Wow. Both the receiving and transmitting antennas were omnidirectional. There's no problem doing this with a dish pointed at a dish, but that low power without directional antennas is impressive.
How about while drilling 1000s of meters underground? How do you transmit data back to the surface? This is a problem faced by oil drilling and exploration companies, and they have a solution for it. Take a guess what it is...
Mud modulation.
Basically, while drilling, mud is pumped down the drill string and back out for cooling and cleaning purposes.
Some genius at one of the major oil drilling companies (maybe Schlumberger?) came up with the crazy idea of modulating the mud pressure to transmit information into the depths of the earth. You can control the drill bit speed, angle of drilling, and monitor all sorts of diagnostics over a mud-based communication channel. The bandwidth is decent (think: dial-up), especially when the drilling tools use an efficient modulation scheme.
>Instead, one has to find an area with very low ground conductivity (a requirement opposite to usual radio transmitter sites), bury two huge electrodes in the ground at different sites, and then feed lines to them from a station in the middle, in the form of wires on poles. Although other separations are possible, the distance used by the ZEVS transmitter located near Murmansk is 60 kilometers. As the ground conductivity is poor, the current between the electrodes will penetrate deep into the Earth, essentially using a large part of the globe as an antenna. The antenna length in Republic, Michigan, was approximately 52 kilometers (32 mi).
Radio through the ground was used by radio hams during WWII, because ham radio though the air was prohibited during the war. People would drive two stakes into the ground about 50 feet apart and talk cross-town.
I looked into this "earth mode" radio recently and even tried it out in my backyard without too much success. My question is, does the FCC have jurisdiction over this? Seems like it's not really radio so much as making a circuit using the earth as the conductor.
Agreed, it's not the distance on itself that is impressive, but the fact that it is achieved with very small off-the-shelf hardware, a short piece of wire as antenna, license-exempt ISM band, on a freely available IoT data network that you even can extend by placing a gateway yourself!
The catch is, thanks to Shannon of course, bandwidth. WSPR will do something like 1.46 baud. That and the 13 meter long antenna.