1.
Grundig
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Grundig is a German manufacturer of consumer electronics, domestic appliances and personal care products. Established in 1945 by Max Grundig in Nuremberg, Grundig became one of the leading manufacturers in Europe offering the widest product range in home electronics after launching its white goods product range in 2013. Arcelik A. Ş. is the owner of Grundig and has 27,000 employees worldwide, Grundig manufacturing plants are located in several European cities delivering Grundig products to more than 65 countries around the world. Since 2011, Grundig has been the first official partner of the German Soccer League. Grundig is a subsidiary of Arçelik A. Ş. established in 1955, located in Istanbul, having operations in durable consumer goods industry with production, marketing and after-sales services, Arçelik A. Ş. Arçelik A. Ş is market leader in white goods in Turkey, the consolidated net sales turnover is TRY12,5 Billion. It holds the position of leadership in Turkey and maintained its undisputed market leadership with Arctic brand in Romania. Grundig began in 1930 with the establishment of a store named Fürth, Grundig & Wurzer, after the Second World War, Max Grundig recognized the need for radios in Germany, and in 1947 produced a kit, while a factory and administration centre were built at Fürth. In 1951, the first television sets were manufactured at the new facility, at the time Grundig was the largest radio manufacturer in Europe. Divisions in Nuremberg, Frankfurt and Karlsruhe were established, a plant was opened in 1960 to manufacture tape recorders in Belfast, Northern Ireland, the first production by Grundig outside Germany. The managing director of the plant Thomas Niedermayer, was kidnapped, the factory was closed with the loss of around 1000 jobs in 1980. In 1972, Grundig GmbH became Grundig AG, after this Philips began to gradually accumulate shares in the company over the years, and assumed complete economic control in 1993. Grundig pulled out of partnership in 1998 owing to unsatisfactory performance. At the end of June 2000 the company relocated its headquarters in Fürth to Nuremberg-Langwasser, Grundig had a turnover of €1.281 billion the following year. In autumn 2002, Grundigs banks did not extend the lines of credit. Grundig AG declared bankruptcy in 2003, in 2004 Britains Alba plc and the Turkish Koçs Beko jointly took over Grundig Home InterMedia System, Grundigs consumer electronics division. In 2007 Alba sold its half of the business to Koç for US$50.3 million, although it retained the license to use the Grundig brand in the UK until 2010, and in Australasia until 2012. In the United States, products marketed under the Grundig brand are manufactured by the Eton Corporation, based in Palo Alto, spains Grupo Vitelcom is licensed to manufacture mobile telephones using the Grundig Mobile brand, and auto parts company Delphi manufactures car radios branded Grundig
2.
Shortwave radio receiver
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Shortwave radio is radio transmission using shortwave frequencies, generally 1. 6–30 MHz, just above the medium wave AM broadcast band. Radio waves in this band can be reflected or refracted from a layer of charged atoms in the atmosphere called the ionosphere. Therefore, short waves directed at an angle into the sky can be reflected back to Earth at great distances and this is called skywave or skip propagation. Shortwave radio is used for broadcasting of voice and music to listeners over very large areas. It is also used for military radar, diplomatic communication. The widest popular definition of the frequency interval is the ITU Region 1 definition, and is the span 1. 6–30 MHz, just above the medium wave band. In reality, the definition of the frequency band is a mess. The broadcast medium wave band now extends above the 200 m/1500 kHz limit, early radio telegraphy had used long wave transmissions. The drawbacks to this included a very limited spectrum available for long distance communication. It was also difficult to beam the radio wave directionally with long wave, prior to the 1920s, the shortwave frequencies above 1.5 MHz were regarded as useless for long distance communication and were designated in many countries for amateur use. Franklin rigged up an antenna at Poldhu Wireless Station, Cornwall. In June and July 1923, wireless transmissions were completed during nights on 97 meters from Poldhu to Marconis yacht Elettra in the Cape Verde Islands, in September 1924, Marconi transmitted daytime and nighttime on 32 meters from Poldhu to his yacht in Beirut. Franklin went on to refine the directional transmission, by inventing the curtain array aerial system, the UK-to-Canada shortwave Beam Wireless Service went into commercial operation on 25 October 1926. Beam Wireless Services from the UK to Australia, South Africa, Shortwave communications began to grow rapidly in the 1920s, similar to the internet in the late 20th century. Shortwave also ended the need for investments in massive longwave wireless stations. The cable companies began to lose large sums of money in 1927, the British government convened the Imperial Wireless and Cable Conference in 1928 to examine the situation that had arisen as a result of the competition of Beam Wireless with the Cable Services. The name of the company was changed to Cable and Wireless Ltd. in 1934, long-distance cables had a resurgence beginning in 1956 with the laying of TAT-1 across the Atlantic Ocean, the first voice frequency cable on this route. This provided 36 high quality telephone channels and was followed by even higher capacity cables all around the world
3.
Radio
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When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
4.
High frequency
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High frequency is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 MHz. It is also known as the band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency, while the band of higher frequencies is known as the very high frequency band. The HF band is a part of the shortwave band of frequencies. The band is used by shortwave broadcasting stations, aviation communication, government time stations, weather stations, amateur radio and citizens band services. By this method HF radio waves can travel beyond the horizon, around the curve of the Earth and it depends on the angle of incidence of the waves, it is lowest when the waves are directed straight upwards, and is higher with less acute angles. This means that at longer distances, where the waves graze the ionosphere at a blunt angle. The lowest usable frequency depends on the absorption in the layer of the ionosphere. This absorption is stronger at low frequencies and is stronger with increased solar activity. When all factors are at their optimum, worldwide communication is possible on HF, at many other times it is possible to make contact across and between continents or oceans. At worst, when a band is dead, no communication beyond the limited groundwave paths is possible no matter what powers, on such an open band, interference originating over a wide area affects many potential users. These issues are significant to military, safety and amateur radio users of the HF bands, other standards development such as STANAG5066 provides for error free data communications through the use of ARQ protocols. Noise, especially man-made interference from devices, tends to have a great effect on the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over broadband over power lines Internet access and this is due to the frequencies on which BPL operates and the tendency for the BPL signal to leak from power lines. Some BPL providers have installed notch filters to block out certain portions of the spectrum, other electronic devices including plasma televisions can also have a detrimental effect on the HF spectrum. In aviation, HF communication systems are required for all trans-oceanic flights and these systems incorporate frequencies down to 2 MHz to include the 2182 kHz international distress and calling channel. The upper section of HF shares many characteristics with the part of VHF. The parts of this section not allocated to radio are used for local communications
5.
Medium frequency
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Medium frequency is the ITU designation for radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band, the MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten to one hectometer. Frequencies immediately below MF are denoted low frequency, while the first band of frequencies is known as high frequency. MF is mostly used for AM radio broadcasting, navigational beacons, maritime ship-to-shore communication. A major use of frequencies is AM broadcasting, AM radio stations are allocated frequencies in the medium wave broadcast band from 526.5 kHz to 1606. Although these are medium frequencies,120 meters is generally treated as one of the shortwave bands, there are a number of coast guard and other ship-to-shore frequencies in use between 1600 and 2850 kHz. These include, as examples, the French MRCC on 1696 kHz and 2677 kHz, Stornoway Coastguard on 1743 kHz,2182 kHz is the international calling and distress frequency for SSB maritime voice communication. It is analogous to Channel 16 on the marine VHF band,500 kHz was for many years the maritime distress and emergency frequency, and there are more NDBs between 510 and 530 kHz. Navtex, which is part of the current Global Maritime Distress Safety System occupies 518 kHz and 490 kHz for important digital text broadcasts. Lastly, there are aeronautical and other mobile SSB bands from 2850 kHz to 3500 kHz, an amateur radio band known as 160 meters or top-band is between 1800 and 2000 kHz. Amateur operators transmit CW morse code, digital signals and SSB voice signals on this band, in recent years, some limited amateur radio operation has also been allowed in the region of 500 kHz in the US, UK, Germany and Sweden. Propagation at MF wavelengths is via ground waves and reflection from the ionosphere, ground waves follow the contour of the Earth. MF broadcasting stations use ground waves to cover their listening areas, however at certain times the D layer can be electronically noisy and absorb MF radio waves, interfering with skywave propagation. When this happens, MF radio waves can easily be received hundreds or even thousands of miles away as the signal will be refracted by the remaining F layer and this can be very useful for long-distance communication, but can also interfere with local stations. Due to the number of available channels in the MW broadcast band. On nights of good skywave propagation, the signals of distant stations may reflect off the ionosphere and interfere with the signals of local stations on the same frequency. These channels are called clear channels, and the stations, called stations, are required to broadcast at higher powers of 10 to 50 kW. Transmitting antennas commonly used on this band include monopole mast radiators, top-loaded wire monopole antennas such as the inverted-L and T antennas, ground wave propagation, the most widely used type at these frequencies, requires vertically polarized antennas like monopoles
6.
Medium wave
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Medium wave is the part of the medium frequency radio band used mainly for AM radio broadcasting. Practical groundwave reception typically extends to 200–300 miles, with distances over terrain with higher ground conductivity. Most broadcast stations use groundwave to cover their listening area, Medium waves can also reflect off charged particle layers in the ionosphere and return to Earth at much greater distances, this is called the skywave. At night, especially in winter months and at times of low solar activity, when this happens, MF radio waves can easily be received many hundreds or even thousands of miles away as the signal will be reflected by the higher F layer. This can allow very long-distance broadcasting, but can also interfere with distant local stations, due to the limited number of available channels in the MW broadcast band, the same frequencies are re-allocated to different broadcasting stations several hundred miles apart. On nights of good skywave propagation, the signals of distant station may interfere with the signals of local stations on the same frequency. These channels are called clear channels, and they are required to broadcast at higher powers of 10 to 50 kW and this arrangement had numerous practical difficulties. The Commerce Department rarely intervened in such cases but left it up to stations to enter into voluntary timesharing agreements amongst themselves, the addition of a third entertainment wavelength,400 meters, did little to solve this overcrowding. In 1923, the Commerce Department realized that as more and more stations were applying for commercial licenses, on 15 May 1923, Commerce Secretary Herbert Hoover announced a new bandplan which set aside 81 frequencies, in 10 kHz steps, from 550 kHz to 1350 kHz. Each station would be assigned one frequency, no longer having to broadcast weather, class A and B stations were segregated into sub-bands. Today in most of the Americas, mediumwave broadcast stations are separated by 10 kHz and have two sidebands of up to ±5 kHz in theory, in the rest of the world, the separation is 9 kHz, with sidebands of ±4.5 kHz. Both provide adequate quality for voice, but are insufficient for high-fidelity broadcasting. In the US and Canada the maximum power is restricted to 50 kilowatts. Those stations which shut down completely at night are known as daytimers. In most cases there are two limits, a lower one for omnidirectional and a higher one for directional radiation with minima in certain directions. The power limit can also be depending on daytime and it is possible, other countries may only operate low-powered transmitters on the same frequency, again subject to agreement. For example, Russia operates a transmitter, located in its Kaliningrad exclave and used for external broadcasting. Due to the demand for frequencies in Europe, many countries operate single frequency networks, in Britain
7.
Ionosphere
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The ionosphere is a region of Earths upper atmosphere, from about 60 km to 1,000 km altitude, and includes the thermosphere and parts of the mesosphere and exosphere. It is ionized by radiation, plays an important part in atmospheric electricity. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth and it owes its existence primarily to ultraviolet radiation from the Sun. The lowest part of the Earths atmosphere, the troposphere extends from the surface to about 10 km, above 10 km is the stratosphere, followed by the mesosphere. In the stratosphere incoming solar radiation creates the ozone layer, at heights of above 80 km, in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. The number of free electrons is sufficient to affect radio propagation. This portion of the atmosphere is ionized and contains a plasma which is referred to as the ionosphere, in this process the light electron obtains a high velocity so that the temperature of the created electronic gas is much higher than the one of ions and neutrals. The reverse process to ionization is recombination, in which an electron is captured by a positive ion. Recombination occurs spontaneously, and causes the emission of a photon carrying away the energy produced upon recombination, as gas density increases at lower altitudes, the recombination process prevails, since the gas molecules and ions are closer together. The balance between two processes determines the quantity of ionization present. Ionization depends primarily on the Sun and its activity, the amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun. Thus there is an effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation, the activity of the Sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location, there are also mechanisms that disturb the ionosphere and decrease the ionization. There are disturbances such as flares and the associated release of charged particles into the solar wind which reaches the Earth. At night the F layer is the layer of significant ionization present. During the day, the D and E layers become more heavily ionized, as does the F layer
8.
Skywave
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In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon and it is mostly used in the shortwave frequency bands. Most long-distance shortwave radio communication—between 3 and 30 MHz—is a result of skywave propagation, since the early 1920s amateur radio operators, limited to lower transmitter power than broadcast stations, have taken advantage of skywave for long distance communication. The ionosphere is a region of the atmosphere, from about 80 km to 1000 km in altitude. When high frequency signals enter the ionosphere obliquely, they are back-scattered from the layer as scatter waves. If the midlayer ionization is strong compared to the signal frequency. Earths surface then reflects the incoming wave back towards the ionosphere. Consequently, like a rock skipping across water, the signal may effectively bounce or skip between the earth and ionosphere two or more times. Since at shallow incidence losses remain quite small, signals of only a few watts can sometimes be received thousands of miles away as a result. This is what enables shortwave broadcasts to all over the world. If the ionization is not great enough, the wave is initially deflected downwards. Sky wave propagation occurs in the waveguide formed by the ground and ionosphere, with a single hop, path distances up to 3500 km may be reached. Transatlantic connections are mostly obtained with two or three hops, the layer of ionospheric plasma with equal ionization is not fixed, but undulates like the surface of the ocean. Varying reflection efficiency from this surface can cause the reflected signal strength to change. Alternatively, signals beamed close to the enter the ionosphere at a shallow angle. VHF signals with frequencies above about 30 MHz usually penetrate the ionosphere and are not returned to the Earths surface, e-skip is a notable exception, where VHF signals including FM broadcast and VHF TV signals are frequently reflected to the Earth during late Spring and early Summer. E-skip rarely affects UHF frequencies, except for very rare occurrences below 500 MHz, frequencies below approximately 10 MHz, including broadcasts in the mediumwave and shortwave bands, propagate most efficiently by skywave at night. Frequencies above 10 MHz typically propagate most efficiently during the day, frequencies lower than 3 kHz have a wavelength longer than the distance between the Earth and the ionosphere
9.
Line-of-sight propagation
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Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves which travel in a direct path from the source to the receiver. Electromagnetic transmission includes light emissions traveling in a straight line, the rays or waves may be diffracted, refracted, reflected, or absorbed by atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles. In contrast to line-of-sight propagation, at low frequency due to radio waves can travel as ground waves. This enables AM broadcast radio stations to transmit beyond the horizon, however, at frequencies above 30 MHz and in lower levels of the atmosphere, neither of these effects are significant. Thus, any obstruction between the antenna and the receiving antenna will block the signal, just like the light that the eye may sense. The farthest possible point of propagation is referred to as the radio horizon, in practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal. Broadcast FM radio, at low frequencies of around 100 MHz, are less affected by the presence of buildings. Low-powered microwave transmitters can be foiled by tree branches, or even heavy rain or snow, if a direct visual fix cannot be taken, it is important to take into account the curvature of the Earth when calculating line-of-sight from maps. Designs for microwave used to use 4/3 earth radius to compute clearances along the path, the presence of objects not in the direct visual line of sight can interfere with radio transmission. This is caused by diffraction effects, for the best propagation, reflected radiation from the ground plane also acts to cancel out the direct signal. This effect, combined with the free-space r−2 propagation loss to a r−4 propagation loss and this effect can be reduced by raising either or both antennas further from the ground, the reduction in loss achieved is known as height gain. Although the frequencies used by mobile phones are in the line-of-sight range, for mobile phone services, these problems are tackled using, rooftop or hilltop positioning of base stations many base stations. A phone can typically see at least three, and usually as many as six at any given time, sectorized antennas at the base stations. Instead of one antenna with omnidirectional coverage, the station may use as few as 3 or as many as 32 separate antennas and this allows the base station to use a directional antenna that is pointing at the user, which improves the signal to noise ratio. If the user moves from one sector to another, the base station automatically selects the proper antenna. Electromagnetic radiation is blocked where the wavelength is longer than any gaps and this means that windowless metal enclosures will completely block cell signs, such as elevator cabins, and parts of trains, cars, and ships. The same problem can affect signals in buildings with steel reinforcement. The radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth, if the Earth was a perfect sphere and there was no atmosphere, the radio horizon would be a circle
10.
Broadcasting
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Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and receivers. Before this, all forms of communication were one-to-one, with the message intended for a single recipient. Over the air broadcasting is usually associated with radio and television, the receiving parties may include the general public or a relatively small subset, the point is that anyone with the appropriate receiving technology and equipment can receive the signal. The field of broadcasting includes both government-managed services such as radio, community radio and public television, and private commercial radio. The U. S. Code of Federal Regulations, title 47, part 97 defines broadcasting as transmissions intended for reception by the general public, private or two-way telecommunications transmissions do not qualify under this definition. For example, amateur and citizens band radio operators are not allowed to broadcast, as defined, transmitting and broadcasting are not the same. Transmissions using a wire or cable, like television, are also considered broadcasts. In the 2000s, transmissions of television and radio programs via streaming digital technology have increasingly been referred to as broadcasting as well, the earliest broadcasting consisted of sending telegraph signals over the airwaves, using Morse code, a system developed in the 1830s by Samuel F. B. Morse, physicist Joseph Henry and Alfred Vail and they developed an electrical telegraph system which sent pulses of electric current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, Morse therefore developed the forerunner to modern International Morse code. Audio broadcasting began experimentally in the first decade of the 20th century, by the early 1920s radio broadcasting became a household medium, at first on the AM band and later on FM. Television broadcasting started experimentally in the 1920s and became widespread after World War II, satellite broadcasting was initiated in the 1960s and moved into general industry usage in the 1970s, with DBS emerging in the 1980s. Originally all broadcasting was composed of signals using analog transmission techniques but in the 2000s. In general usage, broadcasting most frequently refers to the transmission of information, Analog audio vs. HD Radio Analog television vs.9 zettabytes. This is the equivalent of 55 newspapers per person per day in 1986. Historically, there have been several methods used for broadcasting electronic media audio and/or video to the public, Telephone broadcasting. Telephone broadcasting also grew to include telephone services for news and entertainment programming which were introduced in the 1890s. These telephone-based subscription services were the first examples of electrical/electronic broadcasting, Radio broadcasting, audio signals sent through the air as radio waves from a transmitter, picked up by an antenna and sent to a receiver
11.
Shortwave listening
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Shortwave listening, or SWLing, is the hobby of listening to shortwave radio broadcasts located on frequencies between 1700 kHz and 30 MHz. In some developing countries, shortwave listening enables remote communities to obtain regional programming traditionally provided by medium wave AM broadcasters. One 2002 estimate placed the number of listeners worldwide in the hundreds of millions. The practice of radio listening began in the 1920s when shortwave broadcasters were first established in the US. Shortwave listening was popular during times of international conflict such as World War II, the Korean War. The number of organized shortwave listening clubs has diminished along with printed magazines devoted to the hobby, however, many continue to exchange information. The practice of listening to distant stations in the medium wave AM broadcast band was carried over to the shortwave bands, frank Conrad, an early pioneer of medium wave broadcasting with KDKA in Pittsburgh, instituted some of the first shortwave broadcasts around 1921. Stations affiliated with General Electric and Crosley followed shortly after, united States shortwave broadcasters began transmitting popular radio programs in an attempt to attract foreign audiences. During the 1930s, new shortwave receivers appeared on the market as well as popular shortwave magazines, Shortwave stations often offered unique QSL cards for DXers. In Europe, shortwave broadcasts from Britain and the Netherlands such as Philips Radios PCJJ began around 1927, Germany, Italy, the Soviet Union, Britain, and many other countries soon followed, and some classic shortwave broadcasters got their start. The BBC began on shortwave as the BBC Empire Service in 1932 and its broadcasts were aimed principally at English speakers. Radio Moscow was broadcasting on shortwave in English, French, German, Italian, the Voice of America began broadcasting in 1942 after its entry into World War II using the Yankee Doodle musical theme. Shortwave receiver manufacturers contributed to war production, zenith launched the multi-band Trans-Oceanic series of radios in 1942. In some other countries, during the war, listening to foreign stations was a criminal offense, established in 1939, 35-kilowatt Chinese shortwave station XGOY broadcast programming aimed at listening-restricted Japan. The station was bombed by the Japanese. CBS began a listening program in September 1939, on an experimental basis, at the National Lawn Tennis Championships at West Side Tennis Club in Forest Hills. Engineers installed equipment at the CBS booth when the location was found to have good reception, throughout World War II, CBS captured Allied and enemy shortwave communications from more than 60 international stations via secretly located receivers. Major headline news frequently resulted, since big stories often broke first on radio, Shortwave listeners notified families of prisoners of war when studio announcers at stations in Axis powers countries, such as Germany and Japan, read prisoner-written messages
12.
Over-the-horizon radar
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Several OTH radar systems were deployed starting in the 1950s and 1960s as part of early warning radar systems, but these have generally been replaced by airborne early warning systems instead. The high frequency waves used by most radars, called microwaves. This generally limits the range of radar systems to objects on their horizon due to the curvature of the Earth. For example, a radar mounted on top of a 10 m mast has a range to the horizon of about 13 kilometres, taking into account atmospheric refraction effects. If the target is above the surface, this range will be increased accordingly, siting the antenna on a high mountain can increase the range somewhat, but, in general, it is impractical to build radar systems with line-of-sight ranges beyond a few hundred kilometres. OTH radars use various techniques to see beyond that limit and these systems achieve detection ranges of the order of a hundred kilometres from small, conventional radar installations. The most common type of OTH radar uses skywave or skip propagation, in which radio waves are reflected off an ionized layer in the atmosphere. A small amount of signal will be scattered off desired targets back towards the sky, reflect off the ionosphere again. Only one range of frequencies regularly exhibits this behaviour, the frequency or shortwave part of the spectrum from 3 to 30 MHz. The resolution of any radar depends on the width of the beam, for example, a radar with 1 degree beam width and a target at 120 km range will show the target as 2 km wide. To produce a 1 degree beam at the most common frequencies, due to the physics of the reflection process, actual accuracy is even lower, with range resolution on the order of 20 to 40 kilometres and bearing accuracy of 2 to 4 kilometres being suggested. Even a 2 km accuracy is only for early warning. Another problem is that the process is highly dependent on the angle between the signal and the ionosphere, and is generally limited to about 2 to 4 degrees off the local horizon. OTH systems are very expensive to build, and essentially immobile. The easiest way to do this is to use the Doppler effect, by filtering out all the backscatter signal close to the original transmitted frequency, moving targets become visible. Even a small amount of movement can be using this process. This basic concept is used in almost all modern radars, most systems used a second transmitter broadcasting directly up at the ionosphere to measure its movement and adjust the returns of the main radar in real-time. Doing so required the use of computers, another reason OTH systems did not become practical until the 1960s
13.
Amateur radio
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The amateur radio service is established by the International Telecommunication Union through the International Telecommunication Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with a call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics, according to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are regularly involved with amateur radio. About 830,000 amateur radio stations are located in IARU Region 2 followed by IARU Region 3 with about 750,000 stations, a significantly smaller number, about 400,000, are located in IARU Region 1. The origins of amateur radio can be traced to the late 19th century, the First Annual Official Wireless Blue Book of the Wireless Association of America, produced in 1909, contains a list of amateur radio stations. This radio callbook lists wireless telegraph stations in Canada and the United States, as with radio in general, amateur radio was associated with various amateur experimenters and hobbyists. Amateur radio enthusiasts have significantly contributed to science, engineering, industry, research by amateur operators has founded new industries, built economies, empowered nations, and saved lives in times of emergency. Ham radio can also be used in the classroom to teach English, map skills, geography, math, science, the term ham radio was first a pejorative that mocked amateur radio operators with a 19th-century term for being bad at something, like ham-fisted or ham actor. It had already used for bad wired telegraph operators. Subsequently, the community adopted it as a moniker, much like the Know-Nothing Party, or other groups. Other, more entertaining explanations have grown up throughout the years, the many facets of amateur radio attract practitioners with a wide range of interests. Many amateurs begin with a fascination of radio communication and then combine other personal interests to make pursuit of the hobby rewarding, some of the focal areas amateurs pursue include radio contesting, radio propagation study, public service communication, technical experimentation, and computer networking. Amateur radio operators use various modes of transmission to communicate, the two most common modes for voice transmissions are frequency modulation and single sideband. FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted. Radiotelegraphy using Morse code, also known as CW from continuous wave, is the extension of landline telegraphy developed by Samuel Morse. Morse, using internationally agreed message encodings such as the Q code, a similar legacy mode popular with home constructors is amplitude modulation, pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology. Demonstrating a proficiency in Morse code was for years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in regulations in 2003, countries are no longer required to demand proficiency
14.
ITU Region
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The International Telecommunication Union, in its International Radio Regulations, divides the world into three ITU regions for the purposes of managing the global radio spectrum. Each region has its own set of frequency allocations, the reason for defining the regions. Region 1 comprises Europe, Africa, the former Soviet Union, Mongolia, the western boundary is defined by Line B. Region 2 covers the Americas including Greenland, and some of the eastern Pacific Islands, the eastern boundary is defined by Line B. Region 3 contains most of non-FSU Asia east of and including Iran, the definition of the European Broadcasting Area uses some of the definitions of Region 1
15.
Hertz
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The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, megahertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is also used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is also used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels. Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch. Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
16.
Germany
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Germany, officially the Federal Republic of Germany, is a federal parliamentary republic in central-western Europe. It includes 16 constituent states, covers an area of 357,021 square kilometres, with about 82 million inhabitants, Germany is the most populous member state of the European Union. After the United States, it is the second most popular destination in the world. Germanys capital and largest metropolis is Berlin, while its largest conurbation is the Ruhr, other major cities include Hamburg, Munich, Cologne, Frankfurt, Stuttgart, Düsseldorf and Leipzig. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity, a region named Germania was documented before 100 AD. During the Migration Period the Germanic tribes expanded southward, beginning in the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation, in 1871, Germany became a nation state when most of the German states unified into the Prussian-dominated German Empire. After World War I and the German Revolution of 1918–1919, the Empire was replaced by the parliamentary Weimar Republic, the establishment of the national socialist dictatorship in 1933 led to World War II and the Holocaust. After a period of Allied occupation, two German states were founded, the Federal Republic of Germany and the German Democratic Republic, in 1990, the country was reunified. In the 21st century, Germany is a power and has the worlds fourth-largest economy by nominal GDP. As a global leader in industrial and technological sectors, it is both the worlds third-largest exporter and importer of goods. Germany is a country with a very high standard of living sustained by a skilled. It upholds a social security and universal health system, environmental protection. Germany was a member of the European Economic Community in 1957. It is part of the Schengen Area, and became a co-founder of the Eurozone in 1999, Germany is a member of the United Nations, NATO, the G8, the G20, and the OECD. The national military expenditure is the 9th highest in the world, the English word Germany derives from the Latin Germania, which came into use after Julius Caesar adopted it for the peoples east of the Rhine. This in turn descends from Proto-Germanic *þiudiskaz popular, derived from *þeudō, descended from Proto-Indo-European *tewtéh₂- people, the discovery of the Mauer 1 mandible shows that ancient humans were present in Germany at least 600,000 years ago. The oldest complete hunting weapons found anywhere in the world were discovered in a mine in Schöningen where three 380, 000-year-old wooden javelins were unearthed
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Austria
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Austria, officially the Republic of Austria, is a federal republic and a landlocked country of over 8.7 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Hungary and Slovakia to the east, Slovenia and Italy to the south, the territory of Austria covers 83,879 km2. The terrain is mountainous, lying within the Alps, only 32% of the country is below 500 m. The majority of the population speaks local Bavarian dialects of German as their native language, other local official languages are Hungarian, Burgenland Croatian, and Slovene. The origins of modern-day Austria date back to the time of the Habsburg dynasty, from the time of the Reformation, many northern German princes, resenting the authority of the Emperor, used Protestantism as a flag of rebellion. Following Napoleons defeat, Prussia emerged as Austrias chief competitor for rule of a greater Germany, Austrias defeat by Prussia at the Battle of Königgrätz, during the Austro-Prussian War of 1866, cleared the way for Prussia to assert control over the rest of Germany. In 1867, the empire was reformed into Austria-Hungary, Austria was thus the first to go to war in the July Crisis, which would ultimately escalate into World War I. The First Austrian Republic was established in 1919, in 1938 Nazi Germany annexed Austria in the Anschluss. This lasted until the end of World War II in 1945, after which Germany was occupied by the Allies, in 1955, the Austrian State Treaty re-established Austria as a sovereign state, ending the occupation. In the same year, the Austrian Parliament created the Declaration of Neutrality which declared that the Second Austrian Republic would become permanently neutral, today, Austria is a parliamentary representative democracy comprising nine federal states. The capital and largest city, with a population exceeding 1.7 million, is Vienna, other major urban areas of Austria include Graz, Linz, Salzburg and Innsbruck. Austria is one of the richest countries in the world, with a nominal per capita GDP of $43,724, the country has developed a high standard of living and in 2014 was ranked 21st in the world for its Human Development Index. Austria has been a member of the United Nations since 1955, joined the European Union in 1995, Austria also signed the Schengen Agreement in 1995, and adopted the euro currency in 1999. The German name for Austria, Österreich, meant eastern realm in Old High German, and is cognate with the word Ostarrîchi and this word is probably a translation of Medieval Latin Marchia orientalis into a local dialect. Austria was a prefecture of Bavaria created in 976, the word Austria is a Latinisation of the German name and was first recorded in the 12th century. Accordingly, Norig would essentially mean the same as Ostarrîchi and Österreich, the Celtic name was eventually Latinised to Noricum after the Romans conquered the area that encloses most of modern-day Austria, around 15 BC. Noricum later became a Roman province in the mid-first century AD, heers hypothesis is not accepted by linguists. Settled in ancient times, the Central European land that is now Austria was occupied in pre-Roman times by various Celtic tribes, the Celtic kingdom of Noricum was later claimed by the Roman Empire and made a province
18.
Guglielmo Marconi
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He is often credited as the inventor of radio, and he shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun in recognition of their contributions to the development of wireless telegraphy. Marconi was an entrepreneur, businessman, and founder of The Wireless Telegraph & Signal Company in the United Kingdom in 1897 and he succeeded in making a commercial success of radio by innovating and building on the work of previous experimenters and physicists. In 1929, the King of Italy ennobled Marconi as a Marchese, Marconi was born into the Italian nobility as Guglielmo Giovanni Maria Marconi in Bologna on 25 April 1874, the second son of Giuseppe Marconi and his Irish/Scots wife Annie Jameson. Between the ages of two and six, Marconi and his elder brother Alfonso were brought up by his mother in the English town of Bedford, Marconi received further education in Florence at the Istituto Cavallero and, later, in Livorno. Marconi did not do well in school, according to Robert McHenry and he was baptized as a Catholic but had been brought up as a member of the Anglican Church, being married into it. Marconi was confirmed in the Catholic faith and became a member of the Church before his marriage to Maria Christina in 1927. During his early years, Marconi had an interest in science and electricity, the transmission of telegraph messages without connecting wires as used by the electric telegraph. There was a deal of interest in radio waves in the physics community. Righis article renewed Marconis interest in developing a wireless telegraphy based on radio waves. In the summer of 1894, he built a storm alarm made up of a battery, a coherer, and an electric bell, soon after he was able to make a bell ring on the other side of the room by pushing a telegraphic button on a bench. One night in December 1894, Guglielmo woke his mother and invited her into his secret workshop and showed her the experiment that he had created. The next day, he showed his work to his father. In the summer of 1895, Marconi moved his experimentation outdoors, with these improvements the system was capable of transmitting signals up to 2 miles and over hills. The monopole antenna reduced the frequency of the waves compared to the dipole antennas used by Hertz, by this point, he concluded that a device could become capable of spanning greater distances, with additional funding and research, and would prove valuable both commercially and militarily. Marconis experimental apparatus proved to be the first engineering-complete, commercially successful radio transmission system, Marconi wrote to the Ministry of Post and Telegraphs, then under the direction of the honorable Pietro Lacava, explaining his wireless telegraph machine and asking for funding. He never received a response to his letter which was dismissed by the Minister who wrote to the Longara on the document. In 1896, Marconi spoke with his family friend Carlo Gardini, Honorary Consul at the United States Consulate in Bologna, Gardini wrote a letter of introduction to the Ambassador of Italy in London, Annibale Ferrero, explaining who Marconi was and about these extraordinary discoveries. In his response, Ambassador Ferrero advised them not to reveal the results until after they had obtained the copyrights
19.
Longwave
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In radio, longwave, also written as long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with relatively long wavelengths. The term is an one, dating from the early 20th century, when the radio spectrum was considered to consist of long, medium. Most modern radio systems and devices use wavelengths which would then have been considered ultra-short, in contemporary usage, the term longwave is not defined precisely, and its meaning varies across the world. Sometimes, part of the frequency band is included. The International Telecommunication Union Region 1 longwave broadcast band falls wholly within the low band of the radio spectrum. Broader definitions of longwave may extend below and/or above it, in the US, the Longwave Club of America is interested in frequencies below the AM broadcast band, i. e. all frequencies below 535 kHz. Because of their wavelength, radio waves in this frequency range can diffract over obstacles like mountain ranges and travel beyond the horizon. This mode of propagation, called ground wave, is the mode in the longwave band. The attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies, Low frequency ground waves can be received up to 2,000 kilometres from the transmitting antenna. Low frequency waves can also travel long distances by reflecting from the ionosphere, although this method. Reflection occurs at the ionospheric E layer or F layers, skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. Non-directional beacons transmit continuously for the benefit of radio direction finders in marine and they identify themselves by a callsign in Morse code. They can occupy any frequency in the range 190–1750 kHz, in North America, they occupy 190–535 kHz. In ITU Region 1 the lower limit is 280 kHz, there are government broadcast stations in the range 40–80 kHz that transmit coded time signals to radio clocks. Radio controlled clocks receive their time calibration signals with built-in long-wave receivers, long-waves travel by groundwaves that hug the surface of the earth, unlike medium-waves and short-waves. Those higher-frequency signals do not follow the surface of the Earth beyond a few kilometers and these different propagation paths can make the time lag different for every signal received. The military of the United Kingdom, Russian Federation, United States, Germany, in North America during the 1970s, the frequencies 167,179 and 191 kHz were assigned to the short-lived Public Emergency Radio of the United States. Nowadays, in the United States, Part 15 of FCC regulations allow unlicensed use of 136 kHz and this is called Low Frequency Experimental Radio
20.
Wavelength
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In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can also be applied to periodic waves of non-sinusoidal shape. The term wavelength is also applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height. The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
21.
Radio wave
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Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, at 300 GHz, the corresponding wavelength is 1 mm, and at 3 kHz is 100 km. Like all other electromagnetic waves, they travel at the speed of light, naturally occurring radio waves are generated by lightning, or by astronomical objects. Radio waves are generated by radio transmitters and received by radio receivers, the radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses. Radio waves were first predicted by mathematical work done in 1867 by Scottish mathematical physicist James Clerk Maxwell, Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. Radio waves were first used for communication in the mid 1890s by Guglielmo Marconi, different frequencies experience different combinations of these phenomena in the Earths atmosphere, making certain radio bands more useful for specific purposes than others. It does not necessarily require a cleared sight path, at lower frequencies radio waves can pass through buildings, foliage and this is the only method of propagation possible at microwave frequencies and above. On the surface of the Earth, line of propagation is limited by the visual horizon to about 40 miles. This is the used by cell phones, cordless phones, walkie-talkies, wireless networks, FM and television broadcasting. Indirect propagation, Radio waves can reach points beyond the line-of-sight by diffraction, diffraction allows a radio wave to bend around obstructions such as a building edge, a vehicle, or a turn in a hall. Radio waves also reflect from surfaces such as walls, floors, ceilings, vehicles and these effects are used in short range radio communication systems. Ground waves allow mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon, the nonzero resistance of the earth absorbs energy from ground waves, so as they propagate the waves lose power and the wavefronts bend over at an angle to the surface. As frequency decreases, the decrease and the achievable range increases. Military very low frequency and extremely low frequency communication systems can communicate over most of the Earth, and with submarines hundreds of feet underwater. Tropospheric propagation, In the VHF and UHF bands, radio waves can travel somewhat beyond the horizon due to refraction in the troposphere. This is due to changes in the index of air with temperature and pressure. At times, radio waves can travel up to 500 -1000 km due to tropospheric ducting and these effects are variable and not as reliable as ionospheric propagation, below. So radio waves directed at an angle into the sky can return to Earth beyond the horizon, by using multiple skips communication at intercontinental distances can be achieved
22.
History of radio
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The early history of radio is the history of technology that produce and use radio instruments that use radio waves. Within the timeline of radio, many people contributed theory and inventions in what became radio, Radio development began as wireless telegraphy. Later radio history increasingly involves matters of broadcasting, james Clerk Maxwell showed in theoretical and mathematical form in 1864 that electromagnetic waves could propagate through free space. In 1888 Heinrich Rudolf Hertz was able to conclusively prove transmitted airborne electromagnetic waves in an experiment confirming Maxwells theory of electromagnetism, over several years starting in 1894 the Italian inventor Guglielmo Marconi built the first complete, commercially successful wireless telegraphy system based on airborne Hertzian waves. Marconi demonstrated application of radio in military and marine communications and started a company for the development and propagation of radio communication services and equipment. In 1886–88 Heinrich Rudolf Hertz conducted a series of experiments that proved the existence of Maxwells electromagnetic waves, many individuals—inventors, engineers, developers and businessmen—constructed systems based on their own understanding of these and other phenomenon, some predating Maxwell and Hertzs discoveries. Thus wireless telegraphy and radio wave-based systems can be attributed to multiple inventors, development from a laboratory demonstration to a commercial entity spanned several decades and required the efforts of many practitioners. In 1878, David E. Hughes noticed that sparks could be heard in a telephone receiver when experimenting with his carbon microphone and he developed this carbon-based detector further and eventually could detect signals over a few hundred yards. He demonstrated his discovery to the Royal Society in 1880, but was told it was merely induction, thomas Edison came across the electromagnetic phenomenon while experimenting with a telegraph at Menlo Park. He noted an unexplained transmission effect while experimenting with a telegraph and he referred to this as etheric force in an announcement on November 28,1875. Elihu Thomson published his findings on Edisons new force, again attributing it to induction, Edison would go on the next year to take out U. S. Patent 465,971 on a system of wireless communication between ships based on electrostatic coupling using the water and elevated terminals. Although this was not a system the Marconi Company would purchase the rights in 1903 to protect them legally from lawsuits. Between 1886 and 1888 Heinrich Rudolf Hertz published the results of his experiments where he was able to transmit electromagnetic waves through the air, early on after their discovery, radio waves were referred to as Hertzian waves. Tesla, concluding that Hertz had not demonstrated airborne electromagnetic waves, went on to develop a system based on what he thought was the primary conductor, during the demonstration a radio signal was sent from the neighboring Clarendon Laboratory building, and received by apparatus in the lecture theater. Bose wrote in a Bengali essay, Adrisya Alok, The invisible light can pass through brick walls. Therefore, messages can be transmitted by means of it without the mediation of wires, Bose’s first scientific paper, On polarisation of electric rays by double-refracting crystals was communicated to the Asiatic Society of Bengal in May 1895. His second paper was communicated to the Royal Society of London by Lord Rayleigh in October 1895, in December 1895, the London journal The Electrician published Bose’s paper, On a new electro-polariscope
23.
Wireless telegraphy
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Wireless telegraphy is the transmission of electric telegraphy signals without wires. Wireless telegraphy came to mean Morse code transmitted by radio waves, initially called Hertzian waves, the primitive spark radio transmitters used until World War 1 could not transmit audio. The code sounded like musical beeps in the earphone of the receiver, the receiving radio operator would translate the beeps back into text. The first practical wireless telegraphy transmitters and receivers were developed by Guglielmo Marconi beginning in 1895, by 1910 communication by Hertzian waves was universally referred to as radio, and the term wireless telegraphy has been largely replaced by the more modern term radiotelegraphy. The transmission of sound began to displace wireless telegraphy by the 1920s for many applications, continuous wave radiotelegraphy is regulated by the International Telecommunication Union as emission type A1A. Today, due to modern text transmission methods, Morse code radiotelegraphy for commercial use has become obsolete. On shipboard the computer and satellite linked GMDSS system has largely replaced Morse as a means of communication, Telegraphy is taught on a very limited basis by the military. A CW coastal station, KSM, still exists in California, run primarily as a museum by volunteers, Radio beacons, particularly in the aviation service, but also as placeholders for commercial ship-to-shore systems, also transmit Morse but at very slow speeds. The US Federal Communications Commission does still issue a lifetime commercial Radiotelegraph Operator License and this requires passing a simple written test on regulations, a more complex written exam on technology, and demonstrating Morse reception at 20 words per minute plain language and 16 wpm code groups. Wireless telegraphy is still used today by amateur radio hobbyists where it is commonly referred to as radio telegraphy, continuous wave. However its knowledge is not required to obtain any class of amateur license, a number of wireless electrical signaling schemes including electric currents through water and the ground were investigated for telegraphy before practical radio systems became available. The original telegraph used two wires between two stations to form an electrical circuit or loop. This led to speculation that it might be possible to both wires and therefore transmit telegraph signals through the ground without any wires connecting the stations. Other attempts were made to send the current through bodies of water, in order to span rivers. The first wireless voice telecommunication device, invented in 1880, was the photophone, both electrostatic and electromagnetic induction were used to develop wireless telegraph systems that saw limited commercial application. This system was successful technically but not economically, as there turned out to be little interest by train travelers in a telegraph service. During the Great Blizzard of 1888, this system was used to send, the disabled trains were able to maintain communications via their Edison induction wireless telegraph systems, perhaps the first successful use of wireless telegraphy to send distress calls. The most successful creator of an electromagnetic induction telegraph system was William Preece in the United Kingdom, beginning with tests across the Bristol Channel in 1892, Preece was able to telegraph across gaps of about 5 kilometres
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Transmitter
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In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s
25.
Poldhu
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Poldhu is a small area in south Cornwall, England, UK, situated on the Lizard Peninsula, it comprises Poldhu Point and Poldhu Cove. Poldhu means black pool in Cornish, Poldhu lies on the coast of Mounts Bay and is in the northern part of the parish of Mullion, the churchtown is 2 kilometres to the south-east. On the north side of Poldhu Cove is the parish of Gunwalloe, Poldhu Point became the site of one of the main technological advances of the early twentieth century when, on 12 December 1901, a wireless signal was sent to St John’s, Newfoundland, by Marconi. The technology was a precursor to radio, television, satellites, in January 2016 Poldhu Cove was inundated with thousands of pink plastic bottles, brought onto the beach with successive tides. The National Trust said it believed a container had gone overboard from a ship, the station was built partly on cliff top pastures that had been enclosed in 1871 and partly on medieval fields belonging to a nearby settlement, Angrouse. The fifty acre plot was bought in 1900 and building work ran from October 1900 to January 1901, during the work two Bronze Age barrows were flattened and a bronze dagger and urn were recovered. The original twenty mast circular aerial was destroyed in a storm on 17 September 1901, for Marconis experiments a temporary installation of two 200 foot masts was used. The transmitter operated with a power of roughly 13 kW and a wavelength usually estimated at 170 meters, the original mast layout was not rebuilt, it was replaced with a four mast design,215 feet high and forming a 200-foot square. Marconi later used the site for his experiments, with transmissions by Charles Samuel Franklin to Marconi on the yacht Elettra in the Cape Verde Islands in 1923. The groundbreaking results of these took the world by surprise. The station closed in 1934 and was demolished in 1937, six acres were given to the National Trust in 1937 with the rest of the site added in 1960. The site has a monument pillar, erected in November 1937 by the Marconi Company. In 2001 the Marconi Centre, a new museum/meeting building, was opened close to the site by the efforts of the Poldhu Amateur Radio Club, the substantial building near the site, originally the Poldhu Hotel, built in 1899, is currently a care home. The visitors book shows that Marconi stayed there in May and August,1901, Marconi also built an earlier, smaller, experimental wireless station nearby at Housel Bay – The Lizard Wireless Station
26.
Cornwall
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Cornwall is a ceremonial county and unitary authority area of England within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, Cornwall has a population of 551,700 and covers an area of 3,563 km2. Cornwall forms the westernmost part of the south-west peninsula of the island of Great Britain, and this area was first inhabited in the Palaeolithic and Mesolithic periods. It continued to be occupied by Neolithic and then Bronze Age peoples, there is little evidence that Roman rule was effective west of Exeter and few Roman remains have been found. In the mid-19th century, however, the tin and copper mines entered a period of decline, subsequently, china clay extraction became more important and metal mining had virtually ended by the 1990s. Traditionally, fishing and agriculture were the important sectors of the economy. Railways led to a growth of tourism in the 20th century, however, the area is noted for its wild moorland landscapes, its long and varied coastline, its attractive villages, its many place-names derived from the Cornish language, and its very mild climate. Extensive stretches of Cornwalls coastline, and Bodmin Moor, are protected as an Area of Outstanding Natural Beauty, Cornwall is the homeland of the Cornish people and is recognised as one of the Celtic nations, retaining a distinct cultural identity that reflects its history. Some people question the present constitutional status of Cornwall, and a nationalist movement seeks greater autonomy within the United Kingdom in the form of a devolved legislative Cornish Assembly. On 24 April 2014 it was announced that Cornish people will be granted minority status under the European Framework Convention for the Protection of National Minorities. The modern English name Cornwall derives from the concatenation of two ancient demonyms from different linguistic traditions, Corn- records the native Brythonic tribe, the Cornovii. The Celtic word kernou is cognate with the English word horn. -wall derives from the Old English exonym walh, the Ravenna Cosmography first mentions a city named Purocoronavis in the locality. This is thought to be a rendering of Duro-cornov-ium, meaning fort of the Cornovii. The exact location of Durocornovium is disputed, with Tintagel and Carn Brea suggested as possible sites, in later times, Cornwall was known to the Anglo-Saxons as West Wales to distinguish it from North Wales. The name appears in the Anglo-Saxon Chronicle in 891 as On Corn walum, in the Domesday Book it was referred to as Cornualia and in c.1198 as Cornwal. Other names for the county include a latinisation of the name as Cornubia, the present human history of Cornwall begins with the reoccupation of Britain after the last Ice Age. The area now known as Cornwall was first inhabited in the Palaeolithic and Mesolithic periods and it continued to be occupied by Neolithic and then Bronze Age people. The Common Brittonic spoken at the time developed into several distinct tongues
27.
Cape Verde
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Located 570 kilometres off the coast of West Africa, the islands cover a combined area of slightly over 4,000 square kilometres. The Cape Verde archipelago was uninhabited until the 15th century, when Portuguese explorers discovered and colonized the islands, ideally located for the Atlantic slave trade, the islands grew prosperous throughout the 16th and 17th centuries, attracting merchants, privateers, and pirates. The end of slavery in the 19th century led to economic decline, Cape Verde gradually recovered as an important commercial center and stopover for shipping routes. Incorporated as a department of Portugal in 1951, the islands continued to agitate for independence. Since the early 1990s, Cape Verde has been a representative democracy. Lacking natural resources, its economy is mostly service-oriented, with a growing focus on tourism. Its population of around 512,000 is mostly of mixed European and sub-Saharan African heritage, a sizeable diaspora community exists across the world, slightly outnumbering inhabitants on the islands. Historically, the name Cape Verde has been used in English for the archipelago and, since independence in 1975, for the country. In 2013, the Cape Verdean government determined that the Portuguese designation Cabo Verde would henceforth be used for official purposes, such as at the United Nations, Cape Verde is a member of the African Union. The name of the stems from the nearby Cap-Vert, on the Senegalese coast. In 1444 Portuguese explorers had named that landmark as Cabo Verde, on 24 October 2013, the countrys delegation announced at the United Nations that the official name should no longer be translated into other languages. Instead of Cape Verde, the designation Republic of Cabo Verde is to be used, before the arrival of Europeans, the Cape Verde Islands were uninhabited. The islands of the Cape Verde archipelago were discovered by Genoese and Portuguese navigators around 1456, according to Portuguese official records, the first discoveries were made by Genoa-born António de Noli, who was afterwards appointed governor of Cape Verde by Portuguese King Afonso V. Other navigators mentioned as contributing to discoveries in the Cape Verde archipelago are Diogo Gomes, Diogo Dias, Diogo Afonso, in 1462, Portuguese settlers arrived at Santiago and founded a settlement they called Ribeira Grande. Ribeira Grande was the first permanent European settlement in the tropics, in the 16th century, the archipelago prospered from the Atlantic slave trade. Pirates occasionally attacked the Portuguese settlements, sir Francis Drake, an English corsair privateering under a letter of marque granted by the English crown, twice sacked the capital Ribeira Grande in 1585 when it was a part of the Iberian Union. After a French attack in 1712, the town declined in relative to nearby Praia. Decline in the trade in the 19th century resulted in an economic crisis
28.
Curtain array
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Curtain arrays are a class of large multielement directional wire radio transmitting antennas, used in the shortwave radio bands. These are suspended by support wires strung between pairs of steel towers, up to 300 feet high. They are used for long-distance skywave transmission, they transmit a beam of waves at a shallow angle into the sky. Curtain antennas are used by international short wave radio stations to broadcast to large areas at transcontinental distances. Because of their powerful directional characteristics, curtain arrays are used in government propaganda radio stations to beam propaganda broadcasts over national borders into other nations. For example, curtain arrays were used by Radio Free Europe, curtain arrays were originally developed during the 1920s and 1930s when there was a lot of experimentation with long distance shortwave broadcasting. The underlying concept was to achieve improvements in gain and/or directionality over the dipole antenna. Franklin invented the first curtain array aerial system in 1924, known as the Franklin or English system, other early curtain arrays included the Bruce array patented by Edmond Bruce in 1927, and the Sterba curtain, patented by Ernest J. Sterba in 1929. The Bruce array produces a signal, Sterba arrays produce a horizontally-polarised signal. The Sterba array was used by Bell Labs and others during the 1930s and 1940s, the Sterba curtain is however a narrowband design and is only steerable by mechanical means. However, as far back as the mid-1930s, Radio Netherlands was using a rotatable HRS antenna for global coverage, since the 1950s the HRS design has become more or less the standard for long distance high power shortwave broadcasting. Curtain arrays were used in some of the first radar systems, the driven elements are usually half-wave dipoles, fed in phase, mounted in a plane 1/4 wavelength in front of the reflector plane. The reflector wires are oriented parallel to the dipoles, the dipoles may be vertical, radiating in vertical polarization, but are most often horizontal, because horizontally polarized waves are less absorbed by earth reflections. The lowest row of dipoles are mounted more than 1/2 wavelength above the ground and this allows most of the radiation to be concentrated in a narrow main lobe aimed a few degrees above the horizon, which is ideal for skywave transmission. A curtain array may have a gain of 20 dB greater than a dipole antenna. In order to allow the beam to be steered, sometimes the entire array is suspended by cantilever arms from a large tower which can be rotated. Alternatively, some versions are constructed as phased arrays in which the beam can be steered electronically. Adding a constant phase shift between adjacent horizontal dipoles allows the direction of the beam to be rotated in azimuth by a limited angle, V indicates the dipoles are oriented vertically, so the antenna radiates vertically polarized radio waves
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General Post Office
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The General Post Office was officially established in England in 1660 by Charles II and it eventually grew to combine the functions of state postal system and telecommunications carrier. Similar General Post Offices were established across the British Empire, in 1969 the GPO was abolished and the assets transferred to The Post Office, changing it from a Department of State to a statutory corporation. For the more recent history of the system in the United Kingdom, see the article Royal Mail. Originally, the GPO was a monopoly covering the despatch of items from a sender to a specific receiver. The postal service was known as the Royal Mail because it was built on the system for royal. In 1661 the office of Postmaster General was created to oversee the GPO, the GPO created a network of post offices where senders could submit items. All post was transferred from the post office of origination to distribution points called sorting stations, initially it was the recipient of the post who paid the fee, and he had the right to refuse to accept the item if he did not wish to pay. The charge was based on the distance the item had been carried so the GPO had to keep an account for each item. The first general post office in London opened in 1643, just 8 years after King Charles I legalised use of the posts for private correspondence. It was probably on Cloak Lane near Dowgate Hill, coffee houses in the City such as Lloyds and Garraways organised private transport of mail among their patrons. The Royal Mail moved its headquarters to Lombard Street in the City in 1678 to better curtail such practices, when the Central London Railway was built in 1900 its nearby station was named Post Office. Smirkes building was felt to be too small by this time, however, in 1912, the former GPO East was demolished, the current headquarters of BT, a post World War II building, occupies the site of the old Telegraph Office. The theory was used to state control of the mail service into every form of electronic communication possible on the basis that every sender used some form of distribution service. These distribution services were considered in law as forms of electronic post offices and this applied to telegraph and telephone switching stations. In the mid 19th century several private companies were established in the UK. The responsibility for the electric telegraphs was officially transferred to the GPO on Friday,4 February 1870, overseas telegraphs did not fall within the monopoly. The private telegraph companies that existed were bought out. The new combined telegraph service had 1,058 telegraph offices in towns,6,830,812 telegrams were transmitted in 1869 producing revenue of £550,000
30.
Imperial Wireless Chain
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The Imperial Wireless Chain was a strategic international wireless telegraphy communications network, created to link the countries of the British Empire. Although the idea was conceived prior to World War I, Britain was the last of the worlds Great Powers to implement an operational system. The first link in the chain, between Leafield in Oxfordshire and Cairo, Egypt, eventually opened on 24 April 1922, with the final link, between Australia and Canada, opening on 16 June 1928. In 1910 the Colonial Office received a proposal from the Marconi Company. While not then accepted, the Marconi proposal created serious interest in the concept and it was decided that contracting the construction to a commercial wireless company was the favoured option, and a contract was signed with Marconis Wireless Telegraph Company in March 1912. The Government then found itself facing severe criticism and appointed a committee to examine the topic. After further negotiations prompted by Treasury pressure, a contract was ratified by Parliament on 8 August 1913. Of rather more consequence was the outbreak of World War I, the Government also commissioned the Imperial Wireless Telegraphy Committee chaired by Sir Henry Norman, which reported in 1920. However, the report was not acted upon, while British politicians procrastinated, Marconi constructed stations for other nations, linking North and South America, as well as China and Japan, in 1922. The scheme was estimated at £500,000, the beam stations would communicate with those Dominions that chose the new shortwave technology. Parliament finally approved an agreement between the Post Office and Marconi to build beam stations to communicate with Canada, South Africa, India and Australia, on 1 August 1924. It concluded that the companies would not be able to compete in an unrestricted market. In 1934 Imperial and International Communications was renamed as Cable & Wireless Limited, with Cable and Wireless Limited being renamed as Cable, from the beginning of April 1928 the Beam services were operated by the Post Office as agent for Imperial and International Communications Limited. The 1930s saw the arrival of the Great Depression, as well as competition from the International Telephone and Telegraph Corporation and affordable airmail. The ownership of the stations was reversed in 1947, when the Labour Government nationalised Cable and Wireless. By this stage, however, three of the stations had been closed, after the service was centralised during 1939–1940 at Dorchester. The longwave Rugby radio station continued to remain under Post Office ownership throughout, the shortwave Imperial Wireless Chain beam stations operated in pairs, one transmitting and one receiving. These were topped by cross-arm measuring 10 feet high by 90 feet wide, at Tetney the antenna for India was similar to those at Bodmin and Bridgwater, while the Australian aerial was carried on three 275 feet high masts
31.
Submarine communications cable
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A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean. The first submarine communications cables, laid in the 1850s, carried telegraphy traffic, subsequent generations of cables carried telephone traffic, then data communications traffic. Modern cables use optical technology to carry digital data, which includes telephone, Internet. Samuel Morse proclaimed his faith in it as early as 1840, and in 1842, he submerged a wire, insulated with tarred hemp and India rubber, in the water of New York Harbor, the following autumn, Wheatstone performed a similar experiment in Swansea Bay. A good insulator to cover the wire and prevent the current from leaking into the water was necessary for the success of a long submarine line. India rubber had been tried by Moritz von Jacobi, the Prussian electrical engineer, another insulating gum which could be melted by heat and readily applied to wire made its appearance in 1842. Gutta-percha, the juice of the Palaquium gutta tree, was introduced to Europe by William Montgomerie. Twenty years earlier, he had seen made of it in Singapore. It was tried on a wire laid across the Rhine between Deutz and Cologne, walker, electrician to the South Eastern Railway, submerged a two-mile wire coated with gutta-percha off the coast from Folkestone, which was tested successfully. It was simply a copper wire coated with gutta-percha, without any other protection, in 1853 further successful cables were laid, linking Great Britain with Ireland, Belgium and the Netherlands, and crossing The Belts in Denmark. The British & Irish Magnetic Telegraph Company completed the first successful Irish link on May 23 between Portpatrick and Donaghadee using the collier William Hutt, the same ship was used for the link from Dover to Ostend in Belgium, by the Submarine Telegraph Company. Meanwhile, the Electric & International Telegraph Company completed two cables across the North Sea, from Orford Ness to Scheveningen, The Netherlands and they were laid by the Monarch, a paddle steamer which later became the first vessel with permanent cable-laying equipment. In 1858 the Steamship Elba was used to lay a Telegraph cable from Jersey to Guernsey, on to Alderney, problems soon developed with eleven breaks occurring by 1860 due to storms, tidal and sand movements and wear on rocks. A report to the Institution of Civil Engineers in 1860 set out the problems to assist in future cable laying operations, the first attempt at laying a transatlantic telegraph cable was promoted by Cyrus West Field, who persuaded British industrialists to fund and lay one in 1858. However, the technology of the day was not capable of supporting the project, it was plagued with problems from the outset, and was in operation for only a month. Subsequent attempts in 1865 and 1866 with the worlds largest steamship, Great Eastern later went on to lay the first cable reaching to India from Aden, Yemen, in 1870. From the 1850s until 1911, British submarine cable systems dominated the most important market, the British had both supply side and demand side advantages. In terms of supply, Britain had entrepreneurs willing to put forth enormous amounts of capital necessary to build, lay, in terms of demand, Britains vast colonial empire led to business for the cable companies from news agencies, trading and shipping companies, and the British government
32.
Cable & Wireless plc
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Cable & Wireless plc was a British telecommunications company. In the mid-1980s, it became the first company in the UK to offer a telephone service to British Telecom. The company later offered cable TV to its customers, but it sold its assets to NTL in 2000. It remained a significant player in the UK telecoms market and in overseas markets, especially in the former British colonies of the Caribbean. It was also the supplier of communication in the British South Atlantic, including Saint Helena. It was listed on the London Stock Exchange and was a constituent of the FTSE100 Index, the company split in March 2010, with its international division demerging to form Cable & Wireless Communications. The remainder of the Cable & Wireless business became Cable & Wireless Worldwide and was acquired by Vodafone in 2012, Cable and Wireless traces its history back to a number of British telegraph companies founded in the 1860s, and cites Sir John Pender as the founder. The Eastern Telegraph Company expanded the length from 8,860 miles on its founding to 22,400 miles just 15 years later. The Company steadily took over a number of companies founded to connect the West Indies and South America, leading to a change to The Eastern. Throughout World War I all cable services out of Britain were controlled by the government, for the first time cables became targets of warfare in themselves. Eastern Telegraph, the British Royal Navy, and the General Post Office collaborated on cutting all cable links between Germany and North America, the Germans temporarily disabled both the Pacific Cable and the cable across the Indian Ocean, by attacking island stations in each ocean. In 1920 the government decided to keep this cable, despite U. S. protests, and to purchase a second line, World War II revived the cable war of 1914-1918. Electra House, the head office and central cable station, was damaged by German bombing in 1941. Following the Labour Partys victory in the 1945 general elections, the government announced its intention to nationalise Cable and Wireless, the plan to privatise was announced in 1980. The government sold the first half of its share in Cable & Wireless in November 1981, in February 1982, the government granted a licence for a UK telecommunications network, Mercury Communications Ltd, as a rival to British Telecom. It was established as a subsidiary of Cable & Wireless, in 1986, the US long distance industry was deregulated, and many new companies launched into the equal access market. A company called TDX Systems, based in Falls Church, Virginia, was one of these, TDX carried data, and built its own telephone switches at its engineering facility in Chantilly, VA. For a short time TDX touted a position of being one of the providers of phone
33.
Hallicrafters SX-28
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The Hallicrafters SX-28 Super Skyrider was an American shortwave communications receiver produced between 1940 and 1946 that saw wide use by amateur radio, government and military services. The SX-28s distinctive art deco styling was considered sleek and strikingly modern in 1940, the radio frequency coverage was 550 kHz to 43 MHz in six bands. The SX-28 included an Amplified AVC, a Lamb Noise Silencer, Calibrated bandspread, the SX-28 was known for its high fidelity audio together with high sensitivity, stability and selectivity, and good purchase value. The SX-28 saw use by various branches of U. S. and allied military, a number of the receivers were sent to Russia as a part of the Lend Lease Act, subsequently modified to accommodate Russian tubes. Many of the SX-28/28As that exist today are in the hands of amateur radio collectors. The name Skyrider was intended to bestow an aura of exotic adventure to Hallicrafters products and had a history with the company. The first Hallicrafters set to be dubbed with the name was the 1932 S-1, variations and special versions of the SX-28 were produced over the years. During World War II, Hallicrafters continued to redesign portions of the SX-28, aN/GRR-2 - introduced in February 1944 became the U. S. Navy SX-28A, a ruggedized unit built for U. S. Army Signal Corps and U. S. Navy use. BC-348 Hammarlund Super Pro National HRO R-390A de Hensler, Max, charleston, West Virginia, ARCA Press,1988 Moore, Raymond. La Belle, Florida, RSM Communications,1997 Osterman, Fred, reynoldsburg, Ohio, Universal Radio Research,1998 Dachis, Chuck. Atglen, Pennsylvania, Schiffer Books for Collectors,1999 SX-28 and SX-28A Manuals, VOLs
34.
Surface wave
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In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, gravity waves can also occur within liquids, at the interface between two fluids with different densities. Elastic surface waves can travel along the surface of solids, such as Rayleigh or Love waves, in radio transmission, a ground wave is a guided wave that propagates close to the surface of the Earth. In seismology, several types of waves are encountered. Surface waves, in this sense, are commonly known as either Love waves or Rayleigh waves. A seismic wave is a wave travels through the Earth. Love waves have transverse motion, whereas Rayleigh waves have both longitudinal and transverse motion, seismic waves are studied by seismologists and measured by a seismograph or seismometer. Surface waves span a wide range, and the period of waves that are most damaging is usually 10 seconds or longer. Surface waves can travel around the many times from the largest earthquakes. Surface waves are caused when P waves and S waves come to the surface, the term surface wave can describe waves over an ocean, even when they are approximated by Airy functions and are more properly called creeping waves. Examples are the waves at the surface of water and air, another example is internal waves, which can be transmitted along the interface of two water masses of different densities. In theory of hearing physiology, the wave of Von Bekesy. His theory pretended to explain features of the auditory sensation owing to these passive mechanical phenomena. But Jozef Zwislocki and later David Kemp, showed that that was unrealistic, ground wave refers to the propagation of radio waves parallel to and adjacent to the surface of the Earth, following the curvature of the Earth. This radiative ground wave is known as the Norton surface wave, other types of surface wave are the non-radiative Zenneck surface wave or Zenneck-Sommerfeld surface wave, the trapped surface wave and the gliding wave. See also Dyakonov surface waves propagating at the interface of transparent materials with different symmetry, lower frequency radio space waves, below 3 MHz, travel efficiently as ground waves. In ITU nomenclature, this includes, medium frequency, low frequency, very low frequency, ultra low frequency, super low frequency, ground propagation works because lower-frequency waves are more strongly diffracted around obstacles due to their long wavelengths, allowing them to follow the Earths curvature. The Earth has one refractive index and the atmosphere has another, ground waves propagate in vertical polarization, with their magnetic field horizontal and electric field vertical
35.
Very low frequency
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Very low frequency or VLF is the ITU designation for radio frequencies in the range of 3 kHz to 30 kHz and corresponding wavelengths from 100 to 10 kilometres, respectively. The band is known as the myriametre band or myriametre wave as the wavelengths range from one to ten myriametres. Due to its bandwidth, audio transmission is highly impractical in this band. The VLF band is used for a few radio navigation services, government time radio stations, since VLF waves can penetrate at least 40 meters into saltwater, they are used for military communication with submarines. The main mode of long distance propagation is an Earth-ionosphere waveguide mechanism, the Earth is surrounded by a conductive layer of electrons and ions in the upper atmosphere, the ionosphere D layer at 60 km altitude, which reflects VLF radio waves. The conductive ionosphere and the conductive Earth, form a horizontal duct a few VLF wavelengths high, the waves travel in a zigzag path around the Earth, reflected alternately by the Earth and the ionosphere, in TM mode. Therefore, VLF transmissions are very stable and reliable, and are used for distance communication. Propagation distances of 5000 to 20000 km have been realized, however, atmospheric noise is high in the band, including such phenomena as whistlers, caused by lightning. VLF waves can penetrate seawater to a depth of at least 10 to 40 meters, depending on the frequency employed, VLF waves at certain frequencies have been found to cause electron precipitation. A major practical drawback to this band is that because of the length of the waves, vertical antennas must be used because VLF waves propagate in vertical polarization, but a quarter-wave vertical antenna at 30 kHz would be 2.5 kilometers high. So practical transmitting antennas are short, a small fraction of a wavelength long. Due to their low radiation resistance they are inefficient, radiating only 10% to 50% of the power at most. With the rest of the power dissipated in the antenna/ground system resistances, Very high power transmitters are required to radiate enough power for long distance communication. Transmitting antennas for VLF frequencies are very large antennas, up to a mile across. They consist of a series of radio masts, linked at the top with a network of cables. Either the towers themselves or vertical wires serve as monopole radiators, high power stations use variations on the umbrella antenna such as the delta and trideco antennas, or multiply-tuned flattop antennas. For low power transmitters, inverted-L and T antennas are used, a large loading coil is required at the antenna feed point to cancel the capacitive reactance of the antenna to make it resonant. To minimize power dissipated in the ground, these antennas require extremely low resistance ground systems, the high capacitance and inductance and low resistance of the antenna-loading coil combination, makes it act electrically like a high Q tuned circuit
36.
Vacuum tube
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In electronics, a vacuum tube, an electron tube, or just a tube, or valve, is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament and this type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect, the simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode, and a plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids, Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display. In the 1940s the invention of devices made it possible to produce solid-state devices, which are smaller, more efficient, more reliable, more durable. Hence, from the mid-1950s solid-state devices such as transistors gradually replaced tubes, the cathode-ray tube remained the basis for televisions and video monitors until superseded in the 21st century. However, there are still a few applications for which tubes are preferred to semiconductors, for example, the used in microwave ovens. One classification of vacuum tubes is by the number of active electrodes, a device with two active elements is a diode, usually used for rectification. Devices with three elements are used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have additional functions made possible by the additional controllable electrodes. X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission, since these sorts of vacuum tubes have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure, most tubes have glass envelopes, though ceramic and metal envelopes have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal, Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the terminals, some tubes had an electrode terminating at a top cap. The principal reason for doing this was to avoid leakage resistance through the tube base, the bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. There was even a design that had two top cap connections
37.
Amateur radio operator
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As a component of their license, amateur radio operators are assigned a call sign that they use to identify themselves during communication. There are about three million amateur radio operators worldwide, amateur radio operators are also known as radio amateurs or hams. The term ham as a nickname for radio operators originated in a pejorative usage by operators in commercial and professional radio communities. The word was adopted by amateur radio operators. Few governments maintain detailed demographic statistics of their radio operator populations. The majority of radio operators worldwide reside in Japan, the United States, Thailand, South Korea. The top five countries by percentage of the population are Japan, Slovenia, Taiwan, South Korea, only the governments of Yemen and North Korea currently prohibit their citizens from becoming amateur radio operators. In some countries, acquiring an amateur license is difficult because of the bureaucratic processes or fees that place access to a license out of reach for most citizens. Most nations permit foreign nationals to earn an amateur radio license, in the vast majority of countries, the population of amateur radio operators is predominantly male. In China 12% of amateur operators are women, whilst in the United States is it approximately 15%. The Young Ladies Radio League is an organization of female amateur radio operators. A male amateur radio operator can be referred to as an OM, a female amateur radio operator can be referred to as a YL, from the abbreviation used for young lady, regardless of the operators age. Sometimes the wife of a ham operator is called a YF, although these codes are derived from English language abbreviations, their use is common among amateur radio operators worldwide. Incidentally, the most common language heard in the HF amateur bands is English, in most countries there is no minimum age requirement to earn an amateur radio license and become an amateur radio operator. Although the number of radio operators in many countries increases from year to year. In some countries, the age is over 80 years old. The World Wide Young Contesters organization promotes youth involvement, particularly amongst Europeans, a strong tie also exists between the amateur radio community and the Scouting movement to introduce radio technology to youth. WOSMs annual Jamboree On The Air is Scoutings largest activity, with a half million Scouts, when referring to a person, the phrase Silent Key and its abbreviation SK indicates an amateur radio operator who is deceased
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New Zealand
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New Zealand /njuːˈziːlənd/ is an island nation in the southwestern Pacific Ocean. The country geographically comprises two main landmasses—the North Island, or Te Ika-a-Māui, and the South Island, or Te Waipounamu—and around 600 smaller islands. New Zealand is situated some 1,500 kilometres east of Australia across the Tasman Sea and roughly 1,000 kilometres south of the Pacific island areas of New Caledonia, Fiji, because of its remoteness, it was one of the last lands to be settled by humans. During its long period of isolation, New Zealand developed a distinct biodiversity of animal, fungal, the countrys varied topography and its sharp mountain peaks, such as the Southern Alps, owe much to the tectonic uplift of land and volcanic eruptions. New Zealands capital city is Wellington, while its most populous city is Auckland, sometime between 1250 and 1300 CE, Polynesians settled in the islands that later were named New Zealand and developed a distinctive Māori culture. In 1642, Dutch explorer Abel Tasman became the first European to sight New Zealand, in 1840, representatives of Britain and Māori chiefs signed the Treaty of Waitangi, which declared British sovereignty over the islands. In 1841, New Zealand became a colony within the British Empire, today, the majority of New Zealands population of 4.7 million is of European descent, the indigenous Māori are the largest minority, followed by Asians and Pacific Islanders. Reflecting this, New Zealands culture is derived from Māori and early British settlers. The official languages are English, Māori and New Zealand Sign Language, New Zealand is a developed country and ranks highly in international comparisons of national performance, such as health, education, economic freedom and quality of life. Since the 1980s, New Zealand has transformed from an agrarian, Queen Elizabeth II is the countrys head of state and is represented by a governor-general. In addition, New Zealand is organised into 11 regional councils and 67 territorial authorities for local government purposes, the Realm of New Zealand also includes Tokelau, the Cook Islands and Niue, and the Ross Dependency, which is New Zealands territorial claim in Antarctica. New Zealand is a member of the United Nations, Commonwealth of Nations, ANZUS, Organisation for Economic Co-operation and Development, Pacific Islands Forum, and Asia-Pacific Economic Cooperation. Dutch explorer Abel Tasman sighted New Zealand in 1642 and called it Staten Landt, in 1645, Dutch cartographers renamed the land Nova Zeelandia after the Dutch province of Zeeland. British explorer James Cook subsequently anglicised the name to New Zealand, Aotearoa is the current Māori name for New Zealand. It is unknown whether Māori had a name for the country before the arrival of Europeans. Māori had several names for the two main islands, including Te Ika-a-Māui for the North Island and Te Waipounamu or Te Waka o Aoraki for the South Island. Early European maps labelled the islands North, Middle and South, in 1830, maps began to use North and South to distinguish the two largest islands and by 1907, this was the accepted norm. The New Zealand Geographic Board discovered in 2009 that the names of the North Island and South Island had never been formalised and this set the names as North Island or Te Ika-a-Māui, and South Island or Te Waipounamu
39.
10-meter band
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The 10-meter band is a portion of the shortwave radio spectrum internationally allocated to amateur radio and amateur satellite use on a primary basis. The band consists of frequencies stretching from 28.000 to 29.700 MHz, the 10-meter band was allocated on a worldwide basis by the International Radiotelegraph Conference in Washington, D. C. on October 4,1927. Its frequency allocation was then 28000-30000 kc, a 300 kHz segment, from 29.700 MHz to 30.000 MHz, was removed from the amateur radio allocation by the 1947 International Radio Conference of Atlantic City. This was a windfall for amateur enthusiasts, allowing access to fairly inexpensive radios which could easily be modified for use in the 10-meter band. American Novice- and Technician-class licensees were granted CW and SSB segments on the 10-meter band as of 0001 UTC March 21,1987, being a very wide band in HF terms, many different transmission modes can be found on 10 meters. Morse code and other modes are found toward the bottom portion of the band, SSB from 28.300 MHz up. Digital modes, such as PSK-31, are allowed in the upper portion of the band. Due to its spot in the spectrum,10 meters can occasionally be challenging to work. At peak times of the cycle when many sunspots appear on the Suns surface,10 meters can be alive with extremely long-distance signals. Generally speaking, the most effective and efficient propagation of 10-meter radio waves takes place during daylight hours. During periods of increased activity, band openings may begin well before sunrise. Long-distance opportunities via F2 seem to follow the sun across the globe, in North America, for instance, F2 might bring Europe and western Asia in the morning, the Americas during midday, and the Pacific and East Asia in late afternoon and early evening. Even in times of minimum, when F2 is rarely available,10 meters still has some long distance possibilities. Sporadic E propagation can bring in signals from a hundred to thousands of miles away. Sporadic E on 10 meters is mainly a seasonal event, with late spring, a shorter, less-intense period occurs during mid-winter, often between Christmas and the new year. Other, off-peak openings may be seen almost anytime, even during solar minimum, F2 openings often occur on transequatorial paths, for example between Europe and Southern Africa or between Pacific North America and the Eastern Pacific islands. In tropical latitudes 10 meters is open throughout the sunspot cycle, for example, a good path from West Africa to the Caribbean exists on 10 meters even at solar minimum. Although 10 meters has an amateur radio allocation, in some countries the use of portions of 10 meters is allocated by the government by license class
