Frequency Standard

	Frequency Standard A frequency standard is a stable oscillator used for frequency calibration or reference. A frequency standard generates a fundamental frequency with a high degree of accuracy and precision. Harmonics of this fundamental frequency are used to provide reference points. Since time is the reciprocal of frequency, it is relatively easy to derive a time standard from a frequency standard. A standard clock comprises a frequency standard, a device to count off the cycles of the oscillation emitted by the frequency standard, and a means of displaying or outputting the result. Frequency standards in a network or facility are sometimes administratively designated as ''primary'' or ''secondary''. The terms ''primary'' and ''secondary'', as used in this context, should not be confused with the respective technical meanings of these words in the discipline of precise time and frequency. Frequency reference A frequency reference is an instrument used for providing a stable frequency of so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Early NBS Crystal Oscillator Frequency Standards Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: Early Christianity Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early Branch, a stream in Missouri * Early County, Georgia Other uses * ''Early'' (Scritti Politti album), 2005 * ''Early'' (A Certain Ratio album), 2002 * Early (name) * Early effect, an effect in transistor physics * Early Records, a record label * the early part of the morning See also * Earley (other) Earley is a town in England. Earley may also refer to: * Earley (surname), a list of people with the surname Earley * Earley (given name), a variant of the given name Earlene * Earley Lake, a lake in Minnesota Earley parser, an algorithm Earley ... {{disambiguation, geo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Atomic Fountain An atomic fountain is a cloud of atoms that is tossed upwards in the Earth's gravitational field by lasers. If it were visible, it would resemble the water in a fountain. While weightless in the toss, the atoms are measured to set the frequency of an atomic clock.https://www.nist.gov/public_affairs/releases/n99-22.cfm How the NIST-F1 Caesium Fountain Clock Works The primary motivation behind the development of the atomic fountain derives from the Ramsey method of measuring the frequency of atomic transitions. In broad strokes, the Ramsey method involves exposing a cloud of atoms to a brief radiofrequency (rf) electromagnetic field; waiting a time ''T''; briefly exposing the cloud to the rf field again; and then measuring what fraction of the atoms in the cloud have transitioned. If the frequency of the rf field is identical to the atomic transition frequency, 100% of the atoms will have transitioned; if the frequency of the field differs slightly from the transition frequency, so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Standard Frequency And Time Signal Service Standard frequency and time signal service (short: SFTS) is, according to Article 1.53 of the International Telecommunication Union's (ITU) Radio Regulations (RR),ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.53, definition: ''standard frequency and time signal service'' "A radiocommunication service for scientific, technical and other purposes, providing the transmission of specified frequencies, time signals, or both, of stated high precision, intended for general reception". Classification In accordance with ''ITU Radio Regulations'' (article 1) variations of this ''radiocommunication service'' are classified as follows: Standard frequency and time signal service (article 1.53) * Standard frequency and time signal-satellite service In general this ''radiocommunication service '' uses radio stations as follows: * Standard frequency and time signal stations (article 1.95) Frequency allocation The allocation of radio frequencies is provided acc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Rubidium Standard A rubidium standard or rubidium atomic clock is a frequency standard in which a specified hyperfine transition of electrons in rubidium-87 atoms is used to control the output frequency. Synopsis The Rb standard is the most inexpensive, compact, and widely produced atomic clock, used to control the frequency of television stations, cell phone base stations, in test equipment, and global navigation satellite systems like GPS. Commercial rubidium clocks are less accurate than caesium atomic clocks, which serve as primary frequency standards, so the rubidium clock is a secondary frequency standard. All commercial rubidium frequency standards operate by disciplining a crystal oscillator to the rubidium hyperfine transition of 6.8 GHz (). The intensity of light from a rubidium discharge lamp that reaches a photodetector through a resonance cell will drop by about 0.1% when the rubidium vapor in the resonance cell is exposed to microwave power near the transition frequency. The cry ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Atomic Clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions between such states they interact with a very specific frequency of electromagnetic radiation. This phenomenon serves as the basis for the International System of Units' (SI) definition of a second:The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, \Delta \nu_\mathsf, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be when expressed in the unit Hz, which is equal to s−1. This definition is the basis for the system of International Atomic Time (TAI), which is maintained by an ensemble of atomic clocks around the world. The system of Coordinated Universal Time, Coordinated Universal Time (UTC) that is the basis of civil time implements ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Mediumwave Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band. During the daytime, reception is usually limited to more local stations, though this is dependent on the signal conditions and quality of radio receiver used. Improved signal propagation at night allows the reception of much longer distance signals (within a range of about 2,000 km or 1,200 miles). This can cause increased interference because on most channels multiple transmitters operate simultaneously worldwide. In addition, amplitude modulation (AM) is often more prone to interference by various electronic devices, especially power supplies and computers. Strong transmitters cover larger areas than on the FM broadcast band but require more energy and longer antennas. Digital modes are possible but have not reached momentum yet. MW was the main radio ban ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Longwave In radio, longwave, long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium-wave broadcasting band. The term is historic, dating from the early 20th century, when the radio spectrum was considered to consist of longwave (LW), medium-wave (MW), and short-wave (SW) radio bands. Most modern radio systems and devices use wavelengths which would then have been considered 'ultra-short'. In contemporary usage, the term ''longwave'' is not defined precisely, and its intended meaning varies. It may be used for radio wavelengths longer than 1,000 m i.e. frequencies up to 300 kilohertz (kHz), including the International Telecommunication Union's (ITU's) low frequency (LF, 30–300 kHz) and very low frequency (VLF, 3–30 kHz) bands. Sometimes the upper limit is taken to be higher than 300 kHz, but not above the start of the medium wave broadcast band at 520&nb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]