Medium wave

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Typical mast radiator of a commercial medium wave AM broadcasting station, Chapel Hill, North Carolina, U.S. 2008-07-28 Mast radiator.jpg
Typical mast radiator of a commercial medium wave AM broadcasting station, Chapel Hill, North Carolina, U.S.

Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz, [1] using channels spaced every 9 kHz, and in North America an extended MW broadcast band ranges from 525 kHz to 1705 kHz, [2] using 10 kHz spaced channels. The term is a historic one, dating from the early 20th century, when the radio spectrum was divided on the basis of the wavelength of the waves into long wave (LW), medium wave, and short wave (SW) radio bands.

Medium frequency The range 300-3000 kHz of the electromagnetic spectrum

Medium frequency (MF) is the ITU designation for radio frequencies (RF) in the range of 300 kilohertz (kHz) to 3 megahertz (MHz). Part of this band is the medium wave (MW) AM broadcast band. The MF band is also known as the hectometer band as the wavelengths range from ten to one hectometer. Frequencies immediately below MF are denoted low frequency (LF), while the first band of higher frequencies is known as high frequency (HF). MF is mostly used for AM radio broadcasting, navigational radio beacons, maritime ship-to-shore communication, and transoceanic air traffic control.

AM broadcasting radio broadcasting using amplitude modulation

AM broadcasting is a radio broadcasting technology, which employs amplitude modulation (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for medium wave transmissions, but also on the longwave and shortwave radio bands.

Radio spectrum part of the electromagnetic spectrum from 3 Hz to 3000 GHz (3 THz)

The radio spectrum is the part of the electromagnetic spectrum with frequencies from 30 Hertz to 300 GHz. Electromagnetic waves in this frequency range, called radio waves, are extremely widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).

Contents

Propagation characteristics

Wavelengths in this band are long enough that radio waves are not blocked by buildings and hills and can propagate beyond the horizon following the curvature of the Earth; this is called the groundwave. Practical groundwave reception typically extends to 200–300 miles, with greater distances over terrain with higher ground conductivity, and greatest distances over salt water. Most broadcast stations use groundwave to cover their listening area.

Ground conductivity

Ground conductivity refers to the electrical conductivity of the subsurface of the earth. In the International System of Units (SI) it is measured in millisiemens per meter (mS/m).

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, the lower ionospheric D layer virtually disappears. When this happens, MW 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 skywave signals of a distant station may interfere with the signals of local stations on the same frequency. In North America, the North American Regional Broadcasting Agreement (NARBA) sets aside certain channels for nighttime use over extended service areas via skywave by a few specially licensed AM broadcasting stations. These channels are called clear channels, and they are required to broadcast at higher powers of 10 to 50 kW.

Ionosphere The ionized part of Earths upper atmosphere

The ionosphere is the ionized part of Earth's upper atmosphere, from about 60 km (37 mi) to 1,000 km (620 mi) altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.

Skywave propagation of radio waves via the ionosphere

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, at intercontinental distances. It is mostly used in the shortwave frequency bands.

The North American Regional Broadcasting Agreement refers to a series of international treaties that defined technical standards for AM band (mediumwave) radio stations. These agreements also addressed how frequency assignments were distributed among the signatories, with a special emphasis on high-powered clear channel allocations.

Use in the Americas

Initially, broadcasting in the United States was restricted to two wavelengths: "entertainment" was broadcast at 360 meters (833 kHz), with stations required to switch to 485 meters (619 kHz) when broadcasting weather forecasts, crop price reports and other government reports. [3] This arrangement had numerous practical difficulties. Early transmitters were technically crude and virtually impossible to set accurately on their intended frequency and if (as frequently happened) two (or more) stations in the same part of the country broadcast simultaneously the resultant interference meant that usually neither could be heard clearly. 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, [3] did little to solve this overcrowding.

In 1923, the Commerce Department realized that as more and more stations were applying for commercial licenses, it was not practical to have every station broadcast on the same three wavelengths. 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 (extended to 1500, then 1600 and ultimately 1700 kHz in later years). Each station would be assigned one frequency (albeit usually shared with stations in other parts of the country and/or abroad), no longer having to broadcast weather and government reports on a different frequency than entertainment. Class A and B stations were segregated into sub-bands. [4]

United States Department of Commerce government agency

The United States Department of Commerce is the Cabinet department of the United States government concerned with promoting economic growth. Among its tasks are gathering economic and demographic data for business and government decision-making, and helping to set industrial standards. This organization's main purpose is to create jobs, promote economic growth, encourage sustainable development and block harmful trade practices of other nations. The Department of Commerce headquarters is the Herbert C. Hoover Building in Washington, D.C.

Herbert Hoover 31st president of the United States

Herbert Clark Hoover was an American engineer, businessman, and politician who served as the 31st president of the United States from 1929 to 1933. A member of the Republican Party, he held office during the onset of the Great Depression. Prior to serving as president, Hoover led the Commission for Relief in Belgium, served as the director of the U.S. Food Administration, and served as the 3rd U.S. Secretary of Commerce.

Weather forecasting application of science and technology to predict the conditions of the atmosphere for a given location and time

Weather forecasting is the application of science and technology to predict the conditions of the atmosphere for a given location and time. People have attempted to predict the weather informally for millennia and formally since the 19th century. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere at a given place and using meteorology to project how the atmosphere will change.

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. [5] In the rest of the world, the separation is 9 kHz, with sidebands of ±4.5 kHz. Both provide adequate audio quality for voice, but are insufficient for high-fidelity broadcasting, which is common on the VHF FM bands. In the US and Canada the maximum transmitter power is restricted to 50 kilowatts, while in Europe there are medium wave stations with transmitter power up to 2 megawatts daytime. [6]

Americas Landmass comprising North America, Central America and South America

The Americas comprise the totality of the continents of North and South America. Together, they make up most of the land in Earth's western hemisphere and comprise the New World.

Sideband

In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing power as a result of the modulation process. The sidebands carry the information (modulation) transmitted by the signal. The sidebands consist of all the Fourier components of the modulated signal except the carrier. All forms of modulation produce sidebands.

Human voice sound made by a human being using the vocal folds for talking, singing, laughing, crying, screaming, etc

The human voice consists of sound made by a human being using the vocal tract, such as talking, singing, laughing, crying, screaming, etc. The human voice frequency is specifically a part of human sound production in which the vocal folds are the primary sound source.

Most United States AM radio stations are required by the Federal Communications Commission (FCC) to shut down, reduce power, or employ a directional antenna array at night in order to avoid interference with each other due to night-time only long-distance skywave propagation (sometimes loosely called ‘skip’). Those stations which shut down completely at night are often known as "daytimers". Similar regulations are in force for Canadian stations, administered by Industry Canada; however, daytimers no longer exist in Canada, the last station having signed off in 2013, after migrating to the FM band.

Use in Europe

In Europe, each country is allocated a number of frequencies on which high power (up to 2 MW) can be used; the maximum power is also subject to international agreement by the International Telecommunication Union (ITU). [7] In most cases there are two power 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, that a station may not work at nighttime, because it would then produce too much interference. Other countries may only operate low-powered transmitters on the same frequency, again subject to agreement. For example, Russia operates a high-powered transmitter, located in its Kaliningrad exclave and used for external broadcasting, on 1386 kHz. The same frequency is also used by low-powered local radio stations in the United Kingdom, which has approximately 250 medium-wave transmitters of 1 kW and over; [8] other parts of the United Kingdom can still receive the Russian broadcast. International mediumwave broadcasting in Europe has decreased markedly with the end of the Cold War and the increased availability of satellite and Internet TV and radio, although the cross-border reception of neighbouring countries' broadcasts by expatriates and other interested listeners still takes place.

Due to the high demand for frequencies in Europe, many countries operate single frequency networks; in Britain, BBC Radio Five Live broadcasts from various transmitters on either 693 or 909 kHz. These transmitters are carefully synchronized to minimize interference from more distant transmitters on the same frequency.

Overcrowding on the Medium wave band is a serious problem in parts of Europe contributing to the early adoption of VHF FM broadcasting by many stations (particularly in Germany). However, in recent years several European countries (Including Ireland, Poland and, to a lesser extent Switzerland) have started moving away from Medium wave altogether with most/all services moving exclusively to other bands (usually VHF).

In Germany, almost all Medium wave public-radio broadcasts were discontinued between 2012 and 2015 to cut costs and save energy, [9] with the last such remaining programme (Deutschlandradio) being switched off on 31 December 2015. [10]

In The Netherlands all national and regional medium wave stations (public and commercial) were discontinued between 2015 and 2018. The last station that powered down its medium wave transmitter was Groot Nieuws Radio on 31 December 2018 [11] . All stations that were broadcasting on medium wave are now using DAB+. All that is left on the medium wave is a handful of low powered medium wave radio stations (maximum output power is 100 W).

Stereo and digital transmissions

Realistic TM-152 AM stereo tuner c. 1988 Tandy AM Stereo.jpg
Realistic TM-152 AM stereo tuner c. 1988

Stereo transmission is possible and offered by some stations in the U.S., Canada, Mexico, the Dominican Republic, Paraguay, Australia, The Philippines, Japan, South Korea, South Africa, Italy and France. However, there have been multiple standards for AM stereo. C-QUAM is the official standard in the United States as well as other countries, but receivers that implement the technology are no longer readily available to consumers. Used receivers with AM Stereo can be found. Names such as "FM/AM Stereo" or "AM & FM Stereo" can be misleading and usually do not signify that the radio will decode C-QUAM AM stereo, whereas a set labeled "FM Stereo/AM Stereo" or "AMAX Stereo" will support AM stereo.

In September 2002, the United States Federal Communications Commission approved the proprietary iBiquity in-band on-channel (IBOC) HD Radio system of digital audio broadcasting, which is meant to improve the audio quality of signals. The Digital Radio Mondiale (DRM) system standardised by ETSI supports stereo and is the ITU approved system for use outside North America and U.S. territories. Some HD Radio receivers also support C-QUAM AM stereo, although this feature is usually not advertised by the manufacturer.

Antennas

Multiwire T antenna of radio station WBZ, Massachusetts, USA, 1925. T antennas were the first antennas used for medium wave broadcasting, and are still used at lower power Wire T antenna station WBZ 1925.jpg
Multiwire T antenna of radio station WBZ, Massachusetts, USA, 1925. T antennas were the first antennas used for medium wave broadcasting, and are still used at lower power

For broadcasting, mast radiators are the most common type of antenna used, consisting of a steel lattice guyed mast in which the mast structure itself is used as the antenna. Stations broadcasting with low power can use masts with heights of a quarter-wavelength (about 310 millivolts per meter using one kilowatt at one kilometer) to 5/8 wavelength (225 electrical degrees; about 440 millivolts per meter using one kilowatt at one kilometer), while high power stations mostly use half-wavelength to 5/9 wavelength. The usage of masts taller than 5/9 wavelength (200 electrical degrees; about 410 millivolts per meter using one kilowatt at one kilometer) with high power gives a poor vertical radiation pattern, and 195 electrical degrees (about 400 millivolts per meter using one kilowatt at one kilometer) is generally considered ideal in these cases. Usually mast antennas are series-excited (base driven); the feedline is attached to the mast at the base. The base of the antenna is at high electrical potential and must be supported on a ceramic insulator to isolate it from the ground. Shunt-excited masts, in which the base of the mast is at a node of the standing wave at ground potential and so does not need to be insulated from the ground, have fallen into disuse, except in cases of exceptionally high power, 1 MW or more, where series excitation might be impractical. If grounded masts or towers are required, cage or long-wire aerials are used. Another possibility consists of feeding the mast or the tower by cables running from the tuning unit to the guys or crossbars at a certain height.

Directional aerials consist of multiple masts, which need not to be of the same height. It is also possible to realize directional aerials for mediumwave with cage aerials where some parts of the cage are fed with a certain phase difference.

For medium-wave (AM) broadcasting, quarter-wave masts are between 153 feet (47 m) and 463 feet (141 m) high, depending on the frequency. Because such tall masts can be costly and uneconomic, other types of antennas are often used, which employ capacitive top-loading (electrical lengthening) to achieve equivalent signal strength with vertical masts shorter than a quarter wavelength. [12] A "top hat" of radial wires is occasionally added to the top of mast radiators, to allow the mast to be made shorter. For local broadcast stations and amateur stations of under 5 kW, T- and L-antennas are often used, which consist of one or more horizontal wires suspended between two masts, attached to a vertical radiator wire. A popular choice for lower-powered stations is the umbrella antenna, which needs only one mast one-tenth wavelength or less in height. This antenna uses a single mast insulated from ground and fed at the lower end against ground. At the top of the mast, radial top-load wires are connected (usually about six) which slope downwards at an angle of 40–45 degrees as far as about one-third of the total height, where they are terminated in insulators and thence outwards to ground anchors. Thus the umbrella antenna uses the guy wires as the top-load part of the antenna. In all these antennas the smaller radiation resistance of the short radiator is increased by the capacitance added by the wires attached to the top of the antenna.

In some rare cases dipole antennas are used, which are slung between two masts or towers. Such antennas are intended to radiate a skywave. The medium-wave transmitter at Berlin-Britz for transmitting RIAS used a cross dipole mounted on five 30.5-metre-high guyed masts to transmit the skywave to the ionosphere at nighttime.

Receiving antennas

Typical ferrite rod antenna used in AM radio receivers Ferritantenne 2.jpg
Typical ferrite rod antenna used in AM radio receivers

Because at these frequencies atmospheric noise is far above the receiver signal to noise ratio, inefficient antennas much smaller than a wavelength can be used for receiving. For reception at frequencies below 1.6 MHz, which includes long and medium waves, loop antennas are popular because of their ability to reject locally generated noise. By far the most common antenna for broadcast reception is the ferrite-rod antenna, also known as a loopstick antenna. The high permeability ferrite core allows it to be compact enough to be enclosed inside the radio's case and still have adequate sensitivity.

See also

Related Research Articles

Shortwave radio radio frequencies in the range of 1.6-30 megahertz (ITU region 1) or 1.7-30 megahertz (ITU region 2)

Shortwave radio is radio transmission using shortwave radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), and generally extends from 30–3 MHz ; above the medium frequency band (MF), to the end of the HF band.

Low frequency or LF is the ITU designation for radio frequencies (RF) in the range of 30 kilohertz (kHz) to 300 kHz. As its wavelengths range from ten kilometres to one kilometre, respectively, it is also known as the kilometre band or kilometre wave.

Longwave radio broadcast band

In radio, longwave, long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium-wave broadcasting band. The term is historic, dating from the early 20th century, when the radio spectrum was considered to consist of longwave (LW), medium-wave (MW), and short-wave (SW) radio bands. Most modern radio systems and devices use wavelengths which would then have been considered 'ultra-short'.

Warsaw radio mast tower

The Warsaw Radio Mast was the world's tallest structure from 1974 until its collapse on 8 August 1991. It was the second tallest structure ever built, being surpassed as tallest by the Burj Khalifa, completed in 2010.

Langenberg transmission tower architectural structure

The Langenberg transmission tower is a broadcasting station that transmits MW, FM and TV signals. It is located in Langenberg, Velbert, Germany and has had a very turbulent history since its inauguration. The transmitter first went into service in 1927 with 60 kilowatts (kW) of power and a T-aerial hanging on two 100-metre freestanding steel-frame towers insulated against ground.

Droitwich Transmitting Station

The Droitwich transmitting station is a large broadcasting facility for long-wave and medium-wave transmissions, established in 1934 in the civil parish of Dodderhill, just outside the village of Wychbold, near Droitwich in Worcestershire, England. The site is the location of the British Broadcasting Corporation's most powerful long-wave transmitter, which together with the two Scottish long-wave transmitters at Burghead and Westerglen forms a network broadcasting on the same frequency. The masts can be seen to the east from the M5 motorway, between Droitwich and Bromsgrove, as well as to the west from the Herefordshire/Worcestershire border. At night, the two sets of aircraft warning lights are visible from a long distance. Due to the bright red lights illuminated at night, some locals have renamed the site "the devil horns of Wychbold". The station is owned and operated by Arqiva.

Ismaning radio transmitter architectural structure

The Transmitter Ismaning was a large radio transmitting station near Ismaning, Bavaria, Germany. It was inaugurated in 1932. From 1932 to 1934 this transmitter used a T-antenna as transmitting antenna, which was spun between two 115-metre-high free-standing wooden lattice towers, which were 240 metres apart. As this antenna had an unfavourable vertical radiation pattern, which produced much skywave resulting in a too small fading-free reception area at night, in 1934 a new antenna was installed. Therefore, one of the towers was dismantled and rebuilt on a 39-metre-high (128 ft) wooden lattice base. While this work took place, an L-Antenna was used, which was spun between the other tower and a small auxiliary wooden tower. It became defunct in 1977 and was destroyed in 1983.

Mainflingen transmitter mediumwave transmission facility in Germany

The Mainflingen mediumwave transmitter is a mediumwave transmission facility south of the A3 motorway near Mainflingen, Hesse, Germany. Mainflingen was the first mediumwave transmitter for the radio station Deutschlandfunk. It went into service in 1962 with a transmission power of 50 kW, on a frequency of 1538 kHz, at the upper end of the mediumwave band. This frequency has a bad groundwave propagation and therefore a low range at daytime, but an excellent skywave propagation with a long range at night.

The mediumwave transmitter Flevoland is a broadcasting facility for medium wave near Zeewolde in the province of Flevoland, Netherlands, situated at 5°25′ E and 52°23′ N. It has been used for broadcasting on 747 kHz and 1008 kHz with a nominal power of 400 kilowatts. As aerial two guyed steel framework masts with a height of 195 metres are used, which form an anti-fading aerial. These masts are grounded and carry a cage aerial, which is upperward the separation insulator, separating the masts in a height of 95 metres in two parts, connected toward the mast construction. The radiation diagram is directional, with a maximum gain of 4 dB in South-Eastern direction, to compensate for the variation in electrical admittance of terrain in the Netherlands.

FM broadcasting The transmission of audio through frequency modulation

FM broadcasting is a method of radio broadcasting using frequency modulation (FM) technology. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. Theoretically wideband AM can offer equally good sound quality, provided the reception conditions are ideal. FM radio stations use the VHF frequencies. The term "FM band" describes the frequency band in a given country which is dedicated to FM broadcasting.

Orfordness transmitting station

The Orfordness transmitting station was a major radio broadcasting facility at Orford Ness on the Suffolk coast in the United Kingdom. It closed in May 2012 after more than 30 years of service.

Mast radiator type of radio antenna

A mast radiator is a radio mast or tower in which the entire structure functions as an antenna. This design, first used in radiotelegraphy stations in the early 1900s, is commonly used for transmitting antennas operating at low frequencies, in the VLF, LF and MF ranges, in particular those used for AM broadcasting. The metal mast is electrically connected to the transmitter. Its base is usually mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna.

A broadcast transmitter is a transmitter used for broadcasting, an electronic device which radiates radio waves modulated with information content intended to be received by the general public. Examples are a radio broadcasting transmitter which transmits audio (sound) to broadcast radio receivers (radios) owned by the public, or a television transmitter, which transmits moving images (video) to television receivers (televisions). The term often includes the antenna which radiates the radio waves, and the building and facilities associated with the transmitter. A broadcasting station consists of a broadcast transmitter along with the production studio which originates the broadcasts. Broadcast transmitters must be licensed by governments, and are restricted to specific frequencies and power levels. Each transmitter is assigned a unique identifier consisting of a string of letters and numbers called a callsign, which must be used in all broadcasts.

Near vertical incidence skywave, or NVIS, is a skywave radio-wave propagation path that provides usable signals in the distances range — usually 0–650 km (0–400 miles). It is used for military and paramilitary communications, broadcasting, especially in the tropics, and by radio amateurs for nearby contacts circumventing line-of-sight barriers. The radio waves travel near-vertically upwards into the ionosphere, where they are refracted back down and can be received within a circular region up to 650 km from the transmitter. If the frequency is too high, refraction fails to occur and if it is too low, absorption in the ionospheric D layer may reduce the signal strength.

MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave radio stations. MW DX is similar to TV and FM DX in that broadcast band (BCB) stations are the reception targets. However, the nature of the lower frequencies used by mediumwave radio stations is very much different from that of the VHF and UHF bands used by FM and TV broadcast stations, and therefore involves different receiving equipment, signal propagation, and reception techniques.

Folded unipole antenna

The folded unipole antenna is a type of monopole antenna; it consists of a vertical metal rod or mast mounted over a conductive surface called a ground plane. The mast is surrounded by a "skirt" of vertical wires electrically attached to the top of the mast. The skirt wires are connected by a metal ring at the bottom and the feed line is connected between the bottom of the wires and ground.

Umbrella antenna

An umbrella antenna is a top-loaded electrically lengthened monopole antenna, consisting in most cases of a mast fed at the ground end, to which a number of radial wires are connected at the top, sloping downwards. They are used as transmitting antennas below 1 MHz, in the LF and particularly the VLF bands, at frequencies sufficiently low that it is impractical or infeasible to build a full size quarter-wave monopole antenna.

Wiederau transmitter architectural structure

The Wiederau transmitter is the oldest broadcasting facility in Saxony. It is located near Wiederau, a village which is part of the municipality of Pegau, and is used for medium-wave, FM and Television broadcasting.

References

  1. "United Kingdom Frequency Allocation Table" (PDF). ofcom.org.uk p. 16. June 22, 2017. Retrieved August 22, 2017.
  2. "United States Frequency Allocations" (PDF). National Telecommunications and Information Administration, U.S. Department of Commerce. 2016. Retrieved 2017-08-22.
  3. 1 2 "Building the Broadcast Band". Earlyradiohistory.us. Retrieved 2010-05-07.
  4. Christopher H. Sterling; John M. Kittross (2002). Stay tuned: a history of American broadcasting. Psychology Press. p. 95. ISBN   0-8058-2624-6.
  5. "Code of Federal Regulations § 73.44 AM transmission system emission limitations" Archived 2011-09-27 at the Wayback Machine
  6. "MWLIST quick and easy: Europe, Africa and Middle East" . Retrieved 11 December 2015.
  7. "International Telecommunication Union". ITU. Retrieved 2009-04-24.
  8. "MW channels in the UK" . Retrieved 11 December 2015.
  9. "Fast alle ARD-Radiosender stellen Mittelwelle ein". heise.de. 2015-01-06. Retrieved 2015-12-31.
  10. Heumann, Marcus (2015-12-17). "Abschied von der Mittelwelle. Der gefürchtete Wellensalat ist Geschichte". Deutschlandfunk.de. Retrieved 2015-12-31.
  11. Medianieuws. "Laatste dagen voor Groot Nieuws Radio op AM". radio.nl. Retrieved 19 February 2019.
  12. Weeks, W.L 1968, Antenna Engineering, McGraw Hill Book Company, Section 2.6