ELF radio

We give a brief overview of the various phenomena which may he observed in the ELF (extremely low frequency: 3 Hz to 3 kHz) spectral region, terrestrial ELF propagation theory, and discuss applications which make use of the unique characteristics of ELF propagation. The paper is addressed to a non-specialist audience. Our aim is to present a concise summary of the history of ELF to date and to identify books, seminal papers and reviews. Radio waves in the ELF band have been exploited since the 1920s. From these early years, interests in ELF were both practical and scientific. Practical applications of ELF terrestrial wave propagation through the Earth's atmosphere owe much to observations of the fields radiated by lightning.