STUB The less fashionable neighborhoods in the radio spectrum.

So the HF spectrum is still worth something. Not the junk RF dumping ground you've been told.

HF trading links are easy to encrypt, impossible to decrypt or MITM, but rather trivial to DOS. I'd love to know if there's contingency planning for deliberate jamming. A theoretical analysis of the economics of such distruption would be fascinating. E. g. does distruption need to be protracted to have a material impact? Would trading strategies degrade gracefully or fail catastrophically

The US Military is studying full spectrum processing as a backup for satellite based GPS. This includes LF and VLF, already used for DGPS and an evergreen technology in talking one way to submarines at sea.