This low power fm transmitter is designed to use an input from another sound source and transmits on the commercial FM band. This low power fm radio transmitter it is actually quite powerful…
The first stage is the oscillator, and is tuned with the variable capacitor. Select an unused frequency, and carefully adjust C3 until the background noise stops (you have to disable the FM receiver’s mute circuit to hear this).
When assembling the fm transmitter circuit, make sure the rotor of C3 is connected to the +9V supply. This ensures that there will be minimal frequency disturbance when the screwdriver touches the adjustment shaft. You can use a small piece of non copper-clad circuit board to make a screwdriver – this will not alter the frequency.
Q1 is a conventional Colpitts oscillator design. The audio signal applied to the base of Q1 causes the frequency to change, as the transistor’s collector current is modulated by the audio. This provides the frequency modulation (FM) that can be received on any standard FM band receiver.
The inductors are 9.5 turns of 1mm diameter enamelled copper wire. They are close wound on a 3mm diameter former, which is removed after the coils are wound.
The output is a low power of 100 mW, but for some of you this fm rf transmitter can delivers the desired power for broadcasting on your street or with a proper antenna you can cover a small neighborhood. If you need a power wireless fm transmitter use the above menu, you can find transmitters starting with low fm power up to high power fm transmitters.