The dazaro3 Youtube channel has some of the simplest and most practical FM transmitter circuits around, with a bonus that he actually shows them working.
I first experimented with his
three-stage transmitter on a breadboard (LEAP#280)
and got such good results that I then put it in an Altoids can, and finally bought a legit one from dazaro
as a benchmark and a bit of payback for sharing such great designs.
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub
