The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth which has an unobstructed view of four or more GPS satellites. GPS is made up of three segments: Space, Control and User.
Galileo is a global navigation satellite system (GNSS) currently being built by the European Union (EU) and European Space Agency (ESA). The €3.4 billion project is an alternative and complementary to the U.S. Global Positioning System (GPS) and the Russian GLONASS. On 30 November 2007 the 27 EU transportation ministers involved reached an agreement that it should be operational by 2013, but later press releases suggest it was delayed to 2014.
Longitude, identified by the Greek letter lambda (λ), is the geographic coordinate most commonly used in cartography and global navigation for east-west measurement. Constant longitude is represented by lines running from north to south. The line of longitude that passes through the Royal Observatory, Greenwich, in England, establishes the meaning of zero degrees of longitude, or the prime meridian.
Time transfer describes methods for transferring reference clock synchronization from one point to another, often over long distances. Radio-based navigation systems are frequently used as time transfer systems. In some cases, multiple measurements are made over a period of time, and exact time synchronization only determined retrospectively.
GLONASS is a radio-based satellite navigation system, developed by the former Soviet Union and now operated for the Russian government by the Russian Space Forces. It is an alternative and complementary to the United States' Global Positioning System (GPS), the Chinese Compass navigation system, and the planned Galileo positioning system of the European Union (EU). Development on the GLONASS began in 1976, with a goal of global coverage by 1991.
Shortwave radio refers to radio broadcasts on a portion of the radio spectrum in the frequency range of 3,000–30,000 kHz. Because smaller wavelengths correspond to higher frequencies (given the inverse relationship between frequency and wavelength), shortwave radio received its name because its wavelengths are shorter than the longer wavelengths used in early radio communications. A longer wavelength example is the medium wave AM broadcast band: 1 MHz = 300 meters.
Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 kHz 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 radio navigation. Also known as the myriametre band or myriametre wave as the wavelengths range from ten to one myriametres (an obsolete metric unit equal to 10 kilometres).
Low frequency or low freq or LF refers to radio frequencies (RF) in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon, navigation, information, and weather systems. Time signal stations MSF, HBG, DCF77, JJY and WWVB are found in this band.
A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may use multiple transmitters, like the Global Positioning System. Such systems may be used to set computer clocks or clocks meant for human readability.
High frequency (HF) radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted Medium-frequency (MF), and the next higher frequencies are known as Very high frequency (VHF). Shortwave (2.310 - 25.820 MHz) overlaps and is slightly lower than HF.
The Time from NPL is a radio signal broadcast from the Anthorn VLF transmitter near Anthorn, Cumbria which serves as the United Kingdom's national time reference. The time signal is derived from three atomic clocks installed at the transmitter site, and is based on time standards maintained by the UK's National Physical Laboratory (NPL) in Teddington. The service is provided by VT Communications under licence from the NPL and is funded by the Department for Innovation, Universities and Skills.
The Greenwich Time Signal (GTS), popularly known as the pips, is a series of six short tones broadcast at one-second intervals by many BBC Radio stations to mark the precise start of each hour. First introduced in 1924, the viability of continued use of the time signal on radio is under discussion, as the unavoidable time lags associated with digital broadcasting systems make its use less feasible as an aid to calibration.
VNG was Australia's national time signal service. It was inaugurated by the Australian Post Office on 21 September 1964. Originally it transmitted on 4500, 7500 and 12000 kHz from Lyndhurst, Victoria. After 1987 it relocated to Shanes Park, NSW, and transmitted on 2500, 5000, 8638, 12984, and 16000 kHz. VNG broadcast time in binary coded decimal, during seconds 21-58. It also broadcast DUT-1 information during seconds 1-16. Tones were usually of 1 kHz.
BPM is the People's Republic of China's national time signal service, operated by the Chinese Academy of Sciences. It broadcasts at 2.5, 5, 10, and 15 MHz. BPM is idiosyncratic in that it transmits UT1 time between minutes 25 through to 29 and 55 through to 59, which creates an odd click-beep effect when heard below a stronger time signal station such as WWV.
WWV is the call sign of the United States National Institute of Standards and Technology's (NIST) shortwave radio station located in Fort Collins, Colorado. WWV's main function is the continuous dissemination of official U.S. Government time signals. The station broadcasts simultaneously on five distinct frequencies: 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz.
WWVH is the callsign of the U.S. National Institute of Standards and Technology's shortwave radio time signal station in Kekaha, on the island of Kauai in the state of Hawaii. Coordinates: 21°59′16″N 159°45′47″W / 21.98778°N 159.76306°W / 21.98778; -159.76306 WWVH is the Pacific sister station to WWV, and has a similar broadcast format to WWV. Like WWV, WWVH's main function is the dissemination of official U.S.
WWVB is a NIST time signal radio station near Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks throughout North America use to synchronize themselves. The signal transmitted from WWVB is a continuous 60 kHz carrier wave, derived from a set of atomic clocks located at the transmitter site.
RWM is the callsign of a shortwave time signal radio station in Moscow, Russia. RWM transmits on 4996 kHz with 5 kW and on 9996 and 14996 kHz with 8 kW. The mode of transmission is N0N and A1A (CW). Between 0 and 8 minutes past the hour, RWM transmits a straight unmodulated carrier wave. At 9 minutes past, RWM identifies itself in Morse code.
JJY is the call sign of a low frequency time signal radio station. The station is located in Japan and broadcasts from two sites, one on Mount Otakadoya, near Fukushima, and the other on Mount Hagane, located on Kyushu Island. JJY is operated by the National Institute of Information and Communications Technology (NICT), an independent administrative institution affiliated with the Ministry of Internal Affairs and Communications of the Japanese government.
DCF77 is a longwave time signal and standard-frequency radio station. Its primary and backup transmitter are located in Mainflingen, about 25 km south-east of Frankfurt, Germany. It is operated by Media Broadcast GmbH (previously a subsidiary of Deutsche Telekom AG), on behalf of the Physikalisch-Technische Bundesanstalt, Germany's national physics laboratory. DCF77 has been in service as a standard-frequency station since 1959; date and time information was added in 1973.
The Beidou Navigation System or Beidou Satellite Navigation and Positioning System is a project by China to develop an independent satellite navigation system. The current Beidou-1 system (made up of 4 satellites) is experimental and has limited coverage and application. However, China has planned to develop a truly global satellite navigation system consisting of 35 satellites (known as Compass or Beidou-2).
YVTO is the callsign of the official time signal from the Juan Manuel Cagigal Naval Observatory in Caracas, Venezuela. The content of YVTO's signal, which is a continuous 1 kW amplitude modulated carrier wave at 5.000 MHz, is much simpler than that broadcast by some of the other time signal stations around the world, such as WWV. The methods of time transmission from YVTO are very limited. The broadcast employs no form of digital time code.