High Quality FM Transmitter | FM Transmitter Circuit Diagram

High Quality 4-Stage 1 W Homemade FM Transmitter Circuit Diagram

How to make FM transmitter at home

This is a very good quality FM transmitter circuit built using four radio frequency stages: a VHF oscillator built using transistor BF494 (T1), a preamplifier stage 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.

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Working principle

When any input audio signal is provided at the microphone, then frequency-modulated signals are obtained at the collector of oscillator transistor T1. The modulated signal is then amplified by the VHF preamplifier and the pre-driver stage. 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. Adjust the trimmer carefully with the non-metal screwdriver VC1 connected across L1 to generate a frequency within 88-108 MHz. Also, adjust the trimmers VC2 through VC7 to get maximum output at maximum range. You can also use transistor 2N5109 in place of 2N2219

Voltage Regulator IC 7809 provides a regulated 9V supply to the oscillator, so variation in the supply voltage will not affect the frequency generated. Use any 12v adaptor or 12v battery for the operation of this circuit. I recommend using a 12v battery. If you use an adaptor for DC supply, then it may produce some noise, so with ac to dc converter, it requires good filtering to clear the signal without noise.

Please be careful the connecting to the mic terminal. It has a polarity, so if the transmitter has all are right but sound is not detected from the input, then check the polarity of the mic. Did it connect reverse or not?

Assemble the circuit on a good-quality quality general-purpose PCB. Install the antenna properly for maximum range. Coils L1 through L5 are made with 20 SWG copper-enameled wire wound over air-cores having 8mm diameter. They have 4, 6, 6, 5, and 7 turns of wire, respectively.

Maximum Range of this transmitter is approx. 2-3 KM