Simple FM transmitter circuit.

admin February 11, 2012 57 Comments

Two transistor FM transmitter.

Description.

A lot of FM transmitter circuits have been already published here. This just another one, a simple two transistor FM transmitter.The first stage of the circuit is a preamplifier stage based on transistor Q1. This is a collector to base biased amplifier stage where resistor R2 sets the collector current and R1 provided the necessary collector to base bias. C1 is the input DC decoupling capacitor which couples the input audio signal to the Q1 base. C8 is the power supply by-pass capacitor. Next stage is the oscillator cum modulator stage built around transistor Q2. Electrolytic capacitor C2 couples the output of the first stage to the second stage. R3 and R4 are the biasing resistors of Q2. R5 is the emitter resistor of Q2. Inductor L1 and trimmer capacitor C5 forms the tank circuit which is necessary for creating oscillations. The modulated FM signal is available at the collector of Q2 and it is coupled to the antenna using capacitor C9.

Circuit diagram.

simple fm transmitter

Simple FM transmitter circuit

Notes.

  • The circuit can be powered from anything between 6 to 12V DC.
  • Using battery for powering the circuit will improve the performance and reduce noise.
  • A 9V PP3 battery is a good option.
  • If you are going with a battery eliminator, then it must be well filtered and regulated.
  • Trimmer C5 can be used for adjusting the transmission frequency.
  • Antenna can be a 1m copper wire.
  • L1 can be constructed my making 4 turns of 1mm enameled copper wire on a 10mm diameter plastic former.
  • Trimmer capacitor C6 can be adjusted for obtaining the maximum range.
  • Most of the components required for this circuit can be procured from your junk box.
Comments
  • July 16, 2015

    what is the transmission range radius and the power using the specifications above?

  • July 16, 2015

    which is the transmission range diameter and power of this transmitter pls?

  • Roche
    February 3, 2015

    What does that audio in mean?
    A female audio plug or microphone.

  • peter clarke
    May 23, 2014

    hi, I would like to simulate the design before building. I do this all the time now with my projects because it shows up any problems.
    does anyone know the value of the inductor which is on the diagram? I need to put in a value for the inductor before simulating.

    • Seetharaman
      May 24, 2014

      200 micro Henries approximately. (160 to 185 uH)

  • MUFS
    April 30, 2014

    has this circuit checked on simulator ? does it work ?

  • maan
    April 17, 2014

    can we directly coupled with ground without c4?

    • Seetharaman
      April 24, 2014

      C4 is a decoupling capacitor can not be removed

  • maan
    April 17, 2014

    working of c4?

  • mkpoikana inyang
    March 11, 2014

    please how can I get a value for an inductor to be used in any circuit construction

  • gokul
    November 24, 2013

    i have made one for myself .but its range is very poor.can you please tell me how to increase the range.

    • Seetharaman
      April 24, 2014

      ensure a good whip antenna is connected to the transmitter

  • Shedrackshawulu@gmail.com
    November 21, 2013

    Sir pls i need a working fm transmiter diagram dis nite because we have an urgent project tomorow pleas help me sir

  • Sethram@email.com
    November 21, 2013

    Please i need a 10km working fm transmitter for my project tomorrow please help me sir

  • Ukam Elot
    September 23, 2013

    I’m grateful for ur work so far. But, pls i need a book that can guide me on how to build a local FM station. I’m in Nigeria, west Africa.

  • fefe
    September 19, 2013

    how to find the transmitting frequency

  • September 18, 2013

    Find Circuits/Schematics on web that are not visible in google search.
    Install and use in firefox as drop down in search engine bar.

    http://goo.gl/Ro5bBv

  • Rex
    September 11, 2013

    Seetharaman, how do i add crystal to the circuit to make the frequency stable? Show me where to add the crystal

  • September 8, 2013

    Sir, what should be the distance between first and last turns of inductor L1.

  • anonymous
    August 10, 2013

    can i use 5.2 nf instead of 2.2nf!!!

  • apple mind
    June 1, 2013

    Would you plz give me or publish a 100 mtr wirless intercom in10 days as u can .i challenge you

  • shoaib raja
    May 21, 2013

    good one

  • John C Sunil
    March 29, 2013

    can i use a electrct condensor mic in place of audio in?

  • priya
    March 15, 2013

    I want more explanation to get the output of this CKT when we run it in laboratory.when i was going to run it the output of L1 & C5.what i want to do?please reply me.

  • amar
    March 9, 2013

    how to find the transmitting frequency

  • giri
    March 5, 2013

    give me the specifications of antena..

  • pratik
    February 16, 2013

    INductor is availble in market or not..?

  • sarin
    February 3, 2013

    audio in with a mic rite?

  • kabiru garba kwadon
    January 20, 2013

    please help me with the circuit diagram of 2km of fm transmittes.thanks from your boy

  • Mohit
    January 15, 2013

    sir, can you please tell me the use C3 and C4 capacitors ..???
    actually i am going to build one,but theoretically i am not able to find out the use of these two capacitors,

    Someone please help me …

    • Anish
      January 19, 2013

      C3 and C4 are for suppressing the ripple if any. And by ripple I mean any ac components. C3 prevents any noise disturbance to pass into the input of transistor Q2. and C4 suppresses voltage spikes and noise disturbance in the powersupply. Always in small circuits, typically a 100nf condesor will be connected from supply to gnd to bypass the unwanted ac components.

  • Duane C
    December 17, 2012

    I need to know how to make this tuneable. Any help would great. Also I am new at this kind of thing so please make it as simple as possible.

  • vinod
    November 18, 2012

    Hello sir can i know the frequency at which this circuit works

  • Zain Uddin
    July 20, 2012

    Hi Seetharaman,

    Can i use BC107 instead of BC108~? pLease reply ASAP thanks

  • Riya Chakraborty
    July 11, 2012

    please i want a answer about FM transmitter……what is the function of FM transmitter in analog modulation?????????????

  • Kaguai George
    July 10, 2012

    Appreciated,

  • Seetharaman
    June 27, 2012

    Hi Sujeesh you have to use a non metalic screw driver to adjust the trimmer. may be an ebonite rod tip filed similar to screw driver’s tip will be the best.

  • sujeesh
    June 27, 2012

    Sir,
    i made a fm transmitter similar to this circuit.and i can’t tune it correctly.it have one 20pf trimmer and while tuning it made clear reception when i touch in variable resirtor in the circuit.but when i don’t touch it,it will not make clear reception,can you help me? How can i make clear tuning?

  • Seetharaman
    June 25, 2012

    Hi This transmitter range will be similar to 200m FM Transmitter. The tunable frequency range can be between 80 & 150MHz with the adjustment of both L1 coil and trimmer C5.

  • Nirav
    June 24, 2012

    what wiil range of this circuit ? &
    which frequency it will transmit ? &
    how we change the frequency and range of this circuit ?

  • shimul
    April 17, 2012

    what is the frequency range of this circuit?

  • ashnuka
    April 6, 2012

    Thanks.

  • Seetharaman
    April 5, 2012

    Hi Ashnuka for BC108 you can use BC548 or 547 or any low noise NPN transistor but for 2N2369 you have to use 2N2219, 2N1711 or 8050

  • ashnuka
    April 5, 2012

    What are the replacements for both transistors?Can i use BC547 or any npn?

  • manu
    April 1, 2012

    how to prepare our own antenna?

  • jojo
    March 27, 2012

    @Rajkumar
    This is a two stage FM transmitter. First stage is the preamplifier stage where the input audio is amplified for transmission.This stage is served by transistor BC108. Second stage is where the amplified signal is modulated to a carrier wave (produced by tank circuit L1 and C5). This modulation stage is served by transistor Q2 (2N2369)

  • Rajakumar
    March 14, 2012

    Why two different transistors are used for?

  • SK
    March 10, 2012

    how to test ckt using multisim?

    • October 19, 2012

      I have working multisim and proteus simulations of above FMT those who requires mail me @ harbindersidhu@ymail.com

      • Dhaval
        April 23, 2014

        i want the multisim file of this project i hope you replay fast.
        Thank you so much in advance.

  • ramya
    February 26, 2012

    Hi, how much distance is this circuit can deliver?

  • February 15, 2012

    In theory C3 and C6 capacitors will cause damage to transistors. When transistor tries to saturate it will try to reduce the voltage across the capacitors to zero. However, if the capacitors are charged a large amount of current will flow into the transistor.

    An FM transmitter must have a modulator. All I see it amplifiers and filters.

  • M.
    February 12, 2012

    Forgot:
    -How do i make this transmitter stronger?
    -Thanks again!

  • M.
    February 12, 2012

    How long range is this transmitter for?
    How strong is the efect? (mW)
    -Thanks!

  • Edgardo
    February 12, 2012

    Hi, how much distance is this circuit can deliver? this is a good circuit, that requires only minimum of parts from “junk box”
    Thanks in advance.

  • Nafez Fares
    February 12, 2012

    Iam already going to build tone detector by using NE567, to detect this circuit frequency .

    So please can you define the Frequencey of this Transmitter ?
    and it’s calulation equation ?

    In abrief I need Fo .

    Thanksssss alot

    Nafez Fares

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