They change. If you want to try direct tuning you'll want to check with monitoring groups or newest YouTube videos, etc. Otherwise if you are in the US...aka near a secret agent ;-)... scanning around works well enough.

I don't know if this is still the case but they used to use a freeware Windows XP encryption application. The amused author wrote a bit about it, IIRC.

Part of the fun is discovering the communities that follow this stuff.

OP here. I have not found any such community. Do you know any?

I don't but sometimes I enjoy listening to Radio Reloj. It's so unique.