Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals are used, such as for radionavigation. Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... A kilohertz (kHz) is a unit of frequency equal to 1,000 hertz (1,000 cycles per second). ... This article or section does not cite its references or sources. ... A band is a small section of the spectrum of radio communication frequencies, in which channels are usually used or set aside for the same purpose. ... Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... Radio navigation is the application of radio frequencies to determining a position on the earth. ...

Applications

Part of the aerial of Transmitter Grimeton

VLF waves can penetrate water only to a depth of roughly 10 to 40 metres (30 to 130 feet), depending on the frequency and the salinity of the water. They are used to communicate with submarines near the surface. (ELF is used for deeply-submerged vessels.) This frequency range is used for the transmission of instructions to submerged submarines (for example with the transmitter DHO38), since radio waves can penetrate some tens of meters in sea water in this frequency band. They are also used for radio navigation (alpha) and for the transmission of time signals (beta). Early in the history of radio engineering within the band starting from 20 kHz attempts were made to use radiotelephone using amplitude modulation and single-sideband modulation, but the result was unsatisfactory because of the small available bandwidth. The frequency range under 30 kHz also is used for time signals and radio navigation beacons. The very long wave transmitter SAQ at Grimeton near Varberg in Sweden can be visited by the public at certain times, such as on Alexanderson Day. As a rule, very long wave transmitters work in the frequency range between 10 kHz and 30 kHz. There are also stations that work in the frequency range under 10 kHz. This frequency range is subject to no control on the part of the international communications organization (International Telecommunication Union) and may be used in some states license-free. Image:Grimetonmasterna. ... Image:Grimetonmasterna. ... A Yagi-Uda beam antenna Short Wave Curtain Antenna (Moosbrunn, Austria) A building rooftop supporting numerous dish and sectored mobile telecommunications antennas (Doncaster, Victoria, Australia) An antenna or aerial is an arrangement of aerial electrical conductors designed to transmit or receive radio waves which is a class of electromagnetic waves. ... Impact of a drop of water. ... The metre, or meter (U.S.), is a measure of length. ... This article is about a foot as a unit of length. ... Copy of the original phone of Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ... German UC-1 class World War I submarine A model of Günther Priens Unterseeboot 47 (U-47), German WWII Type VII diesel-electric hunter Typhoon class nuclear ballistic missile submarine USS Virginia, a Virginia-class nuclear attack (SSN) submarine A submarine is a specialized watercraft that can operate... An open surface with X-, Y-, and Z-contours shown. ... Extremely low frequency (ELF) is the band of radio frequencies from 3 to 30 Hz. ... The VLF transmitter DHO38 is a VLF transmitter used by the German Navy near Rhauderfehn, Saterland, Germany. ... [[Amplitude modulation]] (AM) is a technique used in electronic communication, most commonly for transmitting information via a carrier wave wirelessly. ... Single-sideband modulation (SSB) is a refinement of the technique of amplitude modulation designed to be more efficient in its use of electrical power and bandwidth. ... VLF transmitter Grimeton The Grimeton VLF transmitter is a VLF transmission facility near Grimeton close to Varberg in Sweden. ... The Alexanderson Day (named after the inventor Ernst Fredrik Werner Alexanderson) is the great day of the open oor at the VLF transmitter Grimeton. ... The International Telecommunication Union (ITU; French: Union internationale des télécommunications, Spanish: Unión Internacional de Telecomunicaciones) is an international organization established to standardize and regulate international radio and telecommunications. ...

In the USA, the time signal station WWVL began transmitting a 500 W signal on 20 kHz in August 1963. It used Frequency Shift Keying (FSK) to send data, shifting between 20 kHz and 26 kHz. The WWVL service was discontinued in July 1972. A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ... It has been suggested that this article or section be merged with audio frequency-shift keying. ...

Many natural radio emissions, such as whistlers, can be also heard in this band. The word emission generally means sending something out. ... A Whistler is a very low frequency radio wave generated by lightning. ...

VLF is also used in Electromagnetic Geophysical Surveys

Details of VLF submarine communication methods

High power land-based transmitters in countries that operate submarines send signals that can be received thousands of miles away. Transmitter sites typically cover many acres, with transmitted power anywhere from 20 kW to 2 MW. Submarines receive the signal using some form of towed antenna which floats just under the surface of the water - for example a BCAA (Buoyant Cable Array Antenna). Modern receivers, such as those produced by Detica, use sophisticated digital signal processing (DSP) techniques to remove the effects of atmospheric noise (largely caused by lightning strikes around the world) and adjacent channel signals, extending the useful reception range. The term DSP, when used by itself, can refer to: // Underground Bhangra DJ Short for Deathlike Silence Productions. ...

Because of the low bandwidth available it is not possible to transmit audio signals, therefore all messaging is done with alphanumeric data at very low bit rates. Three types of modulation are used: In telecommunications, modulation is the process of varying a periodic waveform, i. ...

• OOK / CWK: On-Off Keying / Continuous Wave Keying. Simple Morse code transmission mode where carrier on = mark and off = space. This is the simplest possible form of radio transmission, but it is difficult for transmitters to transmit high power levels, and the signal can easily be swamped by atmospheric noise, so this is only really used for emergencies or basic testing.
• FSK: Frequency-shift keying. The oldest and simplest form of digital radio data modulation. Frequency is increased by 25 Hz (for example) from the carrier to indicate a binary “1” and reduced by 25 Hz to indicate binary “0”. FSK is used at rates of 50 bit/s and 75 bit/s.
• MSK: Minimum-shift keying. A more sophisticated modulation method that uses less bandwidth for a given data rate than FSK. This is the normal mode for submarine communications today, and can be used at data rates up to 300 bit/s.

Two alternative character sets may be used: 5-bit ITA2 or 8-bit ASCII. Since these are military transmissions and are nearly always heavily encrypted, even though it is relatively easy to receive the transmissions and convert them to a string of characters, it is not possible for civilians to read the messages. 1922 Chart of the Morse Code Letters and Numerals Morse code is a method for transmitting information, using standardized sequences of variously spaced short and long elements for the letters, numerals, punctuation, special characters and words of a message. ... It has been suggested that this article or section be merged with audio frequency-shift keying. ... Like the OQPSK modulator (i. ... The Baudot code, named after its inventor Émile Baudot, is a character set predating EBCDIC and ASCII and used originally and primarily on teleprinters. ... There are 95 printable ASCII characters, numbered 32 to 126. ...

PC-based VLF reception

PC based VLF reception is a simple method whereby anyone can pick up VLF signals using the advantages of modern computer technology. An aerial in the form of a coil of insulated wire is connected to the input of the soundcard of the PC (via a jack plug) and placed a few metres away from it. With Fast Fourier transform (FFT) software (e.g.SpecLab). in combination with a sound card allows reception of all frequencies below 24 kilohertz simultaneously in the form of spectrogrammes. Because PC monitors are strong sources of noise in the VLF range, it is recommended to record the spectrograms on hard disk with the PC monitor turned off. These spectrograms show many interesting signals, which may include VLF transmitters, the horizontal electron beam deflection of TV sets and sometimes superpulses and twenty second pulses. A fast Fourier transform (FFT) is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse. ... It has been suggested that this article or section be merged with periodogram. ... Superpulse is the name for very strong radio signals, which are transmitted by the VLF transmitter GBZ and by an unidentified station on 17. ... A twenty second pulse is a pulse signal in the VLF range between 17 kHz and 18 kHz with a duration of 20 seconds. ...

• Using Spectrum Lab for the reception of natural radio - A broadband VLF application.
• Using a PC with soundcard as a VLF receiver - How to use your PC as a receiver for narrow-band signals in the VLF radio spectrum.

List of VLF transmissions

Alpha (also called RSDN-20 ) is a Russian system for long range radio navigation. ... VLF transmitter Grimeton The VLF transmitter Grimeton is a VLF transmission facility near Grimeton close to Varberg in Sweden. ... VLF transmitter Grimeton The VLF transmitter Grimeton is a VLF transmission facility near Grimeton close to Varberg in Sweden. ... The Alexanderson Day (named after the inventor Ernst Fredrik Werner Alexanderson) is the great day of the open oor at the VLF transmitter Grimeton. ... A twenty second pulse is a pulse signal in the VLF range between 17 kHz and 18 kHz with a duration of 20 seconds. ... Superpulse is the name for very strong radio signals, which are transmitted by the VLF transmitter GBZ and by an unidentified station on 17. ... GBZ is the callsign of a British VLF transmitter, which transmits on 19. ... The VLF transmitter Criggion is a VLF transmitter for 19. ... Superpulse is the name for very strong radio signals, which are transmitted by the VLF transmitter GBZ and by an unidentified station on 17. ... Tavolara Island. ... GBZ is the callsign of a British VLF transmitter, which transmits on 19. ... The Anthorn transmitter is a VLF transmitter near Anthorn, Cumbria, which is used for transmitting orders to submarines on 19. ... The VLF transmitter DHO38 is a VLF transmitter used by the German Navy near Rhauderfehn, Saterland, Germany. ... Rhauderfehn is an municipality in Leer district, with approximately 18,000 inhabitants. ...

See also

• OMEGA Navigation System, 1971-1997

Omega is the name for the first truly global radionavigation system for aircraft operated by the United States of America in cooperation with six partner nations. ...

External links

• Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).
• PC-based VLF-reception
• Gallery of VLF-signals
• NASA live streaming ELF -> VLF Receiver
• http://webflash.ess.washington.edu/
• Stanford University VLF group

Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... Extremely low frequency (ELF) is the band of radio frequencies from 3 to 30 Hz. ... Super Low Frequency (SLF) is the frequency range between 30 hertz and 300 hertz. ... Ultra Low Frequency (ULF) is the frequency range between 300 hertz and 3000 hertz. ... Low Frequency or LF refers to Radio Frequencies (RF) in the range of 30–300 kHz. ... Mediumwave radio transmissions (sometimes called Medium frequency or MF) are those between the frequencies of 300 kHz and 3000 kHz. ... High frequency (HF) radio frequencies are between 3 and 30 MHz. ... Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). ... This article is about the radio frequency. ... Microwave Slang for small waves, like at a beach, often used by surfers. ... Extremely high frequency is the highest radio frequency band. ...