Very low frequency (VLF) refers to radio waves with frequencies between 3kHz and 30kHz. VLF is used for communication with submarines due to its ability to travel deep in water and underground. VLF is not commonly used for other types of communication due to its low frequency.
Very low frequency (VLF) is the term used to describe a range of sounds transmitted across a particular radio band. Specifically, very low frequency refers to all radio waves that have frequencies between 3 kilohertz (kHz) and 30 kHz. These are called very low, as the frequencies used to communicate range from 3 hertz (Hz) to 300 gigahertz (GHz).
The International Telecommunication Union regulates radio band frequencies and has a standard for the designation of each frequency band. VLF is not the lowest of the frequency bands. There are three frequency bands that fall even short of this designation, namely ultra low frequency (ULF), super low frequency (SLF), and extremely low frequency (ELF). These three frequency bands cover the spectrum from the bottom 3Hz of usable radio frequencies up to 3kHz, which is the lowest frequency in the very low frequency band.
Each of the different frequency bands has sounds with a range of wavelengths. Within the VLF, wavelengths can range from about 62 miles (100 km) for sound with a frequency of 3 kHz to about 6.2 miles (10 km) for sound with a frequency of 30 kHz. The different frequency bands for radio waves are used in different ways by government, military and public use.
Frequencies transmitted in the very low frequency range are rarely picked up by the antennas used for most communications. This is because most radio communications, including radio station broadcasts and telephone communications, are found in much higher frequency ranges. The antennas used for higher frequencies are improved to pick up those signals better and make sounds clearer.
There are antennas and VLF stations all over the world and these types of signals can be transmitted all over the world. Very low frequency messages are used in a range of different applications due to the behavior of sound waves present in this radio frequency band. The fact that the sound waves found within VLF emissions have long wavelengths means that the sounds can be heard deep in the water and even far underground.
While very low frequency signals are used for many different reasons, probably the most common is to provide a means of communication with submarines underwater. The amount of salt found in seawater affects how deep VLF sounds can travel when sent from the surface. The depth within the water that can be penetrated by the VLF ranges from 30 to 130 feet (10 to 40 meters). In addition to providing a method of communication, the VLF can also be used to help submarines navigate when submerged in the ocean.
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