I think those are very good questions. Technically, they seem to use pretty ordinary gear. The bit rate is super low, about 5 bps so you're not going to be sending over your movies any time soon. It's been tried but nobody ever succeeded and conditions would have be just so for this to work.

Possible applications from a practical point of view not that I can see, though I'm sure that now that it has been shown to be possible there will be attempts to replicate it and from harder locations.

But HAMs are known for doing things the hard way, after all, you could just pick up the phone and talk, that's not what this is about. It's about being able to do it, just like mountain climbing.

UHF is line-of-sight. The article speculates about a transient effect ("marine ducting") that allowed the signal to propagate further this time. It's not likely to be reliably repeatable.

FT8 is ~10 bits/second (think of it as CW/morse code + better modulation + forward error correction).

> Is there some technical innovation here enabling this

I guess you could say the SDR based ICOM IC-9700 [1] transceiver FG8OJ used is enabling this by being reasonably priced [2] and off-the-shelf. It was released in January 2019 and has made experimentation of VHF/UHF more accessible.

[1] https://www.icomamerica.com/en/products/amateur/hf/9700/defa...

[2] https://www.hamradio.com/detail.cfm?pid=H0-016656

- Weather happened to be favorable for a brief window of time

- The FT-8 mode makes barely-possible communication possible