A satellite dish is a type of parabolic antenna that receives or transmits electromagnetic signals to and from another location, which may be a satellite or an aerial, e. The parabolic antenna is a high-gain reflector antenna used for radio television and data communications and also for radiolocation ( RADAR) on the UHF and g. WIFI ANTENNA. A satellite dish is a type of microwave antenna. The parabolic antenna is a high-gain reflector antenna used for radio television and data communications and also for radiolocation ( RADAR) on the UHF and Satellite dishes come in varying sizes and designs, and are commonly used to receive satellite television. Satellite television is Television delivered by the means of Communications satellites as compared to conventional Terrestrial television and Cable Many of the offset type of satellite dishes are sections of a larger parabolic dish.
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Principle of operation
The parabolic shape of a dish reflects the signal to the dish’s focal point. In Mathematics, the parabola (pəˈræbələ from the Greek παραβολή) is a Conic section, the intersection of a right circular Mounted on brackets at the dish's focal point is a device called a feedhorn. In Satellite dish and antenna design parlance a feedhorn (or feed horn) is a Horn antenna used to convey Radio waves between the This feedhorn is essentially the front-end of a waveguide that gathers the signals at or near the focal point and 'conducts' them to a low-noise block downconverter or LNB. A waveguide is a structure which guides waves such as Electromagnetic waves Light, or Sound waves A low-noise block converter ( LNB, for low-noise block, or sometimes LNC, for low-noise converter) is the (receiving or Downlink The LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts the signals from the downlinked C-band and/or Ku-band to the L-band range. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. NATO L band The NATO L band is defined as the frequency band between 40 and 60 G[[Hertz Hz]] (5–7 Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB. Direct broadcast satellite (DBS is a term used to refer to Satellite television broadcasts intended for home reception also referred to more broadly as direct-to-home In Satellite dish and antenna design parlance a feedhorn (or feed horn) is a Horn antenna used to convey Radio waves between the (A new form of omnidirectional satellite antenna, which does not use a directed parabolic dish and can be used on a mobile platform such as a vehicle was announced by the University of Waterloo in 2004. The University of Waterloo (also referred to as UW and Waterloo) is a comprehensive Public university in the city of Waterloo, Ontario [1]
The theoretical gain (directive gain) of a dish increases as the frequency increases. In Telecommunications the term directive gain has the following meanings 1 The actual gain depends on many factors including surface finish, accuracy of shape, feedhorn matching.
With lower frequencies, C-band for example, dish designers have a wider choice of materials. C band is a name given to certain portions of the Electromagnetic spectrum, as well as a range of Wavelengths of Light, used for communications The large size of dish required for lower frequencies led to the dishes being constructed from metal mesh on a metal framework. At higher frequencies, mesh type designs are rarer though some designs have used a solid dish with perforations.
A common misconception is that the LNBF (low-noise block/feedhorn), the device at the front of the dish, receives the signal directly from the atmosphere. A low-noise block converter ( LNB, for low-noise block, or sometimes LNC, for low-noise converter) is the (receiving or Downlink For instance, one BBC News countdown shows a "red data stream" being received by the LNBF directly instead of being beamed to the dish, which because of its parabolic shape will collect the signal into a smaller area and deliver it to the LNBF. BBC News is the BBC's 24 hour rolling news television channel in the United Kingdom and also available in the Republic of Ireland. [2]
Size
Modern dishes intended for home television use are generally 43 cm (18 in) to 80 cm (31 in) in diameter, and are fixed in one position, for Ku-band reception from one orbital position. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth Inches redirects here To see the Les Savy Fav album see Inches. Geometry, a diameter of a Circle is any straight Line segment that passes through the center of the circle and whose Endpoints are on the The Ku band ( pronounced "kay-yoo") is a portion of the Electromagnetic spectrum in the Microwave range of frequencies Prior to the existence of direct broadcast satellite services, home users would generally have a motorised C-band satellite dish of up to 3 metres in diameter for reception of channels from different satellites. Direct broadcast satellite (DBS is a term used to refer to Satellite television broadcasts intended for home reception also referred to more broadly as direct-to-home C band is a name given to certain portions of the Electromagnetic spectrum, as well as a range of Wavelengths of Light, used for communications Overly small dishes can still cause problems, however, including rain fade and interference from adjacent satellites. Rain fade refers primarily to the absorption of a Microwave Radio Frequency (RF signal by atmospheric rain snow or ice and losses are especially prevalent
Europe
In Europe the frequencies used by DBS services are 10. 7 - 12. 75 GHz on two polarisations H and V. This range is divided into a "low band" with 10. 7 - 11. 7 GHz, and a "high band" with 11. 7 - 12. 75 GHz. This results in two frequency bands, each with a bandwidth of about 1 GHz, each with two possible polarizations. In the LNB they become down converted to 950 - 2150 MHz, which is the frequency range allocated for the satellite service on the coaxial cable between LNBF and receiver. Lower frequencies are allocated to cable and terrestrial TV, FM radio, etc. Terrestrial television is a term which refers to modes of television broadcasting which do not involve satellite transmission Only one of these frequency bands fits on the coaxial cable, so each of these bands needs a separate cable from the LNBF to a switching matrix or the receiver needs to select one of the 4 possibilities at a time.
Systems design
In a single receiver residential installation there is a single cable from receiver to LNB and the receiver uses different power supply voltages (14/18V) to select polarization and pilot tones (22 kHz) to instruct the LNB to select one of the two frequency bands. In larger installations each band and polarization is given its own cable, so there are 4 cables from the LNB to a switching matrix, which allows the connection of multiple receivers in a star topology using the same signalling method as in a single receiver installation.
Types
Motor-driven dishes
A satellite dish that is mounted on a pole and driven by a stepper motor can be controlled and rotated to face any satellite position in the sky. A stepper motor (or step motor) is a brushless, synchronous Electric Motor-driven dishes are popular with enthusiasts. There are three competing standards: DiSEqC, USALS, and 36v positioners. DiSEqC (Digital Satellite Equipment Control pronounced "Die-Sec" is a special communication protocol for use between a Satellite receiver and Universal Satellites Automatic Location System (USALS also known (unofficially as DiSEqC 1 Many receivers support all of these standards.
Multi-satellite
Some designs enable simultaneous reception from multiple different satellite positions without re-positioning the dish. The vertical axis operates as an off-axis concave parabolic concave hyperbolic Cassegrain reflector, while the horizontal axis operates as a concave convex Cassegrain. The Cassegrain reflector is a combination of two coaxial reflectors used in Cassegrain telescopes and radio antennas First developed in 1672 by Laurent Cassegrain The spot from the main dish wanders across the secondary, which corrects astigmatism by its varying curvature. See also Aberration in optical systems, Astigmatism (eye An Optical system with astigmatism is one where rays that propagate The elliptic aperture of the primary is designed to fit the deformed illumination by the horns. Due to double spill-over, this makes more sense for a large dish.
VSAT
A common type of satellite dish is the very small aperture terminal (VSAT). A Very Small Aperture Terminal ( VSAT) is a two-way Satellite Ground station with a dish antenna that is smaller than 3 meters (most VSAT This provides two way satellite internet communications for both consumers and private networks for organisations. Satellite Internet services are used in locations where terrestrial Internet access is not available and in locations which move frequently Today most VSATs operate in Ku band, C band is restricted to less populated regions of the world. The Ku band ( pronounced "kay-yoo") is a portion of the Electromagnetic spectrum in the Microwave range of frequencies C band is a name given to certain portions of the Electromagnetic spectrum, as well as a range of Wavelengths of Light, used for communications There is a move which started in 2005 towards new Ka band satellites operating at higher frequencies, offering greater performance at lower cost. The Ka band (Pronounced "Kay-A Band" covers the frequencies of 26 These antennas vary from 74cm to 120cm in most applications though C-band VSATs may be as large as 2. 4m.
Ad hoc
The dish is a reflector antenna and almost anything that reflects radio frequencies can be used as a reflector antenna. This has led to dustbin lids, woks and other items being used as "dishes". Coupled with low noise LNBs and the higher transmission power of DTH satellites, it is easier to get a usable signal on some of these "dishes".
Others
- Individual dishes serving one dwelling: Direct to Home (DTH). A satellite dish is a type of Parabolic antenna that receives or transmits electromagnetic signals to and from another location typically a satellite
- Collective dishes, shared by several dwellings: satellite master antenna television (SMATV) or communal antenna broadcast distribution (CABD).
- Automatic Tracking Satellite Dish
- Big ugly dish
In numismatics
Television has had such an impact in today's life, that it has been the main motif for numerous collectors' coins and medals. Automatic Tracking Satellite Dishes are satellite dishes used while a vehicle is in motion A C-Band Dish (often abbreviated to BUD or Big Ugly Dish) is a Colloquial Name for a TVRO Satellite dish used to receive Satellite Euro gold and silver commemorative coins are special Euro coins minted and issued by member states of the Eurozone. One of the most recent ones is the The 50 Years of Television commemorative coin minted in March 9, 2005. Euro gold and silver commemorative coins are special Euro coins minted and issued by member states of the Eurozone. Events 590 - Bahram Chobin is crowned as king Barham VI of Persia. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. The obverse of the coin shows a "test pattern", while the reverse shows several milestones in the history of television, including satellite dishes.
References
- ^ Team develops in-car satellite TV. University of Waterloo (2006-05-06). The University of Waterloo (also referred to as UW and Waterloo) is a comprehensive Public university in the city of Waterloo, Ontario Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1527 - Spanish and German troops sack Rome; some consider this the end of the Renaissance. Retrieved on 2008-04-29. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1429 - Joan of Arc arrives to relieve the Siege of Orleans.
- ^ News 24 STILL gets an F for physics. Retrieved on 2008-04-29. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1429 - Joan of Arc arrives to relieve the Siege of Orleans.
External links
- European Commission: The right to use a satellite dish.
- DishPointer - Satellite dish alignment with Google Maps.
 General Electric satellite dish |
 Sky Digital "mini-dish" |
 Astro's "mini-dish" |
 Big ugly dish antenna for C-Band |
 Satellite Dishes installed on an apartment complex |
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