in this circuit…

  • Navratna
    January 27, 2012

    This circuit is not working, i hav used 470 pf instead of 500pf plz help.

  • duedeath
    November 20, 2011

    heY! can i have an AM transmitter design? i’m badly neede it.. thanks 🙂

  • jose
    September 3, 2011

    how do we make a 200microhenry??how many tuns?? and what core??
    is it ok to change the 500pF to 40pF???

  • komal
    May 18, 2011

    Is this the perfect,simple & suitable circuits for am transmitter?

  • dan12
    May 14, 2011

    Plz, tell me how the amplified signal from Q1 and carrier signal from tank circuit could be modulated by Q2. I can’t understand the physical principle.

  • EL
    May 12, 2011

    I just simulated this circuit using PSPICE

    then I couldn’t find clean amplitude modulated signal.

    I used Vsin (Offset = 0, amplitude = 1mV, Frequency = 1kHz) rather than cond mic

    and I set the 4.7k potentiometer parameter (set = 0.5).

    I didn’t connect the anntena and just connect voltage marker to that node. other setting is identical to the diagram.

    The simulation result was distorted sine signal (I couldn’t find out any carrier frequency)

    Is there any problem I did?

  • May 11, 2011

    Thank you sir,But How the potentiometer works with the AM transmitter!!!

  • Seetharaman
    May 11, 2011

    Hi Azim if the supply voltage is 12volts DC ensure all capacitors are rated for 16 volts or more on the safe side. This is the simple thumb rule.

  • May 10, 2011

    Thank you Sir, But I Tell How I Understand The capacitors Voltage to The Circuit Diagram Where Not given The Voltage(Ex:C1: 2.2uF).Please Tell Me Any Website or PDF File Which is Help Me.

  • Seetharaman
    May 10, 2011

    Hi Azim all capacitors are to be rated for 12 volts or higher. Capacitor voltage will be written on the capacitor itself. if not with colour code or any alphabet refer to manufacturers catalog.

  • May 10, 2011

    Sir,I am a first year new Electrical & Electronic Engineering student. Please tell me what the volt of C1,C,C3,C4,C5,C6. And you tell me how I understand the capacitors Voltage….Please please…

  • MRelectro
    May 7, 2011

    I just simulated this circuit using PSPICE

    then I couldn’t find clean amplitude modulated signal.

    I used Vsin (Offset = 0, amplitude = 1mV, Frequency = 1kHz) rather than cond mic

    and I set the 4.7k potentiometer parameter (set = 0.5).

    I didn’t connect the anntena and just connect voltage marker to that node. other setting is identical to the diagram.

    The simulation result was distorted sine signal (I couldn’t find out any carrier frequency)

    Is there any problem I did?

  • Seetharaman
    April 19, 2011

    Hi Dadirac7 cooling clip is clip on heat-sink used for T05 T018 packages.First shift positive of the battery to C2 R6 side of R8. This itself will increase the power. for further increase replace Q2 with 2N2218 or 2219, raise the battery voltage to 12 volt.

  • Dadirac7
    April 18, 2011

    Hi Seetharaman:
    Thanks to you I’m in tune. My question now is, whats a cooling clip? Like a heat sink atached to the transistor? I want to increase my transmiting range, can we do anything to the antenna?

  • Seetharaman
    April 15, 2011

    Hi Dadirac7 use a 15mm plastic former (PVC Tube)and close wind 100 turns of 32SWG wire (do not over lap, wind side by side without any gap) use 10 to 50PF variable trimmer to tune to high end of MW band. To tune to lower end of MW you require 500PF.

  • Dadirac7
    April 14, 2011

    Hi: I’m building the AM transmitter and I want to use it in 1460khz. Can I use a variable capacitor 10-50 uF, for C3? Is it posible really to use two 100uH RF Chokes in series to get 200uH for L1? Is there a diferent name for variable capacitor? I can’t comunicate with the people at Radio Shack or do I have to get it (variable capacitor) by mail?

  • chavan priyanka pratap
    March 3, 2011

    Good day!

    Can you please give me instructions on how to make the L1 inductor with the value 200uH?

    This would be a very big help…

  • Seetharaman
    March 1, 2011

    Hi Bale C2 & C4 are ceramic disc capacitors. C3 is a variable capacitor. C1 is electrolytic, positive terminal is to be connected to potentiometer R5.
    Hi Michael you may have to increase C4 by trial and error to get the circuit into oscillation. no other change is required.

  • Bale
    March 1, 2011

    I was wandering if C2,C4,C1 are ceramic caps or electrolytic because they do not hve the + sign on the clr.


  • Michael Bitter
    February 8, 2011

    If I wanted to transmit a signal to 58KHZ and using the formula of Fr= (1/2pi*sqr(lc)) which would give me a C3 of 500PF and a L1 of 15mH. Is there anything else that I would need to do to the circuit to work at this frequency? Thank you.

  • Seetharaman
    October 18, 2010

    HI BARI you can use vero board. my proto was only on a veroboard. now dotted boards are available you have to link them with copper wire. that is good for even HF application.

  • October 18, 2010

    Thanks Seetharaman!! Its working! now i am going to sold it on vero board! Any suggestion?

  • Seetharaman
    October 14, 2010

    Hi Bari Being a MW frequency circuit the stray capacitance should not matter anything.

  • October 13, 2010

    Please tell me if this circuit is designed on bread board, how much its stay capacitance matters? Is it can change the frequency and through the transmission out from the band?

  • Seetharaman
    October 13, 2010

    Hi M-E no change is required except the one suggested on 9th october.

  • M.-E.
    October 12, 2010

    If i wanna make this one for 12 volts -wich resistors, etc. shuold i use?

  • Seetharaman
    October 9, 2010

    Hi Linta the range may be between 100 to 200 ft. You can use a roof top diagonal antenna of 100ft in length with (seven strands wire)the transmitter.
    as such you can improve the power by shifting the battery from R8 Mic end to R8 RF transistor end.

  • linta
    October 8, 2010

    sir plz tell me the range for the circuit?plz
    can it be increase by using larger wire?
    i am waiting?

  • October 3, 2010

    readers are leaders

  • Seetharaman
    September 18, 2010

    Hi Mulla kindly refer to ADMIN reply on dec 17th

  • mulla
    September 4, 2010

    your formula does not have n number of turns of coil.
    can you explain?

  • Fisch'e
    May 23, 2010

    just got the circuit i hunted almost year round and thank u so much. So my problem is how would i interface with PIC to send morse code using AM band.
    you can just inbox me…

  • seetharaman
    May 15, 2010

    Hi Snehal with 500PF you will tune to 500KHz with 10 to 50 PF you will tune to 1500KHz. Higher the capacitor lower the frequency lower the capacitor higher the frequency.

  • snehal
    April 13, 2010

    what value of variable capacitor c3 should i use to obtain transmitting frequency of 500khz?

  • seetharaman
    March 28, 2010

    Hi the power can be increased by adding further RF power amplifier(complicated). a little increase can be done by raising power supply to 12volt and changing Q2 to 2N2219 with cooling clip and reducing emitter resistance to 470 ohms . By increasing C2 to 10n, you are likely to loose little HF response in the modulated Audio. By Disconnecting C1, only the carrier will be produced (blank carrier without information) sufficient to interfere with the nearby receiver not allowing it to receive the required signal (by jamming it & brick wall is not a problem for HF).

  • Alvaro
    March 28, 2010

    Also, how can I adjust the circuit to transmit an empty signal. In other words, how can I adjust it to transmit a signal with no modulation and constant amplitude, so that any radio would just play an empty constant sound. Is it enough to just remove the condenser mic from the circuit, or are other modifications necessary. One more thing, I could only get 10 nF capacitor for C2, will the circuit still work? If not, is there any way to compensate for it?

    Thanks for the help,

  • Alvaro
    March 23, 2010

    Hello, this circuit is just perfect for a project I’m working on, but how can I increase the power output so that the signal will be able to penetrate a thick brick wall? Don’t worry about any legal issues,as my country allows the use of equipment like this for purely academic purposes.


  • Seetharaman
    March 12, 2010

    Hi Niki could not make out head or tail. pl give the details of the circuit on which you have commented

  • March 12, 2010

    Circuit Description :
    *From THE NEGATIVE POLE connect via a 10 k /1/2 watts RESISTOR TO THE “C” of the transisor
    * a 2 N 2222 SILICON n-p-n transistor.

    Initially the ” b ” OF THE transistor to be left open .



    a stronf a.f. oscillation occurs, traceable throuch 2* 32 ohm via a 0.1mf fix capacitor.

    we may use crystal earphone but output very stong ,*danger for ears *, feels a series volume control with one the earphone leds absolutely nessecary e.g 50-100k.



    LIKE E.G. BC 109 ETC….///


  • rahul
    March 3, 2010

    hiiiii a really good circuit diagram for a am transmiter…. but i have a big problem that how to make a 200uh inductor can u help me on this .
    give me the procedure for it . plz
    just send it on my id

    its really urgent for me
    i hope u will help me…….


  • Ehab
    February 11, 2010

    I thank you about your circuits

  • nav
    February 1, 2010

    in d formula
    L = (d²l²)/(18d+40l)

    where is the n used????/

  • Walid
    January 15, 2010

    How does the AM modulation occur in this circuit ?

  • suresh
    January 12, 2010

    we have a problem on making l1 inductor.can u help?

  • suresh
    January 12, 2010

    Does this ckt diagram works?

  • January 5, 2010


  • Seetharaman
    December 23, 2009

    For L1 I have used 77turns of 28SWG enameled wire wound side by side on a 5/8″ dia 8″ ferrite rod. The audio quality is good. C6 I have increased to 220 mfd which improved the audio quality. Also I used 10uF for C5.

  • kurimaw100
    December 16, 2009

    hello.. I cant find a bc109c transistor do you know any alternative transistors? Tnx

  • kurimaw100
    December 16, 2009

    hello.. I cant find a bc109c transistor do of any alternative transistors? Tnx

    • admin
      December 16, 2009

      Other options are BC107, BC548,BC148, 2N2222 etc.

  • November 18, 2009

    hi men , thaks for the diagram , you saved my ass XD i want to ask ou something , how could i build that inductor ? do you have some manual , i have the problem that here in my city electronic stores are very bad so they dont have any inductor XD

    Saludos desde México , oaxaca jejeje

    sorry for the grammar mistakes lol


    • admin
      December 17, 2009

      The approximate inductance of a single-layer air-core coil may be calculated from the simplified formula:
      L = (d²n²)/(18d+40l)
      L = inductance in uH,
      d = coil diameter in inches,
      l = coil length in inches, and
      n = number of turns.
      This formula is a close approximation for coils having a length equal to or greater than 0.4 d.

  • M.-E.
    November 5, 2009

    5. how do i do to connect some sound-sorce like a cd-player or my computer to the transmitter?

    • admin
      December 17, 2009

      You must remove R9 and condenser mic. The sound source can be connected across to the base of Q1 and ground. A coupling capacitor of 10uF must be also added to the base of Q1.

  • M.-E.
    November 5, 2009

    Some Qs:
    1. i don’t have a cond.-mic. -how do i do to use an mic. wich is build with a magnet and a coil? (i don’t remember it’s name right now) strong is this transmitter?
    (in watts)
    3.if i don’t have the transistors bc109 -witch other can i use? do i do to make this transmitter stronger?
    -Thank you!

  • thaer
    November 2, 2009

    thank u

  • rhea coros
    August 28, 2009


    is it ok to use a phone plug instead of a microphine…


  • rhea coros
    August 28, 2009

    is it ok to use a 5K variable resistor instead of a 4.5K?


  • Wolf -LM
    August 13, 2009

    if u have 2 100Uh you could add them in parrallel

  • samuel
    August 6, 2008

    Good day!

    Can you please give me instructions on how to make the L1 inductor with the value 200uH?

    This would be a very big help…Thanks


    • November 3, 2012

      can you pls give me instuction on how to make .

      L1 make copper wire?indutor col with the value 200uh?and this transmitter range pls and on transmitter how mw,sw? transtor us bc109c .2n2219,2n2221.2n2222? Thanks

      • dani
        February 27, 2014

        Hello junaid. This am transmitter circuit is work or not?

Leave a Reply