Bitcoin is usually sent through the medium of mesh networks and satellite. But new experiments are continuously being conducted to protect the privacy and evade the government eye. In the latest experiment, Bitcoin was internationally transmitted by high-frequency radio, during a snowstorm.
Although at first, Coinkite founder Radolfo Novak did not get a response to his call from BTC recipients, the following day found them someone with a software-defined-radio (SDR) and antenna. What followed is a Bitcoin transaction from Toronto, Canada to Michigan, USA, by means of a pre-configured brain-wallet and an app called JS8Call, which can send text strings over radio frequencies.
Bitcoin sent over national border without internet or satellite - just nature’s ionosphere - Nick Szabo, leading cryptographer
According to Novak, a brain-wallet must be well-constructed, so as not to cause any safety issues. The brain-wallet is for remembering the seed phrase in your head and not writing down anywhere, so as to prevent risks. This is especially helpful while escaping an oppressive regime with only the essentials in our bag. Another new feature is the use of high-frequency (HF/HAM) radio, which could also prove to be lifesaving in certain circumstances.
In nations like China, the government has been putting their citizens under surveillance by trying to control the internet - their way of connecting with the outside world. Recently, rumors about Russia planning to adopt a similar strategy have surfaced. As we have learned from post-apocalyptic and dystopian movies, HF radios are handy when all other means of contact with the world prove to be inoperable.
Besides, as Novak also stated, "encrypted communication is not permitted over Amateur radio unless the cipher is public." Therefore, it isn't permissible except maybe during an apocalypse.