Extremely Low Frequency system Dear Ms. Mahon: Thank you for
your letter inquiring about the Extremely Low Frequency system.
Fermilab is not involved in this project, but I think I still
can help you. Searching the Internet, I found information on the
ELF system operated by the U.S. Navy. It is actually not an
underground cable but rather an above-ground antenna consisting
of two "branches." Electrical currents flow from one "branch"
through the ground to the other "branch." Flowing back and
forth, the currents create oscillating fields. Because of the
current flowing through the ground, you thought that there is a
cable. Instead, the Navy just relies on the ground. Choosing
sites with low conductivity rock near the surface, the currents
penetrate the ground hundreds of meters before returning to the
opposite branch above ground. Since the total length of the ELF
antenna (including the long path through the ground) is so huge,
the antenna is able to create electromagnetic waves with an
extremely low frequency