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Submillimeter Array
The Submillimeter Array (SMA) consists of eight diameter radio telescopes arranged as an interferometer for submillimeter wavelength observations. It is the first purpose-built submillimeter interferometer, constructed after successful interferometry experiments using the pre-existing James Clerk Maxwell Telescope and Caltech Submillimeter Observatory (now decommissioned) as an interferometer. All three of these observatories are located at Mauna Kea Observatory on Mauna Kea, Hawaii, and have been operated together as a ten element interferometer in the 230 and 345 GHz bands (eSMA, for extended Submillimeter Array). The baseline lengths presently in use range from . The radio frequencies accessible to this telescope range from which includes rotational transitions of dozens of molecular species as well as continuum emission from interstellar dust grains. Although the array is capable of operating both day and night, most of the observations take place at nighttime when ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio Telescope
A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects, just as optical telescopes are the main observing instrument used in traditional optical astronomy which studies the light wave portion of the spectrum coming from astronomical objects. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night. Since astronomical radio sources such as planets, stars, nebulas and galaxies are very far away, the radio waves coming from them are extremely weak, so radio telescopes require very large antennas to collect enough radio energy to study them, and extremely sensitive receiving equipment. Radio telescopes are typically large parabolic ("dish") antennas similar to those employed in tracking an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Side Lobe
In antenna engineering, sidelobes are the lobes (local maxima) of the far field radiation pattern of an antenna or other radiation source, that are not the ''main lobe''. The radiation pattern of most antennas shows a pattern of "''lobes''" at various angles, directions where the radiated signal strength reaches a maximum, separated by "''nulls''", angles at which the radiated signal strength falls to zero. This can be viewed as the diffraction pattern of the antenna. In a directional antenna in which the objective is to emit the radio waves in one direction, the lobe in that direction is designed to have a larger field strength than the others; this is the "''main lobe''". The other lobes are called "''sidelobes''", and usually represent unwanted radiation in undesired directions. The sidelobe directly behind the main lobe is called the back lobe. The longer the antenna relative to the radio wavelength, the more lobes its radiation pattern has. In transmitting antenna ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superconducting Tunnel Junction
The superconducting tunnel junction (STJ) — also known as a superconductor–insulator–superconductor tunnel junction (SIS) — is an electronic device consisting of two superconductors separated by a very thin layer of insulating material. Current passes through the junction via the process of quantum tunneling. The STJ is a type of Josephson junction, though not all the properties of the STJ are described by the Josephson effect. These devices have a wide range of applications, including high-sensitivity detectors of electromagnetic radiation, magnetometers, high speed digital circuit elements, and quantum computing circuits. Quantum tunneling All currents flowing through the STJ pass through the insulating layer via the process of quantum tunneling. There are two components to the tunneling current. The first is from the tunneling of Cooper pairs. This supercurrent is described by the ac and dc Josephson relations, first predicted by Brian David Josephson in 196 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SMA230GHzInsert
SMA or S.M.A. may refer to: Places * American Samoa, ITU letter code * Santa Maria Airport (Azores) (IATA code) People * Sergeant Major of the Army, U.S. * Sima (Chinese surname), or Sma * Joshua Falk, known as ''SM"A'' Finance * Separately managed account, types of investment account * Special memorandum account, used regarding US Regulation T Organisations * Scouts Musulmans Algériens, the Algerian Muslim Scouts * Sharjah Museums Authority * SMA Engines, a diesel aircraft engine manufacturer * SMA Solar Technology * Society of African Missions, a Catholic missionary organization * Society of Makeup Artists, post-nominal letters Education * Saint Mary's Academy, Dominica * '' Sekolah Menengah Atas'', Indonesian for "senior secondary school" * San Marcos Baptist Academy, Texas, US * Sarasota Military Academy, Florida, US * Science and Mathematics Academy, a program at Aberdeen High School, Maryland, US * Former Staunton Military Academy, Charles Town, Virginia, US Scie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intermediate Frequency
In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference or beat frequency. Intermediate frequencies are used in superheterodyne radio receivers, in which an incoming signal is shifted to an IF for amplification before final detection is done. Conversion to an intermediate frequency is useful for several reasons. When several stages of filters are used, they can all be set to a fixed frequency, which makes them easier to build and to tune. Lower frequency transistors generally have higher gains so fewer stages are required. It's easier to make sharply selective filters at lower fixed frequencies. There may be several such stages of intermediate frequency in a superheterodyne receiver; t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterodyne
A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called ''heterodyning'', which was invented by Canadian inventor-engineer Reginald Fessenden. Heterodyning is used to shift signals from one frequency range into another, and is also involved in the processes of modulation and demodulation. The two input frequencies are combined in a nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a '' mixer''. In the most common application, two signals at frequencies and are mixed, creating two new signals, one at the sum of the two frequencies , and the other at the difference between the two frequencies . The new signal frequencies are called ''heterodynes''. Typically, only one of the heterodynes is required and the other signal is filtered out of the output of the mixer. Heterodyne frequencies are related to the phenomenon of "beats" in acoustics. A major a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Local Oscillator
In electronics, a local oscillator (LO) is an electronic oscillator used with a mixer to change the frequency of a signal. This frequency conversion process, also called heterodyning, produces the sum and difference frequencies from the frequency of the local oscillator and frequency of the input signal. Processing a signal at a fixed frequency gives a radio receiver improved performance. In many receivers, the function of local oscillator and mixer is combined in one stage called a " converter" - this reduces the space, cost, and power consumption by combining both functions into one active device. Applications Local oscillators are used in the superheterodyne receiver, the most common type of radio receiver circuit. They are also used in many other communications circuits such as modems, cable television set top boxes, frequency division multiplexing systems used in telephone trunklines, microwave relay systems, telemetry systems, atomic clocks, radio telescopes, and milita ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single-mode Optical Fiber
In fiber-optic communication, a single-mode optical fiber (SMF), also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode of light - the transverse mode. Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions. These modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves can have the same mode but have different frequencies. This is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, and that gives us a single ray of light. Although the ray travels parallel to the length of the fiber, it is often called transverse mode since its electromagnetic oscillations occur perpendicular (transverse) to the length of the fiber. The 2009 Nobel Prize in Physics was awarded to Charles K. Kao for hi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET. The original 10BASE5 Ethernet uses coaxial cable as a shared medium, while the newer Ethernet variants use twisted pair and fiber optic links in conjunction with switches. Over the course of its history, Ethernet data transfer rates have been increased from the original to the latest , with rates up to under development. The Ethernet standards include several wiring and signaling variants of the OSI physical layer. Systems communicating over Ethernet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multi-mode Optical Fiber
Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 100 Gbit/s. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion. The standard G.651.1 defines the most widely used forms of multi-mode optical fiber. Applications The equipment used for communications over multi-mode optical fiber is less expensive than that for single-mode optical fiber. Typical transmission speed and distance limits are 100 Mbit/s for distances up to 2 km (100BASE-FX), 1 Gbit/s up to 1000 m, and 10 Gbit/s up to 550 m. Because of its high capacity and reliability, multi-mode optical fiber generally is used for backbone applications in buildings. An increasing number of users are taking the benefits of fiber closer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
