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Henderson, Nevada Henderson is a city in Clark County, Nevada, United States, about southeast of downtown Las Vegas. It is the second largest city in Nevada, after Las Vegas, with an estimated population of 320,189 in 2019. The city is part of the Las Vegas Valley. ...
and broadcasts at a frequency of 95.5 MHz. FM broadcasting is a method of
radio broadcasting , Sweden , Norway Radio broadcasting is transmission of audio signal, audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-base ...
using
frequency modulation Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. In analog frequen ...
(FM). Invented in 1933 by American engineer
Edwin Armstrong Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American electrical engineer and inventor, who developed FM (frequency modulation) radio and the superheterodyne receiver system. He held 42 patents and received numerous award ...
, wide-band FM is used worldwide to provide
high fidelity High fidelity (often shortened to hi-fi or hifi) is a term used by listeners, audiophiles, and home audio enthusiasts to refer to high-quality reproduction of sound. This is in contrast to the lower quality sound produced by inexpensive audio e ...
sound over broadcast
radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitte ...
. FM broadcasting is capable of higher fidelity—that is, more accurate reproduction of the original program sound—than other broadcasting technologies, such as
AM broadcasting AM broadcasting is radio broadcasting using amplitude modulation (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for medium wave (also known as "AM band") transmiss ...
. Therefore, FM is used for most broadcasts of
music Music is the art of arranging sounds in time to produce a composition through the elements of melody, harmony, rhythm, and timbre. It is one of the universal cultural aspects of all human societies. General definitions of music include common e ...
or general audio (in the audio spectrum). FM
radio station , Sweden , Norway Radio broadcasting is transmission of audio signal, audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-base ...
s use the
very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF a ...
range of
radio frequencies Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper ...
.


Broadcast bands

Throughout the world, the FM broadcast band falls within the VHF part of the
radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 30 Hz to 300 GHz. Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunic ...
. Usually 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions: * In the
former Soviet republics The post-Soviet states, also known as the former Soviet Union (FSU), the former Soviet Republics and in Russia as the near abroad (russian: бли́жнее зарубе́жье, blizhneye zarubezhye), are the 15 sovereign states that emerged and re ...

former Soviet republics
, and some former
Eastern Bloc#REDIRECT Eastern Bloc#REDIRECT Eastern Bloc {{R from other capitalisation ...
{{R from other capitalisation ...

Eastern Bloc
countries, the older 65.8–74 MHz band is also used. Assigned frequencies are at intervals of 30 kHz. This band, sometimes referred to as the
OIRT The International Radio and Television Organisation (official name in French: Organisation Internationale de Radiodiffusion et de Télévision or OIRT (before 1960 International Broadcasting Organization (IBO), official name in French: ''Organisa ...
band, is slowly being phased out. Where the OIRT band is used, the 87.5–108.0 MHz band is referred to as the CCIR band. * In
Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperial Seal of Japan.svg , alt_coat = Golden circle subdivided ...
, the band 76–95 MHz is used. The frequency of an FM broadcast station (more strictly its assigned nominal center frequency) is usually a multiple of 100 kHz. In most of
South Korea South Korea (Korean: /, RR: ''Hanguk''; literally /, RR: ''Namhan'', or /, MR: ''Namchosŏn'' in North Korean usage), officially the Republic of Korea (ROK; Korean: /, RR: ''Daehan Minguk''), is a country in East Asia, constituting the ...
,
the Americas The Americas (also collectively called America) is a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with their associated i ...
, the
Philippines The Philippines (; fil, Pilipinas or ''Filipinas'' ), officially the Republic of the Philippines ( fil, Republika ng Pilipinas), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republika sang ...

Philippines
and the
Caribbean The Caribbean (, ; es, Caribe; french: Caraïbes; ht, Karayib; also gcf, label=Antillean Creole, Kawayib; nl, Caraïben; Papiamento: ) is a region of the Americas that comprises the Caribbean Sea, its surrounding coasts, and its islands (some of w ...
, only odd multiples are used. Some other countries follow this plan because of the import of vehicles, principally from the United States, with radios that can only tune to these frequencies. In some parts of
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It comprises the westernmost peninsulas of the continental landmass of Eurasia, and is bordered by the Arctic Ocean to the north, the Atlant ...
,
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is the world's largest island, located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is an autonomous territory* * * within the Kingdom of Denmar ...
and
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area and 20% of it ...

Africa
, only even multiples are used. In the UK odd or even are used. In
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a continental part, delimited by the Alps, a peninsula and several islands surrounding it. Italy is located in Southern Europ ...
, multiples of 50 kHz are used. In most countries the maximum permitted frequency error of the unmodulated carrier is specified, which typically should be within 2000 Hz of the assigned frequency. There are other unusual and obsolete FM broadcasting standards in some countries, with non-standard spacings of 1, 10, 30, 74, 500, and 300 kHz. 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 even when closer frequency spacing is technically permitted. The
ITU 260px, ITU Monument, Bern The International Telecommunication Union is a specialized agency of the United Nations responsible for all matters related to information and communication technologies. Established in 1865 as the International Tele ...
publishes Protection Ratio graphs which give the minimum spacing between frequencies based on their relative strengths. Only broadcast stations with large enough geographic separations between their coverage areas can operate on close or the same frequencies.


Technology

's 94.9 MHz, 48 kW transmitter on Lake Mountain, Utah. It radiates circularly polarized radio waves.


Modulation

Frequency modulation Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. In analog frequen ...
or FM is a form of modulation which conveys information by varying the frequency of a
carrier wave upright=1.4, The frequency spectrum of a typical radio signal from an AM or FM radio transmitter. The horizontal axis is frequency; the vertical axis is signal amplitude or power. It consists of a signal (C) at the carrier wave frequency ''f''C, wi ...
; the older
amplitude modulation#REDIRECT Amplitude modulation#REDIRECT Amplitude modulation {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
or AM varies the amplitude of the carrier, with its frequency remaining constant. With FM,
frequency deviationFrequency deviation (f_) is used in FM radio to describe the difference between the minimum and maximum extent of a frequency modulated signal, and the nominal center or carrier frequency. The term is sometimes mistakenly used as synonymous with freq ...
from the assigned
carrier frequency upright=1.4, The frequency spectrum of a typical radio signal from an AM or FM radio transmitter. The horizontal axis is frequency; the vertical axis is signal amplitude or power. It consists of a signal (C) at the carrier wave frequency ''f''C, wi ...
at any instant is directly proportional to the amplitude of the (audio) input signal, determining the instantaneous frequency of the transmitted signal. Because transmitted FM signals use more
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thro ...
than AM signals, this form of modulation is commonly used with the higher ( VHF or UHF) frequencies used by TV, the
FM broadcast band The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations. The range of frequencies used differs between different parts of the world. In Europe and Africa (defined as International Telecommunication Union (ITU ...
, and
land mobile radio system#REDIRECT Land mobile radio system {{R from other capitalisation ...
s. The maximum frequency deviation of the carrier is usually 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 maximum deviation is ±75 kHz. However, some countries specify a lower value for monophonic broadcasts, such as ±50 kHz. Instantaneous spectrum and waterfall plot in the FM broadcast band showing three strong local stations; speech and music show different patterns of frequency vs. time. When the transmitted audio is quiet, the 19 kHz stereo pilot tones can be resolved in the spectrum.


Pre-emphasis and de-emphasis

Random noise has a ''triangular'' frequency spectrum, spectral distribution in an FM system, with the effect that noise occurs predominantly at the higher audio
frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. Frequency is measured in hertz (Hz) which is e ...
within the
baseband Baseband is a signal that has a near-zero frequency range, i.e. a spectral magnitude that is nonzero only for frequencies in the vicinity of the origin (termed ''f'' = 0) and negligible elsewhere. In telecommunications and signal processing, baseb ...
. This can be offset, to a limited extent, by boosting the high frequencies before
transmission Transmission may refer to: Science and technology * Power transmission ** Electric power transmission * Transmission (mechanics), a machine which provides controlled application of power * Transmission (telecommunications), the process of sending ...
and reducing them by a corresponding amount in the receiver. Reducing the high audio frequencies in the receiver also reduces the high-frequency noise. These processes of boosting and then reducing certain frequencies are known as
pre-emphasis Typically, prior to some process, such as transmission over cable, or recording to phonograph record or tape, the input frequency range most susceptible to noise is boosted. This is referred to as "pre-emphasis"before the process the signal will und ...
and
de-emphasis Typically, prior to some process, such as transmission over cable, or recording to phonograph record or tape, the input frequency range most susceptible to noise is boosted. This is referred to as "pre-emphasis"before the process the signal will und ...
, respectively. The amount of pre-emphasis and de-emphasis used is defined by the
time constantIn physics and engineering, the time constant, usually denoted by the Greek letter (tau), is the parameter characterizing the response to a step input of a first-order, linear time-invariant (LTI) system.Concretely, a first-order LTI system is a sys ...
of a simple
RC filter A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. It may be driven by a voltage or current source and these will produce different responses. A first order RC cir ...
circuit. In most of the world a 50  µs time constant is used. In the Americas and
South Korea South Korea (Korean: /, RR: ''Hanguk''; literally /, RR: ''Namhan'', or /, MR: ''Namchosŏn'' in North Korean usage), officially the Republic of Korea (ROK; Korean: /, RR: ''Daehan Minguk''), is a country in East Asia, constituting the ...
, 75 µs is used. This applies to both
mono Mono may refer to: Common meanings * Infectious mononucleosis, "the kissing disease" * Mono-, a numerical prefix representing anything single Music Performers * Mono (Japanese band), a Japanese instrumental band * Mono (UK band), an English elec ...
and
stereo STEREO (Solar Terrestrial Relations Observatory) is a solar observation mission. Two nearly identical spacecraft were launched in 2006 into orbits around the Sun that cause them to respectively pull farther ahead of and fall gradually behind the ...
transmissions. For stereo, pre-emphasis is applied to the left and right channels before
multiplexing In telecommunications and computer networks, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource. For ex ...
. 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 Carrier may refer to: Entertainment * ''Carrier'' (album), a 2013 album by The Dodos * ''Carrier'' (game), a South Pacific World War II board game * ''Carrier'' (TV series), a ten-part documentary miniseries that aired on PBS in April 2008 * ''Car ...
. Modulation control (limiter) devices are used to prevent this. Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis; e.g., dbx in the
BTSC Multichannel Television Sound, better known as MTS, is the method of encoding three additional audio channels into an analog NTSC-format audio carrier. It was developed by the Broadcast Television Systems Committee, an industry group, and sometimes ...
TV sound system, or none at all. Pre-emphasis and de-emphasis was used in the earliest days of FM broadcasting. According to a BBC report from 1946, 100 µs was originally considered in the US, but 75 µs subsequently adopted.


Stereo FM

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 The Empire State Building is a 102-story Art Deco skyscraper in Midtown Manhattan in New York City, United States. It was designed by Shreve, Lamb & Harmon and built from 1930 to 1931. Its name is derived from "Empire State", the nickname of ...
in
New York City New York City (NYC), often simply called New York, is the most populous city in the United States. With an estimated 2019 population of 8,336,817 distributed over about , New York City is also the most densely populated major city in the Unit ...

New York City
. These FM multiplex transmissions started in November 1934 and consisted of the main channel audio program and three
subcarriers A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadc ...
: 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 simultaneously 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 by FM subcarriers, 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-channel audio programs, binaural audio programs and a fax program. The original subcarrier frequency used at KE2XCC was 27.5 kHz. The IF bandwidth was ±5 kHz, as the only goal at the time was to relay AM radio-quality audio. This transmission system used 75 µs audio pre-emphasis like the main monaural audio and subsequently the multiplexed stereo audio. In the late 1950s, several systems to add
stereo STEREO (Solar Terrestrial Relations Observatory) is a solar observation mission. Two nearly identical spacecraft were launched in 2006 into orbits around the Sun that cause them to respectively pull farther ahead of and fall gradually behind the ...
to FM radio were considered by the
FCC The Federal Communications Commission (FCC) is an independent agency of the United States government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction over the ...
. Included were systems from 14 proponents including Crosby, Halstead, Electrical and Musical Industries, Ltd ( EMI), Zenith, and General Electric. The individual systems were evaluated for their strengths and weaknesses during field tests in
Uniontown, Pennsylvania Uniontown is a city in Fayette County, Pennsylvania, United States, southeast of Pittsburgh and part of the Greater Pittsburgh Region. The population was 10,372 at the 2010 census, down from 12,422 at the 2000 census. It is the county seat and la ...
, using
KDKA-FM KDKA-FM (93.7 MHz, "SportsRadio 93.7 The Fan") is a commercial FM radio station licensed to serve Pittsburgh, Pennsylvania. The station is owned by Audacy, Inc. through licensee Audacy License, LLC and broadcasts a sports radio format. Studios are ...
in Pittsburgh as the originating station. The Crosby system was rejected by the FCC because it was incompatible with existing subsidiary communications authorization (SCA) services which used various subcarrier frequencies including 41 and 67 kHz. Many revenue-starved FM stations used SCAs for "storecasting" and other non-broadcast purposes. The Halstead system was rejected due to lack of high frequency stereo separation and reduction in the main channel signal-to-noise ratio. The GE and Zenith systems, so similar that they were considered theoretically identical, were formally approved by the FCC in April 1961 as the standard stereo FM broadcasting method in the United States and later adopted by most other countries. It is important that stereo broadcasts be compatible with mono receivers. For this reason, the left (L) and right (R) channels are algebraically encoded into sum (L+R) and difference (L−R) signals. A mono receiver will use just the L+R signal so the listener will hear both channels through the single loudspeaker. A stereo receiver will add the difference signal to the sum signal to recover the left channel, and subtract the difference signal from the sum to recover the right channel. The (L+R) signal is limited to 30 Hz to 15 kHz to protect a 19 kHz pilot signal. The (L−R) signal, which is also limited to 15 kHz, is amplitude modulated onto a 38 kHz double-sideband suppressed-carrier (DSB-SC) signal, thus occupying 23 kHz to 53 kHz. A 19 kHz ± 2 Hz
pilot tone In telecommunications, a pilot signal is a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes. Uses in different communication sy ...
, at exactly half the 38 kHz sub-carrier frequency and with a precise phase relationship to it, as defined by the formula below, is also generated. The pilot is transmitted at 8–10% of overall
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains information ...
level and used by the receiver to identify a stereo transmission and to regenerate the 38 kHz sub-carrier with the correct phase. The composite stereo multiplex signal contains the Main Channel (L+R), the pilot tone, and the (L−R) difference signal. This composite signal, along with any other sub-carriers, modulates the FM transmitter. The terms composite, multiplex and even MPX are used interchangeably to describe this signal. The instantaneous deviation of the transmitter carrier frequency due to the stereo audio and pilot tone (at 10% modulation) is :\left 0.9_\left_[_\frac_+_\frac\sin4\pi_f_pt_\right_+_0.1\sin2\pi_f_pt_\right_.html" ;"title="\frac_+_\frac\sin4\pi_f_pt_\right_.html" ;"title="0.9 \left [ \frac + \frac\sin4\pi f_pt \right ">0.9 \left [ \frac + \frac\sin4\pi f_pt \right + 0.1\sin2\pi f_pt \right ">\frac_+_\frac\sin4\pi_f_pt_\right_.html" ;"title="0.9 \left [ \frac + \frac\sin4\pi f_pt \right ">0.9 \left [ \frac + \frac\sin4\pi f_pt \right + 0.1\sin2\pi f_pt \right \times 75~\mathrm where A and B are the pre-emphasized left and right audio signals and f_p=19 kHz is the frequency of the pilot tone. Slight variations in the peak deviation may occur in the presence of other subcarriers or because of local regulations. Another way to look at the resulting signal is that it alternates between left and right at 38 kHz, with the phase determined by the 19 kHz pilot signal. Most stereo encoders use this switching technique to generate the 38 kHz subcarrier, but practical encoder designs need to incorporate circuitry to deal with the switching harmonics. Converting the multiplex signal back into left and right audio signals is performed by a decoder, built into stereo receivers. Again, the decoder can use a switching technique to recover the left and right channels. In addition, for a given RF level at the receiver, the signal-to-noise ratio and multipath distortion for the stereo signal will be worse than for the mono receiver. For this reason many stereo FM receivers include a stereo/mono switch to allow listening in mono when reception conditions are less than ideal, and most car radios are arranged to reduce the separation as the signal-to-noise ratio worsens, eventually going to mono while still indicating a stereo signal is being received. As with monaural transmission, it is normal practice to apply pre-emphasis to the left and right channels before encoding and to apply de-emphasis at the receiver after decoding. In the U.S. around 2010, using single-sideband modulation for the stereo subcarrier was proposed. It was theorized to be more spectrum-efficient and to produce a 4 dB s/n improvement at the receiver, and it was claimed that multipath distortion would be reduced as well. A handful of radio stations around the country broadcast stereo in this way, under FCC experimental authority. It may not be compatible with very old receivers, but it is claimed that no difference can be heard with most newer receivers. At present, the FCC rules do not allow this mode of stereo operation.


Quadraphonic FM

In 1969, Louis Dorren invented the Quadraplex system of single station, discrete, compatible four-channel FM broadcasting. There are two additional subcarriers in the Quadraplex system, supplementing the single one used in standard stereo FM. The baseband layout is as follows: * 50 Hz to 15 kHz main channel (sum of all 4 channels) (LF+LR+RF+RR) signal, for mono FM listening compatibility. * 23 to 53 kHz (sine quadrature subcarrier) (LF+LR) − (RF+RR) left minus right difference signal. This signal's modulation in algebraic sum and difference with the main channel is used for 2 channel stereo listener compatibility. * 23 to 53 kHz (cosine quadrature 38 kHz subcarrier) (LF+RR) − (LR+RF) Diagonal difference. This signal's modulation in algebraic sum and difference with the main channel and all the other subcarriers is used for the Quadraphonic listener. * 61 to 91 kHz (sine quadrature 76 kHz subcarrier) (LF+RF) − (LR+RR) Front-back difference. This signal's modulation in algebraic sum and difference with the main channel and all the other subcarriers is also used for the Quadraphonic listener. * 105 kHz SCA subcarrier, phase-locked to 19 kHz pilot, for reading services for the blind, background music, etc. The normal stereo signal can be considered as switching between left and right channels at 38 kHz, appropriately band-limited. The quadraphonic signal can be considered as cycling through LF, LR, RF, RR, at 76 kHz. Early efforts to transmit discrete four-channel quadraphonic music required the use of two FM stations; one transmitting the front audio channels, the other the rear channels. A breakthrough came in 1970 when
KIOI KIOI (101.3 FM) is a hot adult contemporary-formatted radio station licensed to San Francisco, California and owned by iHeartMedia. The station transmitter is in San Bruno Mountains, while studios are in the SoMa district of San Francisco. KPEN ...
(''K-101'') in San Francisco successfully transmitted true quadraphonic sound from a single FM station using the Quadraplex system under Special Temporary Authority from the
FCC The Federal Communications Commission (FCC) is an independent agency of the United States government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction over the ...
. Following this experiment, a long-term test period was proposed that would permit one FM station in each of the top 25 U.S. radio markets to transmit in Quadraplex. The test results hopefully would prove to the FCC that the system was compatible with existing two-channel stereo transmission and reception and that it did not interfere with adjacent stations. There were several variations on this system submitted by GE, Zenith, RCA, and Denon for testing and consideration during the National Quadraphonic Radio Committee field trials for the FCC. The original Dorren Quadraplex System outperformed all the others and was chosen as the national standard for Quadraphonic FM broadcasting in the United States. The first commercial FM station to broadcast quadraphonic program content was WIQB (now called
WWWW-FM WWWW-FM (''W4 Country''), is a country music radio station based in Ann Arbor, Michigan, broadcasting on 102.9 MHz. Owned by Cumulus Media, WWWW-FM has a transmitter at its studios off of South Wagner Road to the northwest of downtown Ann Arbor. ...
) in
Ann ArborANN may refer to: Media * All Night Nippon, Japan * All-Nippon News Network, Japan * Arab News Network, exile Syrian * Asia News Network, Asia * Anime News Network, online * Adventist News Network, online Transportation * Annan railway station, fr ...
/
Saline, Michigan Saline is a city in Washtenaw County, Michigan, Washtenaw County in the U.S. state of Michigan. As of the 2010 census, its population was 8,810. The city is popular for its annual Celtic Festival, which attracts people from all over the U.S. and ...
under the guidance of Chief Engineer Brian Jeffrey Brown.


Noise reduction

Various attempts to add analog
noise reduction Noise reduction is the process of removing noise from a signal. Noise reduction techniques exist for audio and images. Noise reduction algorithms may distort the signal to some degree. All signal processing devices, both analog and digital, have ...
to FM broadcasting were carried out in the 1970s and 1980s: A commercially unsuccessful noise reduction system used with FM radio in some countries during the late 1970s, Dolby FM was similar to
Dolby B A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording. White, Paul. Tape Noise Reduction. Sound on Sound, January 1996Archived at the Waybac ...
but used a modified 25 µs pre-emphasis time constant and a frequency selective
companding After compressing, before expanding In telecommunication and signal processing, companding (occasionally called compansion) is a method of mitigating the detrimental effects of a channel with limited dynamic range. The name is a portmanteau of th ...
arrangement to reduce noise. The pre-emphasis change compensates for the excess treble response that otherwise would make listening difficult for those without Dolby decoders. A similar system named High Com FM was tested in Germany between July 1979 and December 1981 by IRT. It was based on the
Telefunken Telefunken was a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the Allgemeine Elektricitäts-Gesellschaft (AEG) (''General electricity company''). Brief overview The name "Telef ...
High Com broadband compander system, but was never introduced commercially in FM broadcasting. Yet another system was the
CX CX or Cx may refer to: Businesses and organizations * Cathay Pacific, a Hong Kong airline (IATA code CX) * Cemex, a Mexican building materials supply company (New York Stock Exchange symbol "CX") * Connex Melbourne, a former Australian train ope ...
-based noise reduction system FMX implemented in some radio broadcasting stations in the United States in the 1980s.


Other subcarrier services

FM broadcasting has included subsidiary communications authorization (SCA) services capability since its inception, as it was seen as another service which licensees could use to create additional income. Use of SCAs was particularly popular in the US, but much less so elsewhere. Uses for such subcarriers include radio reading services for the blindness, blind, which became common and remain so, private data transmission services (for example sending stock market information to stockbrokers or stolen credit card number denial lists to stores,) subscription commercial-free background music services for shops, paging ("beeper") services, non-native-language programming, and providing a program feed for AM transmitters of AM/FM stations. SCA subcarriers are typically 67 kHz and 92 kHz. Initially the users of SCA services were private analog audio channels which could be used internally or leased, for example Muzak (brand), Muzak-type services. There were experiments with quadraphonic sound. If a station does not broadcast in stereo, everything from 23 kHz on up can be used for other services. The guard band around 19 kHz (±4 kHz) must still be maintained, so as not to trigger stereo decoders on receivers. If there is stereo, there will typically be a guard band between the upper limit of the DSBSC stereo signal (53 kHz) and the lower limit of any other subcarrier. Digital data, Digital services are now also available. A 57 kHz subcarrier (phase-locked loop, phase locked to the third harmonic of the stereo pilot tone) is used to carry a low-bandwidth digital Radio Data System signal, providing extra features such as station name, Alternative frequency, Alternative Frequency (AF), traffic data for commercial GPS receivers and Radio text (RT). This narrowband signal runs at only 1,187.5 bits per second, thus is only suitable for text. A few Proprietary protocol, proprietary systems are used for private communications. A variant of Radio Data System, RDS is the North American Radio Data System, RBDS or "smart radio" system. In Germany the analog ARI system was used prior to RDS to alert motorists that traffic announcements were being broadcast (without disturbing other listeners). Plans to use ARI for other European countries led to the development of RDS as a more powerful system. RDS is designed to be capable of being used alongside ARI despite using identical subcarrier frequencies. In the United States and Canada, digital radio services are being deployed within the FM band rather than using Digital Audio Broadcasting, Eureka 147 or the Japanese standard ISDB. This in-band on-channel approach, as do all digital radio techniques, makes use of advanced audio compression (data), compressed audio. The proprietary iBiquity system, branded as "HD Radio", currently is authorized for "hybrid" mode operation, wherein both the conventional analog FM carrier and digital sideband subcarriers are transmitted. Eventually, presuming widespread deployment of HD Radio receivers, the analog services could theoretically be discontinued and the FM band become all digital.


Transmission power

The output power of a FM broadcasting transmitter is one of the parameters that governs how far a transmission will cover. The other important parameters are the height of the transmitting antenna and the Antenna gain. Transmitter powers should be carefully chosen so that the required area is covered without causing interference to other stations further away. Practical transmitter powers range from a few milliwatts to 80 kW. As transmitter powers increase above a few kilowatts, the operating costs become high and only viable for large stations. The efficiency of larger transmitters is now better than 70% (AC power in to RF power out) for FM only transmission. This compares to 50% before high efficiency switch-mode power supplies and LDMOS amplifiers were used. Efficiency drops dramatically if any digital HD Radio service is added.


Reception distance

VHF radio waves usually do not travel far beyond the visual horizon, so reception distances for FM stations are typically limited to . They can also be blocked by hills and to a lesser extent by buildings. Individuals with more-sensitive receivers or specialized antenna systems, or who are located in areas with more favorable topography, may be able to receive useful FM broadcast signals at considerably greater distances. The knife edge effect can permit reception where there is no direct line of sight between broadcaster and receiver. The reception can vary considerably depending on the position. One example is the Učka mountain range, which makes constant reception of Italian signals from Veneto and Marche possible in a good portion of Rijeka, Croatia, despite the distance being over 200 km (125 miles). Other radio propagation effects such as tropospheric ducting and Sporadic E can occasionally allow distant stations to be intermittently received over very large distances (hundreds of miles), but cannot be relied on for commercial broadcast purposes. Good reception across the country, is one of the main advantages over DAB radio, DAB/+ radio. This is still less than the range of AM radio waves, which because of their lower frequency can travel as ground waves or reflect off the ionosphere, so AM radio stations can be received at hundreds (sometimes thousands) of miles. This is a property of the carrier wave's typical frequency (and power), not its mode of modulation. The range of FM transmission is related to the transmitter's RF power, the antenna gain, and antenna height. Interference from other stations is also a factor in some places. In the U.S, the FCC publishes curves that aid in calculation of this maximum distance as a function of signal strength at the receiving location. Computer modelling is more commonly used for this around the world. Many FM stations, especially those located in severe multipath areas, use extra Dynamic range compression, audio compression/processing to keep essential sound above the background noise for listeners, often at the expense of overall perceived sound quality. In such instances, however, this technique is often surprisingly effective in increasing the station's useful range.


History


United States

FM broadcasting began in the late 1930s, when it was initiated by a handful of early pioneer stations including WGTR (Massachusetts), W1XOJ/W43B/WGTR (shut down in 1953) and W1XTG/WSRS, both transmitting from Paxton, Massachusetts (now listed as Worcester, Massachusetts); WHCN, W1XSL/W1XPW/W65H/WDRC-FM/WFMQ/WHCN, Meriden, Connecticut; and W2XMN, KE2XCC, and WFMN (Alpine, New Jersey), WFMN, Alpine, New Jersey (owned by Edwin Armstrong himself, closed down upon Armstrong's death in 1954). Also of note were General Electric stations W2XDA Schenectady and W2XOY New Scotland, New York—two experimental FM transmitters on 48.5 MHz—which signed on in 1939. The two began regular programming, as W2XOY, on November 20, 1940. Over the next few years this station operated under the call signs W57A, W87A and WGFM, and moved to 99.5 MHz when the FM band was FM broadcasting in the United States, relocated to the 88–108 MHz portion of the radio spectrum. General Electric sold the station in the 1980s. Today this station is WRVE. Other pioneers included WQXR-FM, W2XQR/W59NY/WQXQ/WQXR-FM, New York; WSM-FM (1941–1951), W47NV/WSM-FM Nashville, Tennessee (signed off in 1951); WMNE (Portland, Maine), W1XER/W39B/WMNE, with studios in Boston and later Portland, Maine, but whose transmitter was atop the highest mountain in the northeast United States, Mount Washington, New Hampshire, Mount Washington, New Hampshire (shut down in 1948); and W9XAO/WTMJ-FM Milwaukee, Wisconsin (went off air in 1950). A commercial FM broadcasting band was formally established in the United States as of January 1, 1941, but initially the stations primarily simulcast their AM sister stations, in addition to broadcasting lush orchestral music for stores and offices, classical music to an upmarket listenership in urban areas, and educational programming. On June 27, 1945 the FCC announced the reassignment of the FM band to 80 channels from 88–106 MHz (which was soon expanded to 100 channels from 88–108 MHz). In 1961 WUSN, WEFM (in the Chicago area) and WRVE, WGFM (in Schenectady, New York) were reported as the first stereo stations. By the late 1960s, FM had been adopted for broadcast of stereo "A.O.R.—'Album Oriented Rock' Format", but it was not until 1978 that listenership to FM stations exceeded that of AM stations in North America. During the 1980s and 1990s, Top 40 music stations and later even country music stations largely abandoned AM for FM. Today AM is mainly the preserve of talk radio, news, sports, religious programming, ethnic (minority language) broadcasting and some types of minority interest music. This shift has transformed AM into the "alternative band" that FM once was. (Some AM stations have begun to simulcast on, or switch to, FM signals to attract younger listeners and aid reception problems in buildings, during thunderstorms, and near high-voltage wires. Some of these stations now emphasize their presence on the FM dial.)


Europe

The medium wave band (known as the ''AM'' band because most stations using it employ amplitude modulation) was overcrowded in western Europe, leading to interference problems and, as a result, many MW frequencies are suitable only for speech broadcasting. Belgium, the Netherlands, Denmark and particularly Germany were among the first countries to adopt FM on a widespread scale. Among the reasons for this were: #The medium wave band in Western Europe became overcrowded after World War II, mainly due to the best available medium wave frequencies being used at high power levels by the Allied Occupation Forces, both for broadcasting American Forces Network, entertainment to their troops and for broadcasting Cold War propaganda across the Iron Curtain. #After World War II, broadcasting frequencies were reorganized and reallocated by delegates of the victorious countries in the Copenhagen Frequency Plan. German broadcasters were left with only two remaining AM frequencies and were forced to look to FM for expansion. Public service broadcasters in Republic of Ireland, Ireland and Australia were far slower at adopting FM radio than those in either North America or continental
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It comprises the westernmost peninsulas of the continental landmass of Eurasia, and is bordered by the Arctic Ocean to the north, the Atlant ...
.


Netherlands

Hans Idzerda operated a broadcasting station, PCGG, at The Hague from 1919 to 1924, which employed narrow-band FM transmissions.


United Kingdom

In the United Kingdom the BBC conducted tests during the 1940s, then began FM broadcasting in 1955, with three national networks: the BBC Light Programme, Light Programme, BBC Third Programme, Third Programme and BBC Home Service, Home Service. These three networks used the sub-band 88.0–94.6 MHz. The sub-band 94.6–97.6 MHz was later used for BBC and local commercial services. However, only when commercial broadcasting was introduced to the UK in 1973 did the use of FM pick up in Britain. With the gradual clearance of other users (notably Public Services such as police, fire and ambulance) and the extension of the FM band to 108.0 MHz between 1980 and 1995, FM expanded rapidly throughout the British Isles and effectively took over from LW and MW as the delivery platform of choice for fixed and portable domestic and vehicle-based receivers. In addition, Ofcom (previously the Radio Authority) in the UK issues on demand Restricted Service Licences on FM and also on AM (MW) for short-term local-coverage broadcasting which is open to anyone who does not carry a prohibition and can put up the appropriate licensing and royalty fees. In 2010 around 450 such licences were issued. When the BBC's radio networks were renamed BBC Radio 2, Radio 2, BBC Radio 3, Radio 3 and BBC Radio 4, Radio 4 respectively in 1967 in British radio, 1967 to coincide with the launch of BBC Radio 1, Radio 1, the new station was the only one of the main four to not have an FM frequency allocated, which was the case for 21 years. Instead, Radio 1 shared airtime with Radio 2 FM, on Saturday afternoons, Sunday evenings, weekday evenings (10pm to midnight) and Bank Holidays, eventually having its own FM frequency starting in London in October 1987 on 104.8 MHz at Crystal Palace, London, Crystal Palace. Eventually in 1987 in British radio, 1987 a frequency range of 97.6-99.8 MHz was allocated as police relay transmitters were moved from the 100 MHz frequency, starting in London before being broadly completed by 1989, where Radio 1 in London moved from the latter frequency to 98.8 MHz to the BBC's Wrotham transmitter. This followed the BBC Radio 1 FM frequencies being rolled out to the rest of the UK.


Italy

Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a continental part, delimited by the Alps, a peninsula and several islands surrounding it. Italy is located in Southern Europ ...
adopted FM broadcast widely in the early 1970s, but first experiments made by RAI dated back to 1950, when the "movement for free radio", developed by so-called "pirates", forced the recognition of free speech rights also through the use of "free radio media such as Broadcast transmitters", and took the case to the Constitutional Court of Italy. The court finally decided in favor of Free Radio. Just weeks after the court's final decision there was an "FM radio boom" involving small private radio stations across the country. By the mid 1970s, every city in Italy had a crowded FM radio spectrum.


Greece

Greece was another European country where the FM radio spectrum was used at first by the so-called "pirates" (both in Athens and Thessaloniki, the two major Greek cities) in the mid-1970s, before any national stations had started broadcasting on it; there were many AM (MW) stations in use for the purpose. No later than the end of 1977, the national public service broadcasting company EIRT (later also known as ERT) placed in service its first FM transmitter in the capital, Athens. By the end of the 1970s, most of Greek territory was covered by three National FM programs, and every city had many FM "pirates" as well. The adaptation of the FM band for privately owned commercial radio stations came far later, in 1987.


Australia

FM broadcasting started in Australian capital cities in 1947 on an "experimental" basis, using an Radio National, ABC national network feed, consisting largely of classical music and Parliament, as a programme source. It had a very small audience and was shut down in 1961 ostensibly to clear the television band: TV channel 5 (102.250 video carrier) if allocated would fall within the VHF FM band (98–108 MHz). The official policy on FM at the time was to eventually introduce it on another band, which would have required FM tuners custom-built for Australia. This policy was finally reversed and FM broadcasting was reopened in 1975 using the VHF band, after the few encroaching TV stations had been moved. Subsequently, it developed steadily until in the 1980s many AM stations transferred to FM due to its superior sound quality and lower operating costs. Today, as elsewhere in the developed world, most urban Australian broadcasting is on FM, although AM talk stations are still very popular. Regional broadcasters still commonly operate AM stations due to the additional range the broadcasting method offers. Some stations in major regional centres simulcast on AM and FM bands. Digital radio using the DAB+ standard has been rolled out to capital cities.


New Zealand

Like Australia, New Zealand adopted the FM format relatively late. As was the case with privately owned AM radio in the late 1960s, it took a spate of 'pirate' broadcasters to persuade a control-oriented, technology-averse government to allow FM to be introduced after at least five years of consumer campaigning starting in the mid-1970s, particularly in Auckland. An experimental FM station, FM 90.7 (New Zealand), FM 90.7, was broadcast in Whakatane in early 1982. Later that year, Victoria University of Wellington's Radio Active (New Zealand), Radio Active began full-time FM transmissions. Commercial FM licences were finally approved in 1983, with Auckland-based Magic 91FM, 91FM and 89FM (Auckland), 89FM being the first to take up the offe
New Zealand Pirates
Broadcasting was deregulated in 1989. Like many other countries in Africa and Asia that drive on the left, New Zealand imports vehicles from Japan. The standard radios in these vehicles operate on 76-to-90 MHz, which is not compatible with the 88-to-108 MHz range. Imported cars with Japanese radios can have FM expanders installed which down-convert the higher frequencies above 90 MHz. New Zealand has no indigenous car manufacturers.


Trinidad and Tobago

Trinidad and Tobago's first FM Radio station was 95.1FM, now rebranded as 951 Remix, was launched in March 1976 by the TBC Radio Network.


Turkey

In Turkey, FM broadcasting began in the late 1960s, carrying several shows from the One television network which was transferred from the AM frequency (also known as MW in Turkey). In subsequent years, more MW stations were slowly transferred to FM, and by the end of the 1970s, most radio stations that were previously on MW had been moved to FM, though many talk, news and sport, but mostly religious stations, still remain on MW.


Other countries

Most other countries implemented FM broadcasting through 1960s and expanded their use of FM through the 1990s. Because it takes a large number of FM transmitting stations to cover a geographically large country, particularly where there are terrain difficulties, FM is more suited to local broadcasting than for national networks. In such countries, particularly where there are economic or infrastructural problems, "rolling out" a national FM broadcast network to reach the majority of the population can be a slow and expensive process. Despite this, mostly in east European counties, national FM broadcast networks were established in the late 1960s and 1970s. In all Soviet-dependent countries but GDR, the OIRT band was used. First restricted to 68–73 MHz with 100 kHz channel spacing, then in the 1970s eventually expanded to 65.84–74.00 MHz with 30 kHz channel spacing. The use of FM for domestic radio encouraged listeners to acquire cheap FM-only receivers and so reduced the number able to listen to longer-range AM foreign broadcasters. Similar considerations led to domestic radio in South Africa switching to FM in the 1960s.


ITU Conferences about FM

The frequencies available for FM were decided by some important conferences of ITU. The milestone of those conferences is the Stockholm agreement of 1961 among 38 countries. A 1984 conference in Geneva made some modifications to the original Stockholm agreement particularly in the frequency range above 100 MHz.


FM broadcasting switch-off

In 2017, Norway became the first country so far to completely switch to Digital audio broadcasting, the exception being some local stations remaining on FM until 2020. The switchover to DAB+ meant that especially rural areas obtained a far more diverse radio content compared to the FM-only period; several new radio stations had started transmissions on DAB+ in the years before the FM switch-off.


Small-scale use of the FM broadcast band


Consumer use of FM transmitters

In some countries, small-scale (Part 15 (FCC rules), Part 15 in United States terms) transmitters are available that can transmit a signal from an audio device (usually an MP3 player or similar) to a standard FM radio receiver; such devices range from small units built to carry audio to a car radio with no audio-in capability (often formerly provided by special adapters for audio cassette decks, which are no longer common on car radio designs) up to full-sized, near-professional-grade broadcasting systems that can be used to transmit audio throughout a property. Most such units transmit in full stereo, though some models designed for beginner hobbyists might not. Similar transmitters are often included in satellite radio receivers and some toys. Legality of these devices varies by country. The Federal Communications Commission, U.S. Federal Communications Commission and Industry Canada allow them. Starting on 1 October 2006, these devices became legal in most countries in the European Union. Devices made to the harmonised European specification became legal in the United Kingdom, UK on 8 December 2006. The FM broadcast band is also used by some inexpensive wireless microphones sold as toys for karaoke or similar purposes, allowing the user to use an FM radio as an output rather than a dedicated amplifier and speaker. Professional-grade wireless microphones generally use bands in the Ultra high frequency, UHF region so they can run on dedicated equipment without broadcast interference. Some wireless headphones transmit in the FM broadcast band, with the headphones tunable to only a subset of the broadcast band. Higher-quality wireless headphones use Consumer IR, infrared transmission or UHF ISM bands such as 315 MHz, 863 MHz, 915 MHz, or 2.4 GHz instead of the FM broadcast band.


Assistive listening

Some assistive listening devices are based on FM radio, mostly using the 72.1 to 75.8 MHz band. Aside from the assisted listening receivers, only certain kinds of FM receivers can tune to this band.


Microbroadcasting

Low-power transmitters such as those mentioned above are also sometimes used for neighborhood or campus radio stations, though campus radio stations are often run over carrier current. This is generally considered a form of microbroadcasting. As a general rule, enforcement towards low-power FM stations is stricter than with AM stations, due to problems such as the capture effect, and as a result, FM microbroadcasters generally do not reach as far as their AM competitors.


Clandestine use of FM transmitters

FM transmitters have been used to construct miniature wireless microphones for espionage and surveillance purposes (covert listening devices or so-called "bugs"); the advantage to using the FM broadcast band for such operations is that the receiving equipment would not be considered particularly suspect. Common practice is to tune the bug's transmitter off the ends of the broadcast band, into what in the United States would be TV channel 6 (<87.9 MHz) or aviation navigation frequencies (>107.9 MHz); most FM radios with analog tuners have sufficient overcoverage to pick up these slightly-beyond-outermost frequencies, although many digitally tuned radios have not. Constructing a "bug" is a common early project for electronics hobbyists, and project kits to do so are available from a wide variety of sources. The devices constructed, however, are often too large and poorly shielded for use in clandestine activity. In addition, much pirate radio activity is broadcast in the FM range, because of the band's greater clarity and listenership, the smaller size and lower cost of equipment.


See also


FM broadcasting by country

* FM broadcasting in Australia * FM broadcasting in Canada * FM broadcasting in Egypt * FM broadcasting in India * FM broadcasting in Japan * FM broadcasting in New Zealand * FM broadcasting in Pakistan * FM broadcasting in the UK * FM broadcasting in the United States


FM broadcasting (technical)

*
AM broadcasting AM broadcasting is radio broadcasting using amplitude modulation (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for medium wave (also known as "AM band") transmiss ...
* AM stereo (related technology) *
FM broadcast band The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations. The range of frequencies used differs between different parts of the world. In Europe and Africa (defined as International Telecommunication Union (ITU ...
* FM stereo *
Frequency modulation Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. In analog frequen ...
* TV and FM DX, Long-distance FM reception (FM DX) * Radio music ripping, Ripping music from FM broadcasts * Radio Data System, RDS (Radio Data System)


Lists

* List of broadcast station classes * List of FM radio stations in Bangalore * List of Indian-language radio stations * Lists of radio stations in North America *Lists of radio stations in Ghana


History

* History of radio * Oldest radio station


Bands

*Band I *Band II *Band III


References


External links

; Related technical content * * Compatible Four Channel FM System
Introduction to FM MPX

Frequency Modulation (FM) Tutorial


* [https://web.archive.org/web/20070613004233/https://www.cia.gov/library/publications/the-world-factbook/fields/2013.html Factbook list of stations worldwide]
Invention History – The Father of FM

Audio Engineering Society


- Clifton Laboratories {{DEFAULTSORT:Fm Broadcasting Radio communications Broadcast engineering