AM stereo is a term given to a series of mutually incompatible techniques for radio broadcasting stereo audio in the AM band in a manner that is compatible with standard AM receivers. There are two main classes of systems: independent sideband (ISB) systems, promoted principally by American broadcast engineer Leonard R. Kahn; and quadrature amplitude modulation (QAM) multiplexing systems (conceptually closer to FM stereo).
Initially adopted by many commercial AM broadcasters in the mid to late 1980s, AM stereo broadcasting soon began to decline due to a lack of receivers (most "AM/FM stereo" radios only receive in stereo on FM), a growing exodus of music broadcasters to FM, concentration of ownership of the few remaining stations in the hands of large corporations and the removal of music from AM stations in favour of news/talk or sports broadcasting. By 2001, most of the former AM stereo broadcasters were no longer stereo or had left the AM band entirely.
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 receivers. 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.
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.
This system, known as V-CPM for Variable Angle Compatible Phase Multiplex, was developed by Harris Corporation, a major manufacturer of radio/TV transmitters. It incorporated a left minus right component which was frequency modulated by about 1 kHz. Harris is the successor to the pioneer Gates radio line, which has changed its name in 2014 to Gates-Air. The Harris system eventually changed their pilot tone to be compatible with C-QUAM, after C-QUAM became the more popular and eventually, the FCC approved standard. 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.
This system was developed by electronics manufacturer, Magnavox. 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 downgraded 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.
C-QUAM was developed and promoted primarily by Motorola, a longtime 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.
The C-QUAM exciter replaces the crystal stage in an AM transmitter. The C-QUAM signal, consists of a phase modulated portion which is made up of both the L+R and L-R audio information and a conventional L+R (mono) portion, which is amplitude modulated. C-QUAM is a modified form of quadrature modulation in that the phase modulated audio consists of both the L+R and L-R portions, modulated 90 degrees out of phase with each other.
Including the L+R audio in the phase modulated portion of the signal is the very reason the C-QUAM method of AM Stereo is, as the name implies, 100% compatible with mono AM radios. This technique resolves a distortion issue which arises when left only or right only audio is transmitted using a basic L-R quadrature modulation approach.
C-QUAM had 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.
The Kahn-Hazeltine system also called ISB was developed by American engineer Leonard R. Kahn and the Hazeltine Corporation. 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, 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 7 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 used in limited number of stations, such as WJR. The Belar system, originally designed by RCA in the 1950s, was a simple FM/AM modulation system, with an attenuated L-R signal frequency modulating the carrier (with a 400 µs 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.
In 1975, the Federal Communications Commission (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.
In the early 1980s, other countries, most notably Canada, 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 576 kHz 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.
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/talk 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.
On February 26, 2010, KCJJ (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.
Radio stations around the world are converting to various systems of digital radio, 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 both cannot be broadcast 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.
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.
Using circuitry developed by Motorola, C-QUAM uses quadrature amplitude modulation (QAM) to encode the stereo separation signal. This extra signal is then stripped down in such a way that it is compatible with the envelope detector of older receivers (hence the name C-QUAM, i.e. Compatible QUadrature Amplitude Modulation). A 25 Hz pilot tone is added to trigger receivers; it is not necessary for the reconstruction of the original audio sources.CBOF-FM
CBOF-FM is a French-language Canadian radio station located in Ottawa, Ontario. CBOF's studios are located at the CBC Ottawa Broadcast Centre on Sparks Street.
Owned and operated by the (government-owned) Canadian Broadcasting Corporation (French: Société Radio-Canada), it broadcasts on 90.7 MHz with an effective radiated power of 84,000 watts (class C1) using an omnidirectional antenna located in Camp Fortune, Quebec.
The station has an ad-free news/talk format and is part of the Ici Radio-Canada Première network, which operates across Canada.
The station signed on in 1964 on the AM band on 1250 kHz with 10,000 watts day and night. Before then, Radio-Canada relied on Hull's CKCH, as well as the 50,000-watt signal of Montreal's CBF, to serve Ottawa's francophones. On January 15, 1975 the CRTC approved the CBC's application to increase CBOF's signal from 10,000 watts to 50,000 watts day and night at 1250 kHz. The CRTC approved the CBC's application to convert CBOF from the AM band to the FM band on November 9, 1989. CBOF moved to its current frequency on 90.7 MHz on January 7, 1991 as CBOF-FM. The AM transmitter was later shutdown. Its sister station, which used the CBOF-FM calls before that date, is now known as CBOX-FM.
CBOF-FM, like all Première stations but unlike most FM stations, broadcasts in mono. Briefly, CBOF, still as an AM station, experimented with AM stereo broadcasts between 1984 and 1987, testing all four AM stereo systems (C-QUAM, Kahn/Hazeltine, Harris and Magnavox) proposed at the time.
The station's current local programs are Les matins d'ici, in the mornings from 5:30 a.m. to 9 a.m., and Sur le vif in the afternoons, 3 p.m. to 6 p.m. The early morning program from 5 a.m. to 5:30 a.m., Info matin, originates from CBF-FM Montreal and is also heard in Quebec City. Its Saturday morning local program is Les malins, heard from 7:00 a.m. to 11 a.m.CFCO
CFCO (630 AM and 92.9 FM) is a news, sports, and country music radio station located in Chatham–Kent, Ontario. The station, owned by London, Ontario-based Blackburn Radio, features a heavy local news commitment. The AM station broadcasts in C-QUAM AM Stereo. CFCO is one of the few dedicated country music stations on the AM dial in North America, as well as one of the few to do so in C-QUAM AM Stereo.DZRH
DZRH (666 kHz AM Stereo) is a 24-hour commercial news/talk radio station serving Mega Manila market, which serves as the flagship radio station of the Manila Broadcasting Company in the Philippines. The station has nationwide coverage via its relay stations located within the Philippines. The station's studio is located at MBC Building, Sotto St., CCP Complex on Roxas Boulevard, Pasay City, Philippines, while its transmitter is located at I. Marcelo Street, Brgy. Malanday, Valenzuela City.
DZRH is the oldest radio station in the Philippines and it is a member of the Kapisanan ng mga Brodkaster ng Pilipinas or KBP. The station will celebrate its 80th anniversary on July 15, 2019.KBPS (AM)
KBPS (1450 AM) is a high school radio station in Portland in the U.S. state of Oregon. It is run by Benson Polytechnic High School students enrolled in the radio broadcasting program. It is owned by Portland Public Schools.
KQAC, formerly KBPS-FM, and KBPS share the same building, the FM station no longer has any affiliation with Portland Public Schools other than the space they rent out.
KBPS broadcasts in AM Stereo.KQWB (AM)
KQWB (1660 AM kHz, "Bison 1660") is an American radio station located in Fargo, North Dakota (licensed by the Federal Communications Commission (FCC) to adjacent West Fargo, North Dakota), owned by Jim Ingstad's Radio FM Media. Its studios are located on 7th Avenue South in Fargo, while its transmitter array is located north of Glyndon.
It airs game broadcasts and sports talk programs themed around the athletics programs of North Dakota State University, with Fox Sports Radio as a sustaining service.
The local talk programs are the daily shows 'The Insiders' with Jeff Culhane (Program Director and play by play voice for NDSU Bison football and men's basketball) and Jeremy Jorgensen (Director of Broadcasting at NDSU) and 'The Brakedown' with Keith Brake (Assistant PD and women's play-by-play voice)
Bison 1660 airs live North Dakota State Bison football, men's basketball, baseball, softball, women's basketball, and volleyball games. It also airs live pregame and post game reaction call in shows.
Weekly live coaches shows with head football coach Chris Klieman, men's basketball coach David Richman, and women's basketball coach Maren Walseth air during the season in the evening.
National Fox Sports radio shows include The Dan Patrick Show, The Herd with Colin Cowherd, The Doug Gottlieb show, JT The Brick with Tomm Looney, The Jason Smith Show, and more. KQWB also airs national College Football and NFL broadcasts from Sports USA.KYVA (AM)
KYVA (1230 AM) is a radio station licensed to Gallup, New Mexico, United States, broadcasting a country music format in AM stereo. The station is currently owned by Millennium Media. The station broadcasts Major League Baseball games as a member of the Los Angeles Dodgers Radio Network.Medium wave
Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz, using channels spaced every 9 kHz, and in North America an extended MW broadcast band ranges from 525 kHz to 1705 kHz, using 10 kHz spaced channels. The term is a historic one, dating from the early 20th century, when the radio spectrum was divided on the basis of the wavelength of the waves into long wave (LW), medium wave, and short wave (SW) radio bands.WAQE (AM)
WAQE (1090 AM) is a radio station broadcasting a sports talk format. The station had a Classic Country format until August 29, 2009, when it changed to Sports Talk 1090. The lineup includes Dan Patrick, Jim Rome, and Fox Sports Radio. Licensed to Rice Lake, Wisconsin, United States. The station is owned by TKC, Inc. and features programming from ESPN Radio. WAQE transmits in C-QUAM AM stereo.WBFJ (AM)
WBFJ (1550 AM) is a radio station broadcasting a Christian Talk and Teaching format. Licensed in Winston-Salem, North Carolina, United States, it serves the Piedmont Triad area and is currently owned by Triad Family Network, Inc.WFAS (AM)
WFAS (1230 kHz) is an AM radio station licensed to White Plains, New York and serving Westchester County. The station is owned by Cumulus Media and broadcasts at 1,000 watts from a transmitter site on Secor Road, in Hartsdale, New York.WION
WION (1430 AM, "I-1430") is a radio station with a full service (a mix of locally programmed music, news, and sports) format to the West Central Michigan area with studios in Ionia, Michigan. In 2009, the AM signal was upgraded to change the daytime coverage area from a directional pattern aimed north, to a non-directional signal. This provided better signal for a larger stretch of I-96 and brought Portland and Lowell Michigan into primary daytime coverage. In 2009, the station added an FM translator on 92-7 FM purchased from Horizon Christian Fellowship, which changed frequencies on the dial from its original 103.7. The translator moved to the station's studios on Haynor Road Ionia. The translator covers all of Ionia County on 92.7. A second translator was added in Lowell, Michigan in March 2019 on 100.3 FM. WION's AM signal can be heard as far east as Flint, Michigan, as far south as Tekonsha, Michigan and as far north as Marion, Michigan. WION transmits in C-QUAM AM stereo.
WION began online streaming of its programming on February 1, 2013 on the 60th anniversary of the station. The source of the feed is the actual "over the air" AM stereo signal from a Carver-brand AM stereo receiver. Sourcing the streaming from an AM stereo tuner is done for the purpose of demonstrating to listeners online the potential quality that AM radio can produce with proper processing and care of the station's physical plant.The station returned to being an affiliate of the CBS Radio network in 2010, and a "hybrid" mix of music.
WION began broadcasting in 1953. The call letters stand for "Ionia County".WIRL
WIRL (1290 AM) is a radio station broadcasting an oldies music format. Licensed to Peoria, Illinois, United States, the station serves the Peoria area and broadcasts in AM stereo. The station is currently owned by Alpha Media.
WIRL can also be heard in HD on sister station WPBG HD2. WIRL itself is not licensed to broadcast in HD.WIRY (AM)
WIRY is an AM radio station licensed to Plattsburgh, New York. The locally owned and operated radio station broadcasts at 1340 kHz in C-QUAM AM stereo into a Valcom whip antenna (one of the only stations to do so) with a full-service variety format.
WIRY is primarily music-formatted, featuring an eclectic variety of formats. The station describes its format as a mix of adult contemporary, country music, and oldies.
WIRY is mostly locally operated. The station has a live local morning show and an extensive local news and sports bureau, carrying the Plattsburgh Cardinals hockey team in winter months and high school sports. The station also has several creative advertising programs, including a listing of lunch menus from advertisers and a radio help-wanted show titled "Who's Hiring." Weather forecasts are taken from public domain National Weather Service reports.
The station serves as an affiliate for the New York Yankees, New York Giants, Westwood One, The Beatle Years with Bob Malik, When Radio Was and The Country Music Greats Radio Show.
In addition, the station also streams on the Internet. It has streamed continuously since prior to 2002 and survived the Internet radio bust that forced many stations to stop streaming at that time.
WIRY began leasing FM radio station 100.7 in 2016; the rechristened WIRY-FM will mostly simulcast the AM side, with syndicated music programs likely to air in place of sports (Bill Santa, WIRY's owner, stated that major sports teams prefer AM radio affiliates).WNNC
WNNC (1230 AM) is a radio station broadcasting an oldies music format and licensed to serve the community of Newton, North Carolina, part of the Hickory-Newton-Conover metro area. The station is currently owned by Newton-Conover Communications. WNNC broadcasts in C-QUAM AM stereo.WPAX
WPAX (1240 AM) is a radio station broadcasting an Adult Standards/MOR format. Licensed to Thomasville, Georgia, United States, the station serves the Tallahassee area. The station is currently owned by Lenrob Enterprises, Inc. and features programming from CBS Radio, Jones Radio Network and the Atlanta Braves. WPAX broadcasts in C-QUAM AM stereo.WPLO
WPLO ("La Bonita 610 AM") is an Atlanta area AM broadcasting station, licensed to Grayson, Georgia, that broadcasts Spanish language music programming. It transmits at a frequency of 610 kHz with 1,500 Watts of power during the daytime and 225 Watts during nighttime using a non-directional antenna. WPLO is a Class-D AM broadcasting station according to the Federal Communication Commission. The station has applied to the Federal Communication Commission to change its licensed city to Lawrenceville, Georgia, the location of its current transmitting facility and tower.WQUN
WQUN (1220 AM Stereo) is a radio station licensed to serve Hamden, Connecticut. The station is owned by Quinnipiac University. It airs an Adult Standards music format. Currently, WQUN airs the standards format America's Best Music from Westwood One, formerly Dial Global.
The station has been assigned the WQUN call letters by the Federal Communications Commission since September 27, 1996.WZZB
WZZB (1390 AM, Classic 1390) is a radio station broadcasting a soft adult contemporary music format in AM stereo. Licensed to Seymour, Indiana, United States, the station is currently owned by Midnight Hour Broadcasting, LLC and features programming from Dial Global.
The following 91 stations broadcast in C-QUAM AM stereo.