Saturday, April 16, 2011

Coilless FM transmitter !

 If you are in the problem to make perfect coils for FM Transmitter then this is your time to go on..... See this coil less and easy FM Transmitter.

The RF oscillator using the inverter N2 and 10.7Mhz ceramic filter is driving the parallel combination of N4 to N6 through N3.

Since these inverters are in parallel the output impedance will be low so that it can directly drive an aerial of 1/4th wavelength. Since the output of N4-N6 is square wave there will be a lot of harmonics in it. The 9th harmonics of 10.7Mhz (96.3Mhz) will hence be at the center of the FM band .
N1 is working as an audio amplifier. The audio signals from the microphone are amplified and fed to the varycap diode. The signal varies the capacitance of the varycap and hence varies the oscillator frequency which produce Frequency Modulation.


  1. I built this circuit but in digital fm radio (car fm or mobile fm) the frequency is not set automatically & output signal is very week. The frequency set this circuit is near about 89.5 mhz. Please help me to extend the signal strength & to set frequency near 100mhz.