FM modulator block diagram

This is the block diagram of the FM modulator.
The signal from the microphone is amplified. Then the signal is clipped and filtered.
After that it is used to modulate a super VXO at 10.7 MHz. The signal out of the super VXO is buffered and filtered.

It took some effort to get enough deviation. Getting deviation was not that difficult. It was difficult to get enough deviation and a accurate carrier frequency. I managed to achieve this by used 2 varicaps parallel. The resulting FM sounds alright on a HF receiver tuned at 10.7 MHz.

Abandoned concept:

I tried a different modulator first. I made a PLL at 10.7 MHz using a 74??4046. This chip contains a VCO and a phase detector. FM was made by modulating the loop. It worded but it sounded awful. I found out that the PLL locked when the loop was open. It had a small catch area. Due to some internal coupling I guess.So I used a second a 74??4046 as VCO. It worked. The FM sounded excellent. However I could not make enough deviation without adding a lot of distortion. I don't know why. I think the concept is good the implementation must be wrong. Maybe the phase detector switches to frequency detector mode for high deviations. I stopped working at it as it would take too much time to figure it out. If I had succeeded I would have had a HiFi modulator. This would be overkill for a communication transceiver anyway . So I built a modulator using a VXO.