How FM transmitter/radio works with crystal? What to read?

I want to understand how FM transmitter works when crystal is used. Or how FM transmitters work at all in detail. I watched multiple videos about frequency modulation but all those videos do not explain things like harmonics, etc. So I still don't get it.

Can you suggest links/videos/books on the topic please? I searched Amazon and there are some books on RF but I can't understand from their description if that's what I need.

Thanks,
Alex

a start:

from http://www.arrl.org/

https://www.google.com/url?sa=t&rct=...PoORGdXaJoor1w

the crystal sets the carrier frequency about which the frequency is modulated

The use of crystal in broadband transmissions is explained due to the existence of multiple channels, each one occupying preciselly a specific range in the spectrum. The distinction between each one is made on the receiver side from a crystal of the intermediate frequency, the beat between the carrier and the crystal oscillator.

This is an interesting question.

How it works..............

A crystal is designed to operate at a certain frequency, into a certain specified load. Most crystal are specified to work into a certain amount of capacitive load, say 32 pF. In the case of a crystal-controlled FM transmitter, part of the capacitive load is in the form of a varactor, which is nothing more than a reverse-biased diode, with known capacitance vs voltage parameters. Audio is applied to the varactor, its capacitance changes, and you have FM!

Where it gets interesting (and probably too far out in the weeds) is how much the crystal can be "pulled", which in this case determines the frequency deviation. (Think of frequency deviation to be the equivalent of modulation level, in good ol' AM. IOW, how loud it will be.) The ratio of the crystal's internal motional capacitance to its holder capacitance determines how far it can be pulled.

Which is just a fancy way of saying really good hi-Q crystals are not likely to work in an FM transmitter.

Go to archive.org and find yourself a copy of the old
ARRL Radio Amateur's Handbook. Check out online
archives of Radio Electronics magazine and more
hardcore ham radio mags. That should keep you
busy for a bit.