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Medium wave
Medium wave
(MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. For Europe
Europe
the M W band
W band
ranges from 526.5 kHz to 1606.5 kHz,[1] using channels spaced every 9 kHz, and in North America
North America
an extended MW broadcast band ranges from 525 kHz to 1705 kHz,[2] using 10 kHz spaced channels. The term is an 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.

Contents

1 Propagation characteristics 2 Use in the Americas 3 Use in Europe 4 Stereo and digital transmissions 5 Antennas

5.1 Receiving antennas

6 See also 7 References 8 External links

Propagation characteristics[edit] 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. 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
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 distant station may interfere with the signals of local stations on the same frequency. In North America, the North American Regional Broadcasting Agreement
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
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[edit] See also: North American Regional Broadcasting
Broadcasting
Agreement 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
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] 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] 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[edit] See also: Geneva Frequency Plan of 1975
Geneva Frequency Plan of 1975
and FM radio § Adoption of FM broadcasting
FM broadcasting
worldwide 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
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
Russia
operates a high-powered transmitter, located in its Kaliningrad
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
United Kingdom
can still receive the Russian broadcast. International mediumwave broadcasting in Europe
Europe
has decreased markedly with the end of the Cold War
Cold War
and the increased availability of satellite and Internet
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
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
Medium wave
band is a serious problem in parts of Europe
Europe
contributing to the early adoption of VHF FM broadcasting
FM broadcasting
by many stations (particularly in Germany). However, in recent years several European countries (Including Ireland, Poland
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
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] Stereo and digital transmissions[edit] See also: AM stereo

Realistic TM-152 AM stereo
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
Digital Radio Mondiale
(DRM) IBOC system support stereo and has been approved by the ITU for use outside North America and U.S. territories. Some HD Radio
HD Radio
receivers also support C-QUAM AM stereo, although this feature is usually not advertised by the manufacturer. Antennas[edit]

Multiwire T antenna
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.[11] 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[edit]

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[edit]

AM radio DAB Radio FM radio List of European medium wave transmitters Longwave Medium frequency
Medium frequency
band MW DX Satellite radio Shortwave Wave plan of Geneva

References[edit]

^ " United Kingdom
United Kingdom
Frequency
Frequency
Allocation Table" (PDF). ofcom.org.uk p. 16. June 22, 2017. Retrieved August 22, 2017.  ^ "United States Frequency
Frequency
Allocations" (PDF). National Telecommunications and Information Administration, U.S. Department of Commerce. 2016. Retrieved 2017-08-22.  ^ a b "Building the Broadcast Band". Earlyradiohistory.us. Retrieved 2010-05-07.  ^ Christopher H. Sterling; John M. Kittross (2002). Stay tuned: a history of American broadcasting. Psychology Press. p. 95. ISBN 0-8058-2624-6.  ^ "Code of Federal Regulations § 73.44 AM transmission system emission limitations" Archived 2011-10-25 at WebCite ^ "MWLIST quick and easy: Europe, Africa and Middle East". Retrieved 11 December 2015.  ^ "International Telecommunication
Telecommunication
Union". ITU. Retrieved 2009-04-24.  ^ "MW channels in the UK". Retrieved 11 December 2015.  ^ "Fast alle ARD-Radiosender stellen Mittelwelle ein". heise.de. 2015-01-06. Retrieved 2015-12-31.  ^ Heumann, Marcus (2015-12-17). "Abschied von der Mittelwelle. Der gefürchtete Wellensalat ist Geschichte". Deutschlandfunk.de. Retrieved 2015-12-31.  ^ Weeks, W.L 1968, Antenna Engineering, McGraw Hill Book Company, Section 2.6

External links[edit]

"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 www.mwcircle.org-The Medium Wave Circle. A UK-based club for dedium 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

v t e

Radio spectrum
Radio spectrum
(ITU)

ELF 3 Hz/100 Mm 30 Hz/10 Mm

SLF 30 Hz/10 Mm 300 Hz/1 Mm

ULF 300 Hz/1 Mm 3 kHz/100 km

VLF 3 kHz/100 km 30 kHz/10 km

LF 30 kHz/10 km 300 kHz/1 km

MF 300 kHz/1 km 3 MHz/100 m

HF 3 MHz/100 m 30 MHz/10 m

VHF 30 MHz/10 m 300 MHz/1 m

UHF 300 MHz/1 m 3 GHz/100 mm

SHF 3 GHz/100 mm 30 GHz/10 mm

EHF 30 GHz/10 mm 300 GHz/1 mm

THF 300 GHz/1 mm 3 THz/0.1 mm

v t e

Electromagnetic spectrum

Gamma rays X-rays Ultraviolet Visible Infrared Terahertz radiation Microwave Radio

← higher frequencies       longer wavelengths →

Visible (optical)

Violet Blue Green Yellow Orange Red

Microwaves

W band V band Q band Ka band K band Ku band X band S band C band L band

Radio

EHF SHF UHF VHF HF MF LF VLF ULF SLF ELF

Wavelength
Wavelength
types

Microwave Shortwave Medium wave Longwave

v t e

Analog and digital audio broadcasting

Terrestrial

Radio
Radio
modulation

AM FM COFDM

Frequency
Frequency
allocations

LW (LF) MW (MF) SW (HF) VHF (low / mid / high) L band
L band
(UHF)

Digital systems

CAM-D DAB/DAB+ DRM/DRM+ FMeXtra HD Radio CDR DVB-T2
DVB-T2
Lite

Satellite

Frequency
Frequency
allocations

C band Ku band L band S band

Digital systems

ADR DAB-S DVB-SH S-DMB SDR

Commercial radio providers

1worldspace Sirius XM Holdings SiriusXM Canada

Codecs

AAC AMR-WB+ HDC HE-AAC MPEG-1 Audio Layer II

Subcarrier signals

AMSS DirectBand PAD RDS/RBDS SCA/SCMO DARC

Related topics

Technical (audio)

Audio data compression Audio signal processing

Technical ( AM stereo
AM stereo
formats)

Belar C-QUAM Harris Kahn-Hazeltine Magnavox

Technical (emission)

AM broadcasting AM expanded band Cable radio Digital radio Error detection and correction FM broadcast band FM broadcasting Multipath propagation Shortwave
Shortwave
relay station

Cultural

History of radio International broadcasting

Comparison of radio systems

v t e

Telecommunications

History

Beacon Broadcasting Cable protection system Cable TV Communications satellite Computer network Drums Electrical telegraph Fax Heliographs Hydraulic telegraph Internet Mass media Mobile phone Optical telecommunication Optical telegraphy Pager Photophone Prepay mobile phone Radio Radiotelephone Satellite communications Semaphore Smartphone Smoke signals Telecommunications history Telautograph Telegraphy Teleprinter
Teleprinter
(teletype) Telephone The Telephone Cases Television Timeline of communication technology Undersea telegraph line Videoconferencing Videophone Videotelephony Whistled language

Pioneers

Edwin Howard Armstrong John Logie Baird Paul Baran Alexander Graham Bell Tim Berners-Lee Jagadish Chandra Bose Vint Cerf Claude Chappe Donald Davies Lee de Forest Philo Farnsworth Reginald Fessenden Elisha Gray Erna Schneider Hoover Charles K. Kao Hedy Lamarr Innocenzo Manzetti Guglielmo Marconi Antonio Meucci Radia Perlman Alexander Stepanovich Popov Johann Philipp Reis Nikola Tesla Camille Tissot Alfred Vail Charles Wheatstone Vladimir K. Zworykin

Transmission media

Coaxial cable Fiber-optic communication

Optical fiber

Free-space optical communication Molecular communication Radio
Radio
waves Transmission line

Network topology and switching

Links Nodes Terminal node Network switching (circuit packet) Telephone exchange

Multiplexing

Space-division Frequency-division Time-division Polarization-division Orbital angular-momentum Code-division

Networks

ARPANET BITNET Cellular network Computer CYCLADES Ethernet FidoNet Internet ISDN LAN Mobile NGN NPL network Public Switched Telephone Radio Telecommunications equipment Television Telex WAN Wireless World Wide Web

.