Ultra low frequency

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Ultra low frequency
Frequency range
0.3 to 3
km
Radio bands
ITU
1 (ELF) 2 (SLF) 3 (ULF) 4 (VLF)
5 (LF) 6 (MF) 7 (HF) 8 (VHF)
9 (UHF) 10 (SHF) 11 (EHF) 12 (THF)
EU / NATO / US ECM
IEEE
Other TV and radio
Listening to 500 Hz signal of Ambrose Channel pilot cable in 1920

Ultra low frequency (ULF) is the ITU designation[1] for the frequency range of electromagnetic waves between 300 hertz and 3 kilohertz, corresponding to wavelengths between 1,000 to 100 km. In magnetosphere science and seismology, alternative definitions are usually given, including ranges from 1 mHz to 100 Hz,[2] 1 mHz to 1 Hz,[3] and 10 mHz to 10 Hz.[4]

Many types of waves in the ULF frequency band can be observed in the

Alfvén velocity
that depends on the ambient magnetic field and plasma mass density.

This band is used for communications in mines, as it can penetrate the earth.[5]

Earthquakes

Some monitoring stations have reported that

earthquakes are sometimes preceded by a spike in ULF activity. A remarkable example of this occurred before the 1989 Loma Prieta earthquake in California,[6] although a subsequent study indicates that this was little more than a sensor malfunction.[7] On December 9, 2010, geoscientists announced that the DEMETER satellite observed a dramatic increase in ULF radio waves over Haiti in the month before the magnitude 7.0 Mw 2010 earthquake.[8]
Researchers are attempting to learn more about this correlation to find out whether this method can be used as part of an early warning system for earthquakes.

Earth mode communications

ULF has been used by the military for

Radio amateurs and electronics hobbyists have used this mode for limited range communications using audio power amplifiers connected to widely spaced electrode pairs hammered into the soil. At the receiving end, the signal is detected as a weak electric current between a further pair of electrodes. Using weak signal reception methods with PC-based DSP filtering with extremely narrow bandwidths, it is possible to receive signals at a range of a few kilometers with a transmitting power of 10–100 W and electrode spacing of around 10–50 m.[citation needed
]

See also

References

  1. ^ "Rec. ITU-R V.431-7, Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). ITU. Archived from the original (PDF) on 31 October 2013. Retrieved 20 February 2013.
  2. doi:10.1016/0021-9169(90)90087-4
    .
  3. doi:10.1007/s11214-008-9333-4
    .
  4. ^ O. Molchanov, A. Schekotov, E. Fedorov, G. Belyaev, and E. Gordeev, "Preseismic ULF electromagnetic effect from observation at Kamchatka", Natural Hazards and Earth System Sciences, Volume 3, pp. 203–209, 2003
  5. ^ HF and Lower Frequency Radiation - Introduction Archived 2005-11-09 at the Wayback Machine
  6. OCLC 1795290
    . Retrieved December 18, 2010.
  7. doi:10.1016/j.pepi.2008.11.014
    .
  8. ^ KentuckyFC (December 9, 2010). "Spacecraft Saw ULF Radio Emissions over Haiti before January Quake". Cambridge, Massachusetts: MIT Technology Review. Retrieved December 18, 2010.

External articles

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