I've been thinking about this one for some time, and I have an early proposal that I'd like to flesh out with the brainiacs to see if there are any glaring errors that I've made, before I make a formal purposal to the FCC. No, I'm not joking.
Nice! I thought about "Bitcoin over radio" as well. Didn't get to the point of deciding exactly which frequencies or modes would be best for the task, though. Just thought about the general idea, using the model of a ham radio repeater that serves a given geographical region.
The idea is to have some way of ensuring Bitcoin transactions can still be made, even if the Internet is down/unavailable/suppressed in the region. It would work similar to a ham radio repeater, many of which already support various digital modes.
The repeater (good radio station on a mountaintop or something like that, so it has good reach) would be the only node that would require Internet connectivity. It would have an output frequency (always transmitting), and an input frequency (always receiving).
This doesn't need that, as the rules of the machine can determine when and under what circumstances the datagram is repeated. Similar to how packet radio works, only slower.
The idea is to have the ability to transact by Bitcoin be very survivable. If the traditional Internet connections are knocked out, either by disaster or intentionally by government trying to do suppression/censorship, the ability to do Bitcoin by radio could be very useful.
It'd be usefull anyway, but particularly during a Internet blackout of a limited term. If the Internet is permnently and irreversablely destroyed, Bitcoin won't work anymore; but if that were to ever happen, I think I might have bigger problems.