Just a random video that was suggested to me today:
TL;DW: The guy was able to send a valid LoRa packages over 2500 m without a LoRa radio just by “sort of bit banging” and using harmonics on a ESP32 with a dupont wire dipole antenna.
I found it amazing and terrifying, that he also got around 200 m with a funtenna. The same goes for the 750m with the CH32V203, I mean that is the kind of microcontroller you find in lots of peripherals.
All his work is open source and in this repo: