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Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band. During the daytime, reception is usually limited to more local stations, though this is dependent on the signal conditions and quality of radio receiver used. Improved signal propagation at night allows the reception of much longer distance signals (within a range of about 2,000 km or 1,200 miles). This can cause increased interference because on most channels multiple transmitters operate simultaneously worldwide. In addition,
amplitude modulation Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to t ...
(AM) is often more prone to interference by various electronic devices, especially power supplies and computers. Strong transmitters cover larger areas than on the FM broadcast band but require more energy and longer antennas. Digital modes are possible but have not reached 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 s ...
is gaining popularity and offers AM stations the chance to switch over if no frequency in the FM band is available, (however digital radio still has coverage issues in many parts of Europe). Many countries in Europe have switched off or limited 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 0  Hz to 3,000 GHz (3  THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particula ...
was divided on the basis of the wavelength 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 e ...
(LW), medium wave, and short wave (SW) radio bands.


Spectrum and channel allocation

: For Europe, Africa and Asia the MW band consists of 120 channels with carrier frequencies from 531–1602 kHz spaced every 9 kHz. Frequency coordination avoids the use of adjacent channels in one area. The total allocated spectrum including the modulated audio ranges from 526.5–1606.5 kHz. Australia uses an expanded band up to 1701 kHz. North America uses 118 channels from 530–1700 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.


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 high-fidelity music. However, many stations use audio bandwidths up 10 kHz, which is not Hi-Fi 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 groundwave. Practical groundwave reception of strong transmitters typically extends to 200–300 miles, with greater distances over terrain with higher ground conductivity, 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 and return to Earth at much greater distances; this is called the
skywave 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 ...
. 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 the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
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.


Use in North America

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 creating the conditions for economic growth and opportunity. Among its tasks are gathering economic and demographic data for busi ...
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 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 layer of the planet's atmosphere, the t ...
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 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") transmi ...
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 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 ...
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 Innovation, Science and Economic Development Canada (ISED; french: Innovation, Sciences et Développement économique Canada; french: ISDE, label=none)''Innovation, Science and Economic Development Canada'' is the applied title under the Federal ...
; 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 (I ...
.


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 Alan Crawford 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, with funding from the British Government through the Foreign Secretary's office. It is the world's largest external broadcaster in terms of reception a ...
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 (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 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 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 most often refers to: * The 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 King ...
,
BBC Radio Five Live BBC Radio 5 Live is a British national radio station owned and operated by the BBC that broadcasts mainly news, sport, discussion, interviews and phone-ins. It is the principal BBC radio station covering sport in the United Kingdom, broadcas ...
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. One example is NHK. As of March of 2021, broadcaster
NHK , also known as NHK, is a Japanese public broadcaster. NHK, which has always been known by this romanized initialism in Japanese, is a statutory corporation funded by viewers' payments of a television license fee. NHK operates two terrestria ...
still broadcasts in regional Indonesia, Myanmar and
Tajikistan Tajikistan (, ; tg, Тоҷикистон, Tojikiston; russian: Таджикистан, Tadzhikistan), officially the Republic of Tajikistan ( tg, Ҷумҳурии Тоҷикистон, Jumhurii Tojikiston), is a landlocked country in Centr ...
using Medium Wave transmission.


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.
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 ...
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 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 (IBOC) HD Radio system of 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—p ...
(DRM) system standardised by ETSI supports stereo and is the ITU-approved system for use outside North America and
U.S. territories Territories of the United States are sub-national administrative divisions overseen by the federal government of the United States. The various American territories differ from the U.S. states and tribal reservations as they are not sove ...
. Some HD Radio receivers also support C-QUAM AM stereo, although this feature is usually not advertised by the manufacturer.


Antennas

For broadcasting,
mast radiator Mast, MAST or MASt may refer to: Engineering * Mast (sailing), a vertical spar on a sailing ship * Flagmast, a pole for flying a flag * Guyed mast, a structure supported by guy-wires * Mooring mast, a structure for docking an airship * Radio mas ...
s 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 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. Mast antennas are usually 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 In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines, ...
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 A cage is an enclosure often made of mesh, bars, or wires, used to confine, contain or protect something or someone. A cage can serve many purposes, including keeping an animal or person in captivity, capturing an animal or person, and displayin ...
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 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 In electrical engineering, electrical length is a dimensionless parameter equal to the physical length of an electrical conductor such as a cable or wire, divided by the wavelength of alternating current at a given frequency traveling through th ...
) to achieve equivalent signal strength with vertical masts shorter than a quarter wavelength. 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 An umbrella antenna is a capacitively top-loaded wire 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 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 Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...
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 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 ...
. The medium-wave transmitter at
Berlin-Britz Britz () is a German locality (''Ortsteil'') within the Berlin borough (''Bezirk'') of Neukölln. History The village of ''Britzig'' was first mentioned in 1273. It was incorporated by the 1920 Greater Berlin Act. It is known for being the si ...
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

Because at these frequencies atmospheric noise is far above the receiver
signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in de ...
, 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. For weak signal reception or to discriminate between different signals sharing a common frequency directional antennas are used. For best signal-to-noise ratio these are best located outdoors away from sources of electrical interference. Examples of such medium wave antennas include broadband untuned loops, elongated terminated loops, wave antennas (e.g. the Beverage antenna) and the ferrite sleeve loop antenna.


See also

*
DAB 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 sys ...
* FM radio *
List of European medium wave transmitters This is an incomplete list of medium wave transmitters in Europe Active stations Former stations Those are former prominent AM transmitters: See also * MW DX MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave ...
*
MW DX MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave (also known as '' AM'') 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 ...
* Satellite radio * Geneva Frequency Plan of 1975 *
Monopole antenna A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or ...


References


External links


"Building the Broadcast Band"
��the development of the 520–1700 kHz MW (AM) band * Map of Estimated Effective Ground Conductivity in the USA
MWLIST
��worldwide database of MW and LW stations
The Medium Wave Circle
A UK-based club for Medium Wave 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 Bandplans