Television antenna
A television antenna, or TV aerial, is an antenna designed for the reception of over-the-air broadcast television signals, which are transmitted at frequencies from about 41 to 250 MHz in the VHF band, 470 to 960 MHz in the UHF band in different countries. Television antennas are manufactured in two different types: "indoor" antennas, to be located on top of or next to the television set, "outdoor" antennas, mounted on a mast on top of the owner's house, they can be mounted in a loft or attic, where the dry conditions and increased elevation are advantageous for reception and antenna longevity. Outdoor antennas are more expensive and difficult to install, but are necessary for adequate reception in fringe areas far from television stations; the most common types of indoor antennas are the dipole and loop antennas, for outdoor antennas the yagi, log periodic, for UHF channels the multi-bay reflective array antenna. The purpose of the antenna is to intercept radio waves from the desired television stations and convert them to tiny radio frequency alternating currents which are applied to the television's tuner, which extracts the television signal.
The antenna is connected to the television with a specialized cable designed to carry radio current, called transmission line. Earlier antennas used; the standard today is 75 ohm coaxial cable, less susceptible to interference, which plugs into an F connector on the back of the TV. In most countries, television broadcasting is allowed in the high frequency band from 47 to 68 MHz, called VHF low band or band I in Europe; the boundaries of each band vary somewhat in different countries. Some older television stations broadcast in horizontal polarization which requires that the antenna elements be horizontal, but most broadcast in circular polarization, so that linearly polarized antennas can receive the signal well in any orientation. In the previous standard analog television, used before 2006, the VHF and UHF bands required separate tuners in the television receiver, which had separate antenna inputs; the wavelength of a radio wave equals the speed of light divided by the frequency. The above frequency bands cover a 15:1 wavelength ratio, or 4 octaves.
It is difficult to design a single antenna to receive such a wide wavelength range, there is an octave gap from 216 to 470 MHz between the VHF and UHF frequencies. So traditionally separate antennas have been used to receive the UHF channels. Starting in 2006 many countries in the world switched from broadcasting using an older analog television standard to newer digital television; however the same broadcast frequencies are used, so the same antennas used for the older analog television will receive the new DTV broadcasts. Sellers claim to supply a special "digital" or "high-definition television" antenna advised as a replacement for an existing analog television antenna. Indoor antennas may be mounted on the television itself or stand on a table next to it, connected to the television by a short feedline. Due to space constraints indoor antennas cannot be as large and elaborate as outdoor antennas, they are not mounted at as high an elevation, they are perfectly adequate in urban and suburban areas which are within the strong radiation "footprint" of local television stations, but in rural fringe reception areas only an outdoor antenna may give adequate reception.
A few of the simplest indoor antennas are described below, but a great variety of designs and types exist. Many have a dial on the antenna with a number of different settings to alter the antenna's reception pattern; this should be rotated with the set on while looking at the screen, until the best picture is obtained. The oldest and most used indoor antenna is the rabbit ears or bunny ears, which are provided with new television sets, it is a simple half-wave dipole antenna used to receive the VHF television bands, consisting in the US of 54 to 88 MHz and 174 to 216 MHz, with wavelengths of 5.5 to 1.4 m. It is constructed of two telescoping rods attached to a base, which extend out to about 1 meter length, can be collapsed when not in use. For best reception the rods should be adjusted to be a little less than 1/4 wavelength at the frequency of the television channel being received; however the dipole has a wide bandwidth, so adequate reception is achieved without adjusting the length. The half wave dipole has a low gain of about 2.14 dBi.
Dipole antennas are bi-directional, that is, they have two main lobes in opposite directions, 180° apart. Instead of being fixed in position like other antennas, the elements are mounted on ball-and-socket joints and can be adjusted to various angles in a "V" shape, allowing them to be moved out of the way in crowded quarters. Another reason for the V s
Image stabilization
Image stabilization is a family of techniques that reduce blurring associated with the motion of a camera or other imaging device during exposure. It compensates for pan and tilt of the imaging device, though electronic image stabilization can compensate for rotation, it is used in image-stabilized binoculars and video cameras, astronomical telescopes, smartphones the high-end. With still cameras, camera shake is a particular problem at slow shutter speeds or with long focal length lenses. With video cameras, camera shake causes visible frame-to-frame jitter in the recorded video. In astronomy, the problem of lens-shake is amplified by variation in the atmosphere, which changes the apparent positions of objects over time. In photography, image stabilization can facilitate shutter speeds 2 to 4.5 stops slower, slower effective speeds have been reported. The rule of thumb to determine the slowest shutter speed possible for hand-holding without noticeable blur due to camera shake is to take the reciprocal of the 35 mm equivalent focal length of the lens known as the "1/mm rule".
For example, at a focal length of 125 mm on a 35 mm camera, vibration or camera shake could affect sharpness if the shutter speed is slower than 1⁄125 second. As a result of the 2-to-4.5-stops slower shutter speeds allowed by IS, an image taken at 1⁄125 second speed with an ordinary lens could be taken at 1⁄15 or 1⁄8 second with an IS-equipped lens and produce the same quality. The sharpness obtainable at a given speed can increase dramatically; when calculating the effective focal length, it is important to take into account the image format a camera uses. For example, many digital SLR cameras use an image sensor, 2⁄3, 5⁄8, or 1⁄2 the size of a 35 mm film frame; this means that the 35 mm frame is 1.6, or 2 times the size of the digital sensor. The latter values are referred to as the crop factor, field-of-view crop factor, focal-length multiplier, or format factor. On a 2× crop factor camera, for instance, a 50 mm lens produces the same field of view as a 100 mm lens used on a 35 mm film camera, can be handheld at 1⁄100 second.
However, image stabilization does not prevent motion blur caused by the movement of the subject or by extreme movements of the camera. Image stabilization is only designed for and capable of reducing blur that results from normal, minute shaking of a lens due to hand-held shooting; some lenses and camera bodies include a secondary panning mode or a more aggressive'active mode', both described in greater detail below under optical image stabilization. Image-stabilization features can be a benefit in astrophotography, when the camera is technically—but not effectively—fixed in place; the Pentax K-5 and K-r can use their sensor-shift capability to reduce star trails in reasonable exposure times, when equipped with the O-GPS1 GPS accessory for position data. In effect, the stabilization compensates. There are two types of implementation -- body-based stabilization; these refer to. Both have their disadvantages. An optical image stabilizer abbreviated OIS, IS, or OS, is a mechanism used in a still camera or video camera that stabilizes the recorded image by varying the optical path to the sensor.
This technology is implemented in the lens itself, as distinct from in-body image stabilization, which operates by moving the sensor as the final element in the optical path. The key element of all optical stabilization systems is that they stabilize the image projected on the sensor before the sensor converts the image into digital information. Different companies have different names for the OIS technology, for example: Vibration Reduction – Nikon Image Stabilizer – Canon introduced the EF 75–300 mm f/4–5.6 IS USM) in 1995. In 2009, they introduced their first lens to use a four-axis Hybrid IS.) Anti-Shake – Minolta and Konica Minolta IBIS - In Body Image Stabilisation – Olympus Optical SteadyShot – Sony MegaOIS, PowerOIS – Panasonic and Leica SteadyShot, Super SteadyShot, SteadyShot INSIDE – Sony Optical Stabilization – Sigma Vibration Compensation – Tamron Shake Reduction – Pentax PureView – Nokia UltraPixel – HTC Most high-end smartphones as of late 2014 use optical image stabilization for photos and videos.
In Nikon and Canon's implementation, it works by using a floating lens element, moved orthogonally to the optical axis of the lens using electromagnets. Vibration is detected using two piezoelectric angular velocity sensors, one to detect horizontal movement and the other to detect vertical movement; as a result, this kind of image stabilizer corrects only for pitch and yaw axis rotations, cannot correct for rotation around the optical axis. Some lenses have a secondary mode. This
George Washington
George Washington was an American political leader, military general and Founding Father who served as the first president of the United States from 1789 to 1797. He led Patriot forces to victory in the nation's War of Independence, he presided at the Constitutional Convention of 1787 which established the new federal government, he has been called the "Father of His Country" for his manifold leadership in the formative days of the new nation. Washington received his initial military training and command with the Virginia Regiment during the French and Indian War, he was elected to the Virginia House of Burgesses and was named a delegate to the Continental Congress, where he was appointed Commanding General of the nation's Continental Army. Washington allied with France, in the defeat of the British at Yorktown. Once victory for the United States was in hand in 1783, Washington resigned his commission. Washington played a key role in the adoption and ratification of the Constitution and was elected president by the Electoral College in the first two elections.
He implemented a strong, well-financed national government while remaining impartial in a fierce rivalry between cabinet members Thomas Jefferson and Alexander Hamilton. During the French Revolution, he proclaimed a policy of neutrality while sanctioning the Jay Treaty, he set enduring precedents for the office of president, including the title "President of the United States", his Farewell Address is regarded as a pre-eminent statement on republicanism. Washington utilized slave labor and trading African American slaves, but he became troubled with the institution of slavery and freed them in his 1799 will, he was a member of the Anglican Church and the Freemasons, he urged tolerance for all religions in his roles as general and president. Upon his death, he was eulogized as "first in war, first in peace, first in the hearts of his countrymen." He has been memorialized by monuments, geographical locations and currency, many scholars and polls rank him among the top American presidents. Washington's great-grandfather John Washington immigrated in 1656 from Sulgrave, England to the British Colony of Virginia where he accumulated 5,000 acres of land, including Little Hunting Creek on the Potomac River.
George Washington was born February 22, 1732 at Popes Creek in Westmoreland County and was the first of six children of Augustine and Mary Ball Washington. His father was a justice of the peace and a prominent public figure who had three additional children from his first marriage to Jane Butler; the family moved to Little Hunting Creek to Ferry Farm near Fredericksburg, Virginia. When Augustine died in 1743, Washington inherited ten slaves. Washington did not have the formal education that his older brothers received at Appleby Grammar School in England, but he did learn mathematics and surveying, he was talented in draftsmanship and map-making. By early adulthood, he was writing with "considerable force" and "precision."Washington visited Mount Vernon and Belvoir, the plantation that belonged to Lawrence's father-in-law William Fairfax, which fueled ambition for the lifestyle of the planter aristocracy. Fairfax became Washington's patron and surrogate father, Washington spent a month in 1748 with a team surveying Fairfax's Shenandoah Valley property.
He received a surveyor's license the following year from the College of Mary. He resigned from the job in 1750 and had bought 1,500 acres in the Valley, he owned 2,315 acres by 1752. In 1751, Washington made his only trip abroad when he accompanied Lawrence to Barbados, hoping that the climate would cure his brother's tuberculosis. Washington contracted smallpox during that trip, which immunized him but left his face scarred. Lawrence died in 1752, Washington leased Mount Vernon from his widow. Lawrence's service as adjutant general of the Virginia militia inspired Washington to seek a commission, Virginia's Lieutenant Governor Robert Dinwiddie appointed him as a major in December 1752 and as commander of one of the four militia districts; the British and French were competing for control of the Ohio Valley at the time, the British building forts along the Ohio River and the French doing between Lake Erie and the Ohio River. In October 1753, Dinwiddie appointed Washington as a special envoy to demand that the French vacate territory which the British had claimed.
Dinwiddie appointed him to make peace with the Iroquois Confederacy and to gather intelligence about the French forces. Washington met with Half-King Tanacharison and other Iroquois chiefs at Logstown to secure their promise of support against the French, his party reached the Ohio River in November, they were intercepted by a French patrol and escorted to Fort Le Boeuf where Washington was received in a friendly manner. He delivered the British demand to vacate to French commander Saint-Pierre, but the French refused to leave. Saint-Pierre gave Washington his official answer in a sealed envelope after a few days' delay, he gave Washington's party food and extra winter clothing for the trip back to Virginia. Washington completed the precarious mission in 77 days in difficult winter conditions and achieved a measure of distinction when his report was published in Virginia and London. In February 1754, Dinwiddie promoted Washington to lieutenant colonel and second-in-command of the 300-strong Virginia R
Linear B
Linear B is a syllabic script, used for writing Mycenaean Greek, the earliest attested form of Greek. The script predates the Greek alphabet by several centuries; the oldest Mycenaean writing dates to about 1450 BC. It is descended from the older Linear A, an undeciphered earlier script used for writing the Minoan language, as is the Cypriot syllabary, which recorded Greek. Linear B, found in the palace archives at Knossos, Pylos and Mycenae, disappeared with the fall of Mycenaean civilization during the Late Bronze Age collapse; the succeeding period, known as the Greek Dark Ages, provides no evidence of the use of writing. It is the only one of the Bronze Age Aegean scripts to have been deciphered, by English architect and self-taught linguist Michael Ventris. Linear B consists of over 100 ideographic signs; these ideograms or "signifying" signs symbolize commodities. They are never used as word signs in writing a sentence; the application of Linear B appears to have been confined to administrative contexts.
In all the thousands of clay tablets, a small number of different "hands" have been detected: 45 in Pylos and 66 in Knossos. It is possible that the script was used only by a guild of professional scribes who served the central palaces. Once the palaces were destroyed, the script disappeared. Linear B has 200 signs, divided into syllabic signs with phonetic values and ideograms with semantic values; the representations and naming of these signs have been standardized by a series of international colloquia starting with the first in Paris in 1956. After the third meeting in 1961 at the Wingspread Conference Center in Racine, Wisconsin, a standard proposed by Emmett L. Bennett, Jr. became known as the Wingspread Convention, adopted by a new organization, the Comité International Permanent des Études Mycéniennes, affiliated in 1970 by the fifth colloquium with UNESCO. Colloquia continue: the 13th occurred in 2010 in Paris. Many of the signs are identical or similar to those in Linear A; the grid developed during decipherment by Michael Ventris and John Chadwick of phonetic values for syllabic signs is shown below.
Initial consonants are in the leftmost column. The transcription of the syllable is listed next to the sign along with Bennett's identifying number for the sign preceded by an asterisk. In cases where the transcription of the sign remains in doubt, Bennett's number serves to identify the sign; the signs on the tablets and sealings show considerable variation from each other and from the representations below. Discovery of the reasons for the variation and possible semantic differences is a topic of ongoing debate in Mycenaean studies. In addition to the grid, the first edition of Documents in Mycenaean Greek contained a number of other signs termed "homophones" because they appeared at that time to resemble the sounds of other syllables and were transcribed accordingly: pa2 and pa3 were presumed homophonous to pa. Many of these are shown in the "special values" below; the second edition relates: "It may be taken as axiomatic that there are no true homophones." The unconfirmed identifications of *34 and *35 as ai2 and ai3 were removed.
Pa2 became qa. Other values remain unknown because of scarcity of evidence concerning them. Note that *34 and *35 are mirror images of each other but whether this graphic relationship indicates a phonetic one remains unconfirmed. In recent times, CIPEM inherited the former authority of Bennett and the Wingspread Convention in deciding what signs are "confirmed" and how to represent the various sign categories. In editions of Mycenaean texts, the signs whose values have not been confirmed by CIPEM are always transcribed as numbers preceded by an asterisk. CIPEM allocates the numerical identifiers, until such allocation, new signs are transcribed as a bullet-point enclosed in square brackets:; the signs are approximations―each may be used to represent a variety of about 70 distinct combinations of sounds, within rules and conventions. The grid presents a system of monosyllabic signs of the type V/CV. Clarification of the 14 or so special values tested the limits of the grid model, but Chadwick in the end concluded that with the ramifications, the syllabic signs can unexceptionally be considered monosyllabic.
Possible exceptions, Chadwick goes on to explain, include the two diphthongs, and, as in, ai-ku-pi-ti-jo, for Aiguptios and, au-ke-wa, for Augewās. However, a diphthong is by definition two vowels united into a single sound and therefore might be typed as just V. Thus, as in, e-rai-wo, for elaiwon, is of the type CV. Diphthongs are otherwise treated as two monosyllables:, a-ro-u-ra, for arourans, of the types CV and V. Lengths of vowels and accents are not marked, and the more doubtful and may be regarded as beginning with labialized consonants, rather than two consonants though they may alternate with a two-sign form: o-da-twe-ta and o-da-tu-we-ta for Odatwenta. And begin with palatalized consonants rather than two consonants: -ti-ri-ja for -trja (-τρι
Wind turbine
A wind turbine, or alternatively referred to as a wind energy converter, is a device that converts the wind's kinetic energy into electrical energy. Wind turbines are manufactured in a wide range of horizontal axis; the smallest turbines are used for applications such as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Larger turbines can be used for making contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, are becoming an important source of intermittent renewable energy and are used by many countries as part of a strategy to reduce their reliance on fossil fuels. One assessment claimed that, as of 2009, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands and... the most favourable social impacts" compared to photovoltaic, geothermal and gas. The windwheel of Hero of Alexandria marks one of the first recorded instances of wind powering a machine in history.
However, the first known practical wind power plants were built in Sistan, an Eastern province of Persia, from the 7th century. These "Panemone" were vertical axle windmills, which had long vertical drive shafts with rectangular blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, were used in the gristmilling and sugarcane industries. Wind power first appeared in Europe during the Middle Ages; the first historical records of their use in England date to the 11th or 12th centuries and there are reports of German crusaders taking their windmill-making skills to Syria around 1190. By the 14th century, Dutch windmills were in use to drain areas of the Rhine delta. Advanced wind turbines were described by Croatian inventor Fausto Veranzio. In his book Machinae Novae he described vertical axis wind turbines with V-shaped blades; the first electricity-generating wind turbine was a battery charging machine installed in July 1887 by Scottish academic James Blyth to light his holiday home in Marykirk, Scotland.
Some months American inventor Charles F. Brush was able to build the first automatically operated wind turbine after consulting local University professors and colleagues Jacob S. Gibbs and Brinsley Coleberd and getting the blueprints peer-reviewed for electricity production in Cleveland, Ohio. Although Blyth's turbine was considered uneconomical in the United Kingdom, electricity generation by wind turbines was more cost effective in countries with scattered populations. In Denmark by 1900, there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW; the largest machines were on 24-meter towers with four-bladed 23-meter diameter rotors. By 1908, there were 72 wind-driven electric generators operating in the United States from 5 kW to 25 kW. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year for water-pumping. By the 1930s, wind generators for electricity were common on farms in the United States where distribution systems had not yet been installed.
In this period, high-tensile steel was cheap, the generators were placed atop prefabricated open steel lattice towers. A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931; this was a 100 kW generator on a 30-meter tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 percent, not much different from current wind machines. In the autumn of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in Vermont; the Smith–Putnam wind turbine only ran for 1,100 hours before suffering a critical failure. The unit was not repaired, because of a shortage of materials during the war; the first utility grid-connected wind turbine to operate in the UK was built by John Brown & Company in 1951 in the Orkney Islands. Despite these diverse developments, developments in fossil fuel systems entirely eliminated any wind turbine systems larger than supermicro size. In the early 1970s, anti-nuclear protests in Denmark spurred artisan mechanics to develop microturbines of 22 kW.
Organizing owners into associations and co-operatives lead to the lobbying of the government and utilities and provided incentives for larger turbines throughout the 1980s and later. Local activists in Germany, nascent turbine manufacturers in Spain, large investors in the United States in the early 1990s lobbied for policies that stimulated the industry in those countries. Wind Power Density is a quantitative measure of wind energy available at any location, it is the mean annual power available per square meter of swept area of a turbine, is calculated for different heights above ground. Calculation of wind power density includes the effect of air density. Wind turbines are classified by the wind speed they are designed for, from class I to class III, with A to C referring to the turbulence intensity of the wind. Conservation of mass requires that the amount of air exiting a turbine must be equal. Accordingly, Betz's law gives the maximal achievable extraction of wind power by a wind turbine as 16/27 of the total kinetic energy of the air flowing through the turbine.
The maximum theoretical power output of a wind machine is thus 16/27 times the kinetic energy of the air passing through the effective disk area of the machine. If the effective area of the disk is A, the wind velocity v, the maximum theoretical power output P is: P = 16
Tripod (surveying)
A surveyor's tripod is a device used to support any one of a number of surveying instruments, such as theodolites, total stations, levels or transits. The modern sturdy, but portable, tripod stand with three leg pairs hinged to a triangular metal head was invented and first manufactured for sale by Sir Francis Ronalds in the late 1820s in Croydon, he sold 140 of the stands in the decade 1830-40 and his design was soon imitated by others. Older surveying tripods had different features compared to modern ones. For example, on some older tripods, the instrument had its own footplate and did not need to move laterally relative to the tripod head. For this reason, the head of the tripod was not a flat footplate but was a large diameter fitting. Threads on the outside of the head engaged threads on the instrument's footplate. No other mounting screw was used. Fixed length legs were seen on older instruments. Instrument height was adjusted by changing the angle of the legs. Spaced tripod feet resulted in a lower instrument while spaced legs raised the instrument.
This was less convenient than having variable length legs. Materials for older tripods were predominantly wood and brass, with some steel for high wear items like the feet or foot points; the tripod is placed in the location. The surveyor will press down on the legs' platforms to securely anchor the legs in soil or to force the feet to a low position on uneven, pock-marked pavement. Leg lengths are adjusted to bring the tripod head to a convenient height and make it level. Once the tripod is positioned and secure, the instrument is placed on the head; the mounting screw is pushed up under the instrument to engage the instrument's base and screwed tight when the instrument is in the correct position. The flat surface of the tripod head is called the foot plate and is used to support the adjustable feet of the instrument. Positioning the tripod and instrument over an indicated mark on the ground or benchmark requires intricate techniques. Many modern tripods are constructed of aluminum; the feet are either aluminum tipped with steel.
The mounting screw is brass or brass and plastic. The mounting screw is hollow and has two lateral holes to attach a plumb bob to center the instrument e.g. over a corner or other mark on the ground. After the instrument is centered within a few cm over the mark, the plumb bob is removed and a viewer in the instrument is used to center it; the top is threaded with a 5/8" x 11 tpi screw thread. The mounting screw is held to the underside of the tripod head by a movable arm; this permits the screw to be moved anywhere within the head's opening. The legs are attached to the head with adjustable screws that are kept tight enough to allow the legs to be moved with a bit of resistance; the legs are two part, with the lower part capable of telescoping to adjust the length of the leg to suit the terrain. Aluminum or steel slip joints with a tightening screw are at the bottom of the upper leg to hold the bottom part in place and fix the length. A shoulder strap is affixed to the tripod to allow for ease of carrying the equipment over areas to be surveyed.
Tribrach Raymond Davis, Francis Foote, Joe Kelly, Surveying and Practice, McGraw-Hill Book Company, 1966 LC 64-66263
Weapon mount
A weapon mount is an assembly used to hold a weapon a gun. Weapon mounts can be broken down into two categories: static mounts and non-static mounts. A static mount is a non-portable weapon support component either mounted directly to the ground, on a fortification, or as part of a vehicle. A gun turret protects the crew or mechanism of a weapon and at the same time lets the weapon be aimed and fired in many directions. A turret is a rotating weapon platform one that crosses the armour of whatever it is mounted on with a structure called a barbette or basket and has a protective structure on top. If it has no gunhouse it is a barbette. Turrets are used to mount machine guns, autocannons or large-calibre guns, they may be remotely controlled. A small turret, or sub-turret on a larger one, is called a cupola; the term cupola describes rotating turrets that carry no weapons but instead are sighting devices, as in the case of tank commanders. A finial is an small sub-turret or sub-sub-turret mounted on a cupola turret.
The gun is fixed on its horizontal axis and rotated by turning the turret, with trunnions on the gun used to allow it to elevate. Alternatively, in an oscillating turret the entire upper section of the turret moves to elevate and depress the gun. A casemate is an armoured structure consisting of a static primary surface incorporating a limited-traverse gun mount: this takes the form of either a gun mounted through a fixed armour plate or a mount consisting of a partial cylinder of armour "sandwiched" between plates at the top and bottom. A coaxial mount is mounted beside or above the primary weapon and thus points in the same general direction as the main armament, relying on the host weapon's ability to traverse in order to change arc; the term coaxial is something of a misnomer as the arrangement is speaking paraxial, though for ballistic purposes the axis is the same in practical terms. Nearly all main battle tanks and most infantry fighting vehicles have a coaxial machine gun mounted to fire along a parallel axis to the main gun.
Coaxial weapons are aimed by use of the main gun control. It is used to engage infantry or other "soft" targets where use of shots from the main gun would be dangerous, ineffective or wasteful; some weapons such as the M40 recoilless rifle and the Mk 153 Shoulder-Launched Multipurpose Assault Weapon have a smaller caliber spotting rifle mounted in coaxial fashion to the barrel or launch tube. These weapons fire special cartridges designed to mimic the ballistic arc of the host weapon's ammunition, using tracer or point-detonating rounds so that a gunner can determine where a shot will land in order to place fire accurately. Due to the adoption of more advanced systems such as laser rangefinders, they are used on modern weapons. A fixed mount is incapable of horizontal movement, though not vertical movement; the entire mounting must be moved in order to change direction of fire. Fixed mounts are most found on aircraft, most direct the weapon forward, along the aircraft's vector of movement, so that a pilot can aim by pointing the nose of the aircraft at the target.
Some aircraft designs used different concept of fixed mounts, as found in Schräge Musik or AC-47 Spooky. The Stridsvagn 103 is an unusual turretless main battle tank with a fixed main gun, aimed using the tank's tracks and suspension. Military aircraft often used fixed mounts called hardpoints or weapon stations to attach disposable stores such as missiles and external fuel tanks: these devices mount a standardised set of locking lugs to which many different types of armament can be affixed. Fixed traverse mounts capable of only elevation are common on larger self-propelled guns, as well being the mounting method used by all railroad guns. A pintle mount is a fixed mount that allows the gun to be traversed and/or elevated while keeping the gun in one fixed position: the mounting is either a rod on the underside of the gun that mates with a socket, or an intermediary gun cradle that mounts to the sides of the weapon's barrel or receiver. Due to the stability offered by the mount, the gun does not use a shoulder stock, with many modern examples using spade grips.
It is most found on armoured vehicles, side gun stations on WW2 and earlier bomber aircraft, the door guns of transport helicopters. Early single-shot examples referred to as swivel guns were mounted on the deck rails of naval vessels in the age of sail to deter boarders at close range. Larger guns require a heavier mounting referred to as a pedestal, larger guns a turntable platform: a pedestal mount may be directly manipulated, but larger guns require power assistance or the use of mechanical handwheels for traverse and elevation. Large mounts might include seats for the crew fixed to the gun cradle or the floor of the turntable. Unlike a turret, this type of mount has little or no armour protection at most a gunshield or splinter shield; this is a power-assisted mounting on the outside of whatever it is mounted on bolted down to the surface and with only the control wires crossing the armour. Such mountings are used on armoured fighting vehicles for anti-personnel weapons to avoid exposing a crewmen to return fire, and
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