In broadcasting and radio communications, a call sign is a unique designation for a transmitter station. In the United States of America, they are used for all FCC-licensed transmitters. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or cryptographically encoded to disguise a station's identity; the use of call signs as unique identifiers dates to the landline railroad telegraph system. Because there was only one telegraph line linking all railroad stations, there needed to be a way to address each one when sending a telegram. In order to save time, two-letter identifiers were adopted for this purpose; this pattern continued in radiotelegraph operation. These were not globally unique, so a one-letter company identifier was added. By 1912, the need to identify stations operated by multiple companies in multiple nations required an international standard. Merchant and naval vessels are assigned call signs by their national licensing authorities.
In the case of states such as Liberia or Panama, which are flags of convenience for ship registration, call signs for larger vessels consist of the national prefix plus three letters. United States merchant vessels are given call signs beginning with the letters "W" or "K" while US naval ships are assigned call signs beginning with "N". Both ships and broadcast stations were assigned call signs in this series consisting of three or four letters. Ships equipped with Morse code radiotelegraphy, or life boat radio sets, Aviation ground stations, broadcast stations were given four letter call signs. Maritime coast stations on high frequency were assigned three letter call signs; as demand for both marine radio and broadcast call signs grew American-flagged vessels with radiotelephony only were given longer call signs with mixed letters and numbers. Leisure craft with VHF radios may not be assigned call signs, in which case the name of the vessel is used instead. Ships in the US still wishing to have a radio license are under FCC class SA: "Ship recreational or voluntarily equipped."
Those calls follow the land mobile format of the initial letter K or W followed by 1 or 2 letters followed by 3 or 4 numbers. U. S. Coast Guard small boats have a number, shown on both bows in which the first two digits indicate the nominal length of the boat in feet. For example, Coast Guard 47021 refers to the 21st in the series of 47-foot motor lifeboats; the call sign might be abbreviated to the final two or three numbers during operations, for example: Coast Guard zero two one. Aviation mobile stations equipped with radiotelegraphy were assigned five letter call signs.. Land Stations in Aviation were assigned four letter call signs; these call signs were phased out in the 1960s when flight radio officers were no longer required on international flights. USSR kept FRO's for the Moscow-Havana run until around 2000. All signs in aviation are derived from several different policies, depending upon the type of flight operation and whether or not the caller is in an aircraft or at a ground facility.
In most countries, unscheduled general aviation flights identify themselves using the call sign corresponding to the aircraft's registration number. In this case, the call sign is spoken using the International Civil Aviation Organization phonetic alphabet. Aircraft registration numbers internationally follow the pattern of a country prefix, followed by a unique identifier made up of letters and numbers. For example, an aircraft registered as N978CP conducting a general aviation flight would use the call sign November-niner-seven-eight-Charlie-Papa. However, in the United States a pilot of an aircraft would omit saying November, instead use the name of the aircraft manufacturer or the specific model. At times, general aviation pilots might omit additional preceding numbers and use only the last three numbers and letters; this is true at uncontrolled fields when reporting traffic pattern positions or at towered airports after establishing two-way communication with the tower controller. For example, Skyhawk eight-Charlie-Papa, left base.
In most countries, the aircraft call sign or "tail number"/"tail letters" are linked to the international radio call sign allocation table and follow a convention that aircraft radio stations receive call signs consisting of five letters. For example, all British civil aircraft have a five-letter call sign beginning with the letter G. Canadian aircraft have a call sign beginning with C–F or C–G, such as C–FABC. Wing In Ground-effect vehicles in Canada are eligible to receive C–Hxxx call signs, ultralight aircraft receive C-Ixxx call signs. In days gone by American aircraft used five letter call signs, such as KH–ABC, but they were replaced prior to World War II by the current American system of civilian aircraft call signs. Radio call signs used for communication in manned spaceflight is not formalized or regulated to the same degree as for aircraft; the three nations curren
Country music known as country and western, hillbilly music, is a genre of popular music that originated in the southern United States in the early 1920s. It takes its roots from genres such as folk blues. Country music consists of ballads and dance tunes with simple forms, folk lyrics, harmonies accompanied by string instruments such as banjos and acoustic guitars, steel guitars, fiddles as well as harmonicas. Blues modes have been used extensively throughout its recorded history. According to Lindsey Starnes, the term country music gained popularity in the 1940s in preference to the earlier term hillbilly music. In 2009 in the United States, country music was the most listened to rush hour radio genre during the evening commute, second most popular in the morning commute; the term country music is used today to describe many subgenres. The origins of country music are found in the folk music of working class Americans, who blended popular songs and Celtic fiddle tunes, traditional English ballads, cowboy songs, the musical traditions of various groups of European immigrants.
Immigrants to the southern Appalachian Mountains of eastern North America brought the music and instruments of Europe along with them for nearly 300 years. Country music was "introduced to the world as a Southern phenomenon." The U. S. Congress has formally recognized Bristol, Tennessee as the "Birthplace of Country Music", based on the historic Bristol recording sessions of 1927. Since 2014, the city has been home to the Birthplace of Country Music Museum. Historians have noted the influence of the less-known Johnson City sessions of 1928 and 1929, the Knoxville sessions of 1929 and 1930. In addition, the Mountain City Fiddlers Convention, held in 1925, helped to inspire modern country music. Before these, pioneer settlers, in the Great Smoky Mountains region, had developed a rich musical heritage; the first generation emerged in the early 1920s, with Atlanta's music scene playing a major role in launching country's earliest recording artists. New York City record label Okeh Records began issuing hillbilly music records by Fiddlin' John Carson as early as 1923, followed by Columbia Records in 1924, RCA Victor Records in 1927 with the first famous pioneers of the genre Jimmie Rodgers and the first family of country music The Carter Family.
Many "hillbilly" musicians, such as Cliff Carlisle, recorded blues songs throughout the 1920s. During the second generation, radio became a popular source of entertainment, "barn dance" shows featuring country music were started all over the South, as far north as Chicago, as far west as California; the most important was the Grand Ole Opry, aired starting in 1925 by WSM in Nashville and continuing to the present day. During the 1930s and 1940s, cowboy songs, or Western music, recorded since the 1920s, were popularized by films made in Hollywood. Bob Wills was another country musician from the Lower Great Plains who had become popular as the leader of a "hot string band," and who appeared in Hollywood westerns, his mix of country and jazz, which started out as dance hall music, would become known as Western swing. Wills was one of the first country musicians known to have added an electric guitar to his band, in 1938. Country musicians began recording boogie in 1939, shortly after it had been played at Carnegie Hall, when Johnny Barfield recorded "Boogie Woogie".
The third generation started at the end of World War II with "mountaineer" string band music known as bluegrass, which emerged when Bill Monroe, along with Lester Flatt and Earl Scruggs were introduced by Roy Acuff at the Grand Ole Opry. Gospel music remained a popular component of country music. Another type of stripped-down and raw music with a variety of moods and a basic ensemble of guitar, dobro or steel guitar became popular among poor whites in Texas and Oklahoma, it became known as honky tonk, had its roots in Western swing and the ranchera music of Mexico and the border states. By the early 1950s a blend of Western swing, country boogie, honky tonk was played by most country bands. Rockabilly was most popular with country fans in the 1950s, 1956 could be called the year of rockabilly in country music, with Johnny Cash emerging as one of the most popular and enduring representatives of the rockabilly genre. Beginning in the mid-1950s, reaching its peak during the early 1960s, the Nashville sound turned country music into a multimillion-dollar industry centered in Nashville, Tennessee.
The late 1960s in American music produced a unique blend as a result of traditionalist backlash within separate genres. In the aftermath of the British Invasion, many desired a return to the "old values" of rock n' roll. At the same time there was a lack of enthusiasm in the country sector for Nashville-produced music. What resulted was a crossbred genre known as country rock. Fourth generation music included outlaw country with roots in the Bakersfield sound, country pop with roots in the countrypolitan, folk music and soft rock. Between 1972 and 1975 singer/guitarist John Denver released a se
Height above average terrain
Height above average terrain, or effective height above average terrain, is a measure of how high an antenna site is above the surrounding landscape. HAAT is used extensively in FM radio and television, as it is more important than effective radiated power in determining the range of broadcasts. For international coordination, it is measured in meters by the Federal Communications Commission in the United States, as Canada and Mexico have extensive border zones where stations can be received on either side of the international boundaries. Stations that want to increase above a certain HAAT must reduce their power accordingly, based on the maximum distance their station class is allowed to cover; the FCC procedure to calculate HAAT is: from the proposed or actual antenna site, either 12 or 16 radials were drawn, points at 2, 4, 6, 8, 10 miles radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station; the altitude of the antenna site, minus the average altitude of all the specified points, is the HAAT.
This can create some unusual cases in mountainous regions—it is possible to have a negative number for HAAT. The FCC has divided the Contiguous United States into three zones for the determination of spacing between FM and TV stations using the same frequencies. FM and TV stations are assigned maximum ERP and HAAT values, depending on their assigned zones, to prevent co-channel interference; the FCC regulations for ERP and HAAT are listed under Title 47, Part 73 of the Code of Federal Regulations. Maximum HAAT: 150 metres Maximum ERP: 50 kilowatts Minimum co-channel separation: 241 km Maximum HAAT: 600 metres Maximum ERP: 100 kilowatts Minimum co-channel separation: 290 km. In all zones, maximum ERP for analog TV transmitters is. In addition, Zone I-A consists of all of California south of 40° north latitude, Puerto Rico and the U. S. Virgin Islands. Zones I and I-A have the most "grandfathered" overpowered stations, which are allowed the same extended coverage areas that they had before the zones were established.
One of the most powerful of these stations is WBCT in Grand Rapids, which operates at 320,000 watts and 238 meters HAAT. Zone III consists of all of Florida and the areas of Alabama, Louisiana and Texas within 241.4 kilometers of the Gulf of Mexico. Zone II is all the rest of the Continental United States and Hawaii. Above mean sea level Above ground level Canadian Radio-television and Telecommunications Commission List of broadcast station classes United States Federal Communications Commission 47 CFR Part 73 Index FCC: Mass Media Calculated Contours FCC: HAAT Calculator "Superpower" Grandfathered FM stations
Radio broadcasting is transmission by radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both; the signal types can be digital audio. The earliest radio stations did not carry audio. For audio broadcasts to be possible, electronic detection and amplification devices had to be incorporated; the thermionic valve was invented in 1904 by the English physicist John Ambrose Fleming. He developed a device he called an "oscillation valve"; the heated filament, or cathode, was capable of thermionic emission of electrons that would flow to the plate when it was at a higher voltage. Electrons, could not pass in the reverse direction because the plate was not heated and thus not capable of thermionic emission of electrons. Known as the Fleming valve, it could be used as a rectifier of alternating current and as a radio wave detector; this improved the crystal set which rectified the radio signal using an early solid-state diode based on a crystal and a so-called cat's whisker.
However, what was still required was an amplifier. The triode was patented on March 4, 1906, by the Austrian Robert von Lieben independent from that, on October 25, 1906, Lee De Forest patented his three-element Audion, it wasn't put to practical use until 1912 when its amplifying ability became recognized by researchers. By about 1920, valve technology had matured to the point where radio broadcasting was becoming viable. However, an early audio transmission that could be termed a broadcast may have occurred on Christmas Eve in 1906 by Reginald Fessenden, although this is disputed. While many early experimenters attempted to create systems similar to radiotelephone devices by which only two parties were meant to communicate, there were others who intended to transmit to larger audiences. Charles Herrold started broadcasting in California in 1909 and was carrying audio by the next year.. In The Hague, the Netherlands, PCGG started broadcasting on November 6, 1919, making it, arguably the first commercial broadcasting station.
In 1916, Frank Conrad, an electrical engineer employed at the Westinghouse Electric Corporation, began broadcasting from his Wilkinsburg, Pennsylvania garage with the call letters 8XK. The station was moved to the top of the Westinghouse factory building in East Pittsburgh, Pennsylvania. Westinghouse relaunched the station as KDKA on November 2, 1920, as the first commercially licensed radio station in America; the commercial broadcasting designation came from the type of broadcast license. The first licensed broadcast in the United States came from KDKA itself: the results of the Harding/Cox Presidential Election; the Montreal station that became CFCF began broadcast programming on May 20, 1920, the Detroit station that became WWJ began program broadcasts beginning on August 20, 1920, although neither held a license at the time. In 1920, wireless broadcasts for entertainment began in the UK from the Marconi Research Centre 2MT at Writtle near Chelmsford, England. A famous broadcast from Marconi's New Street Works factory in Chelmsford was made by the famous soprano Dame Nellie Melba on 15 June 1920, where she sang two arias and her famous trill.
She was the first artist of international renown to participate in direct radio broadcasts. The 2MT station began to broadcast regular entertainment in 1922; the BBC was amalgamated in 1922 and received a Royal Charter in 1926, making it the first national broadcaster in the world, followed by Czech Radio and other European broadcasters in 1923. Radio Argentina began scheduled transmissions from the Teatro Coliseo in Buenos Aires on August 27, 1920, making its own priority claim; the station got its license on November 19, 1923. The delay was due to the lack of official Argentine licensing procedures before that date; this station continued regular broadcasting of entertainment and cultural fare for several decades. Radio in education soon followed and colleges across the U. S. began adding radio broadcasting courses to their curricula. Curry College in Milton, Massachusetts introduced one of the first broadcasting majors in 1932 when the college teamed up with WLOE in Boston to have students broadcast programs.
Broadcasting service is – according to Article 1.38 of the International Telecommunication Union´s Radio Regulations – defined as «A radiocommunication service in which the transmission are intended for direct reception by the general public. This service may include sound transmissions, television transmissions or other types of transmission.» Definitions identical to those contained in the Annexes to the Constitution and Convention of the International Telecommunication Union are marked "" or "" respectively. A radio broadcasting station is associated with wireless transmission, though in practice broadcasting transmission take place using both wires and radio waves; the point of this is that anyone with the appropriate receiving technology can receive the broadcast. In line to ITU Radio Regulations each broadcasting station shall be classified by the service in which it operates permanently or temporarily. Broadcasting by radio takes several forms; these include FM stations. There are several subtypes, namely commercial broadcasting, non-commercial educational public broadcasting and non-profit varieties as well as community radio, student-run campus radio stations, and
Kennett is a city in and the county seat of Dunklin County, United States. The city is located in the southeast corner of Missouri, 4 miles east of Arkansas and 20 miles from the Mississippi River, it has a population of 10,932 according to the 2010 Census. It is the largest city in the Bootheel, a agricultural area. White settlers built log cabins in the area in the first half of the 19th century, naming their settlement Chilletecaux in honor of a Delaware Indian chief who lived there; the town was renamed Butler in the late 1840s. Due to mail delivery problems because of other jurisdictions named the same, the settlement was renamed as Kennett, in honor of the mayor of the city of St. Louis, Luther M. Kennett. In the 1890s, a railroad reached the area. In that same period, the state began construction of a massive drainage program in the St. Francis River basin, floodplain and wetlands. In the 20th century, after timber clearing, the area was developed for cultivation of cotton and other commodity crops.
Kennett is located at 36°14′17″N 90°3′6″W. According to the United States Census Bureau, the city has a total area of 6.96 square miles, all land. As part of the southern extremity of Missouri, Kennett has a humid subtropical climate with cool winters and hot, humid summers, ample precipitation through much of the year, is part of USDA Plant Hardiness Zone 7; the monthly daily average temperature ranges from 35.3 °F in January to 80.7 °F in July. On average, there are 4.9 days annually with 100 °F + highs, 63 days of 90 °F + highs, 9.4 days where the temperature does not rise above freezing, 4.8 days with 10 °F or lower minima. The Kennett Micropolitan Statistical Area consists of Dunklin County; as of 2000 the median household income was $26,088 and the median family income was $34,167. Males had a median income of $29,958 versus $18,770 for females; the per capita income for the city was $14,397. Living below the poverty line were 26.1% of the population and 20.5% of families. Those living below the poverty line were 37.5% of those under the age of 18 and 24.0% of those 65 and older.
As of the census of 2010, there were 10,932 people, 4,377 households, 2,849 families residing in the city. The population density was 1,570.7 inhabitants per square mile. There were 4,863 housing units at an average density of 698.7 per square mile. The racial makeup of the city was 80.1% White, 16.2% African American, 0.2% Native American, 0.6% Asian, 0.1% Pacific Islander, 1.3% from other races, 1.7% from two or more races. Hispanic or Latino of any race were 3.5% of the population. There were 4,377 households of which 32.6% had children under the age of 18 living with them, 42.5% were married couples living together, 18.1% had a female householder with no husband present, 4.5% had a male householder with no wife present, 34.9% were non-families. 30.2% of all households were made up of individuals and 12.4% had someone living alone, 65 years of age or older. The average household size was 2.41 and the average family size was 2.95. The median age in the city was 38.4 years. 25.5% of residents were under the age of 18.
The gender makeup of the city was 47.1% male and 52.9% female. List of Kennett mayors Kennett has six public schools operated by the Kennett School District 39; the pre-school is called Kennett Early Learning Center. The elementary schools are H. Byron Masterson Elementary School; the other schools are Kennett Middle School, Kennett High School, Kennett Career and Technical Center. There is a private school, Kennett Christian Academy. In 1979, under the leadership of Pastor J. D. Langford of the First United Pentecostal Church, the Kennett Christian Academy opened its doors with a student body of 60. Since it has been providing Christian education for the area. Kennett is home to two higher education branch institutions. Southeast Missouri State University at Kennett is a branch of the Cape Girardeau main campus and Three Rivers College is a branch of the Poplar Bluff main campus. Class 4-A Two-Time MSHSAA Track Champions 3-Time Class 3 District Baseball Champions 1-Time Class 3 District Volleyball Champions Kennett Memorial Airport is a city-owned, public-use airport located one nautical mile southeast of the central business district of Kennett.
Noll Billings, country music singer for Blackjack Billy Sheryl Crow, Grammy-winning singer/songwriter John M. Dalton, former Missouri governor Gene Handley, professional baseball player Will Johnson, singer/songwriter and member of band Monsters of Folk Paul C. Jones, former congressman from Missouri Dan Landrum, hammered dulcimer player who tours with Yanni Fred Lasswell, cartoonist of Barney Google and Snuffy Smith David Nail, country music recording artist Gib Singleton, Fulbright Scholar Sally Stapleton, Pulitzer-winning photojournalist Trent Tomlinson, country singer Orville Zimmerman, United States Representative for Missouri's 10th congressional district, was a member of Kennett's board of education, 1928-1936 Official website Kennett Chamber of Commerce Historic maps of Kennett in the Sanborn Maps of Missouri Collection at the University of Missouri
WMC-FM is a hot adult contemporary radio station serving the market of Memphis, Tennessee. The station is notable for being an FM "superpower," with a transmitter that exceeds current Federal Communications Commission restrictions. Of stations in the FCC's Zone II, WMC-FM is the most powerful; the station's license is held by Entercom Communications, which purchased it and sister WMC from CBS Radio in 2006. The two radio stations, along with former sister station WMC-TV, were owned by the E. W. Scripps Company, publisher of The Commercial Appeal, prior to 1993. Taking beam tilt into account, the station's effective radiated power is rated at 300,000 watts horizontal polarization and 100,000 watts vertical; the station's antenna is 277 meters high and located along Crestview Drive in Northeast Memphis. Current FCC restrictions were passed in 1962 and mandate a 100 kW maximum across most of the country on the FM band; the station is calculated to exceed power restrictions by 4.6 decibels. However, WMC-FM was grandfathered in.
The station's studios are located in Southeast Memphis. Unlike many other stations, WMC-FM has retained its same general format since the 1970s. In fact, many of the staff members of the radio station have worked there a decade, or longer. Most notably, Ron "Hey Now" Olson had been the station's morning host since the 1980s, partnered with Steve Conley on the morning show since the early 1990s. In January, 2018, after Olson left for Entercom sister station WRVR, his most recent co-host Michelle Lewis took over mornings with newcomer Ryan Anderson. Tom Prestigiacomo had been the afternoon host since 1979, but Prestigiacomo left in 2007 for crosstown rival WKIM-FM, has now left the radio business. WMC-FM started broadcasting on the FM band on May 22, 1947 and was upgraded to its current power level prior to 1962. WMC-FM was the first radio station in the market, the first in Tennessee, to play the Progressive Rock format on the FM band, beginning February 6, 1967, at a time when most FM stations played Frank Sinatra, Patti Page and easy listening instrumentals.
Personalities included Greg Hamilton, Ron Michaels, Jon Scott, David Day. The program director was Mike Powell. Artists included King Crimson, It's a Beautiful Day, Quicksilver Messenger Service; the versions of "Light My Fire" by The Doors and "In-A-Gadda-Da-Vida" by Iron Butterfly were longer than the one most stations played. In the early 1970s, the station was responsible for regionally breaking many new artists such as David Bowie, Alice Cooper, Lynyrd Skynyrd, ZZ Top, Billy Joel and other rock acts of the day. By 1978, as its original rock listeners grew older, WMC-FM evolved to a successful but legendary Top 40/CHR format. By September 1992, the station transitioned into its present Hot AC format. WMC-FM is one of six radio properties in the Memphis market held by Entercom. Entercom purchased WMC-AM, WMC-FM and WMFS from CBS Radio in 2006. Today, the station's playlist consists of Pop/Top 40 music, its studios were located at 1960 Union Avenue. They were moved and are now located at the Entercom complex in the Moriah Woods Business Park, near the intersection of I-240 and Mount Moriah Road in Memphis.
WMC FM 100 official website Query the FCC's FM station database for WMC Radio-Locator information on WMC Query Nielsen Audio's FM station database for WMC List of "grandfathered" FM radio stations in the U. S. FCC Office of Engineering and Technology: FM Broadcast Zones Entercom Memphis stations
FM broadcasting is a method of radio broadcasting using frequency modulation technology. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. Theoretically wideband AM can offer good sound quality, provided the reception conditions are ideal. FM radio stations use the VHF frequencies; the term "FM band" describes the frequency band in a given country, dedicated to FM broadcasting. Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions: In the former Soviet republics, some former Eastern Bloc countries, the older 65.8–74 MHz band is used. Assigned frequencies are at intervals of 30 kHz; this band, sometimes referred to as the OIRT band, is being phased out in many countries.
In those countries the 87.5–108.0 MHz band is referred to as the CCIR band. In Japan, the band 76–95 MHz is used; the frequency of an FM broadcast station is an exact multiple of 100 kHz. In most of South Korea, the Americas, the Philippines and the Caribbean, only odd multiples are used. In some parts of Europe and Africa, only multiples are used. In the UK odd or are used. In Italy, multiples of 50 kHz are used. In most countries the maximum permitted frequency error is specified, the unmodulated carrier should be within 2000 Hz of the assigned frequency. There are other unusual and obsolete FM broadcasting standards in some countries, including 1, 10, 30, 74, 500, 300 kHz. However, to minimise inter-channel interference, stations operating from the same or geographically close transmitter sites tend to keep to at least a 500 kHz frequency separation when closer frequency spacing is technically permitted, with closer tunings reserved for more distantly spaced transmitters, as interfering signals are more attenuated and so have less effect on neighboring frequencies.
Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave. With FM, frequency deviation from the assigned carrier frequency at any instant is directly proportional to the amplitude of the input signal, determining the instantaneous frequency of the transmitted signal; because transmitted FM signals use more bandwidth than AM signals, this form of modulation is used with the higher frequencies used by TV, the FM broadcast band, land mobile radio systems. The maximum frequency deviation of the carrier is specified and regulated by the licensing authorities in each country. For a stereo broadcast, the maximum permitted carrier deviation is invariably ±75 kHz, although a little higher is permitted in the United States when SCA systems are used. For a monophonic broadcast, again the most common permitted. However, some countries specify a lower value for monophonic broadcasts, such as ±50 kHz. Random noise has a triangular spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest audio frequencies within the baseband.
This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. Reducing the high audio frequencies in the receiver reduces the high-frequency noise; these processes of boosting and reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively. The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 µs time constant is used. In the Americas and South Korea, 75 µs is used; this applies to both stereo transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing; the use of pre-emphasis becomes a problem because of the fact that many forms of contemporary music contain more high-frequency energy than the musical styles which prevailed at the birth of FM broadcasting. Pre-emphasizing these high frequency sounds would cause excessive deviation of the FM carrier. Modulation control devices are used to prevent this.
Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis. Long before FM stereo transmission was considered, FM multiplexing of other types of audio level information was experimented with. Edwin Armstrong who invented FM was the first to experiment with multiplexing, at his experimental 41 MHz station W2XDG located on the 85th floor of the Empire State Building in New York City; these FM multiplex transmissions started in November 1934 and consisted of the main channel audio program and three subcarriers: a fax program, a synchronizing signal for the fax program and a telegraph “order” channel. These original FM multiplex subcarriers were amplitude modulated. Two musical programs, consisting of both the Red and Blue Network program feeds of the NBC Radio Network, were transmitted using the same system of subcarrier modulation as part of a studio-to-transmitter link system. In April 1935, the AM subcarriers were replaced with much improved results.
The first FM subcarrier transmissions emanating from Major Armstrong's experimental station KE2XCC at Alpine, New Jersey occurred in 1948. These transmissions consisted of two-cha