1.
Modem
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A modem is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is attempting to produce a signal that can be transmitted easily, modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second. Modems can also be classified by their rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency shift keying with two frequencies, corresponding to two distinct symbols, to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which could transmit and receive four distinct symbols, news wire services in the 1920s used multiplex devices that satisfied the definition of a modem. However, the function was incidental to the multiplexing function, so they are not commonly included in the history of modems. S. SAGE modems were described by AT&Ts Bell Labs as conforming to their newly published Bell 101 dataset standard, while they ran on dedicated telephone lines, the devices at each end were no different from commercial acoustically coupled Bell 101,110 baud modems. The 201A and 201B Data-Phones were synchronous modems using two-bit-per-baud phase-shift keying, the famous Bell 103A dataset standard was also introduced by AT&T in 1962. It provided full-duplex service at 300 bit/s over normal phone lines, frequency-shift keying was used, with the call originator transmitting at 1,070 or 1,270 Hz and the answering modem transmitting at 2,025 or 2,225 Hz. The readily available 103A2 gave an important boost to the use of remote low-speed terminals such as the Teletype Model 33 ASR and KSR, AT&T reduced modem costs by introducing the originate-only 113D and the answer-only 113B/C modems. For many years, the Bell System maintained a monopoly on the use of its phone lines, however, the seminal Hush-a-Phone v. FCC case of 1956 concluded it was within the FCCs jurisdiction to regulate the operation of the Bell System. The FCC found that as long as a device was not electronically attached to the system and this led to a number of devices that mechanically connected to the phone through a standard handset. Since most handsets were supplied by Western Electric and thus of a standard design and this type of connection was used for many devices, such as answering machines. Acoustically coupled Bell 103A-compatible 300 bit/s modems were common during the 1970s, well-known models included the Novation CAT and the Anderson-Jacobson, the latter spun off from an in-house project at Stanford Research Institute. An even lower-cost option was the Pennywhistle modem, designed to be built using parts from electronics scrap, in December 1972, Vadic introduced the VA3400, notable for full-duplex operation at 1,200 bit/s over the phone network. Like the 103A, it used different frequency bands for transmit, in November 1976, AT&T introduced the 212A modem to compete with Vadic
2.
Relay
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A relay is an electrically operated switch. Many relays use an electromagnet to operate a switch, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a separate low-power signal, the first relays were used in long distance telegraph circuits as amplifiers, they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations, a type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a device to perform switching. Magnetic latching relays require one pulse of power to move their contacts in one direction. Repeated pulses from the same input have no effect, magnetic latching relays are useful in applications where interrupted power should not be able to transition the contacts. Magnetic latching relays can have single or dual coils. On a single device, the relay will operate in one direction when power is applied with one polarity. On a dual coil device, when polarized voltage is applied to the coil the contacts will transition. AC controlled magnetic latch relays have single coils that employ steering diodes to differentiate between operate and reset commands, american scientist Joseph Henry is often claimed to have invented a relay in 1835 in order to improve his version of the electrical telegraph, developed earlier in 1831. However, there is little in the way of documentation to suggest he had made the discovery prior to 1837. It is claimed that English inventor Edward Davy certainly invented the electric relay in his electric telegraph c.1835, a simple device, which is now called a relay, was included in the original 1840 telegraph patent of Samuel Morse. The mechanism described acted as an amplifier, repeating the telegraph signal. This overcame the problem of limited range of earlier telegraphy schemes, the word relay appears in the context of electromagnetic operations from 1860. The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts, the armature is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the set is open. Other relays may have more or fewer sets of contacts depending on their function, the relay in the picture also has a wire connecting the armature to the yoke
3.
Satellite Internet access
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Satellite Internet access is Internet access provided through communications satellites. Following the launch of the first satellite, Sputnik 1, by the Soviet Union in October 1957, the first commercial communications satellite was Telstar 1, built by Bell Labs and launched in July 1962. Clarke in a paper in Wireless World in 1945, the first satellite to successfully reach geostationary orbit was Syncom3, built by Hughes Aircraft for NASA and launched August 19,1963. Following the invention of the Internet and the World Wide Web, a significant enabler of satellite-delivered Internet has been the opening up of the Ka band for satellites. In December 1993, Hughes Aircraft Co. filed with the Federal Communications Commission for a license to launch the first Ka-band satellite, in 1995, the FCC issued a call for more Ka-band satellite applications, attracting applications from 15 companies. Among those were EchoStar, Lockheed Martin, GE-Americom, Motorola and KaStar Satellite, the project was abandoned in 2003. It wasn’t until September 2003 when the first Internet-ready satellite for consumers was launched by Eutelsat, in 2004, with the launch of Anik F2, the first high throughput satellite, a class of next-generation satellites providing improved capacity and bandwidth became operational. Internet access services tied to these satellites are targeted largely to rural residents as an alternative to Internet service via dial-up, companies providing home internet service include ViaSat, through its Exede brand, and EchoStar, through subsidiary HughesNet. With this configuration, the number of remote VSATs that can be connected to the hub is virtually limitless, marketed as the center of the new broadband satellite networks are a new generation of high-powered GEO satellites positioned 35,786 kilometres above the equator, operating in Ka-band mode. This spot beam technology allows satellites to reuse assigned bandwidth multiple times which can enable them to much higher overall capacity than conventional broad beam satellites. The spot beams can also increase performance and consequential capacity by focusing more power, note that moving off the tight footprint of a spotbeam can degrade performance significantly. Also, spotbeams can make impossible the use of significant new technologies including Carrier in Carrier modulation. The term bent-pipe is used to describe the shape of the path between sending and receiving antennas, with the satellite positioned at the point of the bend. Simply put, the role in this network arrangement is to relay signals from the end users terminal to the ISPs gateways. The satellite receives, amplifies, and redirects a carrier on a radio frequency through a signal path called a transponder. The satellite has its own set of antennas to receive signals from Earth. These antennas and transponders are part of the payload, which is designed to receive and transmit signals to. The satellites high-gain receiving antenna passes the data to the transponder which filters, translates and amplifies them
4.
Satellite dish
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A satellite dish is a dish-shaped type of parabolic antenna designed to receive electromagnetic signals from satellites, which transmit data transmissions or broadcasts, such as satellite television. The parabolic shape of a dish reflects the signal to the focal point. Mounted on brackets at the focal point is a device called a feedhorn. This feedhorn is essentially the front-end of a waveguide that gathers the signals at or near the focal point, 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. Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB, the theoretical gain of a dish increases as the frequency increases. The actual gain depends on factors including surface finish, accuracy of shape. A typical value for a consumer type 60 cm satellite dish at 11.75 GHz is 37.50 dB, with lower frequencies, C-band for example, dish designers have a wider choice of materials. 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, the device at the front of the dish, modern dishes intended for home television use are generally 43 cm to 80 cm in diameter, and are fixed in one position, for Ku-band reception from one orbital position. Prior to the existence of direct broadcast satellite services, home users would generally have a motorised C-band dish of up to 3 m in diameter for reception of channels from different satellites. Overly small dishes can still cause problems, however, including rain fade, 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 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 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, in a single receiver residential installation there is a single coaxial cable running from the receiver set-top box in the building to the LNB on the dish. The DC electric power for the LNB is provided through the coaxial cable conductors that carry the signal to the receiver. In addition, control signals are transmitted from the receiver to the LNB through the cable. The receiver uses different power supply voltages to select antenna polarization, a satellite finder may aid in aiming. A dish that is mounted on a pole and driven by a motor or a servo can be controlled and rotated to face any satellite position in the sky
5.
Computer
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A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically. The ability of computers to follow a sequence of operations, called a program, such computers are used as control systems for a very wide variety of industrial and consumer devices. The Internet is run on computers and it millions of other computers. Since ancient times, simple manual devices like the abacus aided people in doing calculations, early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century, the first digital electronic calculating machines were developed during World War II. The speed, power, and versatility of computers has increased continuously and dramatically since then, conventionally, a modern computer consists of at least one processing element, typically a central processing unit, and some form of memory. The processing element carries out arithmetic and logical operations, and a sequencing, peripheral devices include input devices, output devices, and input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and this usage of the term referred to a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century, from the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations. The Online Etymology Dictionary gives the first attested use of computer in the 1640s, one who calculates, the Online Etymology Dictionary states that the use of the term to mean calculating machine is from 1897. The Online Etymology Dictionary indicates that the use of the term. 1945 under this name, theoretical from 1937, as Turing machine, devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick, later record keeping aids throughout the Fertile Crescent included calculi which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. The use of counting rods is one example, the abacus was initially used for arithmetic tasks. The Roman abacus was developed from used in Babylonia as early as 2400 BC. Since then, many forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, the Antikythera mechanism is believed to be the earliest mechanical analog computer, according to Derek J. de Solla Price. It was designed to calculate astronomical positions and it was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to circa 100 BC
6.
Low-noise block downconverter
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A low-noise block downconverter is the receiving device mounted on satellite dishes used for satellite TV reception, which collects the radio waves from the dish. Also called a block, low-noise converter, or even low-noise downconverter. The LNB is a combination of low-noise amplifier, frequency mixer, local oscillator and it receives the microwave signal from the satellite collected by the dish, amplifies it, and downconverts the block of frequencies to a lower block of intermediate frequencies. The LNB is usually a box suspended on one or more short booms, or feed arms, in front of the dish reflector. The microwave signal from the dish is picked up by a feedhorn on the LNB and is fed to a section of waveguide. One or more pins, or probes, protrude into the waveguide at right angles to the axis and act as antennas. The lower frequency IF output signal emerges from a socket on the box to which the cable connects. The LNB gets its power from the receiver or set-top box and this phantom power travels to the LNB, opposite to the signals from the LNB. A corresponding component, called a block upconverter, is used at the earth station dish to convert the band of television channels to the microwave uplink frequency. The signal received by the LNB is extremely weak and it has to be amplified before downconversion, the low noise amplifier section of the LNB amplifies this weak signal while adding the minimum possible amount of noise to the signal. The low-noise quality of an LNB is expressed as the noise figure and this is the signal to noise ratio at the input divided by the signal to noise ratio at the output. It is typically expressed as a decibels value, the ideal LNB, effectively a perfect amplifier, would have a noise figure of 0 dB and would not add any noise to the signal. Every LNB off the line has a different noise figure because of manufacturing tolerances. Satellites use comparatively high radio frequencies to transmit their TV signals, as microwave satellite signals do not easily pass through walls, roofs, or even glass windows, it is preferable for satellite antennas to be mounted outdoors. The purpose of the LNB is to use the principle to take a block of relatively high frequencies. These lower frequencies travel through cables with much less attenuation, so there is much more signal left at the receiver end of the cable. It is also easier and cheaper to design electronic circuits to operate at these lower frequencies. The local oscillator frequency determines what block of incoming frequencies is downconverted to the expected by the receiver
7.
Luxury goods
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Luxury goods are often synonymous with superior goods and Veblen goods. Luxury goods are said to have high income elasticity of demand, as people become wealthier and this also means, however, that should there be a decline in income its demand will drop. Income elasticity of demand is not constant with respect to income, although the technical term luxury good is independent of the goods quality, they are generally considered to be goods at the highest end of the market in terms of quality and price. Classic luxury goods include haute couture clothing, accessories, and luggage, many markets have a luxury segment including, for example, automobile, yacht, wine, bottled water, coffee, tea, foods, watches, clothes, jewelry, and high fidelity. The hiring of full-time or live-in domestic servants is a luxury reflecting disparities of income, some financial services, especially in some brokerage houses, can be considered luxury services by default because persons in lower-income brackets generally do not use them. The three dominant trends in the luxury goods market are globalization, consolidation, and diversification. Globalization is a result of the availability of these goods, additional luxury brands. Consolidation involves the growth of big companies and ownership of brands across many segments of luxury products, examples include LVMH, Richemont, and Kering, which dominate the market in areas ranging from luxury drinks to fashion and cosmetics. Leading global consumer companies, such as Procter & Gamble, are attracted to the industry. The luxury goods market has been on a climb for many years. Apart from the setback caused by the 1997 Asian Financial Crisis, the industry has performed well, particularly in 2000. In that year, the luxury goods market – which includes drinks, fashion, cosmetics, fragrances, watches, jewelry, luggage, handbags – was worth close to $170 billion. The United States has been the largest regional market for goods and is estimated to continue to be the leading personal luxury goods market in 2013. The largest sector in this category was luxury drinks, including premium whisky, Champagne and this sector was the only one that suffered a decline in value. In 2012, China surpassed Japan as the worlds largest luxury market, chinas luxury consumption accounts for over 25% of the global market. The Economist Intelligence Unit published a report on the outlook for luxury goods in Asia which explores the trends and forecasts for the luxury goods market across key markets in Asia. In 2014, the sector is expected to grow over the next 10 years because of 440 million consumers spending a total of 880 billion euros. Secular luxury manuscripts were commissioned by the wealthy and differed in the same ways from cheaper books
8.
Ethernet
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Ethernet /ˈiːθərnɛt/ is a family of computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE802.3, 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 medium, while the newer Ethernet variants use twisted pair. Over the course of its history, Ethernet data transfer rates have increased from the original 2.94 megabits per second to the latest 100 gigabits per second. The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet, systems communicating over Ethernet divide a stream of data into shorter pieces called frames. As per the OSI model, Ethernet provides services up to, since its commercial release, Ethernet has retained a good degree of backward compatibility. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols, the primary alternative for some uses of contemporary LANs is Wi-Fi, a wireless protocol standardized as IEEE802.11. Ethernet was developed at Xerox PARC between 1973 and 1974 and it was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation. In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, in 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper. Metcalfe left Xerox in June 1979 to form 3Com and he convinced Digital Equipment Corporation, Intel, and Xerox to work together to promote Ethernet as a standard. The so-called DIX standard, for Digital/Intel/Xerox, specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and it was published on September 30,1980 as The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications, version 2 was published in November,1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the time and resulted in the publication of IEEE802.3 on June 23,1983. Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus, in the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, an Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced for a time, with drivers for DOS, by the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, and Ethernet ports began to appear on some PCs and most workstations. This process was sped up with the introduction of 10BASE-T and its relatively small modular connector. Since then, Ethernet technology has evolved to meet new bandwidth, in addition to computers, Ethernet is now used to interconnect appliances and other personal devices
9.
Superheterodyne receiver
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It was invented by US engineer Edwin Armstrong in 1918 during World War I. Virtually all modern radio receivers use the superheterodyne principle, Superheterodyne is a contraction of supersonic heterodyne, where supersonic indicates frequencies above the range of human hearing. The word heterodyne is derived from the Greek roots hetero- different, however, the signal from a continuous wave transmitter did not have any such inherent modulation and Morse Code from one of those would only be heard as a series of clicks or thumps. Fessendens idea was to run two Alexanderson alternators, one producing a carrier frequency 3 kHz higher than the other. In the receivers detector the two carriers would beat together to produce a 3 kHz tone thus in the headphones the Morse signals would then be heard as a series of 3 kHz beeps, for this he coined the term heterodyne meaning generated by a difference. The superheterodyne principle was devised in 1918 by U. S. Army Major Edwin Armstrong in France during World War I and he invented this receiver as a means of overcoming the deficiencies of early vacuum tube triodes used as high-frequency amplifiers in radio direction finding equipment. The strategic value was so high, however, that the British Admiralty felt the high cost was justified, Armstrong realized that if radio direction-finding receivers could be operated at a higher frequency, this would allow better detection of enemy shipping. However, at time, no practical short wave amplifier existed. Armstrong eventually deduced that this was caused by a supersonic heterodyne between the carrier frequency and the regenerative receivers oscillation frequency. Thus if a station was transmitting on 300 kHz and the receiver was set to 400 kHz, the station would be heard not only at the original 300 kHz. Armstrong realized that this was a solution to the short wave amplification problem, since the beat frequency still retained its original modulation. He termed this the intermediate frequency often abbreviated to IF, in December 1919, Major E. H. Armstrong gave publicity to an indirect method of obtaining short-wave amplification, called the super-heterodyne. Armstrong was able to put his ideas into practice, and the technique was adopted by the military. For early domestic radios, tuned radio frequency receivers were more popular because they were cheaper, easier for an owner to use. Armstrong eventually sold his patent to Westinghouse, who then sold it to RCA. Early superheterodyne receivers used IFs as low as 20 kHz, often based on the self-resonance of iron-cored transformers and this made them extremely susceptible to image frequency interference, but at the time, the main objective was sensitivity rather than selectivity. Using this technique, a number of triodes could be made to do the work that formerly required dozens of triodes. By the mid-1930s however, superheterodynes were using much higher frequencies, with tuned coils similar in construction to the aerial
10.
Communications satellite
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Communications satellites are used for television, telephone, radio, internet, and military applications. There are over 2,000 communications satellites in Earth’s orbit, Wireless communication uses electromagnetic waves to carry signals. These waves require line-of-sight, and are thus obstructed by the curvature of the Earth, the purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated points. Communications satellites use a range of radio and microwave frequencies. To avoid signal interference, international organizations have regulations for which frequency ranges or bands certain organizations are allowed to use and this allocation of bands minimizes the risk of signal interference. The concept of the communications satellite was first proposed by Arthur C. Clarke, building on work by Konstantin Tsiolkovsky and on the 1929 work by Herman Potočnik Das Problem der Befahrung des Weltraums — der Raketen-motor, in October 1945 Clarke published an article titled Extraterrestrial Relays in the British magazine Wireless World. The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals, thus, Arthur C. Clarke is often quoted as being the inventor of the communications satellite and the term Clarke Belt employed as a description of the orbit. Decades later a project named Communication Moon Relay was a project carried out by the United States Navy. Its objective was to develop a secure and reliable method of communication by using the Moon as a passive reflector. The first artificial Earth satellite was Sputnik 1, put into orbit by the Soviet Union on October 4,1957, it was equipped with an on-board radio-transmitter that worked on two frequencies,20.005 and 40.002 MHz. Sputnik 1 was launched as a step in the exploration of space, while incredibly important it was not placed in orbit for the purpose of sending data from one point on earth to another. And it was the first artificial satellite in the leading to todays satellite communications. The first artificial satellite used solely to further advances in communications was a balloon named Echo 1. Echo 1 was the worlds first artificial communications satellite capable of relaying signals to other points on Earth and it soared 1,600 kilometres above the planet after its Aug.12,1960 launch, yet relied on humanitys oldest flight technology — ballooning. Launched by NASA, Echo 1 was a 30-metre aluminized PET film balloon served as a passive reflector for radio communications. The worlds first inflatable satellite — or satelloon, as they were informally known — helped lay the foundation of todays satellite communications, the idea behind a communications satellite is simple, Send data up into space and beam it back down to another spot on the globe. Echo 1 accomplished this by serving as an enormous mirror,10 stories tall
11.
Block upconverter
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A block upconverter is used in the transmission of satellite signals. It converts a band of frequencies from a frequency to a higher frequency. Modern BUCs convert from the L band to Ku band, C band, older BUCs convert from a 70 MHz intermediate frequency to Ku band or C band. Most BUCs use phase-locked loop local oscillators and require an external 10 MHz frequency reference to maintain the correct transmit frequency, BUCs used in remote locations are often 2 or 4 W in the Ku band and 5 W in the C band. The 10 MHz reference frequency is sent on the same feedline as the main carrier. Many smaller BUCs also get their direct current over the feedline, BUCs are generally used in conjunction with low-noise block converters. The BUC, being a device, makes up the transmit side of the system, while the LNB is the down-converting device. An example of a system utilizing both a BUC and an LNB is a VSAT system, used for bidirectional Internet access via satellite. The block upconverter is a block shaped device assembled with the LNB in association with an OMT and this is opposed to other types of frequency upconverter which may be rack mounted indoors or not co-located with the dish. VSAT specific training that demonstrates the use of the block upconverter, BUCs, SSPAs, LNBs GaN vs GaAs VSAT Installation Manual with explanation of the block upconverter Swedish microwave LNB Terrasat Communications Ground Breaking IBUC
12.
Low-voltage differential signaling
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Low-voltage differential signaling, or LVDS, also known as TIA/EIA-644, is a technical standard that specifies electrical characteristics of a differential, serial communications protocol. LVDS operates at low power and can run at high speeds using inexpensive twisted-pair copper cables. Since LVDS is a physical layer specification only, many data communication standards and applications use it, the typical applications are high-speed video, graphics, video camera data transfers, and general purpose computer buses. LVDS is a signaling system, meaning that it transmits information as the difference between the voltages on a pair of wires, the two wire voltages are compared at the receiver. In a typical implementation, the transmitter injects a constant current of 3.5 mA into the wires, the current passes through a termination resistor of about 100 to 120 ohms at the receiving end, and then returns in the opposite direction via the other wire. From Ohms law, the difference across the resistor is therefore about 350 mV. The receiver senses the polarity of voltage to determine the logic level. As long as there is tight electric- and magnetic-field coupling between the two wires, LVDS reduces the generation of electromagnetic noise and this noise reduction is due to the equal and opposite current flow in the two wires creating equal and opposite electromagnetic fields that tend to cancel each other. In addition, the tightly coupled transmission wires will reduce susceptibility to noise interference because the noise will equally affect each wire. The LVDS receiver is unaffected by common mode noise because it senses the differential voltage, the low common-mode voltage of about 1.2 V allows using LVDS with a wide range of integrated circuits with power supply voltages down to 2.5 V or lower. In addition, there are variations of LVDS that use a common mode voltage. One example is sub-LVDS that uses 0.9 V typical common mode voltage, another is Scalable Low Voltage Signaling for 400 mV specified in JEDEC JESD8-13 October 2001 where the power supply can be as low as 800 mV and common mode voltage is about 400 mV. The low differential voltage, about 350 mV, causes LVDS to consume little power compared to other signaling technologies. At 2.5 V supply voltage the power to drive 3.5 mA becomes 8.75 mW, Logic levels, LVDS is not the only low power differential signaling system in use, others include the Fairchild Current Transfer Logic serial I/O. LVDS became popular in the mid 1990s, before that, computer monitor resolutions were not large enough to need such fast data rates for graphics and video. However, in 1992 Apple Computer needed a method to transfer multiple streams of digital video without overloading the existing NuBus on the backplane, Apple and National Semiconductor created QuickRing, which was the first integrated circuit using LVDS. QuickRing was a high speed auxiliary bus for data to bypass the NuBus in Macintosh computers. The multimedia and supercomputer applications continued to expand because both needed to move large amounts of data over links several meters long, FPD-Link became the de facto open standard for this notebook application in the late 1990s and is still the dominant display interface today in notebook and tablet computers
