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PDF generated using the open source mwlib toolkit. Contents Articles Fundamentals Telecommunication Electromagnetic radiation Electromagnetic induction 1 1 15 23 25 25 29 32 37 49 50 54 54 60 60 67 67 87 87 93 96 96 After Sleep - Connexx - In Memory Of An Angel Frequency synthesizer Frequency mixer Very high frequency Ultra high frequency Super high frequency Extremely high frequency.
Fundamentals Telecommunication Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for example. In the modern age of electricity and electronics, telecommunications now also includes the use of electrical devices such as telegraphs, telephones, and teletypes, the use of radio and microwave communications, as well as fiber optics and their associated electronics, plus the use of the orbiting satellites and the Internet.
A Gower telephone, at the Muse des Arts et A revolution in wireless telecommunications began in the first decade Mtiers in Paris of the 20th century, with Guglielmo Marconi winning the Nobel Prize in Physics in for his pioneering developments in wireless radio communications. Other highly notable pioneering inventors and developers in the field of electrical and electronic telecommunications include Charles Wheatstone and Samuel Morse telegraphAlexander Graham Bell telephoneNikola Tesla, Edwin Armstrong, and Lee de Forest radioas well as John Logie Baird and Philo Farnsworth television.
History Ancient systems Greek hydraulic semaphore systems were used as early as the 4th century BC. The hydraulic semaphores, which worked with water filled vessels and Plunking Alvin - F. Gartner* - Untitled signals, functioned as optical telegraphs. However, they could only utilize a very limited range of pre-determined messages, and as with all such optical telegraphs could only be deployed during good visibility conditions.
Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London that signaled the arrival of the Spanish warships.
Systems since the Middle Ages InClaude Chappe, a French engineer, built the first fixed visual telegraphy system or semaphore line between Lille and Paris. As a result of competition from the electrical telegraph, Europe's last commercial semaphore line in Sweden was abandoned in The telegraph and telephone The first commercial electrical telegraph was constructed by Sir Charles Wheatstone and Sir William Fothergill Cooke, and its use began on April 9, Both Wheatstone and Cooke viewed their device as "an improvement to the [already-existing, so-called] electromagnetic telegraph" not as a new device.
Morse and the physicist Joseph Henry Nalbach of the United Plunking Alvin - F. Gartner* - Untitled developed their own, simpler version of the electrical telegraph, independently. Morse successfully demonstrated this system on Sand Castle Pimping - Marvalous Persona X Beach Boy Bay* - Marvalous Beach (File, Album) 2, Morse's most important technical contribution to this telegraph was the rather simple and highly efficient Morse Code, which was an important advance over Wheatstone's complicated and significantly more expensive telegraph system.
The communications efficiency of the Morse Code anticipated that of the Huffman code in digital communications by over years, but Morse and his associate Alfred Vail developed the code purely empirically, unlike Huffman, who gave a detailed theoretical explanation of how his method worked.
The first permanent transatlantic Plunking Alvin - F. Gartner* - Untitled cable was successfully completed on 27 Julyallowing transatlantic electrical communication for the first time. However, that transatlantic cable failed soon, and the project to lay a replacement line was delayed for five years by the American Civil War. Also, these transatlantic cables would have been completely incapable of carrying telephone calls even had the telephone already been invented.
The first transatlantic telephone cable which incorporated hundreds of electronic amplifiers was not operational until Credit for the invention of the electric telephone has been frequently disputed, and new controversies over the issue have arisen from time-to-time. As with other great inventions such as radio, television, the light bulb, and the digital computer, there were several inventors who did pioneering experimental work on voice transmission over a wire, and then they improved on each other's ideas.
The first commercial telephone services were set up in and on both sides of the Atlantic in the cities of New Haven, Connecticut, and London, England. Radio and television InJames Lindsay gave a classroom demonstration of wireless telegraphy via conductive water to his students. Byhe was able to demonstrate a transmission across the Firth of Tay from Dundee, Scotland, to Woodhaven, a distance of about two miles 3kmagain Total Eclipse Of The Heart - Meat Loaf & Bonnie Tyler - Heaven & Hell water as the transmission medium.
Baird's system relied upon the fast-rotating Nipkow disk, and thus it became known as the mechanical television. It formed the basis of experimental broadcasts done by the British Broadcasting Corporation beginning September 30, The first version of such an electronic television to show promise was produced by Philo Farnsworth of the United States, and it was demonstrated to his family in Idaho on September 7, However, it was not until the s that researchers started to investigate packet switching a technology that allows chunks of data to be sent between different computers without first passing through a centralized mainframe.
A four-node network emerged on December 5, This process is important because ARPANET would eventually merge with other networks to form the Internet, and many of the communication protocols that the Internet relies upon today were specified through the Request for Comment process. However, not all important developments were made through the Request for Comment process. Two popular link protocols for local area networks LANs also appeared in the s.
Key concepts Etymology The word telecommunication was adapted from the French word tlcommunication. It is a compound of the Greek prefix tele- -meaning  "far off", and the Latin communicare, meaning "to share". The French word tlcommunication was coined in by the French engineer and  novelist douard Estauni.
A number of key concepts reoccur throughout the literature on modern telecommunication systems. Some of these concepts are discussed below. Basic elements A basic Plunking Alvin - F. Gartner* - Untitled system consists of three primary units that are always present in some form: A transmitter that takes information and converts it to a signal.
A transmission medium, also called the "physical channel" that carries the signal. An example of this is the "free space channel". A receiver that takes the signal from the channel and converts it back into usable information. For example, in a radio broadcasting station the station's large power amplifier is the transmitter; and the broadcasting antenna is the interface between the power amplifier and the "free space channel". The free space channel is the transmission medium; and the receiver's antenna is the interface between the free space channel and the receiver.
Next, the radio receiver is the destination of the radio signal, and this is where it is converted from electricity to sound for people to listen to. Sometimes, telecommunication systems are "duplex" two-way systems with a single box of electronics working as both a transmitter and a receiver, or a transceiver. For example, a cellular telephone is a transceiver. This can be readily explained by the fact that radio transmitters contain power amplifiers that operate with electrical powers measured in the watts or kilowatts, but radio receivers deal with radio powers that are measured in the microwatts or nanowatts.
Hence, transceivers have to be carefully designed and built to isolate their high-power circuitry and their low-power circuitry from each other. Telecommunication over telephone lines is called point-to-point communication because it is between one transmitter and one receiver.
Telecommunication through radio broadcasts is called broadcast communication because it is between one powerful transmitter and numerous low-power but sensitive radio receivers. Analog versus digital communications Communications signals can be either by analog signals or digital signals. There are analog communication systems and digital communication systems. For an analog signal, the signal is varied continuously with respect to the information.
In a digital signal, the information is encoded as a set of discrete values for example, a set of ones and zeros. During the propagation and reception, the information contained in analog signals will inevitably be degraded by undesirable physical noise.
The output of a transmitter is noise-free for all practical purposes. Commonly, the noise in a communication system can be expressed as adding or subtracting from the desirable signal in a completely random way. This form of noise is called "additive noise", with the understanding that the noise can be negative or positive at different instants of time. Noise that is not additive noise is a much more difficult situation to describe or analyze, and these other kinds of noise will be omitted here.
On the Plunking Alvin - F. Gartner* - Untitled hand, unless the additive noise disturbance exceeds a certain threshold, the information contained in digital signals will remain intact. Their resistance to noise represents a key advantage of digital signals over analog.
Telecommunication networks A communications network is a collection of transmitters, receivers, and communications channels that send messages to one another. Some digital communications networks contain one or more routers that work together to transmit information to the correct user. An analog communications network consists of one or more switches that establish a connection between two or more users.
For both types of network, repeaters may be necessary to amplify or recreate the signal when it Plunking Alvin - F.
Gartner* - Untitled being transmitted over long distances. This is to combat attenuation that can render the signal indistinguishable from the noise. Communication channels The term "channel" has two different meanings.
In one meaning, a channel is the physical medium that carries a signal between the transmitter and the receiver. Examples of this include the atmosphere for sound communications, glass optical fibers for some kinds of optical communications, coaxial cables Cyberskin - Optical & Ed Rush* - Chameleon communications by way of the voltages and electric currents in them, and free space for communications using visible light, infrared waves, ultraviolet light, and radio waves.
This last channel is called the "free space channel". The sending of radio Plunking Alvin - F. Gartner* - Untitled from one place to another has nothing to do with the presence or absence of an atmosphere between the two.
Radio waves travel through a perfect vacuum just as easily as they travel through air, fog, clouds, or any other kind of gas besides air. The other meaning of the term "channel" in telecommunications is seen in the phrase communications channel, which is a Plunking Alvin - F. Gartner* - Untitled of a transmission medium so that it can be used to send multiple streams of information simultaneously.
For example, one radio station can broadcast radio waves into free space at frequencies in the neighborhood of Each radio station would transmit radio waves over a frequency bandwidth of about kHz kilohertzcentered at frequencies such as the above, which are called the "carrier frequencies".
Each station in this example is separated from its adjacent stations by kHz, and the difference between kHz and kHz 20kHz is an engineering allowance for the imperfections in the communication system.
In the Island Of Domination - Judas Priest - The Best Of above, the "free space channel" has been divided into communications channels according to frequencies, and each channel is assigned a separate frequency bandwidth in which to broadcast radio waves.
This system of dividing the medium into channels according to frequency is called "frequency-division multiplexing" FDM. Another way of dividing a communications medium into channels is to allocate each sender a recurring segment of time a "time slot", for example, 20 milliseconds out of each secondand to allow each sender to send messages only within its own time slot. This method of dividing the medium into communication channels is called "time-division multiplexing" TDMand is used in optical fiber communication.
Modulation The shaping of a signal to convey information is known as modulation. Modulation can be used to represent a digital message as an analog waveform.
This is commonly called "keying" a term derived from the older use of Morse Code in telecommunications and several keying techniques exist these include phase-shift keying, frequency-shift keying, and amplitude-shift keying.
The "Bluetooth" system, for example, uses phase-shift keying to exchange information between various devices. Telecommunication Modulation can also be used to transmit the information of low-frequency analog signals at higher frequencies.
This is helpful because low-frequency analog signals cannot be effectively transmitted over free space. Hence the information from a low-frequency analog signal must be impressed into a higher-frequency signal known as the "carrier wave" before transmission. There are several different modulation schemes available to achieve this [two of Jelle Paulusma - Stick Around With You most basic being amplitude modulation AM and frequency modulation FM ].
An example of this process is a disc jockey's voice being impressed into a 96MHz carrier wave using frequency modulation the voice would then be received on a radio as the channel "96FM". Society and telecommunication Telecommunication has a significant social, cultural.
Economic impact Microeconomics On the microeconomic scale, companies have used telecommunications to help build global business empires. This is self-evident in the case of online retailer Amazon. Even relatively-poor communities have been noted to use telecommunication to Plunking Alvin - F. Gartner* - Untitled advantage.
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