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1 watt four stage fm transmitter

1 Watt FM Transmitter Project

This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1), a preamplifier built around transistor BF200 (T2), a driver built around transistor 2N2219 (T3) and a power amplifier built around transistor 2N3866 (T4).

A condenser microphone is connected at the input of the oscillator. Working of the 1 Watt transmitter circuit is simple. When you speak near the microphone, frequency-modulated signals are obtained at the collector of oscillator transistor T1.

The FM signals are amplified by the VHF preamplifier and the pre-driver stage. You can also use transistor 2N5109 in place of 2N2219. The preamplifier is a tuned class-A RF amplifier and the driver is a class-C amplifier. Signals are finally fed to the class-C RF power amplifier, which delivers RF power to a 50-ohm horizontal dipole or ground plane antenna.

Use a heat-sink with transistor 2N3866 for heat dissipation (Note: or 2N4427 because it works better at 12 V and delivers up to 1 watt RF power). Carefully adjust trimmer VC1 connected across L1 to generate frequency within 88-108 MHz. Also adjust trimmers VC2 through VC7 to get maximum output at maximum range.

Regulator IC 78C09 provides stable 9V supply to the oscillator, so variation in the supply voltage will not affect the frequency generated. You can also use a 12V battery to power the circuit. Assemble the circuit on a general purpose PCB. Install the antenna properly for maximum range.

Coils L1 through L5 are made with 20 SWG copper-enamelled wire wound over air-cores having 8mm diameter. They have 4, 6, 6, 5 and 7 turns of wire, respectively.

Note: This transmitter is meant only for educational purposes. use of this transmitter with outdoor antenna is illegal in most parts of the world.

FM Transmitter circuit diagram

1 watt four stage fm transmitter circuit diagram

Source: Electronics For You Magazine http://www.electronicsforu.com/electronicsforu/lab/freecircuitslist.asp?id=464&title=Four-Stage%20FM%20Transmitter

25 Comments

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  • Goutham

    How can I get those components?Can you courier them?

  • souvik

    is this circuit works?????????????????????????????????????????

  • kamal sharma

    what is range of this fm transmitter.

  • Rick

    From the schematic that is shown above for the 1 watt FM transmitter, some of the transistors do not appear to have any DC biasing. Is there another schematic for this that includes the DC biasing resistors for these transistors? Also, could one opt to put in a parallel LC tank circuit at the collector of T4 so as not to be dependent on solely a large antennae?

    • keys88

      i agree

    • AlbertH

      You won’t ever get any technical answers from “P. Marian” – he doesn’t understand what he’s put on this site.

      The stages without DC bias are supposed to be working in “Class C” – the transistor is biased by the incoming signal, and is therefore operating in a “switched-mode”. This can be highly efficient, but gives rise to harmonic outputs. The circuit as shown will just cause interference. The oscillator stage will drift wildly in frequency and the stages after it will amplify somewhat but will produce more energy in harmonics than at the correct fundamental frequency.
      The other fatal flaw with this crude circuit is that the oscillator runs at the wanted output frequency. There is a significant risk that the output will couple back into the oscillator causing further instability.
      DO NOT waste your time and money on this stupid circuit.

      10 metres on the wanted frequency, and much further in the aircraft, TV and military bands. If you connect this mess to an antenna, you will end up in prison. It will just generate massive interference.

  • Sudip UPreti

    what is “sh” below transistor T2* and where do it connect with.

    • DorinLTM

      sh comes from shield
      this transistor has 4 terminals, one connected to capsule
      that lead has to be connect to 0V rail

  • Sudip UPreti

    what is “sh” below trasboistor T2* and where do it connect with.

  • Rick

    http://www.electronics-lab.com/projects/rf/001/index.html

    Esté arriba es un projecto montado completo que incluya un transmisor de quatro vatio de poder.

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