Recently some people experimented with LoRa in mines.<p>Seems like the extreme sensitivity (down to -146dBm) is able to deal with the reflections there pretty well down there.<p>But: that's not Through-the-Earth. It's Within-The-Earth.<p>(I have no details regarding the used band, antenna nor exact setup)
> Radio communication within caves is problematic because rock is a conductor and therefore absorbs radio waves.<p>It's funny, I would have bet my house that rock is an insulator.