There's no way this can be blocked by any tyrannical governments either. The governments also use this technology, their facilities are usually a few acres large. But with today's technology you can build one the size of a typical Toolshed.
Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies
from 3 to 30 Hz, and corresponding wavelengths from 100,000 to 10,000 kilometers.
In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands.
1982 aerial view of the U.S. Navy Clam Lake, Wisconsin ELF transmitter facility, used to communicate with deeply submerged submarines.