FM broadcasting in the USA
Encyclopedia
FM broadcasting in the United States began in the 1930s at engineer and inventor Edwin Howard Armstrong's experimental station, W2XMN. The use of FM radio has been associated with higher sound quality in music radio.
FM radio station
s broadcast
at frequencies
of 87.8–108 MHz
. FM radio was developed in the United States by Edwin Armstrong
.
During the 1930s there were a small number of experimental (known as "Apex
") stations attempting to broadcast high fidelity audio using wide-bandwidth AM on VHF frequencies. In 1937 W1XOJ was the first FM radio station, granted a construction permit by the FCC
. On June 17, 1936, FM radio was demonstrated to the FCC for the first time. On January 5, 1940, Edwin H. Armstrong demonstrated FM broadcasting in a long-distance relay network, via five stations in five States. FM radio was assigned the 42 to 50 MHz band of the spectrum in 1940.
After World War II
, the FCC moved FM to the frequencies between 88 and 108 MHz on June 27, 1945. The change in frequency was said to be for avoiding possible interference problems between stations in nearby cities and to make "room" for more FM radio channels. However, the FCC was influenced by RCA chairman David Sarnoff
, who had the covert goal of disrupting the successful FM network that Edwin Armstrong had established on the old band. The 500,000 receivers built for the original FM radio band could be retrofitted with converters, but many were just replaced. The greater expense was to the radio stations themselves that had to rebuild their stations for the new FM radio band. The move of the FM band, an organized campaign of misinformation by RCA (a company that competed with FM radio by focusing on AM radio and the emerging technology of television), and adverse rulings by the FCC severely set back the development of FM radio. As late as 1947, in Detroit, there were only 3,000 FM receivers in use for the new band, and 21,000 obsolete ones for the old band. On March 1, 1941 W47NV began operations in Nashville
, Tennessee
, becoming the first modern commercial FM radio station. However, FM radio did not recover from the setback until the upsurge in high fidelity equipment in the late 1950s.
During the 1970s, FM radio experienced a golden age of integrity programming, with disc jockey
s playing what they wanted, including album cuts not designated as "singles
" and lengthy progressive rock
tracks.
To receive a station, an FM receiver is tuned to the center frequency of the station's channel. The lowest channel, channel 200, extends from 87.8 MHz to 88.0 MHz; thus its center frequency is 87.9 MHz. Channel 201 has a center frequency of 88.1 MHz, and so on, up to channel 300, which extends from 107.8 to 108.0 MHz and has a center frequency of 107.9 MHz.
Because each channel is 0.2 MHz wide, the center frequencies of adjacent channels differ by 0.2 MHz. Because the lowest channel is centered on 87.9 MHz, the tenths digit (in MHz) of the center frequency of any FM station in the United States is always an odd number. FM audio for television channel 6 is broadcast at a carrier frequency of 87.75 MHz, and many radios can tune down this low; a few low-power television stations licensed for channel 6 are operated solely for their right to use this frequency and broadcast only nominal video programming. For the same reason, assignment restrictions between TV stations on channel 6 and nearby FM stations are stringent: there are only two stations in the United States (KSFH
and translator K200AA) licensed to operate on 87.9 MHz, both due to being forced off of another channel. Therefore, in effect, the FM broadcast band comprises only FM channels 201 (88.1 MHz) through 300 (107.9 MHz).
Originally, FM stations in a market were generally spaced four channels (800 kHz) apart. This spacing was developed in response to problems perceived on the original FM band, mostly due to deficiencies in receiver technology of the time. With modern equipment, this is widely understood to be unnecessary, and in many countries shorter spacings are used. Other spacing restrictions relate to mixing products with nearby television, air-traffic control, and two-way radio systems as well as other FM broadcast stations. The most significant such taboo restricts the allocation of stations 10.6 and 10.8 MHz apart, to protect against mixing products which will interfere with an FM receiver's standard 10.7 MHz intermediate frequency
stage.
Commercial broadcasting
is licensed only on channels 221 through 300 (the upper 80 channels, frequencies between 92 and 108 MHz), with 200 through 220 (the lower 21 channels, frequencies between 88 and 92 MHz) being reserved for non-commercial educational
(NCE) broadcasting. In some "Twin city" markets close to the Canadian
or Mexican
border, such as Detroit
, Michigan
and Windsor
, Ontario
, or San Diego
, California
and Tijuana
, Baja California
, commercial stations operating from those countries target U.S. audiences on "reserved band" channels, as neither Canada nor Mexico has such a reservation. Because of this necessary sharing, the FCC reserves a few other channels for such NCE stations.
FM stations in the U.S. are now assigned based on a table of separation distance values from currently licensed stations, based on station "class" (power output, antenna height, and geographical location). These regulations (see Docket 80-90) have resulted in approximately double the number of possible stations, and increases in allowable power levels, over the original bandplan
scheme described above. All powers are specified as effective radiated power
(ERP), which takes into account the magnifying effect (gain
) of multiple antenna elements.
The U.S. is divided into Zone I (roughly the northeastern quarter of the U.S. mainland, excluding the far northern areas), Zone I-A (California
south of 40 degrees latitude
, U.S. Virgin Islands, Puerto Rico
), and Zone II (all other locations). The highest-power stations are class C in zone II, and class B in the others. There are no B stations in zone II, nor any C stations in the others. (See the list of broadcast station classes.) Canada is also divided in this manner, based on the most highly-populated regions.
High power is useful in penetrating buildings, diffracting around hills, and refracting for some distance beyond the horizon. 100,000 watt FM stations can regularly be heard up to 100 miles (160 km) away, and farther (e.g., 150 miles, 240 km) if there are no competing signals.
A few old "grandfathered" stations do not conform to these power rules. WBCT
(93.7) in Grand Rapids
, Michigan
, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. This huge power level does not usually help to increase range as much as one might expect, because VHF frequencies travel in nearly straight lines over the horizon and off into space. Nevertheless, when there were fewer FM stations competing, this station could be heard near Bloomington, Illinois, almost 300 miles (482.8 km) distant.
History of FM radio in the U.S.
In the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
FM radio station
Radio station
Radio broadcasting is a one-way wireless transmission over 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...
s broadcast
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
at frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
of 87.8–108 MHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
. FM radio was developed in the United States by Edwin Armstrong
Edwin Armstrong
Edwin Howard Armstrong was an American electrical engineer and inventor. Armstrong was the inventor of modern frequency modulation radio....
.
During the 1930s there were a small number of experimental (known as "Apex
Apex (radio band)
Apex was an experimental radio broadcasting system introduced in the United States in 1934 that used high frequencies between roughly 25 and 42 MHz and wideband AM modulation to achieve high fidelity sound with less static and distortion than medium wave AM stations in the so-called standard...
") stations attempting to broadcast high fidelity audio using wide-bandwidth AM on VHF frequencies. In 1937 W1XOJ was the first FM radio station, granted a construction permit by the FCC
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
. On June 17, 1936, FM radio was demonstrated to the FCC for the first time. On January 5, 1940, Edwin H. Armstrong demonstrated FM broadcasting in a long-distance relay network, via five stations in five States. FM radio was assigned the 42 to 50 MHz band of the spectrum in 1940.
After World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, the FCC moved FM to the frequencies between 88 and 108 MHz on June 27, 1945. The change in frequency was said to be for avoiding possible interference problems between stations in nearby cities and to make "room" for more FM radio channels. However, the FCC was influenced by RCA chairman David Sarnoff
David Sarnoff
David Sarnoff was an American businessman and pioneer of American commercial radio and television. He founded the National Broadcasting Company and throughout most of his career he led the Radio Corporation of America in various capacities from shortly after its founding in 1919 until his...
, who had the covert goal of disrupting the successful FM network that Edwin Armstrong had established on the old band. The 500,000 receivers built for the original FM radio band could be retrofitted with converters, but many were just replaced. The greater expense was to the radio stations themselves that had to rebuild their stations for the new FM radio band. The move of the FM band, an organized campaign of misinformation by RCA (a company that competed with FM radio by focusing on AM radio and the emerging technology of television), and adverse rulings by the FCC severely set back the development of FM radio. As late as 1947, in Detroit, there were only 3,000 FM receivers in use for the new band, and 21,000 obsolete ones for the old band. On March 1, 1941 W47NV began operations in Nashville
Nashville, Tennessee
Nashville is the capital of the U.S. state of Tennessee and the county seat of Davidson County. It is located on the Cumberland River in Davidson County, in the north-central part of the state. The city is a center for the health care, publishing, banking and transportation industries, and is home...
, Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
, becoming the first modern commercial FM radio station. However, FM radio did not recover from the setback until the upsurge in high fidelity equipment in the late 1950s.
During the 1970s, FM radio experienced a golden age of integrity programming, with disc jockey
Disc jockey
A disc jockey, also known as DJ, is a person who selects and plays recorded music for an audience. Originally, "disc" referred to phonograph records, not the later Compact Discs. Today, the term includes all forms of music playback, no matter the medium.There are several types of disc jockeys...
s playing what they wanted, including album cuts not designated as "singles
Single (music)
In music, a single or record single is a type of release, typically a recording of fewer tracks than an LP or a CD. This can be released for sale to the public in a variety of different formats. In most cases, the single is a song that is released separately from an album, but it can still appear...
" and lengthy progressive rock
Progressive rock
Progressive rock is a subgenre of rock music that developed in the late 1960s and early 1970s as part of a "mostly British attempt to elevate rock music to new levels of artistic credibility." John Covach, in Contemporary Music Review, says that many thought it would not just "succeed the pop of...
tracks.
FM radio channel assignments in the U.S.
In the United States, frequency-modulated broadcasting stations operate in a frequency band extending from 87.8 MHz to 108.0 MHz, for a total of 20.2 MHz. It is divided into 101 channels, each 0.2 MHz wide, designated "channel 200" through "channel 300." In actual practice, no one (except the FCC) uses these channel numbers; the frequencies are used instead.To receive a station, an FM receiver is tuned to the center frequency of the station's channel. The lowest channel, channel 200, extends from 87.8 MHz to 88.0 MHz; thus its center frequency is 87.9 MHz. Channel 201 has a center frequency of 88.1 MHz, and so on, up to channel 300, which extends from 107.8 to 108.0 MHz and has a center frequency of 107.9 MHz.
Because each channel is 0.2 MHz wide, the center frequencies of adjacent channels differ by 0.2 MHz. Because the lowest channel is centered on 87.9 MHz, the tenths digit (in MHz) of the center frequency of any FM station in the United States is always an odd number. FM audio for television channel 6 is broadcast at a carrier frequency of 87.75 MHz, and many radios can tune down this low; a few low-power television stations licensed for channel 6 are operated solely for their right to use this frequency and broadcast only nominal video programming. For the same reason, assignment restrictions between TV stations on channel 6 and nearby FM stations are stringent: there are only two stations in the United States (KSFH
KSFH
KSFH FM 87.9 is a student radio station broadcasting an active rock radio format. Licensed to serve Mountain View, California, USA, the station's broadcast range is the San Francisco Bay Area. The station is owned by private school Saint Francis High School, and is completely run by its students,...
and translator K200AA) licensed to operate on 87.9 MHz, both due to being forced off of another channel. Therefore, in effect, the FM broadcast band comprises only FM channels 201 (88.1 MHz) through 300 (107.9 MHz).
Originally, FM stations in a market were generally spaced four channels (800 kHz) apart. This spacing was developed in response to problems perceived on the original FM band, mostly due to deficiencies in receiver technology of the time. With modern equipment, this is widely understood to be unnecessary, and in many countries shorter spacings are used. Other spacing restrictions relate to mixing products with nearby television, air-traffic control, and two-way radio systems as well as other FM broadcast stations. The most significant such taboo restricts the allocation of stations 10.6 and 10.8 MHz apart, to protect against mixing products which will interfere with an FM receiver's standard 10.7 MHz intermediate frequency
Intermediate frequency
In communications and electronic engineering, an intermediate frequency is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called...
stage.
Commercial broadcasting
Commercial broadcasting
Commercial broadcasting is the broadcasting of television programs and radio programming by privately owned corporate media, as opposed to state sponsorship...
is licensed only on channels 221 through 300 (the upper 80 channels, frequencies between 92 and 108 MHz), with 200 through 220 (the lower 21 channels, frequencies between 88 and 92 MHz) being reserved for non-commercial educational
Non-commercial educational
The term non-commercial educational applies to a radio station or TV station that does not accept on air advertisements , as defined in the United States by the Federal Communications Commission . NCE stations do not pay broadcast license fees for their non-profit uses of the radio spectrum...
(NCE) broadcasting. In some "Twin city" markets close to the Canadian
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...
or Mexican
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
border, such as Detroit
Detroit, Michigan
Detroit is the major city among the primary cultural, financial, and transportation centers in the Metro Detroit area, a region of 5.2 million people. As the seat of Wayne County, the city of Detroit is the largest city in the U.S. state of Michigan and serves as a major port on the Detroit River...
, 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"....
and Windsor
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...
, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, or San Diego
San Diego, California
San Diego is the eighth-largest city in the United States and second-largest city in California. The city is located on the coast of the Pacific Ocean in Southern California, immediately adjacent to the Mexican border. The birthplace of California, San Diego is known for its mild year-round...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and Tijuana
Tijuana
Tijuana 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...
, Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
, commercial stations operating from those countries target U.S. audiences on "reserved band" channels, as neither Canada nor Mexico has such a reservation. Because of this necessary sharing, the FCC reserves a few other channels for such NCE stations.
FM stations in the U.S. are now assigned based on a table of separation distance values from currently licensed stations, based on station "class" (power output, antenna height, and geographical location). These regulations (see Docket 80-90) have resulted in approximately double the number of possible stations, and increases in allowable power levels, over the original bandplan
Bandplan
A bandplan or band plan is a plan for using a particular band of radio frequencies, that are a portion of the electromagnetic spectrum . Each bandplan defines the frequency range to be included, how channels are to be defined, and what will be carried on those channels...
scheme described above. All powers are specified as effective radiated power
Effective radiated power
In radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
(ERP), which takes into account the magnifying effect (gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
) of multiple antenna elements.
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
south of 40 degrees latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
, U.S. Virgin Islands, Puerto Rico
Puerto Rico
Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...
), and Zone II (all other locations). The highest-power stations are class C in zone II, and class B in the others. There are no B stations in zone II, nor any C stations in the others. (See the list of broadcast station classes.) Canada is also divided in this manner, based on the most highly-populated regions.
High power is useful in penetrating buildings, diffracting around hills, and refracting for some distance beyond the horizon. 100,000 watt FM stations can regularly be heard up to 100 miles (160 km) away, and farther (e.g., 150 miles, 240 km) if there are no competing signals.
A few old "grandfathered" stations do not conform to these power rules. WBCT
WBCT
WBCT is a radio station in Grand Rapids, Michigan with a country music format.The station has had a country music format since July 24, 1992. WBCT's transmitter is at the WWMT Tower in Gun Lake . The antenna is approximately up the structure...
(93.7) in Grand Rapids
Grand Rapids, Michigan
Grand Rapids is a city in the U.S. state of Michigan. The city is located on the Grand River about 40 miles east of Lake Michigan. As of the 2010 census, the city population was 188,040. In 2010, the Grand Rapids metropolitan area had a population of 774,160 and a combined statistical area, Grand...
, 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"....
, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. This huge power level does not usually help to increase range as much as one might expect, because VHF frequencies travel in nearly straight lines over the horizon and off into space. Nevertheless, when there were fewer FM stations competing, this station could be heard near Bloomington, Illinois, almost 300 miles (482.8 km) distant.
See also
- FM broadcastingFM broadcastingFM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
- FM broadcast bandFM broadcast bandThe FM broadcast band, used for FM broadcast radio by radio stations, differs between different parts of the world. In Europe and Africa , it spans from 87.5 to 108.0 megahertz , while in America it goes only from 88.0 to 108.0 MHz. The FM broadcast band in Japan uses 76.0 to 90 MHz...
- AM broadcastingAM broadcastingAM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave...
- AM stereoAM stereoAM stereo is a term given to a series of mutually incompatible techniques for wireless radio broadcasting stereo audio in the AM band in a manner that is compatible with standard AM receivers...
- List of broadcast station classes
- History of radioHistory of radioThe early history of radio is the history of technology that produced radio instruments that use radio waves. Within the timeline of radio, many people contributed theory and inventions in what became radio. Radio development began as "wireless telegraphy"...
- RDS (Radio Data System)Radio Data SystemRadio Data System, or RDS, is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardises several types of information transmitted, including time, station identification and programme information.Radio Broadcast Data...
- Oldest radio stationOldest radio stationThe title of oldest radio station is disputed by several in Europe , and in the United States and Canada.Several potential contenders for the title of "oldest radio station" are listed below, organized by sign-on date:-Stations:...
External links
Related websites- Stereo for Dummies Many graphs that show waveforms at different points in the FM Multiplex process
- FM Transmitters