AM broadcasting
Encyclopedia
AM broadcasting is the process of radio broadcasting using amplitude modulation
. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave bands also. Once AM was the only commerically important method for broadcast signal modulation. Today, it competes with FM broadcasting
for mobile reception of music and speech, as well as with various digital modes distributed from terrestrial and satellite transmitters.
AM radio began with the first, experimental broadcast on Christmas Eve of 1906 by Canadian experimenter Reginald Fessenden
, and was used for small-scale voice and music broadcasts up until World War I
. San Francisco, California radio station KCBS
claims to be the direct descendant of KQW, founded by radio experimenter Charles "Doc" Herrold, who made regular weekly broadcasts in San Jose, California as early as June 1909. On that basis KCBS has claimed to be the world's oldest broadcast station and celebrated its 100th anniversary in the summer of 2009. The great increase in the use of AM radio came late in the following decade as radio experimentation increased worldwide following World War I. The first licensed commercial radio
services began on AM in the 1920s. XWA of Montreal, Quebec
(later CFCF, now CINW) claims status as the first commercial broadcaster in the world, with regular broadcasts commencing on May 20, 1920. The first licensed American radio station was started by Frank Conrad
, KDKA
in Pittsburgh
, Pennsylvania
. Radio programming
boomed during the "Golden Age of Radio" (1920s–1950s). Dramas, comedy and all other forms of entertainment were produced, as well as broadcasts of news and music.
, Digital Audio Broadcast (DAB), Satellite Radio
or HD (digital) Radio
. An AM receiver detects amplitude variations in the radio wave
s at a particular frequency. It then amplifies changes in the signal voltage
to drive a loudspeaker
or earphones. The earliest crystal radio receiver
s used a crystal diode detector with no amplification.
In North American broadcasting practice, transmitter power input to the antenna
for commercial AM stations ranges from about 250 watt
s to 50,000 watts. Experimental licenses were issued for up to 500,000 watts radiated power, for stations intended for wide-area communication during disasters including Cincinnati station WLW
, which used such power on occasion before World War II. WLW's superpower transmitter still exists at the station's suburban transmitter site, but it was decommissioned in the early 1940s and no current commercial broadcaster in the US or Canada is authorized for such power levels. Some other countries do authorize higher power operation (for example the Mexican
station XERF formerly operated at 250,000 watts). Antenna design must consider the coverage desired and must direct the transmitted signal so as not to interfere with other stations operating on the same or adjacent frequencies.
Medium-wave and short-wave radio signals act differently during daytime and nighttime. During the day, AM signals travel by groundwave, diffracting around the curve of the earth over a distance up to a few hundred miles (or kilometers) from the signal transmitter. However, after sunset, changes in the ionosphere
cause AM signals to travel by skywave
, enabling AM radio stations to be heard much farther from their point of origin than is normal during the day. This phenomenon can be easily observed by scanning an AM radio dial at night. As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly (or use directional antenna
s) after sunset, or even to suspend broadcasting entirely during nighttime hours. Such stations are commonly referred to as daytimers. In Australia AM stations are not required to reduce their power at night and consequently stations such as the 50,000-watt 3LO can be heard in some parts of New Zealand
at night.
In the United States and Canada, some AM radio stations are granted clear channel status, meaning that they broadcast on frequencies with few other stations allocated, allowing an extended coverage area. Relatively few stations enjoy clear-channel status. Commercial broadcasters generally rely on the ground-wave coverage only as their target market for advertising.
The hobby of listening to long distance signals is known as DX or DX'ing, from an old telegraph
abbreviation
for "distance". Several non-profit hobby
ist clubs are devoted exclusively to DXing the AM broadcast band
, including the National Radio Club
and International Radio Club of America. Similarly, people listening to short wave transmissions are SWLing
.
's Radio Regulations
and, on the national level, by each country's telecommunications administration (the FCC
in the U.S.
, for example) subject to international agreements.
Frequencies between the broadcast bands are used for other forms of radio communication, and are not broadcast services intended for reception by the general public.
and news
programming, while music radio
and public radio mostly shifted to FM broadcasting
in the late 1970s. However, in the late 1960s and 1970s, top 40 rock and roll stations in the US and Canada such as WABC
and CHUM
transmitted highly processed and extended audio to 11 kHz, successfully attracting huge audiences. In the UK during the 1980s, BBC Radio 4
(a largely speech channel) had an FM location, whereas BBC Radio 1
, a music channel, was confined to AM broadcasts over much of the UK. Frequency response
is typically 40 Hz–5 kHz with a 50 dB
Signal to noise(S/N) ratio.
The limitation on AM fidelity comes from current receiver design. Moreover, to fit more transmitters on the AM broadcast band in the United States, maximum transmitted audio bandwidth is limited to 10.2 kHz by a National Radio Systems Committee
(NRSC) standard adopted by the FCC in June 1989, resulting in a channel occupied bandwidth of 20.4 kHz. The former audio limitation was 15 kHz resulting in a channel occupied bandwidth of 30 kHz.
AM radio signals can be severely disrupted in large urban centres by metal structures, tall buildings and sources of radio frequency interference (RFI) and electrical noise, such as electrical motors, fluorescent lights, or lightning. As a result, AM radio in many countries has lost its dominance as a music broadcasting service, and in many cities is now relegated to news, sports, religious and talk radio
stations. Some musical genres – particularly country, oldies, nostalgia and ethnic/world music – survive on AM, especially in areas where FM frequencies
are in short supply or in thinly populated or mountainous areas where FM coverage is poor.
transmissions are possible (see AM stereo
), and hybrid digital broadcast systems are now being used around the world. In the United States
, iBiquity
's proprietary HD Radio
has been adopted and approved by the FCC for medium wave transmissions, while Digital Radio Mondiale
is a more open effort often used on the shortwave bands
, and can be used alongside many AM broadcasts. Both of these standards are capable of broadcasting audio of significantly greater fidelity than that of standard AM with current bandwidth limitations, and a theoretical frequency response of 0–16 kHz, in addition to stereo sound and text data.
While FM radio can also be received by cable, AM radio generally cannot, although an AM station can be converted into an FM cable signal. In Canada
, cable operators that offer FM cable services are required by the CRTC to distribute all locally available AM stations in this manner. In Switzerland a system known as "wire broadcasting" (Telefonrundspruch in German) transmitted AM signals over telephone lines in the longwave
band until 1998, when it was shut down.
and pirate radio
broadcasters, especially those in the United States
under the FCC's Part 15 rules, broadcast on AM to achieve greater range than is possible on the FM band
. On mediumwave (AM), such radio stations are often found between 1610 kHz and 1710 kHz. Hobbyists also use low-power AM transmitters to provide local programming for antique radio equipment in areas where AM programming is not widely available or is of questionable quality; in such cases the transmitter, which is designed to cover only the immediate property and perhaps nearby areas, is connected to a computer or music player.
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave bands also. Once AM was the only commerically important method for broadcast signal modulation. Today, it competes with FM broadcasting
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
for mobile reception of music and speech, as well as with various digital modes distributed from terrestrial and satellite transmitters.
History
AM was the dominant method of broadcasting during the first eighty years of the 20th century and remains widely used into the 21st.AM radio began with the first, experimental broadcast on Christmas Eve of 1906 by Canadian experimenter Reginald Fessenden
Reginald Fessenden
Reginald Aubrey Fessenden , a naturalized American citizen born in Canada, was an inventor who performed pioneering experiments in radio, including early—and possibly the first—radio transmissions of voice and music...
, and was used for small-scale voice and music broadcasts up until World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
. San Francisco, California radio station KCBS
KCBS (AM)
KCBS is an all-news radio station in San Francisco, California, that is a key West Coast flagship radio station of the CBS Radio Network and Westwood One. Its transmitter is located in Novato, California. KCBS currently has studios on Battery Street, where it shares the location with co-owned KPIX...
claims to be the direct descendant of KQW, founded by radio experimenter Charles "Doc" Herrold, who made regular weekly broadcasts in San Jose, California as early as June 1909. On that basis KCBS has claimed to be the world's oldest broadcast station and celebrated its 100th anniversary in the summer of 2009. The great increase in the use of AM radio came late in the following decade as radio experimentation increased worldwide following World War I. The first licensed commercial radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
services began on AM in the 1920s. XWA of Montreal, Quebec
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
(later CFCF, now CINW) claims status as the first commercial broadcaster in the world, with regular broadcasts commencing on May 20, 1920. The first licensed American radio station was started by Frank Conrad
Frank Conrad
Frank Conrad was a radio broadcasting pioneer who worked as the Assistant Chief Engineer for the Westinghouse Electric Corporation in Pittsburgh, Pennsylvania,...
, KDKA
KDKA (AM)
KDKA is a radio station licensed to Pittsburgh, Pennsylvania, USA. Created by the Westinghouse Electric Corporation on November 2, 1920, it is one of the world's first modern radio stations , a distinction that has also been challenged by other stations, although it has claimed to be the first in...
in Pittsburgh
Pittsburgh, Pennsylvania
Pittsburgh is the second-largest city in the US Commonwealth of Pennsylvania and the county seat of Allegheny County. Regionally, it anchors the largest urban area of Appalachia and the Ohio River Valley, and nationally, it is the 22nd-largest urban area in the United States...
, Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
. Radio programming
Radio programming
Radio programming is the Broadcast programming of a Radio format or content that is organized for Commercial broadcasting and Public broadcasting radio stations....
boomed during the "Golden Age of Radio" (1920s–1950s). Dramas, comedy and all other forms of entertainment were produced, as well as broadcasts of news and music.
Operation
AM radio technology is simpler than Frequency Modulated (FM) radioFM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
, Digital Audio Broadcast (DAB), Satellite Radio
Satellite radio
Satellite radio is an analogue or digital radio signal that is relayed through one or more satellites and thus can be received in a much wider geographical area than terrestrial FM radio stations...
or HD (digital) Radio
HD Radio
HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals...
. An AM receiver detects amplitude variations in the radio wave
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
s at a particular frequency. It then amplifies changes in the signal voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
to drive a loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
or earphones. The earliest crystal radio receiver
Crystal radio receiver
thumb|Boy listening to a modern crystal radioA crystal radio receiver, also called a crystal set or cat's whisker receiver, is a very simple radio receiver, popular in the early days of radio. It needs no battery or power source and runs on the power received from radio waves by a long wire antenna...
s used a crystal diode detector with no amplification.
In North American broadcasting practice, transmitter power input to the antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
for commercial AM stations ranges from about 250 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s to 50,000 watts. Experimental licenses were issued for up to 500,000 watts radiated power, for stations intended for wide-area communication during disasters including Cincinnati station WLW
WLW
WLW is a clear channel talk radio station located in Cincinnati, Ohio, run by Clear Channel Communications. The station broadcasts locally on 700 kHz AM...
, which used such power on occasion before World War II. WLW's superpower transmitter still exists at the station's suburban transmitter site, but it was decommissioned in the early 1940s and no current commercial broadcaster in the US or Canada is authorized for such power levels. Some other countries do authorize higher power operation (for example the Mexican
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
station XERF formerly operated at 250,000 watts). Antenna design must consider the coverage desired and must direct the transmitted signal so as not to interfere with other stations operating on the same or adjacent frequencies.
Medium-wave and short-wave radio signals act differently during daytime and nighttime. During the day, AM signals travel by groundwave, diffracting around the curve of the earth over a distance up to a few hundred miles (or kilometers) from the signal transmitter. However, after sunset, changes in the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
cause AM signals to travel by skywave
Skywave
Skywave is the propagation of electromagnetic waves bent back to the Earth's surface by the ionosphere. As a result of skywave propagation, a broadcast signal from a distant AM broadcasting station at night, or from a shortwave radio station can sometimes be heard as clearly as local...
, enabling AM radio stations to be heard much farther from their point of origin than is normal during the day. This phenomenon can be easily observed by scanning an AM radio dial at night. As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly (or use directional antenna
Directional antenna
A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....
s) after sunset, or even to suspend broadcasting entirely during nighttime hours. Such stations are commonly referred to as daytimers. In Australia AM stations are not required to reduce their power at night and consequently stations such as the 50,000-watt 3LO can be heard in some parts of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
at night.
In the United States and Canada, some AM radio stations are granted clear channel status, meaning that they broadcast on frequencies with few other stations allocated, allowing an extended coverage area. Relatively few stations enjoy clear-channel status. Commercial broadcasters generally rely on the ground-wave coverage only as their target market for advertising.
The hobby of listening to long distance signals is known as DX or DX'ing, from an old telegraph
Telegraphy
Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...
abbreviation
Abbreviation
An abbreviation is a shortened form of a word or phrase. Usually, but not always, it consists of a letter or group of letters taken from the word or phrase...
for "distance". Several non-profit hobby
Hobby
A hobby is a regular activity or interest that is undertaken for pleasure, typically done during one's leisure time.- Etymology :A hobby horse is a wooden or wickerwork toy made to be ridden just like a real horse...
ist clubs are devoted exclusively to DXing the AM broadcast band
MW DX
MW DX, short for mediumwave DXing, is the hobby of receiving the reception of distant mediumwave radio stations. MW DX is similar to TV and FM DX in that broadcast band stations are the reception targets...
, including the National Radio Club
National Radio Club
The National Radio Club is a non-profit hobbyist organization formed in 1933 via the amalgamation of several regional radio clubs; it is devoted to the activity of DX'ing on the AM broadcast band...
and International Radio Club of America. Similarly, people listening to short wave transmissions are SWLing
Shortwave listening
Shortwave listening is the hobby of listening to shortwave radio broadcasts located on frequencies between 1700 kHz and 30 MHz. Listeners range from casual users seeking international news and entertainment programming to hobbyists immersed in the technical aspects of radio reception and DXing...
.
Broadcast frequency bands
AM radio is broadcast on several frequency bands. The allocation of these bands is governed by the ITUInternational Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
's Radio Regulations
Radio Regulations
The Radio Regulations is an intergovernmental treaty text of the International Telecommunication Union , the Geneva-based specialised agency of the United Nations which coordinates and standardises the operation of telecommunication networks and services and advances the development of...
and, on the national level, by each country's telecommunications administration (the FCC
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
in the U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, for example) subject to international agreements.
- Long wave is 148.5 kHz–283.5 kHz, with 9 kHz channel spacing generally used. Long wave is used for radio broadcasting in Europe, Africa and parts of Asia (ITU regionITU regionThe International Telecommunication Union , in its International Radio Regulations, divides the world into three ITU regions for the purposes of managing the global radio spectrum...
1), and is not allocated in the Western Hemisphere. In the United States and Canada, Bermuda and U.S. territories this band is mainly reserved for aeronauticsAeronauticsAeronautics is the science involved with the study, design, and manufacturing of airflight-capable machines, or the techniques of operating aircraft and rocketry within the atmosphere...
navigational aids, though a small section of the band could theoretically be used for microbroadcastingMicrobroadcastingMicrobroadcasting is the process of broadcasting a message to a relatively small audience. This is not to be confused with low-power broadcasting....
under the United States Part 15 rules. Due to the propagation characteristics of long wave signals, the frequencies are used most effectively in latitudes north of 50°. - Medium wave is 520 kHz–1,610 kHz. In the Americas (ITU region 2) 10 kHz spacing is used; elsewhere it is 9 kHz. ITU region 2 also authorizes the Extended AM broadcast bandExtended AM broadcast bandThe extended mediumwave broadcast band, commonly known as the [AM] expanded band, is a broadcast frequency allocation which moved the upper limit of the AM bandplan from 1610 to 1700 kHz.- History :...
between 1610 kHz and 1710 kHz. Medium wave is by far the most heavily used band for commercial broadcasting. This is the "AM radio" that most people are familiar with. - Short waveShortwaveShortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
is 2.3 MHz–26.1 MHz, divided into 14 broadcast bands. Shortwave broadcasts generally use a narrow 5 kHz channel spacing. Short wave is used by audio services intended to be heard at great distances from the transmitting station. The long range of short wave broadcasts comes at the expense of lower audio fidelityHigh fidelityHigh fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
. The mode of propagation for short wave is different (see high frequencyHigh frequencyHigh frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
). AM is used mostly by broadcast services – other shortwave users may use a modified version of AM such as SSBSingle-sideband modulationSingle-sideband modulation or Single-sideband suppressed-carrier is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth....
or an AM-compatible version of SSB such as SSB with carrier reinserted.
Frequencies between the broadcast bands are used for other forms of radio communication, and are not broadcast services intended for reception by the general public.
Limitations
Because of its susceptibility to atmospheric and electrical interference, AM broadcasting now attracts mainly talk radioTalk radio
Talk radio is a radio format containing discussion about topical issues. Most shows are regularly hosted by a single individual, and often feature interviews with a number of different guests. Talk radio typically includes an element of listener participation, usually by broadcasting live...
and news
News
News is the communication of selected information on current events which is presented by print, broadcast, Internet, or word of mouth to a third party or mass audience.- Etymology :...
programming, while music radio
Music radio
Music radio is a radio format in which music is the main broadcast content. After television replaced old time radio's dramatic content, music formats became dominant in many countries...
and public radio mostly shifted to FM broadcasting
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
in the late 1970s. However, in the late 1960s and 1970s, top 40 rock and roll stations in the US and Canada such as WABC
WABC
WABC may refer to:* WABC , a radio station licensed to New York, New York, United States* WABC-TV, a television station licensed to New York, New York, United States* Classic Gold WABC, a defunct British radio station...
and CHUM
CHUM
CHUM may refer to:* The former CHUM Radio division now known as Bell Media Radio* CHUM , a Toronto AM station* CHUM-FM, a Toronto FM station...
transmitted highly processed and extended audio to 11 kHz, successfully attracting huge audiences. In the UK during the 1980s, BBC Radio 4
BBC Radio 4
BBC Radio 4 is a British domestic radio station, operated and owned by the BBC, that broadcasts a wide variety of spoken-word programmes, including news, drama, comedy, science and history. It replaced the BBC Home Service in 1967. The station controller is currently Gwyneth Williams, and the...
(a largely speech channel) had an FM location, whereas BBC Radio 1
BBC Radio 1
BBC Radio 1 is a British national radio station operated by the British Broadcasting Corporation which also broadcasts internationally, specialising in current popular music and chart hits throughout the day. Radio 1 provides alternative genres after 7:00pm including electronic dance, hip hop, rock...
, a music channel, was confined to AM broadcasts over much of the UK. Frequency response
Frequency response
Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
is typically 40 Hz–5 kHz with a 50 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
Signal to noise(S/N) ratio.
The limitation on AM fidelity comes from current receiver design. Moreover, to fit more transmitters on the AM broadcast band in the United States, maximum transmitted audio bandwidth is limited to 10.2 kHz by a National Radio Systems Committee
National Radio Systems Committee
The National Radio Systems Committee is an organization sponsored by the Consumer Electronics Association and the National Association of Broadcasters . Its main purpose is to set industry technical standards for radio broadcasting in the United States...
(NRSC) standard adopted by the FCC in June 1989, resulting in a channel occupied bandwidth of 20.4 kHz. The former audio limitation was 15 kHz resulting in a channel occupied bandwidth of 30 kHz.
AM radio signals can be severely disrupted in large urban centres by metal structures, tall buildings and sources of radio frequency interference (RFI) and electrical noise, such as electrical motors, fluorescent lights, or lightning. As a result, AM radio in many countries has lost its dominance as a music broadcasting service, and in many cities is now relegated to news, sports, religious and talk radio
Talk radio
Talk radio is a radio format containing discussion about topical issues. Most shows are regularly hosted by a single individual, and often feature interviews with a number of different guests. Talk radio typically includes an element of listener participation, usually by broadcasting live...
stations. Some musical genres – particularly country, oldies, nostalgia and ethnic/world music – survive on AM, especially in areas where FM frequencies
FM broadcast band
The FM broadcast band, used for FM broadcast radio by radio stations, differs between different parts of the world. In Europe and Africa , it spans from 87.5 to 108.0 megahertz , while in America it goes only from 88.0 to 108.0 MHz. The FM broadcast band in Japan uses 76.0 to 90 MHz...
are in short supply or in thinly populated or mountainous areas where FM coverage is poor.
Other distribution methods
StereoStereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
transmissions are possible (see AM stereo
AM stereo
AM stereo is a term given to a series of mutually incompatible techniques for wireless radio broadcasting stereo audio in the AM band in a manner that is compatible with standard AM receivers...
), and hybrid digital broadcast systems are now being used around the world. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, iBiquity
IBiquity
iBiquity Digital Corporation is a company formed by the merger of USA Digital Radio and Lucent Digital Radio, with the goal of creating an in-band on-channel digital radio system for the United States and around the world...
's proprietary HD Radio
HD Radio
HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals...
has been adopted and approved by the FCC for medium wave transmissions, while Digital Radio Mondiale
Digital Radio Mondiale
Digital Radio Mondiale is a set of digital audio broadcasting technologies designed to work over the bands currently used for AM broadcasting, particularly shortwave...
is a more open effort often used on the shortwave bands
Shortwave bands
Shortwave bands are frequency allocations for use within the shortwave radio spectrum . They are the primary medium for applications such as maritime communications, international broadcasting and worldwide amateur radio activity because they take advantage of ionospheric skip propagation to send...
, and can be used alongside many AM broadcasts. Both of these standards are capable of broadcasting audio of significantly greater fidelity than that of standard AM with current bandwidth limitations, and a theoretical frequency response of 0–16 kHz, in addition to stereo sound and text data.
While FM radio can also be received by cable, AM radio generally cannot, although an AM station can be converted into an FM cable signal. In Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, cable operators that offer FM cable services are required by the CRTC to distribute all locally available AM stations in this manner. In Switzerland a system known as "wire broadcasting" (Telefonrundspruch in German) transmitted AM signals over telephone lines in the longwave
Longwave
In radio, longwave refers to parts of radio spectrum with relatively long wavelengths. The term is a historic one dating from the early 20th century, when the radio spectrum was considered to consist of long, medium and short wavelengths...
band until 1998, when it was shut down.
Microbroadcasting
Some microbroadcastersMicrobroadcasting
Microbroadcasting is the process of broadcasting a message to a relatively small audience. This is not to be confused with low-power broadcasting....
and pirate radio
Pirate radio
Pirate radio is illegal or unregulated radio transmission. The term is most commonly used to describe illegal broadcasting for entertainment or political purposes, but is also sometimes used for illegal two-way radio operation...
broadcasters, especially those in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
under the FCC's Part 15 rules, broadcast on AM to achieve greater range than is possible on the FM band
FM broadcast band
The FM broadcast band, used for FM broadcast radio by radio stations, differs between different parts of the world. In Europe and Africa , it spans from 87.5 to 108.0 megahertz , while in America it goes only from 88.0 to 108.0 MHz. The FM broadcast band in Japan uses 76.0 to 90 MHz...
. On mediumwave (AM), such radio stations are often found between 1610 kHz and 1710 kHz. Hobbyists also use low-power AM transmitters to provide local programming for antique radio equipment in areas where AM programming is not widely available or is of questionable quality; in such cases the transmitter, which is designed to cover only the immediate property and perhaps nearby areas, is connected to a computer or music player.
See also
- Amplitude modulationAmplitude modulationAmplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
- Amplitude Modulation Signalling SystemAmplitude modulation signalling systemThe amplitude modulation signalling system is a digital system for adding low bit rate information to an analogue amplitude modulated broadcast signal in the same manner as the Radio Data System for frequency modulated broadcast signals.This system has been standardized in March 2006 by ETSI as...
, a digital system for adding low bitrate information to an AM broadcast signal. - MW DXMW DXMW DX, short for mediumwave DXing, is the hobby of receiving the reception of distant mediumwave radio stations. MW DX is similar to TV and FM DX in that broadcast band stations are the reception targets...
ing, the hobby of receiving distant AM radio stations on the mediumwave band. - FM broadcastingFM broadcastingFM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
- Analog transmissionAnalog transmissionAnalog transmission is a transmission method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable...
- Extended AM broadcast bandExtended AM broadcast bandThe extended mediumwave broadcast band, commonly known as the [AM] expanded band, is a broadcast frequency allocation which moved the upper limit of the AM bandplan from 1610 to 1700 kHz.- History :...
- CAM-DCAM-DCompatible Amplitude Modulation - Digital or CAM-D is a proposed hybrid digital radio format for AM broadcasting, put forth by well-known broadcast engineer Leonard R. Kahn....
, a hybrid digital radio format for AM broadcasting - List of 50 kW AM radio stations in the United States
- Lists of radio stations in North America
- Oldest radio stationOldest radio stationThe title of oldest radio station is disputed by several in Europe , and in the United States and Canada.Several potential contenders for the title of "oldest radio station" are listed below, organized by sign-on date:-Stations:...