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 h ...
(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
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 ( ...
. 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 (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
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 ( ...
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 sy ...
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, particul ...
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, tr ...
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
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, high frequency band (HF), which extends from 3 to 30 MHz (10 ...
(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
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 conductivity is an extremely importan ...
, 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 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 secto ...
. 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 agre ...
(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 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 who served as the 31st president of the United States from 1929 to 1933 and a member of the Republican Party (United States), Republican Party, holding o ...
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 ...
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 large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...
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
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisd ...
(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 ( ...
.
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 broadcasting, international broadcaster owned and operated by the BBC, with funding from the Government of the United Kingdom, British Government through the Foreign Secretary, Foreign Secretary's o ...
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
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
(ITU).
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 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
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.
Frequencies immediately below VHF ...
FM broadcasting
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 high fidelity sound over broadcast radio. FM broadcasting is c ...
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 still broadcasts in regional
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
,
Myanmar
Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
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 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 federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisd ...
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 private ...
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. The name refers to the new digital signals being broadcast in the same AM or FM band (in-band) ...
(IBOC)
HD Radio
HD Radio (HDR) is a trademark for an in-band on-channel (IBOC) digital radio broadcast technology. It generally simulcasts an existing analog radio station in digital format with less noise and with additional text information. HD Radio is used ...
system of
digital audio broadcasting
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 syst ...
, 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—pa ...
(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
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
A guyed mast or guyed tower is a tall thin vertical structure that depends on guy lines (diagonal tensioned cables attached to the ground) for stability. The mast itself has the compressive strength to support its own weight, but does not h ...
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, tr ...
(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, line ...
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 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. 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
Radiation resistance, \ R_\mathsf\ or \ R_\mathsf\ , is proportional to the part of an antenna's feedpoint electrical resistance that is caused by power loss from the emission of radio waves from the antenna.
Radiation resistance is an ''effect ...
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 a ...
added by the wires attached to the top of the antenna.
In some rare cases
dipole antenna
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole w ...
s 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 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 d ...
, 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 antenna
A loop antenna is a radio antenna consisting of a loop or coil of wire, tubing, or other electrical conductor, that is usually fed by a balanced source or feeding a balanced load. Within this physical description there are two (possibly three) ...
s 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
*
FM radio
*
List of European medium wave transmitters
*
MW DX
*
Satellite radio
Satellite radio is defined by the International Telecommunication Union (ITU)'s ITU Radio Regulations (RR) as a '' broadcasting-satellite service''. The satellite's signals are broadcast nationwide, across a much wider geographical area than ...
*
Geneva Frequency Plan of 1975
The Geneva Frequency Plan of 1975 (Aka "The Final Acts of the Regional Administrative LF/MF Broadcasting Conference (Regions 1 and 3) Geneva, 1975" or simply "GE75") is the internationally agreed frequency plan which was drawn up to implement th ...
*
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
MWLISTworldwide 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 EastList of long- and medium wave transmitters with Google Maps links to transmission sites
{{DEFAULTSORT:Medium wave
Bandplans