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Medium wave (MW) is the part of the
medium frequency 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 hectom ...

medium frequency
(MF)
radio band The radio spectrum is the part of the electromagnetic spectrum with frequencies from 30 Hz to 300 GHz. Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunic ...
used mainly for AM radio broadcasting. The spectrum provides about 120 channels with limited sound quality. During daytime, only local stations can be received. Propagation in the night allows strong signals within a range of about 2,000 km. This can cause massive interference because on most channels, about 20 to 50 transmitters operate simultaneously worldwide. In addition to that,
amplitude modulation#REDIRECT Amplitude modulation#REDIRECT Amplitude modulation {{Redirect category shell|1= {{R from other capitalisation ...
{{Redirect category shell|1= {{R from other capitalisation ...
(AM) is prone to interference by all sorts of electronic devices, especially power supplies and computers. Strong transmitters cover larger areas than on the
FM broadcast band The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations. The range of frequencies used differs between different parts of the world. In Europe and Africa (defined as International Telecommunication Union (ITU ...
but require more energy. Digital modes are possible but have not reached the momentum yet. MW was the main radio band for broadcasting from the beginnings in the 1920s into the 1950s until FM with a better sound quality took over. In Europe,
digital radio Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. Types In digital broadcasting systems ...
is gaining popularity and offers AM stations the chance to switch over if no frequency in the FM band is available. Many countries in Europe have switched off their MW transmitters since the 2010s. The term is a historic one, dating from the early 20th century, when the
radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 30 Hz to 300 GHz. Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunic ...
was divided on the basis of the
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
of the waves into
long wave 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 ea ...
(LW), medium wave, and
short wave Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3–30 MHz (100 to 10 metre ...
(SW) radio bands.


Spectrum and channel allocation

For Europe, Africa and Asia the MW band consists of 120 channels with centre frequencies from 531 to 1602 kHz spaced every 9 kHz. The total official spectrum including the modulated audio ranges from 526.5 kHz to 1606.5 kHz. Australia uses an expanded band up allocated up to 1701 kHz. North America uses 118 channels from 530 to 1700 kHz using 10 kHz spaced channels. The range above 1610 kHz is primarily only used by low power stations. It is the preferred range for services with automated traffic, weather and tourist information. Frequency coordination avoids the use of adjacent channels in one area.


Sound quality

The 9/10 kHz channel stepping on MW requires limiting the audio bandwidth to 4.5/5 kHz because the audio spectrum is transmitted twice on each side band. This is adequate for talk and news but not for good quality music. However, many stations use audio bandwidths up 10 kHz, which is not
Hi-Fi High fidelity (often shortened to hi-fi or hifi) is a term used by listeners, audiophiles, and home audio enthusiasts to refer to high-quality reproduction of sound. This is in contrast to the lower quality sound produced by inexpensive audio e ...
but sufficient for casual listening. In the UK, most stations use a bandwidth of 6.3 kHz. With AM, it largely depends on the frequency filters of each receiver how the audio is reproduced. This is a major disadvantage compared to FM and digital modes where the demodulated audio is more objective. Extended audio bandwidths cause interference on adjacent channels.


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
groundwaveA diving thumb In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within li ...
. Practical groundwave reception of strong transmitters typically extends to 200–300 miles, with greater distances over terrain with higher
ground conductivityGround conductivity map of the US 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). Radio propagation Ground conduc ...
, and greatest distances over salt water. The groundwave reaches further on lower medium wave frequencies. Medium waves can also reflect off charged particle layers in the
ionosphere The ionosphere () is the ionized part of Earth's upper atmosphere, from about to 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 ...
and return to Earth at much greater distances; this is called the
skywave off the ionosphere (red) during skywave propagation 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 atmosphe ...
. At night, especially in winter months and at times of low solar activity, the lower ionospheric
D layer The ionosphere () is the ionized part of Earth's upper atmosphere, from about to 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 ...
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 The F region of the ionosphere is home to the F layer of ionization, also called the Appleton–Barnett layer, after the English physicist Edward Appleton and New Zealand physicist and meteorologist Miles Barnett. As with other ionospheric sectors, ...
. 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 The North American Regional Broadcasting Agreement (NARBA, es|Convenio Regional Norteamericano de Radiodifusión) refers to a series of international treaties that defined technical standards for AM band (mediumwave) radio stations. These agreemen ...
(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.


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. 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, did little to solve this overcrowding. In 1923, the
Commerce Department The United States Department of Commerce is an executive department of the U.S. federal government concerned with promoting economic growth. Among its tasks are gathering economic and demographic data for business and government decision makin ...
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 Herbert Clark Hoover (August 10, 1874 – October 20, 1964) was an American politician, businessman, and engineer, who served as the 31st president of the United States from 1929 to 1933. A member of the Republican Party, he held office dur ...

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 Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest level of the planet's atmosphere, the tro ...
and government reports on a different frequency than entertainment. Class A and B stations were segregated into sub-bands. In the US and Canada the maximum transmitter power is restricted to 50 kilowatts, while in
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It comprises the westernmost peninsulas of the continental landmass of Eurasia, and is bordered by the Arctic Ocean to the north, the Atlant ...
there are medium wave stations with transmitter power up to 2 megawatts daytime. Most United States
AM radio AM broadcasting is radio broadcasting using amplitude modulation (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for medium wave (also known as "AM band") transmiss ...
stations are required by the
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction over the ...
(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 off the ionosphere (red) during skywave propagation 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 atmosphe ...
propagation Propagation can refer to: *Chain propagation in a chemical reaction mechanism *Crack propagation, the growth of a crack during the fracture of materials *Propaganda, non-objective information used to further an agenda *Reproduction, and other forms ...
(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 Innovation, Science and Economic Development Canada (ISED; legally, the Department of Industry; french: Innovation, Sciences et Développement économique Canada), is the department of the Government of Canada with a mandate of fostering a growing, ...
; however, daytimers no longer exist in Canada, the last station having signed off in 2013, after migrating to the
FM band The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations. The range of frequencies used differs between different parts of the world. In Europe and Africa (defined as International Telecommunication Union (ITU ...
.


Use in Europe

Many countries have switched off most of their MW transmitters due to cost-cutting and low usage of MW by the listeners. Among those are Germany, France, Russia, Poland, Sweden, the Benelux, Austria, Switzerland, and most of the Balkans. Large networks of transmitters are remaining in the UK, Spain, Romania and Italy. In the Netherlands and Scandinavia, some new idealistically driven stations have launched low power services on the former high power frequencies. This also applies to the ex-offshore pioneer
Radio Caroline Radio Caroline is a British radio station founded in 1964 by Ronan O'Rahilly and George Drummond initially to circumvent the record companies' control of popular music broadcasting in the United Kingdom and the BBC's radio broadcasting monopoly ...
that now has a licence to use 648 kHz, which was used by the
BBC World Service The BBC World Service is an international broadcaster owned and operated by the BBC. It is the world's largest of any kind. It broadcasts radio news, speech and discussions in more than 40 languages to many parts of the world on analogue and ...
over decades. As the MW band is thinning out, many local stations from the remaining countries as well as from North Africa and the Middle East can now be received all over Europe, but often only weak with much interference. 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 260px|ITU Monument, Bern The International Telecommunication Union is a specialized agency of the United Nations responsible for all matters related to information and communication technologies. Established in 1865 as the International Tele ...
(ITU). In most cases there are two power limits: a lower one for
omnidirectional Omnidirectional refers to the notion of existing in every direction. Omnidirectional devices include: * Omnidirectional antenna, an antenna that radiates equally in all directions * VHF omnidirectional range, a type of radio navigation system for ...
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 operate 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. International medium wave broadcasting in Europe has decreased markedly with the end of the
Cold War The Cold War was a period of geopolitical tension between the Soviet Union and the United States and their respective allies, the Eastern Bloc and the Western Bloc, after World War II. Historians do not fully agree on the dates, but the per ...
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. In the late 20th century, overcrowding on the Medium wave band was a serious problem in parts of Europe contributing to the early adoption of VHF
FM broadcasting in Henderson, Nevada and broadcasts at a frequency of 95.5 MHz. FM broadcasting is a method of radio broadcasting using frequency modulation (FM). Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide hig ...
by many stations (particularly in Germany). Due to the high demand for frequencies in Europe, many countries set up single frequency networks; in
Britain Britain usually refers to: * United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United Kingdom * Ro ...
,
BBC Radio Five Live BBC Radio 5 Live (also known as just 5 Live) is the BBC's national radio service that broadcasts mainly news, sport, discussion, interviews and phone-ins. It is the principal BBC radio station covering sport in the United Kingdom, broadcasting ...
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.


Use in Asia

In Asia and the Middle East, many high powered transmitters remain in operation. China operates many single-frequency networks.


Stereo and digital transmissions

Stereo transmission is possible and is or was 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 AM stereo is a term given to a series of mutually incompatible techniques for radio broadcasting stereo audio in the AM band in a manner that is compatible with standard AM receivers. There are two main classes of systems: independent sideband (ISB) ...
.
C-QUAM C-QUAM (Compatible QUadrature Amplitude Modulation) is the method of AM stereo broadcasting used in Canada, the United States and most other countries. It was invented in 1977 by Norman Parker, Francis Hilbert, and Yoshio Sakaie, and published in ...
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 labelled "FM Stereo/AM Stereo" or "AMAX Stereo" will support AM stereo. In September 2002, the United States
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction over the ...
approved the proprietary
iBiquity iBiquity Digital Corporation is a company formed by the merger of USA Digital Radio and Lucent Digital Radio. Based in Columbia, Maryland, with additional offices in Basking Ridge, New Jersey, and Auburn Hills, Michigan, iBiquity is a privately ...
in-band on-channel In-band on-channel (IBOC) is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency. By utilizing additional digital subcarriers or sidebands, digital information is "multiplexed" on a ...
(IBOC)
HD Radio#REDIRECT HD Radio#REDIRECT HD Radio {{R from other capitalisation ...
{{R from other capitalisation ...
system of
digital audio broadcasting Digital audio broadcasting (DAB) is a digital radio standard for broadcasting digital audio radio services in many countries around the world but not in North America where HD Radio is the standard for digital radio. The DAB standard was initiate ...

digital audio broadcasting
, which is meant to improve the audio quality of signals. The
Digital Radio Mondiale Digital Radio Mondiale (DRM; ''mondiale'' being Italian and French for "worldwide") is a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting, partic ...
(DRM) system standardised by ETSI supports stereo and is the ITU approved system for use outside
North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to ...

North America
and [[United States territory|U.S. territories. Some HD Radio receivers also support C-QUAM AM stereo, although this feature is usually not advertised by the manufacturer.


Antennas

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 In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
(about 310 millivolts per meter using one kilowatt at one kilometre) to 5/8 wavelength (225 electrical degrees; about 440 millivolts per meter using one kilowatt at one kilometre), 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 kilometre) with high power gives a poor vertical radiation pattern, and 195 electrical degrees (about 400 millivolts per meter using one kilowatt at one kilometre) 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 [[electrical insulator|insulator to isolate it from the ground. Shunt-excited masts, in which the base of the mast is at a [[node (physics)|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 aerial|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 [[tower array|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 and 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.Weeks, W.L 1968, ''Antenna Engineering'', McGraw Hill Book Company, Section 2.6 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-antenna|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 [[Earth anchor|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 off the ionosphere (red) during skywave propagation 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 atmosphe ...
. The medium-wave transmitter at [[Transmitter Berlin-Britz|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

[[Image: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|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

* [[DAB radio * [[FM broadcasting|FM radio * [[List of European medium wave transmitters * [[MW DX * [[Satellite radio * [[Geneva Frequency Plan of 1975 * [[Monopole antenna


References


External links


"Building the Broadcast Band"
the development of the 520–1700 kHz MW (AM) band * [[:File:United States Effective Ground Conductivity Map.png|Map of Estimated Effective Ground Conductivity in the USA
MWLIST
worldwide database of MW and LW stations
www.mwcircle.org
The Medium Wave Circle. A [[UK-based club for dedium wave [[DXing|DX'ers and enthusiasts.
MWLIST quick and easy: Europe, Africa and Middle East
List of long- and medium wave transmitters with Google Maps links to transmission sites {{DEFAULTSORT:Medium wave [[Category:Bandplans