Thanks for all the replies: my phrasing was indeed bad I guess!

A "public channel" is a very broad definition, and most communication channels, including those used for encrypted communication, are by design more or less "public".

Situation with GPS that feels similar to "number stations" (which I only know about thanks to Boards of Canada's album "Geogaddi", tbh^^) is that encrypted messages are deliberatily broadcasted, not that the channel is in some way "public". The latter also applies to all encrypted internet traffic, I guess.

Technically all RF communications are "public." You have to use encryption if you want security.

Would point to point laser seem like it's RF and not readily snooped without detection?

Unless you are in a vacuum, a laser that can reach a useful distance can be observed due to atmospheric scattering.

true!

Yeah GPS is not the people's airwaves it is operated by the US Space Force, I suggest you read up on your history.

OK, I have to further narrow down my statement then: a publicly readable medium (or one-way channel).

I didn't want to imply that regular people could simply inject data into what's emitted by GPS satellites.

Sorry if that wasn't clear, but I am aware that GPS is operated by the US military.