FM telephone bug.

admin May 2, 2008 19 Comments


A simple telephone transmitter circuit that is ideal for transmitting the telephone conversation through small distances.The circuit is very simple and uses only few components.The entire circuit can be easily included in the telephone itself or in the junction box.The circuit is powered from the telephone line itself.

The transistor Q2 is wired as a a Colpitts oscillator to produce oscillations in the FM transmission band.The audio signal from the telephone line is coupled to the the base of Q2 to obtain the frequency modulation.The LED D1 acts as a power on indicator.

Circuit diagram with Parts list.



  • Any radio frequency  PNP transistor like A933   can be used for Q2.
  • For L1 make  8 turns of  0 .6mm dia enameled copper wire  on a 3.6mm dia steel bolt.
  • For antenna use a 15cm long 0.6 mm dia copper wire.
  • This is rubbish
    April 6, 2015

    There is no In1 and In2 and Out1 and Out2 on a telephone line.
    Not even three.

  • maryam rashed
    July 22, 2014

    please send me full discription of this circuit function
    thank you

  • chaitali
    April 11, 2012

    hey can u send me the detailed description of dis circuit its unable to understand d working with such less info. can u do it asap??? i wud lyk to do dis as my project please..

  • prabha
    February 26, 2012

    plz give a detailed description of the to connect with it possible to connect with a mobile or wireless phone?

    February 23, 2012

    HI !

  • February 19, 2012

    Pliz wd u send me a clear discription of this whole circuit. Thnks

  • Faisal shehzad
    October 4, 2011

    Plz the description is not enough to understand the working of this.Is there any recevier required for convarsation or what?I cant understand.Plz send me complete discription of this circuit.thanx

  • Jewel
    July 23, 2011

    How to make turns, over or around the bolt.

  • Seetharaman
    December 8, 2010

    Hi Segzy The bridge rectifier circuit will be completed through the connected telephone instrument. if the instrument is not connected then the circuit will not work.

  • Segzy
    December 7, 2010

    Is d2 bridge retifier?where is Q2?wher wil in and out go?

  • seetharaman
    August 26, 2010

    Hi Elgardo Disconnect your incomming line to your telephone. connect Out 1 & 2 to your telephone. connect the incomming line to In 1 & 2.

    August 25, 2010

    Hi Seetharaman, can you e-mail me the drawing how to connect the IN1,2 and The OUT 1,2 for clarification? i am slow on this connection.

  • seetharaman
    July 3, 2010

    Hi Bryce the signal available on the telephone cable will be transmitted. (The coversation – signal from both the caller and called ones mic will be transmitted)

  • bryce
    July 2, 2010

    is the telephone insterment the mic

  • seetharaman
    June 30, 2010

    Hi Bryce In is to be connected to telephone line and out to the telephone instrument.
    Range will be around 100feet.

  • bryce
    June 30, 2010

    what is the wireless range of this circuit

  • bryce
    June 30, 2010

    what is IN 1 and 2 ,and OUT 1 and 2

  • jojo
    January 13, 2009

    Its designed by our logo designer! We will be having a fresh look very soon!

    regards & thanks for adding to the feed reader.

  • November 24, 2008

    Good post, I like your writing style! I’ve added to my feed reader, and will be reading your posts from now on. Just a quick question – did you design your header image yourself, or have it done professionally? If you had it done by a professional, who was it?

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