Medium wave
Medium wave (MW) is a part of the
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 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).[citation needed] 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
Spectrum and channel allocation
area kHz (centre) spacing channels Europe, Asia, Africa 522–1,602 9 kHz 120 Australia 522–1,710 9 kHz 131 North and South America 530–1,700 10 kHz 118
For Europe, Africa and Asia the MW band consists of 120 channels with carrier frequencies from 531 to 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 to 1606.5 kHz.[1] Australia uses an expanded band up to 1701 kHz.
North America uses 118 channels from 530 to 1700 kHz[2] 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 channel steps of 9 and 10 kHz require limiting the audio bandwidth to 4.5 and 5 kHz[3] 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.[4] 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
Medium waves can also reflect off charged particle layers in the
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.[5] 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,[5] did little to solve this overcrowding.
In 1923, the Commerce Department realized that as more and more stations were applying for commercial licenses, it was not practical to have every station broadcast on the same three wavelengths. On 15 May 1923, Commerce Secretary Herbert Hoover announced a new bandplan which set aside 81 frequencies, in 10 kHz steps, from 550 kHz to 1350 kHz (extended to 1500, then 1600 and ultimately 1700 kHz in later years). Each station would be assigned one frequency (albeit usually shared with stations in other parts of the country and/or abroad), no longer having to broadcast weather and government reports on a different frequency than entertainment. Class A and B stations were segregated into sub-bands.[6]
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.[7]
Most United States
Use in Europe
Many countries have switched off most of their MW transmitters in the 2010s due to cost-cutting and low usage of MW by the listeners. Among those are Germany,[8] France, Russia, Poland, Sweden, the Benelux, Austria, Switzerland, Slovenia 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 that now has a licence to use 648 kHz, which was used by the BBC World Service 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).[9]
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 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
Use in Asia
In Asia and the Middle East, many high-powered transmitters remain in operation. China, Indonesia, South Korea, North Korea, Japan, Thailand, Vietnam, Philippines, Saudi Arabia, Egypt, and India still use medium wave.
China operates many single-frequency networks across the country.
As of May 2023, many Japanese broadcasters like NHK broadcast in medium wave, with many high power transmitters operating across Japan. There are also some low power relay transmitters.
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
Antennas
For broadcasting,
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 (
In some rare cases
Receiving antennas
Because at these frequencies atmospheric noise is far above the receiver
See also
- Digital Radio Mondiale, a digital standard that is applicable on the medium wave
- DAB radio
- FM radio
- List of European medium wave transmitters
- MW DX
- Satellite radio
- Geneva Frequency Plan of 1975
- Monopole antenna
References
- ^ United Kingdom Frequency Allocation Table (PDF) (Report). 22 June 2017. p. 16. Retrieved August 22, 2017 – via ofcom.org.uk.
- U.S. Department of Commerce. January 2016. Retrieved 2017-08-22.
- ^ "§ 73.44 AM transmission system emission limitations". Code of Federal Regulations. Archived from the original on 27 September 2011.
- ^ "Medium Wave in Central Europe". 21 January 2020.
- ^ a b "Building the Broadcast Band". Earlyradiohistory.us. Retrieved 2010-05-07.
- ISBN 0-8058-2624-6.
- ^ "MWLIST quick and easy: Europe, Africa and Middle East". Retrieved 11 December 2015.
- ^ "Fast alle ARD-Radiosender stellen Mittelwelle ein". heise.de. 2015-01-06. Retrieved 2015-12-31.
- ^ "International Telecommunication Union". ITU. Retrieved 2009-04-24.
- ^ Weeks, W.L 1968, Antenna Engineering, McGraw Hill Book Company, Section 2.6
- ^ "4: MW Aerials – Antennas – Medium Wave Circle". Retrieved 2021-11-28.
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