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Good FM Transmitter Circuit

This house FM transmitter for your stereo or any other amplifier provides a good signal strength up to a distance of 500 meters with a power output of about 200 mW. It works off a 9V battery.

The audio-frequency modulation stage is built around transistor BF494 (T1), which is wired as a VHF oscillator and modulates the audio signal present at the base. Using preset VR1, you can adjust the audio signal level.

Audio FM transmitter circuit diagram

quality fm transmitter circuit schematic

The VHF frequency is decided by coil L1 and variable capacitor VC1. Reduce the value of VR2 to have a greater power output.
The next stage is built around transistor BC548 (T2), which serves as a Class-A power amplifier. This stage is inductively coupled to the audio-frequency modulation stage. The antenna matching network consists of variable capacitor VC2 and capacitor C9. Adjust VC2 for the maximum transmission of power or signal strength at the receiver.

If you design a good pcb layout you can use it as a car fm transmitter.
For frequency stability, use a regulated DC power supply and house the transmitter inside a metallic cabinet. For higher antenna gain, use a telescopic antenna in place of the simple wire. Coils L1 and L2 are to be wound over the same air core such that windings for coil L2 start from the end point for coil L1. Coil winding
details are given below:
L1: 5 turns of 24 SWG wire closely wound over a 5mm dia. air core
L2: 2 turns of 24 SWG wire closely wound over the 5mm dia. air core
L3: 7 turns of 24 SWG wire closely wound over a 4mm dia. air core
L4: 5 turns of 28 SWG wire on an intermediate-frequency transmitter (IFT) ferrite core
Check the related posts for some stereo fm transmitter circuits.

30 Comments

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  • Dines

    pleas 1/4 or 1/2 watt fm transmiter diagram with Pcb & full detail.

  • abdulsalam habib

    may ALLAH bless anyone dat wl going to help me here is jst a working fm transmitter i need if possibl pls send it to my mail pls am jst like your brother that is in need pls i beg u

  • ram

    Good one. But can you provide any document or some reference book for how the oscillation frequency changes with input voltage?

  • sanjay

    hi I want 1 watt fm transmitter if anyone provide me please call me 9096934596.

  • KROKKENOSTER

    You are as far as I know nowhere on Earth allowed to broadcast more than 100 mW so it can work as a cordless microphone. Another problem is that the battery voltage going up and down while you use it and then the frequency will shift up and down. All I could do with a commercial kit was to use a battery of 12 volts and then a stabilizer to regulate to the nominal 9 volts needed The audio quality can be quite good but check the output of your modulator as sometimes that is the reason why the sound as bad as can be. You are picking the jails’ door lock by going for higher power as some guys want to do. If you want to broadcast for more than 100 mW then you will have to use a commercial transmitter and you must get it licensed by your local authorities. A friend of mine of some years ago built a transmitter that the diagram was in our course manuals. He was broadcasting on Short Wave 7 MHz He was caught and had to pay a heck of a fine or would have to go to jail for 12 months BE CAREFUL

  • robustman

    check qn8027 chip.it is a nice FM transmitter.price isnt expensive.

  • Sibaram Datta

    Friends I have built this quality fm tr with a pcb purchase from kits n spares with all components. Smile to say that after construction of this Tr with a 9v supply & a stick antenna its range is only 100mtr. So friends it is nothing but wastage of money. Any one cant help you to extend its range to 500mtr & output of 250mw as written in the circuits. All circuits that published in the net is forged.

    • Mukesh Kumar Purohit

      @ Sibaram Datta
      i have also purchase quality fm transmitter from kits n spares.
      i accembled all the component in order accordingly as specified
      in the Circuit Digram.
      But i have an issue , that is
      1. It’s transmitting range is 2 to 3 mitter
      2. It is transmitting in 2 different Frequency. (Ie. 87.50Mhz and 92.5 Mhz )
      3. Transmitter audio quality is low.

      Please help me about the issue. Plz say what is the problem and how to
      solve these issue.

  • dick

    what is the frequency of this transmitter

  • Raj

    I heared- The output transistor conducts an
    average of 25mA. It has an average
    voltage of 8V across it. Then it HEATS
    with 25mA x 8V= 218mW. Its radio
    output power is about 10mW to
    20mW.

    • P. Marian

      Change it with BF199 and replace C8 with a 1nF capacitor and then see how this is going on.

  • Raj

    Plz plz tell me- How much diameter of IFT ferrite core? I’m going to built!!!!

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