Thats very thoughtful if them, I have to give it to them. It was one of the best ideas so far to elude the issue the use of Internet could possibly pose. Using radio signals means there would have to be a host and having a host server makes the network centralized in a way and bitcoin is a decentralized network. Perhaps the intent is to tap into existing radio station signals but then it still poses a problem, same issue with the internet as to how far the network would go. When you get to the rural areas, you'll find out that, there are no signals except there is a max close by and this would still be a challenge for bitcoin and as such, we would need more.