AM stereo
Encyclopedia
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
receiver
s. There are two main classes of systems: independent sideband
(ISB) systems, promoted principally by American
broadcast engineer Leonard Kahn; and quadrature amplitude modulation
(QAM) multiplexing
systems (conceptually closer to FM stereo).
After the early experiments with two stations, a number of systems were invented to broadcast a stereo signal in a way which was compatible with standard AM receivers.
FM stereo was first implemented in 1961. In the United States
, FM overtook AM as the dominant broadcast radio band in the late 1970s and early 1980s.
, a major manufacturer of radio/TV transmitters. Harris is the successor to the pioneer Gates radio line. Harris was the early leader in the AM stereo wars. It was implemented by a large number of stations in the 1980s, but the FCC temporarily rescinded their approval of the Harris system, causing most to switch to Motorola's C-QUAM system. This Harris system eventually changed their pilot tone to be compatible with C-QUAM. CKLW in Windsor, Ontario
, Canada
(also serving nearby Detroit, Michigan
) was among the first stations to broadcast in Harris AM stereo. The Harris system is currently no longer used in its original form.
. It is a phase modulation system. It was initially declared the AM stereo standard by the FCC in 1980, but the FCC later declared that stations were free to choose any system. As with the Harris system, it was popular in the 1980s, but most stations stopped broadcasting in stereo, or upgraded to the C-QUAM system as time went on. 1190 WOWO
in Fort Wayne, Indiana
was the (then) 50,000-watt clear channel Magnavox flagship station.
was developed and promoted primarily by Motorola, a long time manufacturer of two-way radio equipment. It became the dominant system by the late 1980s, and was declared the official standard by the FCC in 1993. While many stations in the USA have since discontinued broadcasting in Stereo, many still have the necessary equipment to do so. C-QUAM is still popular in other parts of the world, such as Canada
, Japan
, and Australia
which it was declared the official standard.
QUAM uses quadrature phase and amplitude modulation
: the phase of the audio is rotated ahead or behind the carrier and the amplitude of each phase is also changed; thus giving 16 points for reference (used also in dialup modems to get past the 9600 baud limit on analog lines). The QUAM signal (L-R info) is then phase modulated on the transmitter (the QUAM exciter replaced the crystal in the AM transmitter) and the L+R still modulated the transmitter as it had in the past. C-QUAM is a modified QUAM and thus called Compatible (C- in C-QUAM).
C-QUAM has been long criticized by the Kahn-Hazeltine system's creator, Leonard Kahn as being inferior to his system. First generation C-QUAM receivers suffered from "platform motion" effects when listening to stations received via skywave
. Later improvements by Motorola minimized the platform motion effect and increased audio quality and stereo separation, especially on AMAX
certified receivers in the 1990s.
. This system used an entirely different principle; using independently modulated upper and lower sidebands. While a station using the system would sound best with proper decoding, it was also possible to use two standard AM radios (one tuned above and the other below the primary carrier) to achieve the stereophonic effect, although with poor stereo separation and fidelity compared to a proper Kahn system AM stereo receiver. One of the best known stations to use the Kahn system was 890 WLS (AM)
, Chicago. WLS still transmits in AM stereo today but uses the Motorola C-QUAM system instead.
However, the Kahn system suffered from lower stereo separation above 5 kHz (reaching none at 10 kHz whereas FM stereo has 40 db or more separation at 15 kHz) and the radio antenna array on directional AM (common on a lot of nighttime and some daytime stations) had to have a flat response across the entire 20 kHz AM channel. If the array had a higher reactance value (leading to a higher Standing wave ratio
) on one side of the frequency vs the other, it would affect the audio response of that channel and thus the stereo signal would be affected. Also, Kahn refused to license any radio receivers manufacturers with his design, although multi-system receivers were manufactured by various companies such as Sony
, Sansui
, and Sanyo
, which could receive any of the four AM stereo systems.
Nonetheless, this system remained competitive with C-QUAM into the late 1980s and Kahn was very vocal about its advantages over Motorola's system. Kahn filed a lawsuit claiming that the Motorola system did not meet FCC emission bandwidth specifications, but by that time, C-QUAM had already been declared as the single standard for AM stereo in the USA.
Kahn's AM stereo design was later revamped for monaural use and used in the Power-Side system, in which a decreased signal in one sideband is used to improve coverage and loudness, especially with directional antenna arrays. Power-Side became the basis for CAM-D
, Compatible AM Digital, a new digital system being promoted by Leonard Kahn and used on several AM stations.
Kahn receiver chips have also been used as an inexpensive method for providing high frequency (world band) receivers with synchronous detection technology.
.
The Belar system was a simple FM/AM modulation system, with an attenuated L-R signal frequency modulating the carrier (with a 400uS pre-emphasis) in the extent of +/- 320 Hz around the center frequency, and the L+R doing the normal "high level" AM modulation (usually referred to as Plate Modulation in transmitters using a tube in the final stage, where the audio is applied to the plate voltage of the tube; in solid state transmitters, various different techniques are available that are more efficient at lower power levels). The Belar system (by the company of the same name) was dropped due to issues with its design though it was much easier to implement than the other systems. It and the Kahn system did not suffer from platform motion (which was a killer for AM stereo at night; platform motion is where the stereo balance would shift from one side to the other and then back to center) but the use of low level frequency modulation did not permit a high separation of L and R channels.
(FCC) started a series of five year tests to determine which of the five competing standards would be selected. By the end of the testing period, the Belar system was dropped. In 1980, the FCC announced that the Magnavox
system would become the standard. This announcement was met with harsh criticism and a series of lawsuits. On March 4, 1982, the FCC revoked their endorsement to the Magnavox standard and let the marketplace decide, meaning that all four standards were allowed. After the 1982 decision, many stations implemented one of the four standards. Initially, all systems remained competitive, but by the later 1980s, Motorola
C-QUAM
had a clear majority of stations and receivers. Around this same time, Harris Corporation
dropped their system and instead endorsed C-QUAM. During this time, radio manufactures either made receivers which decoded just one system, or decoded all four. The multiple systems used greatly confused consumers and severely impacted consumer adoption. As a result of this confusion, and the continued growth of the FM band, interest in AM stereo dwindled.
In 1993, the FCC declared Motorola's C-QUAM system the standard. To ensure that all AM stereo receivers maintained the same sound quality, the National Association of Broadcasters
and the Electronic Industries Association started the AMAX
certification program.
, Australia
and Japan
approved and implemented AM stereo systems. Most governments approved a single standard, usually Motorola's C-QUAM, which greatly reduced confusion and increased user adoption.
Following the launch of the American-owned, ship-based pirate radio
station Laser 558
off the British coast, there were announcements that another such station, provisionally called Stereo Hits 576, would soon follow, using AM stereo on an adjacent frequency to Laser. Nothing ever came of this project and 576kHz was adopted by Radio Caroline
instead.
In many countries, especially those where the AM band is still dominant, AM stereo radios are still manufactured and stations still broadcast stereo signals.
or Sports/Sports Talk
formats. Many of the stations that initially implemented AM stereo are clear-channel 50,000 watt stations, and are more concerned with listening range than stereo sound (although there is no proof that use of AM stereo affects listening range). As a result, these stations still have the necessary equipment to broadcast in stereo, but it is left unused (or converted to HD Radio
). Also, many former AM stereo stations were bought up by broadcasting conglomerates, which generally discourage AM stereo broadcasting. In the United States, most stations currently using AM stereo are small, independently owned and broadcast a variety or music format.
(AM 1630) in Coralville, Iowa, aired a four hour quadraphonic
radio broadcast of the Robb Spewak show. The show spotlighted music from the quadraphonic era on the 40th anniversary of the format's release in America and was engineered by Tab Patterson. All the music was from discrete 4-channel tapes, then encoded into Dolby Pro-Logic II and transmitted using their stereo C-QUAM transmitter. It was the first time AM radio was featured in this surround sound capacity.
, such as Digital Radio Mondiale
, DAB
or HD Radio
(in the United States). Some of these digital radio systems, most notably HD Radio
have "hybrid modes" which let a station broadcast a standard AM signal along with the digital information. While these transmission modes allow standard AM, they are not compatible with any AM stereo system (meaning you can't broadcast both at the same time).
Digital AM broadcasting systems, such as HD Radio have been criticized by supporters of AM stereo as sounding "harsh" and "artificial", but supporters of Digital systems argue that the extended frequency response, increased dynamic range, lack of noise and lower distortion make up for the compression artifacts. However, HD Radio also increases adjacent channel noise due to the digital sidebands, which pose serious problems for nighttime broadcasts. Some have proposed to use HD Radio in the daytime and AM stereo at night.
Many HD radios are based on a common chipset
that decodes C-QUAM.
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
radio broadcasting stereo audio
Audio frequency
An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...
in the AM
Mediumwave
Medium wave is the part of the medium frequency radio band used mainly for AM radio broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz...
band in a manner that is compatible with standard AM
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...
receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
s. There are two main classes of systems: independent sideband
Independent sideband
Independent sideband is an AM single sideband mode which is used with some AM radio transmissions. Normally each sideband carries identical information, but ISB modulates two different input signals — one on the upper sideband, the other on the lower sideband...
(ISB) systems, promoted principally by American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
broadcast engineer Leonard Kahn; and quadrature amplitude modulation
Quadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
(QAM) multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
systems (conceptually closer to FM stereo).
History
Early experiments with stereo AM radio involved two separate stations (both AM or sometimes one AM and one FM) broadcasting the left and right audio channels. This system was not very practical, as it required the listener to use two separate radios. Synchronization was problematic, often resulting in "ping-pong" effects between the two channels. Reception was also likely to be different between the two stations, and many listeners used mismatching models of receivers.After the early experiments with two stations, a number of systems were invented to broadcast a stereo signal in a way which was compatible with standard AM receivers.
FM stereo was first implemented in 1961. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, FM overtook AM as the dominant broadcast radio band in the late 1970s and early 1980s.
Timeline
- 1924 — WPAJ (now WDRC (AM)WDRC (AM)WDRC is a radio station owned by Buckley Broadcasting Corporation. It operates full time with 5,000 Watts of power with studios and transmitters located in Bloomfield, Connecticut....
) broadcast in stereo from New Haven, ConnecticutNew Haven, ConnecticutNew Haven is the second-largest city in Connecticut and the sixth-largest in New England. According to the 2010 Census, New Haven's population increased by 5.0% between 2000 and 2010, a rate higher than that of the State of Connecticut, and higher than that of the state's five largest cities, and...
, using two transmitters: one on 1120 kHz and the other on 1320 kHz. However stereo separation was poor, to preserve compatibility for mono listeners. - 1960 — AM stereo first demonstrated on XETRA-AM, TijuanaTijuanaTijuana is the largest city on the Baja California Peninsula and center of the Tijuana metropolitan area, part of the international San Diego–Tijuana metropolitan area. An industrial and financial center of Mexico, Tijuana exerts a strong influence on economics, education, culture, art, and politics...
, MexicoMexicoThe 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...
, using the Kahn independent sidebandIndependent sidebandIndependent sideband is an AM single sideband mode which is used with some AM radio transmissions. Normally each sideband carries identical information, but ISB modulates two different input signals — one on the upper sideband, the other on the lower sideband...
system. - 1963 — WHAZWHAZ (AM)-WMYY:-External links:...
runs a stereo program on eight AM stations, four on each channel. - 1980 — After five years of testing the five systems, the United States Federal Communications CommissionFederal Communications CommissionThe 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...
(FCC) selected the MagnavoxMagnavoxMagnavox is a US electronics company founded by Edwin Pridham and Peter L. Jensen, who invented the moving-coil loudspeaker in 1915 at their lab in Napa, California. They formed Magnavox in 1917 in order to market their inventions....
system as the official AM stereo standard. The FCC's research is immediately accused of being flawed and incomplete. - 1982 — After a series of lawsuits and accusations, the FCC decides to "let the marketplace decide" and revokes the MagnavoxMagnavoxMagnavox is a US electronics company founded by Edwin Pridham and Peter L. Jensen, who invented the moving-coil loudspeaker in 1915 at their lab in Napa, California. They formed Magnavox in 1917 in order to market their inventions....
certification as the AM stereo standard for political reasons. Belar drops out of the AM stereo race, leaving MotorolaMotorolaMotorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
C-QUAMC-QUAMC-QUAM is the method of AM stereo broadcasting used in Canada, the United States and most other countries. It was invented in 1977 by Norman Parker, Francis Hilbert, and Yoshio Sakaie, and published in an IEEE journal....
, Harris CorporationHarris CorporationHarris Corporation is a Florida-based international communications equipment company that produces wireless equipment, electronic systems, and both terrestrial and spaceborne antennas for use in the government, defense, and commercial sectors. It is also the largest private-sector employer in...
, Magnavox, and the Kahn/Hazeltine independent sidebandIndependent sidebandIndependent sideband is an AM single sideband mode which is used with some AM radio transmissions. Normally each sideband carries identical information, but ISB modulates two different input signals — one on the upper sideband, the other on the lower sideband...
system. - 1984 — General MotorsGeneral MotorsGeneral Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
, Ford, ChryslerChryslerChrysler Group LLC is a multinational automaker headquartered in Auburn Hills, Michigan, USA. Chrysler was first organized as the Chrysler Corporation in 1925....
, and a number of import automakers begin installing C-QUAM AM stereo receivers in automobiles, beginning with the 1985 model year. Harris CorporationHarris CorporationHarris Corporation is a Florida-based international communications equipment company that produces wireless equipment, electronic systems, and both terrestrial and spaceborne antennas for use in the government, defense, and commercial sectors. It is also the largest private-sector employer in...
abandons its AM stereo system and puts its support behind C-QUAM (Harris continues to manufacture C-QUAM equipment today). - 1985 — AM stereo broadcasting officially begins in AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, with the C-QUAM standard. - 1988 — CanadaCanadaCanada 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...
and MexicoMexicoThe 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...
adopt C-QUAM as their standard for AM stereo. - 1992 — JapanJapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
adopts C-QUAM as its standard for AM stereo. - 1993 — The FCC makes C-QUAM the AM stereo standard for stations in the U.S., and also grants "stereo preference" for radio stations requesting to move to the AM expanded band (1610–1700 kHz), although such stations have never actually been required to transmit in stereo.
- 1993 — The AMAXAMAXAMAX is a United States certification program developed by the Electronic Industries Association and the National Association of Broadcasters in 1993. This quality control program addressed both consumer receiver developments and air chains of broadcast AM transmission stations...
certification program begins. This was to set an official manufacturing standard for high-quality AM radio receivers, with a wider audio bandwidth for higher fidelity reception of strong signals, and optionally C-QUAM AM stereo. Despite the availability of AMAX receivers from companies like SonySony, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
, General ElectricGeneral ElectricGeneral Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
, DenonDenonis a Japanese electronics company that was involved in the early stages of development of digital audio technology, while specializing in the manufacture of high-fidelity professional and consumer audio equipment. For many decades, Denon was a brand name of Nippon-Columbia, including the Nippon...
, and AMAX-certified car radios from the domestic and Japanese automakers, most electronics manufacturers did not wish to implement the more costly AMAX tuner (radio)Tuner (radio)A radio tuner is a subsystem that receives radio broadcasts and converts them into audio-frequency signals which can be fed into an amplifier driving a loudspeaker. FM tuner, AM tuner, Digital Audio Broadcasting DAB tuner, etc. are types of radio tuner dealing with transmissions using different...
design in their radios, so most AM radios today remain in mono with limited fidelity. - 2006 to present — AM stereo gains new life through the support for C-QUAM decoding in most receivers designed for HD RadioHD RadioHD 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...
. These new digital radios receive AM stereo signals, although the AM transmitters are now limited to 10 kHz audio bandwidth and the HD receivers flip Left and Right channels in decoding C-QUAM stereo.
Broadcasting systems
The Magnavox PMX, Harris Corporation V-CPM, and Motorola C-QUAM (Compatible — Quadrature Amplitude Modulation) were all based around modulating the phase and amplitude of the carrier, placing the stereo information in the phase modulated portion, while the standard mono (L+R) information is in the amplitude modulation. The systems all did this in similar (but not completely compatible) ways. The original Harris Corporation system was later changed to match the Motorola C-QUAM pilot tone for indicating the station was in stereo, thus making it compatible with all C-QUAM receivers.Harris System
This system was developed by Harris CorporationHarris Corporation
Harris Corporation is a Florida-based international communications equipment company that produces wireless equipment, electronic systems, and both terrestrial and spaceborne antennas for use in the government, defense, and commercial sectors. It is also the largest private-sector employer in...
, a major manufacturer of radio/TV transmitters. Harris is the successor to the pioneer Gates radio line. Harris was the early leader in the AM stereo wars. It was implemented by a large number of stations in the 1980s, but the FCC temporarily rescinded their approval of the Harris system, causing most to switch to Motorola's C-QUAM system. This Harris system eventually changed their pilot tone to be compatible with C-QUAM. CKLW in Windsor, Ontario
Windsor, Ontario
Windsor is the southernmost city in Canada and is located in Southwestern Ontario at the western end of the heavily populated Quebec City – Windsor Corridor. It is within Essex County, Ontario, although administratively separated from the county government. Separated by the Detroit River, Windsor...
, 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...
(also serving nearby Detroit, Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
) was among the first stations to broadcast in Harris AM stereo. The Harris system is currently no longer used in its original form.
Magnavox System
This system was developed by electronics manufacturer, MagnavoxMagnavox
Magnavox is a US electronics company founded by Edwin Pridham and Peter L. Jensen, who invented the moving-coil loudspeaker in 1915 at their lab in Napa, California. They formed Magnavox in 1917 in order to market their inventions....
. It is a phase modulation system. It was initially declared the AM stereo standard by the FCC in 1980, but the FCC later declared that stations were free to choose any system. As with the Harris system, it was popular in the 1980s, but most stations stopped broadcasting in stereo, or upgraded to the C-QUAM system as time went on. 1190 WOWO
WOWO
Located in Fort Wayne, Indiana, WOWO is an independent news/talk radio station transmitting on 1190 kHz at 50,000 watts during the daylight hours and 9,800 watts during the nighttime hours. An application is on file with the Federal Communications Commission to add a fourth tower to the three...
in Fort Wayne, Indiana
Indiana
Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...
was the (then) 50,000-watt clear channel Magnavox flagship station.
Motorola C-QUAM
C-QUAMC-QUAM
C-QUAM is the method of AM stereo broadcasting used in Canada, the United States and most other countries. It was invented in 1977 by Norman Parker, Francis Hilbert, and Yoshio Sakaie, and published in an IEEE journal....
was developed and promoted primarily by Motorola, a long time manufacturer of two-way radio equipment. It became the dominant system by the late 1980s, and was declared the official standard by the FCC in 1993. While many stations in the USA have since discontinued broadcasting in Stereo, many still have the necessary equipment to do so. C-QUAM is still popular in other parts of the world, such as 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...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
which it was declared the official standard.
QUAM uses quadrature phase and amplitude modulation
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...
: the phase of the audio is rotated ahead or behind the carrier and the amplitude of each phase is also changed; thus giving 16 points for reference (used also in dialup modems to get past the 9600 baud limit on analog lines). The QUAM signal (L-R info) is then phase modulated on the transmitter (the QUAM exciter replaced the crystal in the AM transmitter) and the L+R still modulated the transmitter as it had in the past. C-QUAM is a modified QUAM and thus called Compatible (C- in C-QUAM).
C-QUAM has been long criticized by the Kahn-Hazeltine system's creator, Leonard Kahn as being inferior to his system. First generation C-QUAM receivers suffered from "platform motion" effects when listening to stations received via 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...
. Later improvements by Motorola minimized the platform motion effect and increased audio quality and stereo separation, especially on AMAX
AMAX
AMAX is a United States certification program developed by the Electronic Industries Association and the National Association of Broadcasters in 1993. This quality control program addressed both consumer receiver developments and air chains of broadcast AM transmission stations...
certified receivers in the 1990s.
Kahn-Hazeltine
The Kahn-Hazeltine system was developed by American engineer Leonard Kahn and the Hazeltine CorporationHazeltine Corporation
Hazeltine Corporation was a defense electronics company which is now part of BAE Systems Inc.-History:The company was founded in 1924 by investors to exploit the Neutrodyne patent of Dr. Alan Hazeltine...
. This system used an entirely different principle; using independently modulated upper and lower sidebands. While a station using the system would sound best with proper decoding, it was also possible to use two standard AM radios (one tuned above and the other below the primary carrier) to achieve the stereophonic effect, although with poor stereo separation and fidelity compared to a proper Kahn system AM stereo receiver. One of the best known stations to use the Kahn system was 890 WLS (AM)
WLS (AM)
WLS is a Chicago clear-channel AM station on 890 kHz. It uses C-QUAM AM stereo and transmits with 50,000 watts from transmitter and towers on the south edge of Tinley Park, Illinois....
, Chicago. WLS still transmits in AM stereo today but uses the Motorola C-QUAM system instead.
However, the Kahn system suffered from lower stereo separation above 5 kHz (reaching none at 10 kHz whereas FM stereo has 40 db or more separation at 15 kHz) and the radio antenna array on directional AM (common on a lot of nighttime and some daytime stations) had to have a flat response across the entire 20 kHz AM channel. If the array had a higher reactance value (leading to a higher Standing wave ratio
Standing wave ratio
In telecommunications, standing wave ratio is the ratio of the amplitude of a partial standing wave at an antinode to the amplitude at an adjacent node , in an electrical transmission line....
) on one side of the frequency vs the other, it would affect the audio response of that channel and thus the stereo signal would be affected. Also, Kahn refused to license any radio receivers manufacturers with his design, although multi-system receivers were manufactured by various companies such as Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
, Sansui
Sansui
) is a Japanese manufacturer of audio and video equipment. Headquartered in Tokyo, Japan, it is part of Grande Holdings, a Chinese Hong Kong-based conglomerate, which also owns Japanese brands Akai and Nakamichi....
, and Sanyo
Sanyo
is a major electronics company and member of the Fortune 500 whose headquarters is located in Moriguchi, Osaka prefecture, Japan. Sanyo targets the middle of the market and has over 230 Subsidiaries and Affiliates....
, which could receive any of the four AM stereo systems.
Nonetheless, this system remained competitive with C-QUAM into the late 1980s and Kahn was very vocal about its advantages over Motorola's system. Kahn filed a lawsuit claiming that the Motorola system did not meet FCC emission bandwidth specifications, but by that time, C-QUAM had already been declared as the single standard for AM stereo in the USA.
Kahn's AM stereo design was later revamped for monaural use and used in the Power-Side system, in which a decreased signal in one sideband is used to improve coverage and loudness, especially with directional antenna arrays. Power-Side became the basis for CAM-D
CAM-D
Compatible 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....
, Compatible AM Digital, a new digital system being promoted by Leonard Kahn and used on several AM stations.
Kahn receiver chips have also been used as an inexpensive method for providing high frequency (world band) receivers with synchronous detection technology.
Belar System
The Belar system was used in limited number of stations, such as WJRWJR
WJR is a radio station in Detroit, Michigan, United States. It broadcasts a news/talk format. It is a class A clear channel station whose broadcasts can be heard throughout most of the Midwest, eastern United States and Canada at night, making it one of the most powerful radio stations in the...
.
The Belar system was a simple FM/AM modulation system, with an attenuated L-R signal frequency modulating the carrier (with a 400uS pre-emphasis) in the extent of +/- 320 Hz around the center frequency, and the L+R doing the normal "high level" AM modulation (usually referred to as Plate Modulation in transmitters using a tube in the final stage, where the audio is applied to the plate voltage of the tube; in solid state transmitters, various different techniques are available that are more efficient at lower power levels). The Belar system (by the company of the same name) was dropped due to issues with its design though it was much easier to implement than the other systems. It and the Kahn system did not suffer from platform motion (which was a killer for AM stereo at night; platform motion is where the stereo balance would shift from one side to the other and then back to center) but the use of low level frequency modulation did not permit a high separation of L and R channels.
Adoption in the United States
In 1975, the Federal Communications CommissionFederal 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...
(FCC) started a series of five year tests to determine which of the five competing standards would be selected. By the end of the testing period, the Belar system was dropped. In 1980, the FCC announced that the Magnavox
Magnavox
Magnavox is a US electronics company founded by Edwin Pridham and Peter L. Jensen, who invented the moving-coil loudspeaker in 1915 at their lab in Napa, California. They formed Magnavox in 1917 in order to market their inventions....
system would become the standard. This announcement was met with harsh criticism and a series of lawsuits. On March 4, 1982, the FCC revoked their endorsement to the Magnavox standard and let the marketplace decide, meaning that all four standards were allowed. After the 1982 decision, many stations implemented one of the four standards. Initially, all systems remained competitive, but by the later 1980s, Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
C-QUAM
C-QUAM
C-QUAM is the method of AM stereo broadcasting used in Canada, the United States and most other countries. It was invented in 1977 by Norman Parker, Francis Hilbert, and Yoshio Sakaie, and published in an IEEE journal....
had a clear majority of stations and receivers. Around this same time, Harris Corporation
Harris Corporation
Harris Corporation is a Florida-based international communications equipment company that produces wireless equipment, electronic systems, and both terrestrial and spaceborne antennas for use in the government, defense, and commercial sectors. It is also the largest private-sector employer in...
dropped their system and instead endorsed C-QUAM. During this time, radio manufactures either made receivers which decoded just one system, or decoded all four. The multiple systems used greatly confused consumers and severely impacted consumer adoption. As a result of this confusion, and the continued growth of the FM band, interest in AM stereo dwindled.
In 1993, the FCC declared Motorola's C-QUAM system the standard. To ensure that all AM stereo receivers maintained the same sound quality, the National Association of Broadcasters
National Association of Broadcasters
The National Association of Broadcasters is a trade association, workers union, and lobby group representing the interests of for-profit, over-the-air radio and television broadcasters in the United States...
and the Electronic Industries Association started the AMAX
AMAX
AMAX is a United States certification program developed by the Electronic Industries Association and the National Association of Broadcasters in 1993. This quality control program addressed both consumer receiver developments and air chains of broadcast AM transmission stations...
certification program.
Global adoption
In the early 1980s, other countries, most notably CanadaCanada
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...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
approved and implemented AM stereo systems. Most governments approved a single standard, usually Motorola's C-QUAM, which greatly reduced confusion and increased user adoption.
Following the launch of the American-owned, ship-based 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...
station Laser 558
Laser 558
Laser 558 was an offshore pirate radio station launched in May 1984 by a consortium of British and American business and broadcasting executives, some of whom have never been named. Laser 558 used disc jockeys recruited from the USA. The station was aboard the ship the MV Communicator in...
off the British coast, there were announcements that another such station, provisionally called Stereo Hits 576, would soon follow, using AM stereo on an adjacent frequency to Laser. Nothing ever came of this project and 576kHz was adopted by Radio Caroline
Radio Caroline
Radio Caroline is an English radio station founded in 1964 by Ronan O'Rahilly to circumvent the record companies' control of popular music broadcasting in the United Kingdom and the BBC's radio broadcasting monopoly...
instead.
In many countries, especially those where the AM band is still dominant, AM stereo radios are still manufactured and stations still broadcast stereo signals.
Current status
Globally, interest in and use of AM stereo has been declining steadily since the 1990s, as many music stations have continued to move to the FM band. As a result, the vast majority of AM stations broadcast News/TalkTalk 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...
or Sports/Sports Talk
Sports radio
Sports radio is a radio format devoted entirely to discussion and broadcasting of sporting events. A popular format with an almost exclusively male demographic in most areas, sports radio is characterized by an often-boisterous on-air style and extensive debate and analysis by both hosts and...
formats. Many of the stations that initially implemented AM stereo are clear-channel 50,000 watt stations, and are more concerned with listening range than stereo sound (although there is no proof that use of AM stereo affects listening range). As a result, these stations still have the necessary equipment to broadcast in stereo, but it is left unused (or converted to 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...
). Also, many former AM stereo stations were bought up by broadcasting conglomerates, which generally discourage AM stereo broadcasting. In the United States, most stations currently using AM stereo are small, independently owned and broadcast a variety or music format.
- Japan: Between 1992 and 1996, 16 commercial broadcasting companies in JapanJapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
adopted C-QUAM because of the narrow Japanese FM band; it covers only 14 MHz (76-90 MHz), as opposed to the 20.5 MHz used in the rest of the world (87.5-108 MHz). However, it is now quite rare to see AM radios with stereo the function at appliance stores in Japan because of the decline in AM stereo stations and the limited available area, mainly in densely populated areas. Seven of the 16 stereo stations have since reverted to mono, 5 in 2010 alone :ja:AMステレオ放送. Another, JOKRTBS Radio & Communicationsis the flagship radio station of Japan Radio Network in Tokyo, Japan. The company was founded by Tokyo Broadcasting System, Inc. on March 21, 2000...
(AM 954), is reverting on January 31, 2011, leaving only 8 stations broadcasting in stereo. - Australia: AM stereo was popular in AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
because AM covers a wide geographic area compared to FM, in addition to the government's adoption of a single standard (Motorola C-QUAM) several years sooner than the USA, and Australia's relatively late adoption of FM (the frequencies in the FM band were originally allocated for TV). As of June 2008 no MelbourneMelbourneMelbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...
AM stations broadcast C-QUAM AM stereo. At its peak popularity in the late 1980s the majority of stations did. - Europe: After some experiments in the 1980s, AM stereo was deemed to be unsuitable for the crowded band conditions and narrow bandwidths associated with AM broadcasting in Europe. However, MotorolaMotorolaMotorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
C-QUAM AM stereo remains in use today on a handful of stations in FranceFranceThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, ItalyItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, and GreeceGreeceGreece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
. - Canada: AM stereo was more widely adopted in CanadaCanadaCanada 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...
than in the USA. This may have been due to the Canadian government's decision to use a single standard, and the Canadian Radio-television and Telecommunications Commission (CRTC) licensing stations by format and their hit/non-hit rules for FM (hence, more music stations on AM). However, unlike in the USA, some former AM stereo stations have moved to the FM band and left the AM band altogether instead of simply reverting to mono.
Surround Sound
On February 26, 2010, KCJJKCJJ
KCJJ is a radio station licensed to serve Iowa City, Iowa, USA. The station is owned by Steve Bridges' River City Radio. The station was assigned the KCJJ call sign by the Federal Communications Commission in 1982.-Programming:...
(AM 1630) in Coralville, Iowa, aired a four hour quadraphonic
Quadraphonic
Quadraphonic sound – the most widely used early term for what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are independent of one another...
radio broadcast of the Robb Spewak show. The show spotlighted music from the quadraphonic era on the 40th anniversary of the format's release in America and was engineered by Tab Patterson. All the music was from discrete 4-channel tapes, then encoded into Dolby Pro-Logic II and transmitted using their stereo C-QUAM transmitter. It was the first time AM radio was featured in this surround sound capacity.
Decline in use
Radio stations around the world are converting to various systems of digital radioDigital radio
Digital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...
, such as 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...
, DAB
Digital audio broadcasting
Digital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....
or 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...
(in the United States). Some of these digital radio systems, most notably 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...
have "hybrid modes" which let a station broadcast a standard AM signal along with the digital information. While these transmission modes allow standard AM, they are not compatible with any AM stereo system (meaning you can't broadcast both at the same time).
Digital AM broadcasting systems, such as HD Radio have been criticized by supporters of AM stereo as sounding "harsh" and "artificial", but supporters of Digital systems argue that the extended frequency response, increased dynamic range, lack of noise and lower distortion make up for the compression artifacts. However, HD Radio also increases adjacent channel noise due to the digital sidebands, which pose serious problems for nighttime broadcasts. Some have proposed to use HD Radio in the daytime and AM stereo at night.
Many HD radios are based on a common chipset
Chipset
A chipset, PC chipset, or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...
that decodes C-QUAM.
External links
- France Bleu (FrenchFrench languageFrench is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
) - AM stereo tuner source
- An A.M. Stereo enthusiast's website
- Another AM stereo enthusiast's website
- AM Stereo Audio Soundbites over the air
- Technical data on AM HD/IBOC
- http://www.wa2fnq.com/fnq/amstrdoc.htm Amateur experiments with AM stereo