Is that Russian station still sending signals? I watched a YouTube thing about it. I think nobody cracked the code as to what it’s doing.
1. Most of the time you don't have a message to send, so you send random numbers. Maybe you have an agreed upon header to signal to your spy that the following bytes are significant
2. Maybe you don't have any spies, and just want your adversary to think you have spies, so you blast your numbers station into their territory just to make them nervous. Who knows, someday maybe you'll have spies, and you wouldn't want to announce this change by suddenly having a numbers station.
Some number stations could be a low-cost effort to keep other nations busy.
There are a few still transmitting, if you mean number stations.
If you mean UVB-76 then I'm pretty sure it's just them parking the frequency for when the American imperialists set the sky ablaze. (You can apparently hear the operators listening to music or watching memes every now and again so it's obviously not a hugely important broadcast)
My only exposure to number stations is the podcast "99% Invisible", an entertaining account sprinkled with audio clips of various stations: https://99percentinvisible.org/episode/numbers-stations/
NIST also makes broadcasts for things like timekeeping. You can listen to 5k or 10k Hz and it’ll tell you what time it is. Handy for checking that your gear works.
The human-readable broadcasts are at 2.5, 5, 10, 15, and 20 MHz.
https://www.nist.gov/pml/time-and-frequency-division/time-di...