This is a very good quality FM transmitter circuit built using four radio frequency stages: 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.
When any input audio signal provide at the microphone, then frequency-modulated signals are obtained at the collector of oscillator transistor T1. Modulated signal 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 trimmer carefully with the non metal screwdriver VC1 connected across L1 to generate frequency within 88-108 MHz. Also adjust 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 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 operation of this circuit. I recommend to use a 12 v battery , If you use adaptor for dc supply then it may produce some noise , so with ac to dc converter it requires good filtering to clear signal without noise.
Please carefull with the connecting to mic terminal . it has polarity , so if transmitter has all are right but sound not detected from input then check the polarity of mic. It connected reverse or not ?
Assemble the circuit on a good quality 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.
Maximum Range of this transmitter is approx 2-3 KM
Resistor- 22k-1, 10k-1, 2.2k-2, 1k-2, 18Ω-1, 68k-1
Trimmer- 22p 2, 40p-1
Mic-1, ic7809 voltage regulator, copper insulated polished wire for making coil(L1,L2,L3)