Ham radio can be used to receive encrypted messages, so it can be used to send and receive bitcoins over very long distances.
Imagine a scenario in the future where only Brazil has internet as we know it today and allows bitcoin to be used.
We could use ham radio using encrypted communications for bitcoin sweep.
Then again, ham radio communication seems easier to restrict than the internet.
By the way, do you think in such scenario would be possible to use an old fashioned modem to connect with internet in Brazil using ham radio?
Being forced to radio sort of indicates to me a very severe situation. I would guess that under a situation where free communications were severely restricted, any attempt to carry on data conversations would result in a very quick visit from a drone.
About ten years ago I got interested enough in all the funny noises on radio bands and got an RX320 radio then ported some software to my operating system of choice. Someone told me that they were 'computers talking' when I was a kid (70's) and I always wondered what they were saying to one another. I found that there are a lot of modulation types and it is quite possible to receive data from all over the Pacific at least. I went back to work about that time and have yet to get back into the hobby.
My current belief is that while it might be possible to keep any eye on things like spot prices and such, but again, I imagine that any attempt to actually send would be nothing more than a beacon telling the authorities where to find you. Or at least your radio gear.