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41-570: The JITC had its roots in the TRI-TAC program of the 1970s, which sought to streamline and test the technology behind field and tactical command systems. The program began officially in 1971, and work started in 1976 at Fort Huachuca in southern Arizona. The TRI-TAC program tested various field equipment for years, but ran into problems with working with other branches of the Department of Defense's testing programs. With an eye to fix this problem,

82-415: A burning glass . Parabolic reflectors are popular for use in creating optical illusions . These consist of two opposing parabolic mirrors, with an opening in the center of the top mirror. When an object is placed on the bottom mirror, the mirrors create a real image , which is a virtually identical copy of the original that appears in the opening. The quality of the image is dependent upon the precision of

123-430: A hemisphere ( 2 3 π R 2 D , {\textstyle ({\frac {2}{3}}\pi R^{2}D,} where D = R ) , {\textstyle D=R),} and a cone ( 1 3 π R 2 D ) . {\textstyle ({\frac {1}{3}}\pi R^{2}D).} π R 2 {\textstyle \pi R^{2}}

164-471: A parabola revolving around its axis. The parabolic reflector transforms an incoming plane wave travelling along the axis into a spherical wave converging toward the focus. Conversely, a spherical wave generated by a point source placed in the focus is reflected into a plane wave propagating as a collimated beam along the axis. Parabolic reflectors are used to collect energy from a distant source (for example sound waves or incoming star light). Since

205-493: A 20 feet (6.1 m). Quick Reaction Satellite Antenna Group (QRSAG) antenna, while the outlying spoke terminals rely on an 8 feet (2.4 m) parabolic dish antenna. Today, much of the TRI-TAC and GMF equipment is obsolete – its bulky circuit-switched equipment having been replaced in the last decade by fly-away quad-band systems containing compact IP-based routers, switches, and encryption equipment. There were, however,

246-416: A mirror that was parabolic would correct spherical aberration as well as the chromatic aberration seen in refracting telescopes . The design he came up with bears his name: the " Gregorian telescope "; but according to his own confession, Gregory had no practical skill and he could find no optician capable of actually constructing one. Isaac Newton knew about the properties of parabolic mirrors but chose

287-420: A narrow beam of radio waves for point-to-point communications in satellite dishes and microwave relay stations, and to locate aircraft, ships, and vehicles in radar sets. In acoustics , parabolic microphones are used to record faraway sounds such as bird calls , in sports reporting, and to eavesdrop on private conversations in espionage and law enforcement. Strictly, the three-dimensional shape of

328-420: A number of GMF terminals still supporting active forces in the extreme operating conditions of Iraq and Afghanistan. Parabolic reflector A parabolic (or paraboloid or paraboloidal ) reflector (or dish or mirror ) is a reflective surface used to collect or project energy such as light , sound , or radio waves . Its shape is part of a circular paraboloid , that is, the surface generated by

369-583: A reflector must be correct to within about 20 nm. For comparison, the diameter of a human hair is usually about 50,000 nm, so the required accuracy for a reflector to focus visible light is about 2500 times less than the diameter of a hair. For example, the flaw in the Hubble Space Telescope mirror (too flat by about 2,200 nm at its perimeter) caused severe spherical aberration until corrected with COSTAR . Microwaves, such as are used for satellite-TV signals, have wavelengths of

410-416: A spherical shape for his Newtonian telescope mirror to simplify construction. Lighthouses also commonly used parabolic mirrors to collimate a point of light from a lantern into a beam, before being replaced by more efficient Fresnel lenses in the 19th century. In 1888, Heinrich Hertz , a German physicist, constructed the world's first parabolic reflector antenna. The most common modern applications of

451-462: Is a paraboloidal mirror which is rotated about axes that pass through its centre of mass, but this does not coincide with the focus, which is outside the dish. If the reflector were a rigid paraboloid, the focus would move as the dish turns. To avoid this, the reflector is flexible, and is bent as it rotates so as to keep the focus stationary. Ideally, the reflector would be exactly paraboloidal at all times. In practice, this cannot be achieved exactly, so

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492-637: Is configured for 16 or 32 kbit/s, which with overhead translates to 48 kbit/s true capacity. The 93B/94A terminals have a capacity of 24 16/32 kbit/s multiplexed channels. All of the GMF terminals have external connections for an AN/TSQ-111 Tech Control Facility, field phones, or a 70 MHz IF wideband input, plus are sealed for sustained operations in a chemical/biological/radiological (CBR) environment. GMF communicates via Super High Frequency (SHF) X-band Defense Satellite Communication System (DSCS) satellites. The 85B/100A hub terminals typically use

533-653: Is configured in a hub-spoke arrangement with the hub terminal being able to ingest four feeds from the outlying spoke terminals. Of the four designated GMF terminals, the AN/TSC-85B and AN/TSC-100A are equipped for point-to-point or hub operations and the AN/TSC-93B and AN/TSC-94A are spoke terminals. The 85B/100A hubs are capable of ingesting up to 48 multiplexed and encrypted channels from a maximum of four spoke terminals simultaneously, but can double that capability with an external multiplexer (96 channels). Each channel

574-462: Is greatest, and where the axis of symmetry intersects the paraboloid. However, if the reflector is used to focus incoming energy onto a receiver, the shadow of the receiver falls onto the vertex of the paraboloid, which is part of the reflector, so part of the reflector is wasted. This can be avoided by making the reflector from a segment of the paraboloid which is offset from the vertex and the axis of symmetry. The whole reflector receives energy, which

615-457: Is offset from the axis of rotation. To make less accurate ones, suitable as satellite dishes, the shape is designed by a computer, then multiple dishes are stamped out of sheet metal. Off-axis-reflectors heading from medium latitudes to a geostationary TV satellite somewhere above the equator stand steeper than a coaxial reflector. The effect is, that the arm to hold the dish can be shorter and snow tends less to accumulate in (the lower part of)

656-421: Is rotated around axes that pass through the focus and around which it is balanced. If the dish is symmetrical and made of uniform material of constant thickness, and if F represents the focal length of the paraboloid, this "focus-balanced" condition occurs if the depth of the dish, measured along the axis of the paraboloid from the vertex to the plane of the rim of the dish, is 1.8478 times F . The radius of

697-681: Is the aperture area of the dish, the area enclosed by the rim, which is proportional to the amount of sunlight the reflector dish can intercept. The area of the concave surface of the dish can be found using the area formula for a surface of revolution which gives A = π R 6 D 2 ( ( R 2 + 4 D 2 ) 3 / 2 − R 3 ) {\textstyle A={\frac {\pi R}{6D^{2}}}\left((R^{2}+4D^{2})^{3/2}-R^{3}\right)} . providing D ≠ 0 {\textstyle D\neq 0} . The fraction of light reflected by

738-411: Is the focal length, D {\textstyle D} is the depth of the dish (measured along the axis of symmetry from the vertex to the plane of the rim), and R {\textstyle R} is the radius of the dish from the center. All units used for the radius, focal point and depth must be the same. If two of these three quantities are known, this equation can be used to calculate

779-570: Is then focused onto the receiver. This is frequently done, for example, in satellite-TV receiving dishes, and also in some types of astronomical telescope ( e.g. , the Green Bank Telescope , the James Webb Space Telescope ). Accurate off-axis reflectors, for use in solar furnaces and other non-critical applications, can be made quite simply by using a rotating furnace , in which the container of molten glass

820-459: The Siege of Syracuse . This seems unlikely to be true, however, as the claim does not appear in sources before the 2nd century CE, and Diocles does not mention it in his book. Parabolic mirrors and reflectors were also studied extensively by the physicist Roger Bacon in the 13th century AD. James Gregory , in his 1663 book Optica Promota (1663), pointed out that a reflecting telescope with

861-427: The natural logarithm of x , i.e. its logarithm to base " e ". The volume of the dish is given by 1 2 π R 2 D , {\textstyle {\frac {1}{2}}\pi R^{2}D,} where the symbols are defined as above. This can be compared with the formulae for the volumes of a cylinder ( π R 2 D ) , {\textstyle (\pi R^{2}D),}

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902-926: The Fort Huachuca operations into the Joint Interoperability Test Center (also abbreviated as JITC – somewhat confusingly – but not the same as the Joint Interoperability Test Command). Operations were further consolidated in 1988, and then in 1989 the Test Center gained its final name of the Joint Interoperability Test Command (JITC). These final rounds of consolidation were concurrent with a Department of Defense push towards "interoperability", which aimed to ensure that military technology could work across branches of

943-643: The Joint Service program called TRI-TAC developed by GTE-Sylvania in the mid-1970s. The Tri-Service Tactical signal system is a tactical command, control, and communications program. It is a joint service effort to develop and field advanced tactical and multichannel switched communications equipment. The program was conceived to achieve interoperability between service tactical communications systems, establish interoperability with strategic communications systems, take advantage of advances in technology, and eliminate duplication in service acquisitions. GMF

984-479: The Scheffler reflector is not suitable for purposes that require high accuracy. It is used in applications such as solar cooking , where sunlight has to be focused well enough to strike a cooking pot, but not to an exact point. A circular paraboloid is theoretically unlimited in size. Any practical reflector uses just a segment of it. Often, the segment includes the vertex of the paraboloid, where its curvature

1025-569: The TRI-TAC program was rebranded and refocused in 1984 to become the Joint Tactical Command, Control, and Communications Agency (JTC3A). This led to the Fort Huachuca part of the operations to be renamed as the Joint Interoperability Test Force (JITF). Continued problems with cooperation and coordination between different testing agencies in the 80's led to another round of consolidation, which turned

1066-401: The axis (or if the emitting point source is not placed in the focus), parabolic reflectors suffer from an aberration called coma . This is primarily of interest in telescopes because most other applications do not require sharp resolution off the axis of the parabola. The precision to which a parabolic dish must be made in order to focus energy well depends on the wavelength of the energy. If

1107-474: The dish is wrong by a quarter of a wavelength, then the reflected energy will be wrong by a half wavelength, which means that it will interfere destructively with energy that has been reflected properly from another part of the dish. To prevent this, the dish must be made correctly to within about ⁠ 1 / 20 ⁠ of a wavelength. The wavelength range of visible light is between about 400 and 700 nanometres (nm), so in order to focus all visible light well,

1148-467: The dish, from a light source in the focus, is given by 1 − arctan ⁡ R D − F π {\textstyle 1-{\frac {\arctan {\frac {R}{D-F}}}{\pi }}} , where F , {\displaystyle F,} D , {\displaystyle D,} and R {\displaystyle R} are defined as above. The parabolic reflector functions due to

1189-480: The dish. The principle of parabolic reflectors has been known since classical antiquity , when the mathematician Diocles described them in his book On Burning Mirrors and proved that they focus a parallel beam to a point. Archimedes in the third century BCE studied paraboloids as part of his study of hydrostatic equilibrium , and it has been claimed that he used reflectors to set the Roman fleet alight during

1230-648: The equivalent: P = R 2 2 D {\textstyle P={\frac {R^{2}}{2D}}} ) and Q = P 2 + R 2 {\textstyle Q={\sqrt {P^{2}+R^{2}}}} , where F , D , and R are defined as above. The diameter of the dish, measured along the surface, is then given by: R Q P + P ln ⁡ ( R + Q P ) {\textstyle {\frac {RQ}{P}}+P\ln \left({\frac {R+Q}{P}}\right)} , where ln ⁡ ( x ) {\textstyle \ln(x)} means

1271-406: The focus to the dish can be transmitted outward in a beam that is parallel to the axis of the dish. In contrast with spherical reflectors , which suffer from a spherical aberration that becomes stronger as the ratio of the beam diameter to the focal distance becomes larger, parabolic reflectors can be made to accommodate beams of any width. However, if the incoming beam makes a non-zero angle with

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1312-410: The geometric properties of the paraboloidal shape: any incoming ray that is parallel to the axis of the dish will be reflected to a central point, or " focus ". (For a geometrical proof, click here .) Because many types of energy can be reflected in this way, parabolic reflectors can be used to collect and concentrate energy entering the reflector at a particular angle. Similarly, energy radiating from

1353-585: The military, between different arms of the same branch of the military, and even between nations as coalition military action became more frequent. The focus of the JITC shifted towards interoperability and information technology testing in the 90's. By 2011 it employed more than 1,300 military personnel and contractors to test and certify military technology. JITC facilities are located at Fort Huachuca, Arizona and Fort George G. Meade , Maryland. An additional JITC mission used to exist at Indian Head, Maryland , but

1394-451: The order of ten millimetres, so dishes to focus these waves can be wrong by half a millimetre or so and still perform well. It is sometimes useful if the centre of mass of a reflector dish coincides with its focus . This allows it to be easily turned so it can be aimed at a moving source of light, such as the Sun in the sky, while its focus, where the target is located, is stationary. The dish

1435-503: The parabolic reflector are in satellite dishes , reflecting telescopes , radio telescopes , parabolic microphones , solar cookers , and many lighting devices such as spotlights , car headlights , PAR lamps and LED housings. The Olympic Flame is traditionally lit at Olympia, Greece , using a parabolic reflector concentrating sunlight , and is then transported to the venue of the Games. Parabolic mirrors are one of many shapes for

1476-423: The principles of reflection are reversible, parabolic reflectors can also be used to collimate radiation from an isotropic source into a parallel beam . In optics , parabolic mirrors are used to gather light in reflecting telescopes and solar furnaces , and project a beam of light in flashlights , searchlights , stage spotlights , and car headlights . In radio , parabolic antennas are used to radiate

1517-471: The reflector is called a paraboloid . A parabola is the two-dimensional figure. (The distinction is like that between a sphere and a circle.) However, in informal language, the word parabola and its associated adjective parabolic are often used in place of paraboloid and paraboloidal . If a parabola is positioned in Cartesian coordinates with its vertex at the origin and its axis of symmetry along

1558-495: The rim is 2.7187  F . The angular radius of the rim as seen from the focal point is 72.68 degrees. The focus-balanced configuration (see above) requires the depth of the reflector dish to be greater than its focal length, so the focus is within the dish. This can lead to the focus being difficult to access. An alternative approach is exemplified by the Scheffler reflector , named after its inventor, Wolfgang Scheffler . This

1599-420: The third. A more complex calculation is needed to find the diameter of the dish measured along its surface . This is sometimes called the "linear diameter", and equals the diameter of a flat, circular sheet of material, usually metal, which is the right size to be cut and bent to make the dish. Two intermediate results are useful in the calculation: P = 2 F {\textstyle P=2F} (or

1640-488: The y-axis, so the parabola opens upward, its equation is 4 f y = x 2 {\textstyle 4fy=x^{2}} , where f {\textstyle f} is its focal length. (See " Parabola#In a cartesian coordinate system ".) Correspondingly, the dimensions of a symmetrical paraboloidal dish are related by the equation: 4 F D = R 2 {\textstyle 4FD=R^{2}} , where F {\textstyle F}

1681-477: Was closed in December 2016 resulting in testing moving to either Fort Huachuca, Arizona or Fort Meade, Maryland. This United States government–related article is a stub . You can help Misplaced Pages by expanding it . This United States military article is a stub . You can help Misplaced Pages by expanding it . TRI-TAC Ground Mobile Forces (GMF) is the term given to the tactical SATCOM portion of

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