I don't want to hold myself out as an expert in this area, because I'm not, but wouldn't it make sense concentrating efforts, from a bitcoin perspective, on pure over air transactions than the wifi stuff, which is useful, but doesn't address internet outage situations?

siggy47

radio

About encryption and/or commercial activity on the ham bands:

HR4BTC

Short answer is no, you could do it with a variety of radio types and methods.

This is one example of how it was done.  https://news.bitcoin.com/no-internet-no-problem-how-to-send-bitcoin-by-amateur-radio/

The key would be anyway way you were able to effectively pass the data to someone who could then transmit the data to the mempool would be sufficient.  Theoretically, you could even do that with voice. 