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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. Fast Fourier transform (FFT) software 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. 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. Also known as the myriameter band or myriameter wave as the wavelengths range from ten to one myriameters (an obsolete metric unit equal to 10 kilometers). VLF waves can penetrate water to a depth of roughly 10 to 40 metres (30 to 130 feet), depending on the frequency and the salinity of the water. VLF is used to communicate with submarines near the surface (for example using the transmitter DHO38), while ELF is used for deeply-submerged vessels. VLF is also used for radio navigation beacons (alpha) and time signals (beta). VLF is also used in eletromagnetic geophysical surveys. [1] 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 below 9kHz is not allocated by the International Telecommunication Union and may be used in some nations license-free. Many natural radio emissions, such as whistlers, can also be heard in this band. 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. 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. List of VLF transmissions Callsign Frequency Location of transmitter Remarks - 11.905 kHz Russia (various locations) Alpha-Navigation - 12.649 kHz Russia (various locations) Alpha-Navigation - 14.881 kHz Russia (various locations) - 15.625 kHz - Frequency for horizontal deflection of electron beam of TV sets (PAL) - 15.734 kHz - Frequency for horizontal deflection of electron beam of TV sets (NTSC) GBR 15.8 kHz Rugby, England (Regular transmissions ceased April 2003) Many publications listed its frequency as 16 kHz JXN 16.4 kHz Helgeland (Norway) SAQ 17.2 kHz Grimeton (Sweden) Only active at special occasions (Alexanderson Day) - ca. 17.5 kHz ? Twenty second pulses ? 17.8 kHz ? Transmits occasionally Superpulses RDL/UPD/UFQE/UPP/UPD8 18.1 kHz Russia (various locations) HWU 18.3 kHz Le Blanc (France) Frequently inactive for longer periods RKS 18.9 kHz Russia (various locations) Rarely active GBZ 19.6 kHz Criggion (Britain) Many operation modes, even Superpulses. Closed 2003. NWC 19.8 kHz Exmouth, Western Australia (AUS) Used for submarine communication, 1 megawatt. ICV 20.27 kHz Tavolara (Italia) RJH63, RJH66, RJH69, RJH77, RJH99 20.5 kHz Russia (various locations) Time signal transmitter Beta ICV 20.76 kHz Tavolara (Italia) HWU 20.9 kHz Le Blanc (France) RDL 21.1 kHz Russia (various locations) rarely active HWU 21.75 kHz Le Blanc (France) GBZ 22.1 kHz Anthorn (Britain) - 22.2 kHz Ebino (Japan) ? 22.3 kHz Russia? Only active on 2nd of each month for a short period between 11:00 and 13:00 (respectively 10:00 and 12:00 in winter), if 2nd of each month is not a Sunday RJH63, RJH66, RJH69, RJH77, RJH99 23 kHz Russia (various locations) Time signal transmitter Beta DHO38 23.4 kHz near Rhauderfehn (Germany) submarine communication NAA 24 kHz Cutler, Maine (USA) Used for submarine communication, at 2 megawatts, it is the most powerful station in the world
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