There’s been some chat in the CAKE thread about Through Zero FM - to oversimplify, FM that stays in tune. Turns out that this is actually possible with our beloved 3340, with “a bit of extra circuitry”.
I found this as an example:
from here: Juergen Haible
It’s a bit rich for my blood, but I thought I’d share it as a point of interest for anybody looking to explore this more.