It won't get you from where you are to China though.

No but something like WSPR or FT8 would. Needs a license though.

FT8 has such a small payload that you couldn't fit an emoji, much less an average English sentence.

There's no authentication so anyone can pretend to be you. Traditional methods of verifying the sender (HMAC) would take so many hours to transmit that the physical propagation paths you're communicating through will probably collapse before you deliver the smallest verified message.

If you need to communicate information, FT-8 is not for you.

Agreed but if you're trapped in a war zone, time is one thing you have. And equipment for FT8 is simple to build yourself. It's also very difficult to trace. And you can take up some fields used for other stuff and convert them to data (like the sender). This would be illegal on amateur bands since it's required to identify oneself but again in a war situation this is less relevant since any covert communication will probably be forbidden anyway.

You do need a time source though. GPS is generally used for that but it doesn't need to be extremely accurate with FT-8 like with some other protocols.

I would imagine using it for a regular "I'm ok" message for the home front in such a situation using pre-arranged contents.

At a whole 3kbps and line of sight!

Local police already equipped with signal jammer cars. Usually only used in college entrance exam period. They also appeared in recent protest in Jiangyou city.

Can you recommend a guide? I’m interested in trying it out.

Look up Meshtastic. It’s kinda fun. Can chat with random people around you. But I don’t think it’s really that useful unless you have a really good spot like an antenna on your roof with no trees or buildings in the way.

It's not that finicky in practice. I live in a heavily wooded area and I can still see plenty of nodes, some pretty far away. Trees are actually somewhat helpful there because you can easily rig up a node up high by throwing a line over a branch.

I live in the suburbs, not really any high rises around be but some townhouses, I can “see” 180 nodes, but I can’t reliably message my friend 1km away. I get a lot of messages on the public chat but if I send one it’s a 50/50 if it will be acknowledged by any nodes.

I tried it while staying in a high rise hotel and the experience was great. Instant acknowledgement and super reliable communication

That would be LoRa. LoRA is a different thing.