Ultra Low Frequency (ULF)] comprises the frequency range between 300 and 3000 hertz (3 Kilohertz). This band is used for communications in mines for its ability to easily penetrate the earth's surface.

Do not confuse ULF with UHF, since the latter is used, for example, in the receivers of television by air (that use antennas receiving of the channels by air), and goes of the 470 MHz to 890 MHz.

On the back of certain tube TVs you will find the acronym or UHF denomination, or similar variants, that indicate the type of frequency that your TV receiver uses. Earth Mode Communications

ULF has been used by military forces for secure communications across the land. The NATO AGARD publications of the '60s detailed many systems, despite the suspicion of many things not commented because of their military interest.

Communications across the land using driving fields is known as "Earth Mode" and was used for the first time in World War I. Amateur radio and electronics specialists used this system for limited communications using radio amplifiers connected to electrodes inserted into the ground.

The amplitude range of waves that comprise the ULF is as follows:

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