[owenversteeg]

Right, but that's only one direction. I thought I put it in my comment, but I'm only curious about bidirectional stuff. The best path forward here seems to be WSPR- like stuff, but that requires larger transmitters on the order of tens of meters.

[PoachedSausage]

That's the problem, an asymmetry in transceiver size does not really lend itself to bidirectional unless its relatively short distances like cellular phone networks.