Re: FM Tx OSCILLATOR
Just one comment on the extra diode in the modulation circuit. This will provide fairly flat modulation sensitivity across the tuning band BUT, it will introduce a lot of distortion. I experimented with a design some time ago and used a very similar setup with additional DC feedback from my VCO tune line. I got very flat mod sensitivity (under 10kHz error from 75kHz peak deviation). When I measured the %THD of the demodulated audio, it was well over 2%. Without the extra varactor, it dropped to 0.1% Nothing I tried would bring it down near acceptable levels (≤0.5%) without losing flatness again.
At the end I used a digital pot to compensate the audio mod level against frequency to keep the distortion low using a single varactor diode for frequency control and audio mod.
E