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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.
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