A monochromic image is composed of one color. The term monochrome comes from the Ancient Greek: translit. Monochromos, lit.'having one color'. A monochromatic object or image reflects colors in shades of limited hues. Images using only shades of grey are called black-and-white. However, scientifically speaking, monochromatic light refers to visible light of a narrow band of wavelengths. Of an image, the term monochrome is taken to mean the same as black and white or, more grayscale, but may be used to refer to other combinations containing only tones of a single color, such as green-and-white or green-and-red, it may refer to sepia displaying tones from light tan to dark brown or cyanotype images, early photographic methods such as daguerreotypes and tintypes, each of which may be used to produce a monochromatic image. In computing, monochrome has two meanings: it may mean having only one color, either on or off, allowing shades of that color. A monochrome computer display is able to display only a single color green, red or white, also shades of that color.
In film photography, monochrome is the use of black-and-white film. All photography was done in monochrome. Although color photography was possible in the late 19th century used color films, such as Kodachrome, were not available until the mid-1930s. In digital photography, monochrome is the capture of only shades of black by the sensor, or by post-processing a color image to present only the perceived brightness by combining the values of multiple channels; the weighting of individual channels may be selected to achieve a desired artistic effect. If the red channel is eliminated and the green and blue combined the effect will be similar to that of orthochromatic film or the use of a cyan filter on panchromatic film; the selection of weighting thus allows a wide range of artistic expression in the final monochromatic image. For production of an anaglyph image the original color stereogram source may first be reduced to monochrome in order to simplify the rendering of the image; this is sometimes required in cases where a color image would render in a confusing manner given the colors and patterns present in the source image and the selection filters used.
In physics, monochromatic light is electromagnetic radiation of a single frequency. In the physical sense, no source of electromagnetic radiation is purely monochromatic, since that would require a wave of infinite duration as a consequence of the Fourier transform's localization property. Controlled sources such as lasers operate in a range of frequencies. In practice, filtered light, diffraction grating separated light and laser light are all referred to as monochromatic. Light sources can be compared and one be labeled as “more monochromatic”. A device which isolates a narrow band of frequencies from a broader-bandwidth source is called a monochromator though the bandwidth is explicitly specified, thus a collection of frequencies is understood. Duotone – the use of two ink colors in printing Halftone – the use of black and white in a pattern, perceived as shades of grey Polychrome – of multiple colors, the opposite of monochrome Monochromacy Monochromatic color Selective color – use of monochrome and color selectively within an image Monochrome painting – monochromes in art
405-line television system
The 405-line monochrome analogue television broadcasting system was the first electronic television system to be used in regular broadcasting. It was introduced with the BBC Television Service in 1936, suspended for the duration of World War II, remained in operation in the UK until 1985, it was used between 1961 and 1982 in Ireland, as well as from 1957 to 1973 for the Rediffusion Television cable service in Hong Kong. Sometimes called the Marconi-EMI system, it was developed in 1934 by the EMI Research Team led by Sir Isaac Shoenberg; the figure of 405 lines had been chosen following discussions over Sunday lunch at the home of Alan Blumlein. The system used interlacing. In the 405 system the scanning lines were broadcast in two complementary fields, 50 times per second, creating 25 frames per second; the actual image was 377 lines high and interlaced, with additional unused lines making the frame up to 405 lines to give the slow circuitry time to prepare for the next frame. At the time of its introduction the 405-line system was referred to as "high definition" - which it was, compared to earlier systems, although of lower definition than 625-line and standards.
In 1934 the British government set up a committee to advise on the future of TV broadcasting. The committee recommended; the recommendation was accepted and tenders were sought from industry. Two tenders were received: one from the Baird company offering a 240-line mechanical system, the other from EMI offering a 405-line all-electronic one; the Television Committee advised that they were unable to choose between the two systems and that both tenders should be accepted, the two systems to be run together for an experimental period. Broadcasting of the resulting BBC Television Service from its Alexandra Palace site began in November 1936, at first time-sharing broadcasts with the 240-line Baird system; this became the standard for all British TV broadcasts until the 1960s. It soon became apparent that television reception was possible well outside the original intended service area. In February 1938, engineers at the RCA Research Station, Long Island, New York, in the USA, were able to receive the BBC signal 5,000 km away, due to the signal being "bounced" back to earth from the ionosphere.
A few minutes of programming were recorded on 16mm movie film. This is now considered to be the only surviving example of live British television; the images recorded included two of the original three BBC announcers, Jasmine Bligh and Elizabeth Cowell, an excerpt from an unknown period costume drama, the BBC's station identification transmitted at the beginning and end of the day's programmes. The BBC temporarily ceased transmissions on 1 September 1939, the day of the German invasion of Poland, as war was imminent. After the BBC Television Service recommenced in 1946, distant reception reports were received from various parts of the world, including Italy, South Africa, the Middle East, North America and the Caribbean; the BBC lost its monopoly of the British television market in 1954, the following year the commercial network ITV, comprising a consortium of regional companies, was launched. In 1964, the BBC launched its BBC2 service on UHF using only a 625-line system, which older sets could not receive.
For several years BBC1 and ITV transmitted BBC2 the 625-line standard. The introduction of colour on BBC2 in 1967 necessitated an more complex dual-standard set to receive all three channels. In November 1969 BBC1 and ITV started broadcasting in 625-line PAL colour on UHF; as their programming was now produced using the new standard, the 405-line broadcasts served only as a rebroadcast in monochrome for people who did not have the newer receivers. Thereafter, receivers were of a simpler single standard design which could not receive the legacy 405-line transmissions. One reason for the long switchover period was the difficulty in matching the coverage level of the new UHF 625-line service with the high level of geographic coverage achieved with the 405-line VHF service; the last 405-line transmissions were seen on 4 January 1985 in Scotland. This left only the UHF PAL system in operation in the UK; the frequencies used by the 405-line system were left empty, but were sold off. Ireland's use of the 405-line system began in 1961, with the launch of Telefís Éireann, but only extended to two main transmitters and their five relays, serving the east and north of the country.
This was because many people in these areas had 405-line sets for receiving UK broadcasts from Wales or Northern Ireland. Telefís Éireann's primary standard was 625-line; the last 405-line relays, in County Donegal, were turned off in 1982.
Television, sometimes shortened to tele or telly, is a telecommunication medium used for transmitting moving images in monochrome, or in color, in two or three dimensions and sound. The term can refer to a television set, a television program, or the medium of television transmission. Television is a mass medium for advertising and news. Television became available in crude experimental forms in the late 1920s, but it would still be several years before the new technology would be marketed to consumers. After World War II, an improved form of black-and-white TV broadcasting became popular in the United States and Britain, television sets became commonplace in homes and institutions. During the 1950s, television was the primary medium for influencing public opinion. In the mid-1960s, color broadcasting was introduced in most other developed countries; the availability of multiple types of archival storage media such as Betamax, VHS tape, local disks, DVDs, flash drives, high-definition Blu-ray Discs, cloud digital video recorders has enabled viewers to watch pre-recorded material—such as movies—at home on their own time schedule.
For many reasons the convenience of remote retrieval, the storage of television and video programming now occurs on the cloud. At the end of the first decade of the 2000s, digital television transmissions increased in popularity. Another development was the move from standard-definition television to high-definition television, which provides a resolution, higher. HDTV may be transmitted in various formats: 1080p, 720p. Since 2010, with the invention of smart television, Internet television has increased the availability of television programs and movies via the Internet through streaming video services such as Netflix, Amazon Video, iPlayer and Hulu. In 2013, 79 % of the world's households owned; the replacement of early bulky, high-voltage cathode ray tube screen displays with compact, energy-efficient, flat-panel alternative technologies such as LCDs, OLED displays, plasma displays was a hardware revolution that began with computer monitors in the late 1990s. Most TV sets sold in the 2000s were flat-panel LEDs.
Major manufacturers announced the discontinuation of CRT, DLP, fluorescent-backlit LCDs by the mid-2010s. In the near future, LEDs are expected to be replaced by OLEDs. Major manufacturers have announced that they will produce smart TVs in the mid-2010s. Smart TVs with integrated Internet and Web 2.0 functions became the dominant form of television by the late 2010s. Television signals were distributed only as terrestrial television using high-powered radio-frequency transmitters to broadcast the signal to individual television receivers. Alternatively television signals are distributed by coaxial cable or optical fiber, satellite systems and, since the 2000s via the Internet; until the early 2000s, these were transmitted as analog signals, but a transition to digital television is expected to be completed worldwide by the late 2010s. A standard television set is composed of multiple internal electronic circuits, including a tuner for receiving and decoding broadcast signals. A visual display device which lacks a tuner is called a video monitor rather than a television.
The word television comes from Ancient Greek τῆλε, meaning'far', Latin visio, meaning'sight'. The first documented usage of the term dates back to 1900, when the Russian scientist Constantin Perskyi used it in a paper that he presented in French at the 1st International Congress of Electricity, which ran from 18 to 25 August 1900 during the International World Fair in Paris; the Anglicised version of the term is first attested in 1907, when it was still "...a theoretical system to transmit moving images over telegraph or telephone wires". It was "...formed in English or borrowed from French télévision." In the 19th century and early 20th century, other "...proposals for the name of a then-hypothetical technology for sending pictures over distance were telephote and televista." The abbreviation "TV" is from 1948. The use of the term to mean "a television set" dates from 1941; the use of the term to mean "television as a medium" dates from 1927. The slang term "telly" is more common in the UK; the slang term "the tube" or the "boob tube" derives from the bulky cathode ray tube used on most TVs until the advent of flat-screen TVs.
Another slang term for the TV is "idiot box". In the 1940s and throughout the 1950s, during the early rapid growth of television programming and television-set ownership in the United States, another slang term became used in that period and continues to be used today to distinguish productions created for broadcast on television from films developed for presentation in movie theaters; the "small screen", as both a compound adjective and noun, became specific references to television, while the "big screen" was used to identify productions made for theatrical release. Facsimile transmission systems for still photographs pioneered methods of mechanical scanning of images in the early 19th century. Alexander Bain introduced the facsimile machine between 1843 and 1846. Frederick Bakewell demonstrated a working laboratory version in 1851. Willoughby Smith discovered the photoconductivity of the element selenium in 1873; as a 23-year-old German university student, Paul Julius Gottlieb Nipkow proposed and patented the Nipkow disk in 1884.
This was a spinning disk with a spiral pattern of holes in it, so each hole scanned a line of the image. Although he never built a working model
DVB-T is an abbreviation for "Digital Video Broadcasting — Terrestrial". This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing modulation, it is the format used worldwide for Electronic News Gathering for transmission of video and audio from a mobile newsgathering vehicle to a central receive point. Rather than carrying one data carrier on a single radio frequency channel, COFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulates a set of spaced adjacent sub-carrier frequencies. In the case of DVB-T, there are two choices for the number of carriers known as 8K-mode; these are 1,705 or 6,817 sub-carriers that are 4 kHz or 1 kHz apart. DVB-T offers three different modulation schemes. DVB-T has been adopted or proposed for digital television broadcasting by many countries, using VHF 7 MHz and UHF 8 MHz channels whereas Taiwan, Colombia and Trinidad and Tobago use 6 MHz channels.
Examples include the UK's Freeview. The DVB-T Standard is published as EN 300 744, Framing structure, channel coding and modulation for digital terrestrial television; this is available from the ETSI website, as is ETSI TS 101 154, Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream, which gives details of the DVB use of source coding methods for MPEG-2 and, more H.264/MPEG-4 AVC as well as audio encoding systems. Many countries that have adopted DVB-T have published standards for their implementation; these include the D-book in the UK, the Italian DGTVi, the ETSI E-Book and the Nordic countries and Ireland NorDig. DVB-T has been further developed into newer standards such as DVB-H, a commercial failure and is no longer in operation, DVB-T2, finalised in August 2011. DVB-T as a digital transmission delivers data in a series of discrete blocks at the symbol rate. DVB-T is a COFDM transmission technique, it allows the receiver to cope with strong multipath situations.
Within a geographical area, DVB-T allows single-frequency network operation, where two or more transmitters carrying the same data operate on the same frequency. In such cases the signals from each transmitter in the SFN needs to be time-aligned, done by sync information in the stream and timing at each transmitter referenced to GPS; the length of the Guard Interval can be chosen. It is a trade-off between SFN capability; the longer the guard interval the larger is the potential SFN area without creating intersymbol interference. It is possible to operate SFNs which do not fulfill the guard interval condition if the self-interference is properly planned and monitored. With reference to the figure, a short description of the signal processing blocks follows. Source coding and MPEG-2 multiplexing: Compressed video, compressed audio, data streams are multiplexed into MPEG program streams. One or more MPEG-PS's are joined together into an MPEG transport stream. Allowed bitrates for the transported data depend on a number of coding and modulation parameters: it can range from about 5 to about 32 Mbit/s.
Splitter: Two different MPEG-TSs can be transmitted at the same time, using a technique called Hierarchical Transmission. It may be used to transmit, for example a standard definition SDTV signal and a high definition HDTV signal on the same carrier; the SDTV signal is more robust than the HDTV one. At the receiver, depending on the quality of the received signal, the STB may be able to decode the HDTV stream or, if signal strength lacks, it can switch to the SDTV one. MUX adaptation and energy dispersal: The MPEG-TS is identified as a sequence of data packets, of fixed length. With a technique called energy dispersal, the byte sequence is decorrelated. External encoder: A first level of error correction is applied to the transmitted data, using a non-binary block code, a Reed-Solomon RS code, allowing the correction of up to a maximum of 8 wrong bytes for each 188-byte packet. External interleaver: Convolutional interleaving is used to rearrange the transmitted data sequence, in such a way that it becomes more rugged to long sequences of errors.
Internal encoder: A second level of error correction is given by a punctured convolutional code, denoted in STBs menus as FEC. There are five valid coding rates: 1/2, 2/3, 3/4, 5/6, 7/8. Internal interleaver: Data sequence is rearranged again, aiming to reduce the influence of burst errors; this time, a block interleaving technique is adopted, with a pseudo-random assignment scheme. Mapper: The digital bit sequence is mapped into a base band modulated sequence of complex symbols. There are three valid modulation schemes: QPSK, 16-QAM, 64-QAM. Frame adaptation: the complex symbols are grouped in blocks of const
Republic of Ireland
Ireland known as the Republic of Ireland, is a country in north-western Europe occupying 26 of 32 counties of the island of Ireland. The capital and largest city is Dublin, located on the eastern part of the island, whose metropolitan area is home to around a third of the country's over 4.8 million inhabitants. The sovereign state shares its only land border with a part of the United Kingdom, it is otherwise surrounded by the Atlantic Ocean, with the Celtic Sea to the south, St George's Channel to the south-east, the Irish Sea to the east. It is a parliamentary republic; the legislature, the Oireachtas, consists of a lower house, Dáil Éireann, an upper house, Seanad Éireann, an elected President who serves as the ceremonial head of state, but with some important powers and duties. The head of government is the Taoiseach, elected by the Dáil and appointed by the President; the state was created as the Irish Free State in 1922 as a result of the Anglo-Irish Treaty. It had the status of Dominion until 1937 when a new constitution was adopted, in which the state was named "Ireland" and became a republic, with an elected non-executive president as head of state.
It was declared a republic in 1949, following the Republic of Ireland Act 1948. Ireland became a member of the United Nations in December 1955, it joined the European Economic Community, the predecessor of the European Union, in 1973. The state had no formal relations with Northern Ireland for most of the twentieth century, but during the 1980s and 1990s the British and Irish governments worked with the Northern Ireland parties towards a resolution to "the Troubles". Since the signing of the Good Friday Agreement in 1998, the Irish government and Northern Ireland Executive have co-operated on a number of policy areas under the North-South Ministerial Council created by the Agreement. Ireland ranks among the top twenty-five wealthiest countries in the world in terms of GDP per capita, as the tenth most prosperous country in the world according to The Legatum Prosperity Index 2015. After joining the EEC, Ireland enacted a series of liberal economic policies that resulted in rapid economic growth.
The country achieved considerable prosperity between the years of 1995 and 2007, which became known as the Celtic Tiger period. This was halted by an unprecedented financial crisis that began in 2008, in conjunction with the concurrent global economic crash. However, as the Irish economy was the fastest growing in the EU in 2015, Ireland is again ascending league tables comparing wealth and prosperity internationally. For example, in 2015, Ireland was ranked as the joint sixth most developed country in the world by the United Nations Human Development Index, it performs well in several national performance metrics, including freedom of the press, economic freedom and civil liberties. Ireland is a member of the European Union and is a founding member of the Council of Europe and the OECD; the Irish government has followed a policy of military neutrality through non-alignment since prior to World War II and the country is not a member of NATO, although it is a member of Partnership for Peace. The 1922 state, comprising 26 of the 32 counties of Ireland, was "styled and known as the Irish Free State".
The Constitution of Ireland, adopted in 1937, provides that "the name of the State is Éire, or, in the English language, Ireland". Section 2 of the Republic of Ireland Act 1948 states, "It is hereby declared that the description of the State shall be the Republic of Ireland." The 1948 Act does not name the state as "Republic of Ireland", because to have done so would have put it in conflict with the Constitution. The government of the United Kingdom used the name "Eire" and, from 1949, "Republic of Ireland", for the state; as well as "Ireland", "Éire" or "the Republic of Ireland", the state is referred to as "the Republic", "Southern Ireland" or "the South". In an Irish republican context it is referred to as "the Free State" or "the 26 Counties". From the Act of Union on 1 January 1801, until 6 December 1922, the island of Ireland was part of the United Kingdom of Great Britain and Ireland. During the Great Famine, from 1845 to 1849, the island's population of over 8 million fell by 30%. One million Irish died of starvation and/or disease and another 1.5 million emigrated to the United States.
This set the pattern of emigration for the century to come, resulting in constant population decline up to the 1960s. From 1874, under Charles Stewart Parnell from 1880, the Irish Parliamentary Party gained prominence; this was firstly through widespread agrarian agitation via the Irish Land League, that won land reforms for tenants in the form of the Irish Land Acts, secondly through its attempts to achieve Home Rule, via two unsuccessful bills which would have granted Ireland limited national autonomy. These led to "grass-roots" control of national affairs, under the Local Government Act 1898, in the hands of landlord-dominated grand juries of the Protestant Ascendancy. Home Rule seemed certain when the Parliament Act 1911 abolished the veto of the House of Lords, John Redmond secured the Third Home Rule Act in 1914. However, the Unionist movement had been growing since 1886 among Irish Protestants after the introduction of the first home rule bill, fearing discrimination and loss of economic and social privileges if Irish Catholics achieved real political power
Digital audio is sound, recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is encoded as numerical samples in continuous sequence. For example, in CD audio, samples are taken 44100 times per second each with 16 bit sample depth. Digital audio is the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s, it replaced analog audio technology in many areas of audio engineering and telecommunications in the 1990s and 2000s. In a digital audio system, an analog electrical signal representing the sound is converted with an analog-to-digital converter into a digital signal using pulse-code modulation; this digital signal can be recorded, edited and copied using computers, audio playback machines, other digital tools. When the sound engineer wishes to listen to the recording on headphones or loudspeakers, a digital-to-analog converter performs the reverse process, converting a digital signal back into an analog signal, sent through an audio power amplifier and to a loudspeaker.
Digital audio systems may include compression, storage and transmission components. Conversion to a digital format allows convenient manipulation, storage and retrieval of an audio signal. Unlike analog audio, in which making copies of a recording results in generation loss and degradation of signal quality, digital audio allows an infinite number of copies to be made without any degradation of signal quality. Digital audio technologies are used in the recording, mass-production, distribution of sound, including recordings of songs, instrumental pieces, sound effects, other sounds. Modern online music distribution depends on digital recording and data compression; the availability of music as data files, rather than as physical objects, has reduced the costs of distribution. Before digital audio, the music industry distributed and sold music by selling physical copies in the form of records and cassette tapes. With digital-audio and online distribution systems such as iTunes, companies sell digital sound files to consumers, which the consumer receives over the Internet.
An analog audio system converts physical waveforms of sound into electrical representations of those waveforms by use of a transducer, such as a microphone. The sounds are stored on an analog medium such as magnetic tape, or transmitted through an analog medium such as a telephone line or radio; the process is reversed for reproduction: the electrical audio signal is amplified and converted back into physical waveforms via a loudspeaker. Analog audio retains its fundamental wave-like characteristics throughout its storage, transformation and amplification. Analog audio signals are susceptible to noise and distortion, due to the innate characteristics of electronic circuits and associated devices. Disturbances in a digital system do not result in error unless the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturb the sequence of symbols, it is therefore possible to have an error-free digital audio system in which no noise or distortion is introduced between conversion to digital format, conversion back to analog.
A digital audio signal may optionally be encoded for correction of any errors that might occur in the storage or transmission of the signal. This technique, known as channel coding, is essential for broadcast or recorded digital systems to maintain bit accuracy. Eight-to-fourteen modulation is a channel code used in the audio compact disc. A digital audio system starts with an ADC; the ADC converts at a known bit resolution. CD audio, for example, has a sampling rate of 44.1 kHz, has 16-bit resolution for each stereo channel. Analog signals that have not been bandlimited must be passed through an anti-aliasing filter before conversion, to prevent the aliasing distortion, caused by audio signals with frequencies higher than the Nyquist frequency. A digital audio signal may be transmitted. Digital audio can be stored on a CD, a digital audio player, a hard drive, a USB flash drive, or any other digital data storage device; the digital signal may be altered through digital signal processing, where it may be filtered or have effects applied.
Sample-rate conversion including upsampling and downsampling may be used to conform signals that have been encoded with a different sampling rate to a common sampling rate prior to processing. Audio data compression techniques, such as MP3, Advanced Audio Coding, Ogg Vorbis, or FLAC, are employed to reduce the file size. Digital audio can be carried over digital audio interfaces such as AES3 or MADI. Digital audio can be carried over a network using audio over Ethernet, audio over IP or other streaming media standards and systems. For playback, digital audio must be converted back to an analog signal with a DAC which may use oversampling. Pulse-code modulation was invented by British scientist Alec Reeves in 1937 and was used in telecommunications applications long before its first use in commercial broadcast and recording. Commercial digital recording was pioneered in Japan by NHK and Nippon Columbia and their Denon brand, in the 1960s; the first commercial digital recordings were released in 1971.
The BBC began to experiment with digital audio in the 1960s. By the early 1970s, it had developed a 2-channel recorder
Low frequency or LF is the ITU designation for radio frequencies in the range of 30 kilohertz to 300 kHz. As its wavelengths range from ten kilometres to one kilometre it is known as the kilometre band or kilometre wave. LF radio waves exhibit low signal attenuation, making them suitable for long-distance communications. In Europe and areas of Northern Africa and Asia, part of the LF spectrum is used for AM broadcasting as the "longwave" band. In the western hemisphere, its main use is for aircraft beacon, navigation and weather systems. A number of time signal broadcasts are broadcast in this band; because of their long wavelength, low frequency radio waves can diffract over obstacles like mountain ranges and travel beyond the horizon, following the contour of the Earth. This mode of propagation, called ground wave, is the main mode in the LF band. Ground waves must be vertically polarized, so vertical monopole antennas are used for transmitting; 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 occasionally travel long distances by reflecting from the ionosphere, although this method, called skywave or "skip" propagation, is not as common as at higher frequencies. Reflection occurs at F layers. Skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. In Europe and Japan, many low-cost consumer devices have since the late 1980s contained radio clocks with an LF receiver for these signals. Since these frequencies propagate by ground wave only, the precision of time signals is not affected by varying propagation paths between the transmitter, the ionosphere, the receiver. In the United States, such devices became feasible for the mass market only after the output power of WWVB was increased in 1997 and 1999. Radio signals below 50 kHz are capable of penetrating ocean depths to 200 metres, the longer the wavelength, the deeper.
The British, Indian, Swedish, United States and other navies communicate with submarines on these frequencies. In addition, Royal Navy nuclear submarines carrying ballistic missiles are under standing orders to monitor the BBC Radio 4 transmission on 198 kHz in waters near the UK, it is rumoured that they are to construe a sudden halt in transmission of the morning news programme Today, as an indicator that the UK is under attack, whereafter their sealed orders take effect. In the US, the Ground Wave Emergency Network or GWEN operated between 150 and 175 kHz, until replaced by satellite communications systems in 1999. GWEN was a land based military radio communications system which could survive and continue to operate in the case of a nuclear attack; the 2007 World Radiocommunication Conference made this band a worldwide amateur radio allocation. An international 2.1 kHz allocation, the 2200 meter band, is available to amateur radio operators in several countries in Europe, New Zealand and French overseas dependencies.
The world record distance for a two-way contact is over 10,000 km from near Vladivostok to New Zealand. As well as conventional Morse code many operators use slow computer-controlled Morse code or specialized digital communications modes; the UK allocated a 2.8 kHz sliver of spectrum from 71.6 kHz to 74.4 kHz beginning in April 1996 to UK amateurs who applied for a Notice of Variation to use the band on a noninterference basis with a maximum output power of 1 Watt ERP. This was withdrawn on 30 June 2003 after a number of extensions in favor of the European-harmonized 136 kHz band. Slow Morse Code from G3AQC in the UK was received 3,275 miles away, across the Atlantic Ocean, by W1TAG in the US on 21-22 November 2001 on 72.401 kHz. In the United States, there is a exemption within FCC Part 15 regulations permitting unlicensed transmissions in the frequency range of 160 to 190 kHz. Longwave radio hobbyists refer to this as the' LowFER' band, experimenters, their transmitters are called'LowFERs'.
This frequency range between 160 kHz and 190 kHz is referred to as the 1750 Meter band. Requirements from 47CFR15.217 and 47CFR15.206 include: The total input power to the final radio frequency stage shall not exceed one watt. The total length of the transmission line and ground lead shall not exceed 15 meters. All emissions below 160 kHz or above 190 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier; as an alternative to these requirements, a field strength of 2400/F microvolts/meter may be used. In all cases, operation may not cause harmful interference to licensed services. Many experimenters in this band are amateur radio operators. A regular service transmitting RTTY marine meteorological information in SYNOP code on LF is the German Meteorological Service; the DWD operates station DDH47 on 147.3 kHz using standard ITA-2 alphabet with a transmission speed of 50 baud and FSK modulation with 85 Hz shift. In parts of the world where there is no longwave broadcasting service, Non-directional beacons used for aeronavigation operate on 190–300 kHz.
In Europe and Africa, the NDB allocation starts on 283.5 kHz. The LORAN-C radio navigation system operated on 100 kHz. In the past, the Decca Navigator System operated betw