The first obvious possibility is for TCP/UDP connections over some protocol such as 802.11(commonly known as WiFi). This can be secured with simple to complex crypto so only users authorized to connect on a network can connect, so the network can't be compromised in that area.
Then, of course, there's sending the blockchain and transactions over radio without internet surrounding it. This would generally use encoding(the bitcoin protocol), error-checking(CRC32 or crypto-based MAC), and modulation. For short distances, we could get away with something like 64-
QAM, falling back to simpler constellation patterns due to signal loss. In severe cases, or where it is not necessary to have high bandwidth(nodes once theyhave the blockchain), PSK can be used as it is a bit more resilient. While most PSK is at "normal" bandwidths at least in the tens of kilobits per second, PSK31 used in amateur radio is more resilient but offers bandwidth comparable to typing speed, around 10 bytes per second. Securing it would be another challenge as there would need to be some sort of handshaking and authentication on the link. Anyone could easily interfere with this link, though, by using jammers, or badly soldered high school electronics projects that spark a bit.
This may be alleviated using highly directional antennas. With the correct set of reflectors and good aim, one can reduce the signal spread to a few degrees off center. Satellite links can also be used if one can find a satellite which will relay the data to the correct location or at least into the general internet.
So, you would save a lot of time, worry, and eyestrain(from technical documents) by using (relatively)high-distance wi-fi, or encapsulating internet protocols carrying Bitcoin packets on other radio links. Except in extreme cases, encoding the blockchain and other communication over radio is overkill, except in possibly a specialized miner setting where miners(ASICs or FPGAs) use their own radio signals to connect to a master machine. Still, it would be easier to use ethernet, USB, or WiFi.