Long range AM transmitter.

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Description.

Here is the circuit diagram of an easy to build long range AM transmitter circuit based on three transistors.With correct tuning and a matching antenna, the transmitter can deliver signals up to a distance of 2 kilometers.

The audio signal to be transmitted is given to the base of the transistor Q1 via the audio driver transformer T1.The modulated signal is developed at the collector of transistor Q1.The frequency of the transmitted signal can be tuned adjusting the gang condenser C7.The required amplification of the modulated signal is done by the two transistors Q2 and Q3.The  two  transistor amplifier stages are connected in parallel for obtaining maximum power. The signal to be transmitted is coupled to the antenna via the capacitor C4.

Circuit diagram with Parts list.

long-range-am-transmitter-circuit

Notes.

  • The inductor L1 can be made by making 56 turns of 365 WG enameled copper wire on a 1 cm former.
  • The transformer T1 can be a general purpose audio driver transformer seen in transistor radios.
  • Inductor L2 can be a 10 mH general purpose radio frequency choke.
  • Use a 1 meter insulated copper wire as antenna.
  • The circuit can be powered from a 9V PP3 battery.
  • Adjust the value of C7 for maximum range.
  • Also, you can experiment with the length of antenna for maximum range.
  • The resonator F1 used here is a two terminal type without a ground pin. If you are using a three terminal one, the ground pin must be connected to the circuit’s ground.

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22 thoughts on “Long range AM transmitter.”

  2. Phillip Dunstall

    can the long range Am transmitter be made into am stereo transmitter like an amercian C-quam Configuration

  6. Rex

    Seetharaman, i want to build this Am transmitter, but i want to be sure if it is working, or has anyone tried it before?

  9. Ryan

    What is the maximum and minimum capacitance for the C7? I’m thinking of just building one.

    1. seetharaman

      It is 10 to 270PF PVC dielectric variable capacitor. It is 2 / 3 band trasistorised AM radio tuning capacitor. It will be available in all electronic spare shops who deal in discrete electronic components

    1. seetharaman

      Hallo the following is a simple AM receiver you can change the number of turns in the coil to change its range of frequencies. You can start with a simple single layer wound 28SWG super enmelled copper wire wind 90 turns on 12mm dia wooden piece or plastic conduit piece. For above short wave frequency use 12 to 15 turns of 24 swg as above. use a PVC 2J gang for tuning the correct frequency. use a good antenna and earth for best performance.
      http://www.wiringdiagrams21.com/2010/03/30/simple-op-amp-radio-circuit-diagram/

  12. wayne

    could you please tell me what ferquency the resonator is neaded for the am broadcast band , 3.587 MHZ is up around 50 metters may I’m wrong thanks

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