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
Leeds /liːdz/ is a city in West Yorkshire, England. Historically in Yorkshires West Riding, the history of Leeds can be traced to the 5th century when the name referred to an area of the Kingdom of Elmet. The name has applied to many administrative entities over the centuries. It changed from being the appellation of a small borough in the 13th century, through several incarnations. In the 17th and 18th centuries Leeds became a centre for the production. During the Industrial Revolution, Leeds developed into a mill town, wool was the dominant industry but flax, engineering, iron foundries, printing. From being a market town in the valley of the River Aire in the 16th century Leeds expanded and absorbed the surrounding villages to become a populous urban centre by the mid-20th century. The city has the third largest jobs total by local authority area with 480,000 in employment and self-employment at the beginning of 2015. Leeds is also ranked as a world city by the Globalization and World Cities Research Network. Leeds is served by four universities, and has the fourth largest student population in the country and has the fourth largest urban economy. After London, Leeds is the largest legal and financial centre in the UK, with over 30 national and international banks located in the city. Leeds is also the UKs third largest manufacturing centre with around 1,800 firms and 39,000 employees, the largest sub-sectors are engineering, printing and publishing, food and drink, chemicals and medical technology. Outside of London, Leeds has the third busiest railway station, Public transport, rail and road communications networks in the region are focused on Leeds and there are a number of twinning arrangements with towns and cities in other countries. The name Leeds derives from the old Brythonic word Ladenses meaning people of the fast-flowing river and this name originally referred to the forested area covering most of the Brythonic kingdom of Elmet, which existed during the 5th century into the early 7th century. An inhabitant of Leeds is locally known as a Loiner, a word of uncertain origin, the term Leodensian is also used, from the citys Latin name. Leeds developed as a town in the Middle Ages as part of the local agricultural economy. Before the Industrial Revolution it became a centre for the manufacture of woollen cloth. Leeds handled one sixth of Englands export trade in 1770, growth, initially in textiles, was accelerated by the building of the Aire and Calder Navigation in 1699 and the Leeds and Liverpool Canal in 1816
Arsenal Football Club is a professional football club based in Highbury, London, that plays in the Premier League, the top flight of English football. The club has won 13 League titles,12 FA Cups, Arsenal was the first club from the South of England to join The Football League, in 1893. They entered the First Division in 1904, and have accumulated the second most points. Relegated only once, in 1913, they continue the longest streak in the top division, in the 1930s, Arsenal won five League Championships and two FA Cups, and another FA Cup and two Championships after the war. In 1970–71, they won their first League and FA Cup Double, between 1989 and 2005, they won five League titles and five FA Cups, including two more Doubles. They completed the 20th century with the highest average league position, Herbert Chapman won Arsenals first national trophies, but died prematurely. He helped introduce the WM formation, floodlights, and shirt numbers, Arsène Wenger has been the longest-serving manager and has won the most trophies. His teams set several English records, the longest win streak, the longest unbeaten run, in 1886, Woolwich munitions workers founded the club as Dial Square. In 1913, the crossed the city to Arsenal Stadium in Highbury. They became Tottenham Hotspurs nearest club, commencing the North London derby, in 2006, they moved down the road to the Emirates Stadium. Arsenal earned €435. 5m in 2014–15, with the Emirates Stadium generating the highest revenue in world football, based on social media activity from 2014–15, Arsenals fanbase is the fifth largest in the world. In 2016, Forbes estimated the club was the second most valuable in England, on 1 December 1886, munitions workers in Woolwich, now South East London, formed Arsenal as Dial Square, with David Danskin as their first captain. Named after the heart of the Royal Arsenal complex, they took the name of the complex a month later. Royal Arsenal F. C. s first home was Plumstead Common, though spent most of their time in South East London playing on the other side of Plumstead. Royal Arsenal won Arsenals first trophies in 1890 and 1891, Royal Arsenal renamed themselves for a second time upon becoming a limited liability company in 1893. They registered their new name, Woolwich Arsenal, with The Football League when the club ascended later that year, Woolwich Arsenal was the first southern member of The Football League, starting out in the Second Division and winning promotion to the First Division in 1904. Falling attendances, due to financial difficulties among the munitions workers, businessmen Henry Norris and William Hall took the club over, and sought to move them elsewhere. In 1913, soon after relegation back to the Second Division, Woolwich Arsenal moved to the new Arsenal Stadium in Highbury and this saw their third change of name, the following year, they reduced Woolwich Arsenal to simply The Arsenal
Tottenham Hotspur F.C.
Tottenham Hotspur Football Club /ˈtɒtnəm, -tənəm/, commonly referred to as Spurs, is an English football club located in Tottenham, Haringey, London, that competes in the Premier League. The clubs home stadium is White Hart Lane and their newly developed training ground is in Bulls Cross on the northern borders of the London Borough of Enfield. Founded in 1882, Tottenham won the FA Cup for the first time in 1901, Tottenham were the first club in the 20th century to achieve the League and FA Cup Double, winning both competitions in the 1960–61 season. After successfully defending the FA Cup in 1962, in 1963 they became the first British club to win a UEFA club competition – the European Cup Winners Cup, in 1967, Spurs won the FA Cup for a third time in the 1960s. In the 1970s Tottenham won the League Cup on two occasions and were the winner of the UEFA Cup in 1972, becoming the first British club to win two different major European trophies. In the 1980s Spurs won several trophies, the FA Cup twice, FA Community Shield, in the 1990s the club won the FA Cup and the League Cup. When they won the League Cup once more in 2008, it meant that they had won a trophy in each of the last six decades – an achievement only matched by Manchester United. The clubs Latin motto is Audere est Facere, and its emblem is a cockerel standing upon a football, the club has a long-standing rivalry with nearby neighbours Arsenal, with head-to-head fixtures known as the North London derby. The club was formed in 1882, as Hotspur F. C. and played in the Southern League from 1896 until 1908, when they were elected into the Football League Second Division. Before this promotion Tottenham had won the FA Cup in 1901, since then, Tottenham have won the FA Cup a further seven times, the Football League twice, the Football League Cup four times, the UEFA Cup twice and also the UEFA Cup Winners Cup. The Cup Winners Cup victory in 1963 made Tottenham the first English team to win a UEFA competition, in 1960–61 they became the first team to complete The Double in the 20th century. Tottenham played their first matches at Tottenham Marshes on the public pitches. It was at this ground that Spurs first played archrivals Arsenal, there were occasions on which fights would break out on the marshes in dispute of the teams that were allowed to use the best pitches. Crowd sizes were regularly increasing and a new site was becoming needed to accommodate these supporters, in 1898 the club moved from the marshes to Northumberland Park and charged an admission fee of 3d. They only remained at this ground for a year as in April 1899,14,000 fans turned up to watch Spurs play Woolwich Arsenal. The ground was no able to cope with the larger crowds and Spurs were forced to move to a new larger site 100 yards down the road. The White Hart Lane ground was originally a disused nursery owned by the brewery Charringtons, the landlord spotted the increased income he could enjoy if Tottenham played their matches behind his pub and in 1899 the club moved in. They brought with them the stand they used at Northumberland Park which gave shelter to 2,500 fans, notts County were the first visitors to the Lane in a friendly watched by 5,000 people and provided in £115 in receipts, Spurs won 4–1
West Ham United F.C.
West Ham United Football Club is a professional football club based in Stratford, East London, England. They compete in the Premier League, the top tier of English football, in 2016 the club re-located to the London Stadium. The club was founded in 1895 as Thames Ironworks and reformed in 1900 as West Ham United and they moved to the Boleyn Ground in 1904, which remained their home ground for more than a century. The team initially competed in the Southern League and Western League before joining the Football League in 1919 and they were promoted to the top flight in 1923, when they also losing finalists in the first FA Cup Final held at Wembley. In 1940, the won the inaugural Football League War Cup. West Ham have been winners of the FA Cup three times, in 1964,1975, and 1980, and have also been runners-up twice, in 1923, and 2006. The club have reached two major European finals, winning the European Cup Winners Cup in 1965 and finishing runners up in the competition in 1976. West Ham also won the Intertoto Cup in 1999 and they are one of eight clubs never to have fallen below the second tier of English football, spending 59 of 91 league seasons in the top flight, up to and including the 2016–17 season. The clubs highest league position to date came in 1985–86 when they achieved third place in the then First Division, three West Ham players were members of the 1966 World Cup final-winning England team, captain Bobby Moore and goalscorers Geoff Hurst and Martin Peters. The club, Thames Ironworks were the first ever winners of the West Ham Charity Cup in 1895 contested by clubs in the West Ham locality and they turned professional in 1898 upon entering the Southern League Second Division, and were promoted to the First Division at the first attempt. The following year they came second from bottom, but had established themselves as a fully fledged competitive team and they comfortably fended off the challenge of local rivals Fulham in a relegation play-off, 5–1 in late April 1900 and retained their First Division status. In 1899, they acquired their now-traditional home kit combination of claret shirts and sky blue sleeves in a wager involving Aston Villa players, because of the original works team roots and links, they are still known as the Irons or the Hammers amongst fans and the media. West Ham Utd joined the Western League for the 1901 season while continuing to play in the Southern Division 1. In 1907, West Ham were crowned the Western League Division 1B Champions, the reborn club continued to play their games at the Memorial Grounds in Plaistow but moved to a pitch in the Upton Park area in the guise of the Boleyn Ground stadium in 1904. The Cup Final match itself ended 2–0 to Bolton, the team enjoyed mixed success in Division 1 but retained their status for ten years and reached the FA Cup semi-final in 1933. In 1932, the club was relegated to Division Two and long term custodian Syd King was sacked after serving the club in the role of manager for 32 years, following relegation, King had mental health problems. He appeared drunk at a meeting and soon after committed suicide. The club spent most of the next 30 years in division, first under Paynter
Queens Park Rangers F.C.
Queens Park Rangers Football Club is a professional association football club based in White City, London, that plays in the Championship, the second tier of English football. Their honours include winning the League Cup in 1967, as well as finishing top of the tier in 1983 and 2011. QPR were also runners-up of the Football League First Division in 1975–76, Queens Park Rangers were founded in 1886 after the merger of Christchurch Rangers and St. Judes Institute. Owing to their proximity to other west London clubs, QPR maintain long-standing rivalries with other clubs in the area. The most notable of these are Chelsea, Fulham and Brentford, outside London, QPR also traditionally share rivalries with Watford, Luton and Cardiff, although in recent years these fixtures have become less prominent. For the current season see 2015–16 Queens Park Rangers F. C. season The club was formed in 1886, the resulting team was called Queens Park Rangers, because most of the players came from the Queens Park area of north-west London. QPR were promoted as champions of Division 3 South in the 1947–48 season, Dave Mangnall was the manager as the club participated in four seasons of the Second Division, being relegated in 1951–52. Tony Ingham was signed from Leeds United and went on to make the most ever league appearances for QPR, arguably the clubs greatest ever manager, Alec Stock, arrived prior to the start of the 1959–60 season. The 1960–61 season saw QPR achieve their biggest win to date, in time, Stock, together with Jim Gregory who arrived as chairman in the mid-1960s, helped to achieve a total transformation of the club and its surroundings. It is still the major trophy that QPR have won. It was also the first League Cup final to be held at Wembley Stadium, after winning promotion in 1968 to the top flight for the first time in their history, Rangers were relegated after just one season and spent the next four years in Division Two. Terry Venables joined from Spurs at the beginning of the 1969–70 season, during this time, new QPR heroes emerged including Phil Parkes, Don Givens, Dave Thomas and Stan Bowles. These new signings were in addition to home-grown talent such as Dave Clement, Ian Gillard, Mick Leach, after completing their 42-game season, QPR sat at the top of the league, one point ahead of Liverpool who went on to defeat Wolverhampton Wanderers to clinch the title. Wolves were relegated to the Second Division that same season, following Sextons departure in 1977 the club eventually slipped into the Second Division in 1979. In 1980 Terry Venables took over as manager and the club installed a plastic pitch, in 1982 QPR, still playing in the Second Division, reached the FA Cup Final for the only time in the clubs history, facing holders Tottenham Hotspur. Tottenham won 1–0 in a replay, the following season QPR went on to win the Second Division championship and returned to English footballs top division. After a respectable fifth-place finish, and UEFA Cup qualification, the following year, in 1988 the club had a new chairman, Richard Thompson. Who at 24 was the Premier Leagues youngest ever chairman, over the next seven years, various managers came and went from Loftus Road and the club spent many seasons finishing mid table but avoided relegation
Chelsea Football Club is an English professional football club based in Fulham, London, that competes in the Premier League. Founded in 1905, the home ground since then has been Stamford Bridge. Chelsea had their first major success in 1955, when they won the league championship and they then won various cup competitions between 1965 and 1996. The clubs greatest period of success has come during the last two decades, winning 21 trophies since 1997. Chelsea are the only London club to win the UEFA Champions League, and one of four clubs, Chelseas regular kit colours are royal blue shirts and shorts with white socks. The clubs crest has changed several times in attempts to re-brand the club. The current crest, featuring a lion rampant regardant holding a staff, is a modification of the one introduced in the early 1950s. The club have the sixth-highest average all-time attendance in English football and their average home gate for the 2015–16 season was 41,500, the seventh highest in the Premier League. Since 2003, Chelsea have been owned by Russian billionaire Roman Abramovich, in 2016, they were ranked by Forbes magazine as the seventh most valuable football club in the world, at £1.15 billion. In 1904, Gus Mears acquired the Stamford Bridge athletics stadium with the aim of turning it into a football ground, an offer to lease it to nearby Fulham was turned down, so Mears opted to found his own club to use the stadium. Chelsea were founded on 10 March 1905 at The Rising Sun pub, opposite the main entrance to the ground on Fulham Road. The club won promotion to the First Division in their second season and they reached the 1915 FA Cup Final, where they lost to Sheffield United at Old Trafford, and finished third in the First Division in 1920, the clubs best league campaign to that point. Chelsea attracted large crowds and had a reputation for signing big-name players, former Arsenal and England centre-forward Ted Drake became manager in 1952 and proceeded to modernise the club. The following season saw UEFA create the European Champions Cup, but after objections from The Football League, Chelsea failed to build on this success, and spent the remainder of the 1950s in mid-table. Drake was dismissed in 1961 and replaced by player-coach Tommy Docherty, Docherty built a new team around the group of talented young players emerging from the clubs youth set-up and Chelsea challenged for honours throughout the 1960s, enduring several near-misses. They were on course for a treble of League, FA Cup and League Cup going into the stages of the 1964–65 season, winning the League Cup. In three seasons the side were beaten in three major semi-finals and were FA Cup runners-up, under Dochertys successor, Dave Sexton, Chelsea won the FA Cup in 1970, beating Leeds United 2–1 in a final replay. Chelsea took their first European honour, a UEFA Cup Winners Cup triumph, the year, with another replayed win
Wimbledon Football Club was an English football club formed in Wimbledon, south-west London, in 1889 and based at Plough Lane from 1912 to 1991. Founded as Wimbledon Old Centrals, the club were a team for most of their history. The team rose quickly from obscurity during the 1980s and were promoted to the then top-flight First Division in 1986, the team remained in the First Division and its successor the FA Premier League until they were relegated in 2000. In 2001, after rejecting a variety of local sites and others further afield. A group of supporters responded by forming a new club, AFC Wimbledon, Wimbledon played their first match in Milton Keynes in 2003, and adopted the name Milton Keynes Dons in 2004. Wimbledon Old Central Football Club were formed in 1889, taking its name from the Old Central School on Wimbledon Common where players had been pupils. The clubs first match was a 1–0 victory over Westminster, Wimbledon won the Clapham League again in 1900–01, as well as two minor trophies. The club was restarted a year later under the name Wimbledon Borough, though Borough was dropped from the name after barely a year. The club continued to play on Wimbledon Common and at other locations in the Wimbledon area until 1912. Wimbledon joined the Athenian League for 1919–20, and in the season in its new division finished as runners-up. The club then joined the Isthmian League, winning four Isthmian League titles during the 1930s, and reaching the FA Amateur Cup final in 1934–35, Wimbledon began to prosper. The club reached another FA Amateur Cup final in 1946–47, Wimbledon won the Isthmian League for the fifth time in 1958–59 before starting a period of domination that saw three successive championships – 1961–62, 1962–63 and 1963–64. Following these successes the decision was taken to turn professional for the 1964–65 season, Wimbledon had continued success in their new league, finishing as runners-up at the first attempt. They then became the first non-League team that century to beat a First Division side away from home by defeating Burnley at Turf Moor. In the fourth round the good form continued, as the team held the reigning First Division champions Leeds United to a 0–0 draw at Elland Road. Goalkeeper Dickie Guy saved a penalty from Peter Lorimer to earn a replay, after winning the Southern League three times running from 1974–75 to 1976–77, Wimbledon were elected to The Football League in place of Workington for the 1977–78 season. The 1977–78 season was a satisfactory Football League debut for Wimbledon, Allen Batsford had resigned as manager on 2 January 1978 to be succeeded by Dario Gradi, who guided the club to promotion in 1978–79. Wimbledons first stay in the Third Division was not a successful one, the team struggled, and were relegated in bottom place, winning just 10 league games all season
Manchester is a major city and metropolitan borough in Greater Manchester, England, with a population of 514,414 as of 2013. It lies within the United Kingdoms second-most populous urban area, with a population of 2.55 million, Manchester is fringed by the Cheshire Plain to the south, the Pennines to the north and east and an arc of towns with which it forms a continuous conurbation. The local authority is Manchester City Council and it was historically a part of Lancashire, although areas of Cheshire south of the River Mersey were incorporated during the 20th century. Throughout the Middle Ages Manchester remained a township but began to expand at an astonishing rate around the turn of the 19th century. Manchesters unplanned urbanisation was brought on by a boom in textile manufacture during the Industrial Revolution, Manchester achieved city status in 1853. The Manchester Ship Canal opened in 1894, creating the Port of Manchester and its fortunes declined after the Second World War, owing to deindustrialisation. The city centre was devastated in a bombing in 1996, but it led to extensive investment, in 2014, the Globalization and World Cities Research Network ranked Manchester as a beta world city, the highest-ranked British city apart from London. Manchester is the third-most visited city in the UK and it is notable for its architecture, culture, musical exports, media links, scientific and engineering output, social impact, sports clubs and transport connections. Manchester Liverpool Road railway station was the worlds first inter-city passenger railway station and in the city scientists first split the atom, the name Manchester originates from the Latin name Mamucium or its variant Mancunium and the citizens are still referred to as Mancunians. These are generally thought to represent a Latinisation of an original Brittonic name, both meanings are preserved in languages derived from Common Brittonic, mam meaning breast in Irish and mother in Welsh. The suffix -chester is a survival of Old English ceaster and their territory extended across the fertile lowland of what is now Salford and Stretford. Central Manchester has been settled since this time. A stabilised fragment of foundations of the version of the Roman fort is visible in Castlefield. After the Roman withdrawal and Saxon conquest, the focus of settlement shifted to the confluence of the Irwell, much of the wider area was laid waste in the subsequent Harrying of the North. Thomas de la Warre, lord of the manor, founded and constructed a church for the parish in 1421. The church is now Manchester Cathedral, the premises of the college house Chethams School of Music. The library, which opened in 1653 and is open to the public today, is the oldest free public reference library in the United Kingdom. Manchester is mentioned as having a market in 1282, around the 14th century, Manchester received an influx of Flemish weavers, sometimes credited as the foundation of the regions textile industry
Birmingham is a major city and metropolitan borough of West Midlands, England lying on the River Rea, a small river that runs through Birmingham. It is the largest and most populous British city outside London, the city is in the West Midlands Built-up Area, the third most populous urban area in the United Kingdom, with a population of 2,440,986 at the 2011 census. Birminghams metropolitan area is the second most populous in the UK with a population of 3.8 million and this also makes Birmingham the 8th most populous metropolitan area in Europe. By 1791 it was being hailed as the first manufacturing town in the world, perhaps the most important invention in British history, the industrial steam engine, was invented in Birmingham. From the summer of 1940 to the spring of 1943, Birmingham was bombed heavily by the German Luftwaffe in what is known as the Birmingham Blitz. The damage done to the infrastructure, in addition to a deliberate policy of demolition and new building by planners, led to extensive demolition. Today Birminghams economy is dominated by the service sector and its metropolitan economy is the second largest in the United Kingdom with a GDP of $121. 1bn, and its six universities make it the largest centre of higher education in the country outside London. Birmingham is the fourth-most visited city in the UK by foreign visitors, Birminghams sporting heritage can be felt worldwide, with the concept of the Football League and lawn tennis both originating from the city. Its most successful football club Aston Villa has won seven league titles, people from Birmingham are called Brummies, a term derived from the citys nickname of Brum. This originates from the citys name, Brummagem, which may in turn have been derived from one of the citys earlier names. There is a distinctive Brummie accent and dialect, Birminghams early history is that of a remote and marginal area. The main centres of population, power and wealth in the pre-industrial English Midlands lay in the fertile and accessible river valleys of the Trent, the Severn and the Avon. The area of modern Birmingham lay in between, on the upland Birmingham Plateau and within the wooded and sparsely populated Forest of Arden. Birmingham as a settlement dates from the Anglo-Saxon era, within a century of the charter Birmingham had grown into a prosperous urban centre of merchants and craftsmen. By 1327 it was the third-largest town in Warwickshire, a position it would retain for the next 200 years, by 1700 Birminghams population had increased fifteenfold and the town was the fifth-largest in England and Wales. The importance of the manufacture of goods to Birminghams economy was recognised as early as 1538. Equally significant was the emerging role as a centre for the iron merchants who organised finance, supplied raw materials. The 18th century saw this tradition of free-thinking and collaboration blossom into the phenomenon now known as the Midlands Enlightenment
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
Virgin Media PLC is a British company which provides fixed and mobile telephone, television and broadband internet services to businesses and consumers in the United Kingdom. Its headquarters are in Hook, Hampshire, United Kingdom, the company has been a subsidiary of Liberty Global plc, an international television and telecommunications company headquartered in London, since June 2013. Virgin Media previously had a listing on the NASDAQ Stock Market and was a constituent of the NASDAQ-100 index. It also had a listing on the London Stock Exchange. The company was formed in March 2006 by the merger of NTL and Telewest, in November 2006 the company signed a deal with Sir Richard Branson to license the Virgin brand for the combined business. All of the companys services were rebranded under the Virgin Media name in February 2007. At the same date it had around 3 million mobile telephony customers, Virgin Media competes primarily with Sky, BT Group, EE, O2, TalkTalk, Vodafone and Three. The companys origins lie in both Telewest and NTL, which merged in March 2006, Telewest began in 1984 in Croydon under the name Croydon Cable, and was acquired by United Cable of Denver in 1988. The company expanded during the 1990s and adopted the Telewest name in 1992 following the merger of its then-parent TCI and US West. It expanded into cable television access in 1999 by purchasing the remaining 50% stake in Cable London, one of the first cable TV companies in the UK, from NTL, adding 400,000 homes in north London. In April 2000 Telewest merged with Flextech, and in November extended its network with the acquisition of Eurobell. NTL was established by Barclay Knapp and George Blumenthal in 1993 as International CableTel, initially, Cabletel acquired local cable franchises covering Guildford, Northern Ireland and parts of Central Scotland and South Wales. In 1996 CableTel acquired National Transcommunications Limited, the privatised UK Independent Broadcasting Authority transmission network, in 1998 CableTel adopted NTL as its new name. NTL purchased the ISP Virgin. net in 2004, having originally operated it as a joint venture with Virgin Group since it launched in November 1996. It sold ADSL broadband services through BT landlines to those living outside areas served by NTLs cable network and also offered subscription-based, prior to acquiring Virgin. net, NTL offered a similar package called NTL Freedom. Telewest and NTL began discussions regarding a merger in late 2003, thanks to their geographically distinct areas, NTL and Telewest had co-operated previously, as in redirecting potential customers living outside their respective areas. On 3 October 2005, NTL announced a US$16 billion purchase of Telewest, to prevent this, Telewest instead acquired NTL. In December 2005 NTL, Telewest and mobile network operator Virgin Mobile UK announced that talks had taken place regarding a merger