What Does Extremely Low Frequency (ELF) Mean?
Extremely low frequency (ELF) is the designation given by the International Telecommunication Union (ITU) for radio waves or electromagnetic radiation with frequencies that range from just 3 Hz to 30 Hz and with corresponding wavelengths. But in atmospheric science, ELF is alternatively given a range of 3 Hz to 3,000 Hz. ELF signals are usually generated by naturally occurring phenomena such as lightning strikes and natural disturbances in the earth. Electric power lines also give out ELF waves.
Techopedia Explains Extremely Low Frequency (ELF)
Extremely low frequency, as the name suggests, are EM waves with very low frequencies, which mean that their wavelengths are extremely long. This also requires very wide antennas, about 2,175 to 3,700 miles (3500 to 6000 km) wide, to create the signals. Techniques such as electrical lengthening help to create radio stations with smaller sizes but the power requirement to run the system is still quite considerable, partly because the systems are inefficient. The U.S. has made the only two ELF stations ever created, but were decommissioned in September 2004.
