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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

27 Comments

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  • kennynvayahoo-com

    I just look around old transistor radios I scrap for parts…and look around the tuning capacitor, or near that section…usually there is an rf amp, or vhf oscillator, or similar transistor there..

  • kennynvayahoo-com

    I found a transistor that might work…a NTE229 …or a C784…do you have either of these..??

    K

  • Jeeshan pasha

    Sir what is the means of
    t2 sh
    z

    plz reply me

    • Rick

      ‘SH’ is the shield (as T2 has four legs). The shield leg is the one that’s attached to the shell of the transistor, and must be connected directly to ground.

      Personally, I wouldn’t waste my time and money on building something as unstable as this contraption.

  • onnyx

    Hi. I want to know how much will it cost to ship it to south africa.

  • Amin

    This circuit works perfectly and whoever says it doesnt work has to bulid uy first and then comment about it….you can use 2s9018 instead of BF200 and carefully follow the instructions about building the coils

  • amir

    if i use 2sc3950 transistor at final stage,what do you think?is it better or no?

  • amarnath

    wht is the range of this transmitter?

    • Jukka

      I have made this circuit and it actually worked fine. Range about 2-3 km in urban area. It is not very stable. The frequency will change if you take it outside (temperature change ?)or even go near it. Instead of T1 I used 2n3904 and T2 2n2219

      I put audio input instead of microphone and resistor between T4 and L4 because transistor heated too much. Resistor is probably bad for transmission. Fan or good heat sink would be better.

      I got stronger rf output from collector of T4.

      This circuit also works with rf amplifier.

      Tuning this circuit is really a hard chore. I started from T1 and moved to next capacitor when current raised. You are near right tuning when T4 and T3 starts to heat up. Current with 12-14 V about 600-700 mA

    • Rick

      It’s a pure waste of time and money building something like this as it simply will not work. The most that you could expect would be a bunch of howls and squeals that will transcend over a wide rf spectrum. In short, what you would be building here amounts to nothing more than a jammer which is against FCC regulations. In that sense, the range would be immaterial here.

  • Rick

    Don’t waste your time and money building this contraption as it is highly unstable, and will jam frequencies over a wide band.

  • Saleem

    what is VC (variant capacitor) how we can find in the market

    I mean is there some more information about this

    please repply

  • Anish AD

    Sir, please tell me the replacement of BF200 transistor. In my place this transistor not available so please replay me….

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