Ultra low frequency

Ultra low frequency

The Ultra Low Frequency (ULF) is the frequency range between 300 hertz and 3 kilohertz. Many types of waves in the ULF frequency band can be observed in the magnetosphere and on the ground. These waves represent important physical processes in the near-Earth plasma environment. The speed of the ULF waves is often associated with the Alfven 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. [ [http://www.weather.nps.navy.mil/~psguest/EMEO_online/module3/module_3_1.html HF and Lower Frequency Radiation - Introduction ] ]

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 Loma Prieta Earthquake in California in 1989. 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 secure communications through the ground. NATO AGARD publications from the 1960s detailed many such systems, although one suspects the contents of the published papers left a lot unsaid about what actually was developed secretly for defense purposes. Communications through the ground using conduction fields is known as "Earth Mode" communications and was first used in WWI. 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 two further pairs 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 10-100W and electrode spacing of around 10-50m.

ee also

*Voice frequency

References

External articles

* Tomislav Stimac, " [http://www.vlf.it/frequency/bands.html Definition of frequency bands (VLF, ELF... etc.)] ". IK1QFK Home Page (vlf.it).
* [http://spaceweather.com/glossary/inspire.html NASA live streaming ELF -> VLF Receiver]
* Amateur Radio Below 10kHz " [http://homepage.ntlworld.com/lapthorn/earthmode.htm G3XBM's page on Earth Mode Communication] "
* Review of Earth Mode Communications " [http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD0640319 1966 abstract about Earth Mode Comms by Ames, Frazier and Orange] "
* Radio communications within the earth's crust " [http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1138037 Abstract of article by Burrows written in 1963] "


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • ultra low frequency — noun any radiofrequency between 300 and 3000 hertz. Abbrev.: ULF …  

  • Ultra high frequency — (UHF) designates a range (band) of electromagnetic waves with frequencies between 300 MHz and 3 GHz (3,000 MHz). Also known as the decimeter band or decimeter wave as the wavelengths range from ten to one decimeters. Radio waves with frequencies… …   Wikipedia

  • extremely low frequency — ypač žemas dažnis statusas T sritis radioelektronika atitikmenys: angl. extremely low frequency vok. Tiefstfrequenz, f rus. сверхнизкая частота, f pranc. fréquence ultra basse, f …   Radioelektronikos terminų žodynas

  • Consumer Ultra-Low Voltage — (CULV) is a computing platform developed by Intel.[1][2] It has been estimated that this market could reach 10 million CULV laptops shipped within 2009.[3] Competing platforms are the VIA Nano, AMD Yukon, AMD Nile notebook platform, and graphic… …   Wikipedia

  • Ultra basse frequence — Ultra basse fréquence On appelle ultra basse fréquence (ULF), Ultra low frequency en anglais, la bande de radiofréquences qui s étend de 300 à 3 000 Hz (longueur d onde de 1 000 à 100 km). Quand il ne s agit pas d ondes… …   Wikipédia en Français

  • Ultra basse fréquence (ULF) — Ultra basse fréquence On appelle ultra basse fréquence (ULF), Ultra low frequency en anglais, la bande de radiofréquences qui s étend de 300 à 3 000 Hz (longueur d onde de 1 000 à 100 km). Quand il ne s agit pas d ondes… …   Wikipédia en Français

  • very low frequency antenna — labai žemų dažnių antena statusas T sritis radioelektronika atitikmenys: angl. very low frequency antenna vok. Ultralangwellenantenne, f rus. антенна диапазона очень низких частот, f pranc. antenne pour ondes ultra longues, f …   Radioelektronikos terminų žodynas

  • Ultra baja frecuencia — (Siglas en inglés Ultra Low Frequency (ULF) comprende el rango de frecuencias entre 300 y 3000 hercios (3 Kilohercios). Esta banda es utilizada para comunicaciones en minas por su capacidad de penetrar fácilmente la superficie terrestre. No… …   Wikipedia Español

  • Ultra basse fréquence — On appelle ultra basse fréquence (ULF), Ultra low frequency en anglais, la bande de radiofréquences qui s étend de 300 à 3 000 Hz (longueur d onde de 1 000 à 100 km). Quand il ne s agit pas d ondes radioélectriques, ces… …   Wikipédia en Français

  • Frequency Specific Microcurrent — is a therapy based on neutralizing and eliminating disease radiations through the use of electronic equipment. The effect is achieved through neutralizing those frequencies that are alleged to be incorrect for the damaged or affected… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”