AM broadcasting

AMAM radioAM stationAM broadcastA.M.AM bandAM radio stationAM radio stationsAM stationsAM dial
AM broadcasting is a radio broadcasting technology, which employs amplitude modulation (AM) transmissions.wikipedia
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Medium wave

mediumwaveAMMW
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") transmissions, but also on the longwave and shortwave radio bands. Medium wave (also known as Medium frequency (MF)), which is by far the most commonly used AM broadcasting band.
Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting.

Longwave

long waveLWlong-wave
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") transmissions, but also on the longwave and shortwave radio bands. Longwave (also known as Low frequency (LF)) (148.5–283.5 kHz) Broadcasting stations in this band are assigned transmitting frequencies in the range 153–279 kHz, and generally maintain 9 kHz spacing.
In Europe, Africa, and large parts of Asia (International Telecommunication Union Region 1), where a range of frequencies between 148.5 and 283.5 kHz is used for AM broadcasting in addition to the medium-wave band, the term longwave usually refers specifically to this broadcasting band, which falls wholly within the low frequency band of the radio spectrum (30–300 kHz).

FM broadcasting

FMFM radioFM station
Subsequently, AM radio's audiences have also greatly shrunk due to competition from FM (frequency modulation) radio, Digital Audio Broadcasting (DAB), satellite radio, HD (digital) radio and Internet streaming.
FM broadcasting is capable of better sound quality than DAB/+ radio, and AM broadcasting under normal listening conditions, so it is used for most music broadcasts.

HD Radio

HDHD2HD-2
Subsequently, AM radio's audiences have also greatly shrunk due to competition from FM (frequency modulation) radio, Digital Audio Broadcasting (DAB), satellite radio, HD (digital) radio and Internet streaming. 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.
HD Radio (HDR) is a trademarked term for the in-band on-channel (IBOC) digital radio technology used by AM and FM radio stations mostly in the United States, Canada and Mexico (with a few implementations outside North America) to transmit audio and data by using a digital signal embedded "on-frequency" immediately above and below a station's standard analog signal, providing the means to listen to the same program in either HD (digital radio with less noise) or as a standard broadcast (analog radio with standard sound quality).

Golden Age of Radio

old-time radioradioold time radio
AM radio remained the dominant method of broadcasting for the next 30 years, a period called the "Golden Age of Radio", until television broadcasting became widespread in the 1950s and received most of the programming previously carried by radio.
Between 1900 and 1920 the first technology for transmitting sound by radio was developed, AM (amplitude modulation), and AM broadcasting sprang up around 1920.

Amplitude modulation

AMamplitude modulatedamplitude-modulated
AM broadcasting is a radio broadcasting technology, which employs amplitude modulation (AM) transmissions. In 1975 the U.S. Federal Communications Commission (FCC) requested proposals for AM stereo standards, and four competing standards were submitted: Harris Corporation's V-CPM (Variable angle Compatible Phase Multiplex), Magnavox's PMX, Motorola's C-QUAM (Compatible Quadrature Amplitude Modulation), and Kahn-Hazeltine independent sideband system." All except the Kahn-Hazeltine system used variations on the same idea: the mono (Left + Right) signal was transmitted in the amplitude modulation as before, while the stereo (Left — Right) information was transmitted by phase modulation.
AM is often used to refer to mediumwave AM radio broadcasting.

Spark-gap transmitter

spark gap transmitterspark transmitterspark transmitters
The idea of broadcasting — the unrestricted transmission of signals to a widespread audience — dates back to the founding period of radio development, even though the earliest radio transmissions, originally known as "Hertzian radiation" and "wireless telegraphy", used spark-gap transmitters that could only transmit the dots-and-dashes of Morse code.
A fundamental limitation of spark-gap transmitters is that they generate a series of brief transient pulses of radio waves called damped waves; they are unable to produce the continuous waves used to carry audio (sound) in modern AM or FM radio transmission.

Talk radio

TalkNews/TalkNews Talk Information
Thus, AM broadcasters tend to specialise in spoken-word formats, such as talk radio, all news and sports, leaving the broadcasting of music mainly to FM and digital stations.
Two radio stations—KMOX, 1120 AM in St. Louis, Missouri, and KABC, 790 AM in Los Angeles—adopted an all-talk show format in 1960, and both claim to be the first to have done so.

Radio broadcasting

radio stationradio stationsstation
AM broadcasting is a radio broadcasting technology, which employs amplitude modulation (AM) transmissions.
These include AM and FM stations.

Digital Audio Broadcasting

DABDAB+DAB Digital Radio
Subsequently, AM radio's audiences have also greatly shrunk due to competition from FM (frequency modulation) radio, Digital Audio Broadcasting (DAB), satellite radio, HD (digital) radio and Internet streaming.
Traditionally, radio programmes were broadcast on different frequencies via AM and FM, and the radio had to be tuned into each frequency as needed.

Carbon microphone

carbon transmittercarbon button microphonesbutton microphone
The next step, adopted from standard wire-telephone practice, was to insert a simple carbon microphone into the transmission line, to modulate the carrier wave signal to produce AM audio transmissions.
Carbon microphones, usually modified telephone transmitters, were widely used in early AM radio broadcasting systems, but their limited frequency response, as well as a fairly high noise level, led to their abandonment in those applications by the late 1920s.

LP record

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AM radio offered the highest sound quality available in a home audio device prior to the introduction of the high-fidelity, long-playing record in the late 1940s.
Neither of these was necessarily a great advantage in practice because of the limitations of AM broadcasting.

KDKA (AM)

KDKAKDKA-AMKDKA radio
KDKA (1020 kHz AM) is a Class A (clear channel) radio station, owned and operated by Entercom and licensed to Pittsburgh, Pennsylvania.

WWJ (AM)

WWJ8MKWWJ-AM
WWJ, 950 kHz (a regional broadcast frequency), is an all-news AM radio station located in Detroit, Michigan.

WFAN (AM)

WFANWEAFWFAN-AM
Its flagship station, WEAF (now WFAN) in New York City, sold blocks of airtime to commercial sponsors that developed entertainment shows containing commercial messages.
WFAN, (660 AM, also known as Sports Radio 66 AM and 101.9 FM or The FAN) is a radio station licensed to New York City and is owned and operated by Entercom.

WABC (AM)

WABCWJZWABC-AM
The Radio Corporation of America (RCA), General Electric and Westinghouse organized a competing network around its own flagship station, RCA's WJZ (now WABC) in New York City, but were hampered by AT&T's refusal to lease connecting lines or allow them to sell airtime.
WABC (770 AM) – branded on-air as 77 WABC – is a commercial talk radio station licensed to New York City, New York, serving the greater New York metropolitan area.

Satellite radio

satelliteradiosubscription radio
Subsequently, AM radio's audiences have also greatly shrunk due to competition from FM (frequency modulation) radio, Digital Audio Broadcasting (DAB), satellite radio, HD (digital) radio and Internet streaming.
As of 2013, the main competition to satellite radio is streaming Internet services, such as Pandora and Spotify, as well as FM and AM Radio.

Crystal radio

crystal setcrystadinecrystal radio receiver
Homemade crystal radios spread rapidly during the next 15 years, providing ready audiences for the first radio broadcasts.
Even so, they are usually only able to receive stations within distances of about 25 miles for AM broadcast stations, although the radiotelegraphy signals used during the wireless telegraphy era could be received at hundreds of miles, and crystal receivers were even used for transoceanic communication during that period.

Radiotelephone

radiotelephonyradio telephoneradiophone
With this in mind, most early radiotelephone development envisioned that the device would be more profitably developed as a "wireless telephone" for personal communication, or for providing links where regular telephone lines could not be run, rather than for the uncertain finances of broadcasting.
In comparison, AM radio uses about 8 kHz, and narrowband (voice or communication-quality) FM uses 9 kHz.

Electromagnetic interference

interferenceradio frequency interferenceRF interference
However, the simplicity of AM transmission also makes it vulnerable to "static" (radio noise, radio frequency interference) created by both natural atmospheric electrical activity such as lightning, and electrical and electronic equipment, including fluorescent lights, motors and vehicle ignition systems.
EMI frequently affects AM radios.

Independent sideband

Independent-sideband
In 1975 the U.S. Federal Communications Commission (FCC) requested proposals for AM stereo standards, and four competing standards were submitted: Harris Corporation's V-CPM (Variable angle Compatible Phase Multiplex), Magnavox's PMX, Motorola's C-QUAM (Compatible Quadrature Amplitude Modulation), and Kahn-Hazeltine independent sideband system." All except the Kahn-Hazeltine system used variations on the same idea: the mono (Left + Right) signal was transmitted in the amplitude modulation as before, while the stereo (Left — Right) information was transmitted by phase modulation.
Independent sideband (ISB) is an AM single sideband mode which is used with some AM radio transmissions.

Low frequency

LFlow-endlow-frequency
Longwave (also known as Low frequency (LF)) (148.5–283.5 kHz) Broadcasting stations in this band are assigned transmitting frequencies in the range 153–279 kHz, and generally maintain 9 kHz spacing.
In Europe and areas of Northern Africa and Asia, part of the LF spectrum is used for AM broadcasting as the "longwave" band.

Medium frequency

MFMedium freq.Medium frequency radio propagation
Medium wave (also known as Medium frequency (MF)), which is by far the most commonly used AM broadcasting band.
Part of this band is the medium wave (MW) AM broadcast band.

AMAX

Another common limitation on AM fidelity is the result of receiver design, although some efforts have been made to improve this, notably through the AMAX standards adopted in the United States.
This quality control program addressed both consumer receiver developments and air chains of broadcast AM transmission stations.

Digital Radio Mondiale

DRMDRM+digital
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.
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, particularly shortwave, and FM broadcasting.