Super low frequency
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Frequency range
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30 to 300 Hz
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Wavelength range
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10,000 to 1,000 km
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Super low frequency (SLF) is the ITU designation[1] for electromagnetic waves (radio waves) in the frequency range between 30 hertz and 300 hertz. They have corresponding wavelengths of 10,000 to 1,000 kilometers. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz). Another conflicting designation which includes this frequency range is Extremely Low Frequency (ELF), which in some contexts refers to all frequencies up to 300 hertz.
Because of the extreme difficulty of building transmitters that can generate such long waves, frequencies in this range have been used in very few manmade communication systems. However, SLF waves can penetrate seawater to a depth of hundreds of meters. Therefore, in recent decades the U.S., Russian and Indian military have built huge radio transmitters using SLF frequencies to communicate with their submarines.[2] The U.S. naval service is called Seafarer and operates at 76 hertz. It became operational in 1989 but was discontinued in 2004 due to advances in VLF communication systems. The Russian service is called ZEVS and operates at 82 hertz. The Indian Navy has an operational ELF communication facility at the INS Kattabomman naval base to communicate with its Arihant class and Akula class submarines.[2][3]
The requirements for receivers at SLF frequencies is less stringent than transmitters, because the signal strength (set by atmospheric noise) is far above the noise floor of the receiver, so small, inefficient antennas can be used. Radio amateurs have received signals in this range using simple receivers built around personal computers, with coil or loop antennas connected to the PCs sound card. Signals are analysed by a software fast Fourier transform algorithm and converted into audible sound.[4]
See also
External articles
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Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).
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NASA live streaming ELF -> VLF Receiver
References
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^ "Rec. ITU-R V.431-7, Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). ITU. Retrieved 20 February 2013.
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^ a b "Navy gets new facility to communicate with nuclear submarines prowling underwater".
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^ http://www.janes.com/article/11147/india-makes-headway-with-elf-site-construction
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^ "Radio waves below 22 kHz".
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ELF
3 Hz/100 Mm
30 Hz/10 Mm
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SLF
30 Hz/10 Mm
300 Hz/1 Mm
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ULF
300 Hz/1 Mm
3 kHz/100 km
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VLF
3 kHz/100 km
30 kHz/10 km
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LF
30 kHz/10 km
300 kHz/1 km
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MF
300 kHz/1 km
3 MHz/100 m
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HF
3 MHz/100 m
30 MHz/10 m
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VHF
30 MHz/10 m
300 MHz/1 m
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UHF
300 MHz/1 m
3 GHz/100 mm
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SHF
3 GHz/100 mm
30 GHz/10 mm
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EHF
30 GHz/10 mm
300 GHz/1 mm
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THF
300 GHz/1 mm
3 THz/0.1 mm
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