FM broadcasting
Encyclopedia
FM broadcasting is a broadcasting
technology pioneered by Edwin Howard Armstrong which uses frequency modulation
(FM) to provide high-fidelity sound over broadcast radio
. The term "FM band" describes the "frequency band in which FM is used for broadcasting". This term is slightly misleading, since it equates a modulation method with a range of frequencies.
. Usually 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions:
The frequency of an FM broadcast station (more strictly its assigned nominal centre frequency) is usually an exact multiple of 100 kHz. In most of the Americas and the Caribbean
, only odd multiples are used. In some parts of Europe
, Greenland
and Africa
, only even multiples are used. In Italy
, multiples of 50 kHz are used. There are other unusual and obsolete standards in some countries, including 0.001, 0.01, 0.03, 0.074, 0.5, and 0.3 MHz.
by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. This form of modulation is commonly used in the FM broadcast band.
has a triangular spectral
distribution in an FM system, with the effect that noise occurs predominantly at the highest 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 frequencies in the receiver also reduces the high-frequency noise. These processes of boosting and then 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 North America and South Korea
, 75 µs is used. This applies to both mono
and stereo
transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing.
The amount of pre-emphasis that can be applied is limited by 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. They cannot be pre-emphasized as much because it would cause excessive deviation of the FM carrier
. Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis; e.g., dbx
in the BTSC
TV sound system, or none at all.
to FM radio were considered by the FCC
. Included were systems from 14 proponents including Crosley, Halstead, Electrical and Musical Industries, Ltd (EMI
), Zenith Electronics Corporation and General Electric. The individual systems were evaluated for their strengths and weaknesses during field tests in Uniontown, Pennsylvania
using KDKA-FM
in Pittsburgh as the originating station. The Crosley system was rejected by the FCC because it degraded the signal-to-noise ratio
of the main channel and did not perform well under multipath RF conditions. In addition, it did not allow for SCA
services because of its wide FM sub-carrier bandwidth. 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 USA and later adopted by most other countries.
It is important that stereo broadcasts should 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 in 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) Main channel signal is transmitted as baseband audio
in the range of 30 Hz to 15 kHz. The (L−R) Sub-channel signal is modulated onto a 38 kHz double-sideband suppressed carrier (DSBSC) signal occupying the baseband range of 23 to 53 kHz.
A 19 kHz pilot tone, 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. This is transmitted at 8–10% of overall modulation
level and used by the receiver to regenerate the 38 kHz sub-carrier with the correct phase.
The final multiplex signal from the stereo generator contains the Main Channel (L+R), the pilot tone, and the sub-channel (L−R). This composite signal, along with any other sub-carriers, modulates the FM transmitter.
The instantaneous deviation of the transmitter carrier frequency due to the stereo audio and pilot tone (at 10% modulation) is
where A and B are the pre-emphasized Left and Right audio signals and
=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.
Converting the multiplex signal back into left and right audio signals is performed by a stereo decoder, which is built into stereo receivers.
In order to preserve stereo separation and signal-to-noise parameters, 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.
Stereo FM signals are more susceptible to noise
and multipath distortion
than are mono FM signals.
In addition, for a given RF level at the receiver, the signal-to-noise ratio
for the stereo signal will be worse than for the mono receiver. For this reason many FM stereo 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.
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:
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
) in Ann Arbor/Saline, Michigan
under the guidance of Chief Engineer Brian Brown.
The subcarrier system has been further extended to add other services. Initially these were private analog audio channels which could be used internally or rent
ed out. Radio reading service
s for the blind
are also still common, and there were experiment
s with quadraphonic
sound. If stereo is not on a station, 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
services are now also available. A 57 kHz subcarrier (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 Alternative Frequency (AF) and Network (NN). This narrowband
signal runs at only 1187.5 bits per second, thus is only suitable for text. A few proprietary
systems are used for private communications. A variant of RDS
is the North American RBDS
or "smart radio" system. In Germany the analog ARI system was used prior to RDS for broadcasting traffic announcements to motorists (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
, digital radio
services are being deployed within the FM band rather than using Eureka 147
or the Japanese standard ISDB
. This in-band on-channel
approach, as do all digital radio
techniques, makes use of advanced compressed audio
. The proprietary iBiquity
system, brand
ed 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.
In the USA services (other than stereo, quad and RDS) using subcarriers are sometimes referred to as subsidiary communications authorisation
(SCA) services. Uses for such subcarriers include book/newspaper reading services for blind listeners, private data transmission services (for example sending stock market information to stockbrokers or stolen credit card number blacklists to stores) subscription commercial-free background music services for shops, paging ("beeper") services and providing a program feed for AM transmitters of AM/FM stations. SCA subcarriers are typically 67 kHz and 92 kHz.
arrangement to reduce noise. See: Dolby noise reduction system
.
For FM stereo, the maximum distance covered is significantly reduced. This is due to the presence of the 38 kHz subcarrier modulation. Vigorous audio processing improves the coverage area of an FM stereo station.
, the FM station of General Electric
's main factory in Schenectady, NY. In countries outside of Europe it took many years for FM to be adopted by the majority of radio listeners.
The first commercial FM broadcasting stations were in the United States, but initially they were primarily used to broadcast classical music to an upmarket listenership in urban areas, and for educational programming. By the late 1960s FM had been adopted by fans of "Alternative Rock" music ("A.O.R. - 'Album Oriented Rock' Format"), but it wasn't 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.
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:
Public service broadcasters in Ireland
and Australia were far slower at adopting FM radio than those in either North America
or continental Europe
.
in 1947 but did not catch on and was shut down in 1961 to expand the television
band. It was not reopened until 1975. Subsequently, it developed steadily until in the 1980s many AM stations transferred to FM because of its superior sound quality. Today, as elsewhere in the developed world, most Australian broadcasting is on FM, although AM talk stations are still very popular.
in early 1982. Later that year, Victoria University of Wellington
's Radio Active began full-time FM transmissions. Commercial FM licences were approved in 1983, with Auckland-based 91FM
and 89FM
being the first to take up the offer. http://www.oldradio.com/archives/international/nzp.html
, the BBC
began FM broadcasting in 1955, with three national networks carrying the Light Programme, Third Programme and Home Service (renamed Radio 2, Radio 3 and Radio 4 respectively in 1967). 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. 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 2006, almost 500 such licenses were issued.
. 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.
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 becoming less 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 may not. Similar transmitters are often included in satellite radio
receivers and some toys.
Legality of these devices varies by country. The 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 UK
on 8 December 2006.
s, but professional-grade wireless microphones generally use bands in the UHF
region so they can run on dedicated equipment without broadcast interference. Such inexpensive wireless microphones are generally 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.
. This is generally considered a form of microbroadcasting
. As a general rule, enforcement towards low-power FM stations is stricter than AM stations due to issues such as the capture effect
, and as a result, FM microbroadcasters generally do not reach as far as their AM competitors.
and surveillance
purposes (covert listening device
s 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); most FM radios with analog tuners have sufficient overcoverage to pick up these slightly-beyond-outermost frequencies, although many digitally tuned radios do 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.
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...
technology pioneered by Edwin Howard Armstrong which uses frequency modulation
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
(FM) to provide high-fidelity sound over broadcast radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
. The term "FM band" describes the "frequency band in which FM is used for broadcasting". This term is slightly misleading, since it equates a modulation method with a range of frequencies.
Broadcast bands
Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrumRadio spectrum
Radio spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies – that is, frequencies lower than around 300 GHz ....
. Usually 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions:
- In the former Soviet republicsCommonwealth of Independent StatesThe Commonwealth of Independent States is a regional organization whose participating countries are former Soviet Republics, formed during the breakup of the Soviet Union....
, and some former Eastern BlocEastern blocThe term Eastern Bloc or Communist Bloc refers to the former communist states of Eastern and Central Europe, generally the Soviet Union and the countries of the Warsaw Pact...
countries, the older 65–74 MHz band is also used. Assigned frequencies are at intervals of 30 kHz. This band, sometimes referred to as the OIRT band, is slowly being phased out in many countries. In those countries the 87.5–108.0 MHz band is referred to as the CCIR band. - In JapanJapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, the band 76–90 MHz is used.
The frequency of an FM broadcast station (more strictly its assigned nominal centre frequency) is usually an exact multiple of 100 kHz. In most of the Americas and the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
, only odd multiples are used. In some parts of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, only even multiples are used. In Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, multiples of 50 kHz are used. There are other unusual and obsolete standards in some countries, including 0.001, 0.01, 0.03, 0.074, 0.5, and 0.3 MHz.
Modulation
Frequency modulation (FM) is a form of modulation which conveys information over a carrier waveCarrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. This form of modulation is commonly used in the FM broadcast band.
Pre-emphasis and de-emphasis
Random noiseNoise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
has a triangular spectral
Frequency spectrum
The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.Any signal...
distribution in an FM system, with the effect that noise occurs predominantly at the highest 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...
within the baseband
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
. This can be offset, to a limited extent, by boosting the high frequencies before transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
and reducing them by a corresponding amount in the receiver. Reducing the high frequencies in the receiver also reduces the high-frequency noise. These processes of boosting and then reducing certain frequencies are known as pre-emphasis
Preemphasis
In processing electronic audio signals, pre-emphasis refers to a system process designed to increase the magnitude of some frequencies with respect to the magnitude of other frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as...
and de-emphasis
Deemphasis
In telecommunication, de-emphasis is the complement of pre-emphasis, in the antinoise system called emphasis. Emphasis is a system process designed to decrease, , the magnitude of some frequencies with respect to the magnitude of other frequencies in order to improve the overall signal-to-noise...
, respectively.
The amount of pre-emphasis and de-emphasis used is defined by the time constant
Time constant
In physics and engineering, the time constant, usually denoted by the Greek letter \tau , is the risetime characterizing the response to a time-varying input of a first-order, linear time-invariant system.Concretely, a first-order LTI system is a system that can be modeled by a single first order...
of a simple RC filter
RC circuit
A resistor–capacitor circuit ', or RC filter or RC network, is an electric circuit composed of resistors and capacitors driven by a voltage or current source...
circuit. In most of the world a 50 µs time constant is used. In North America and South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...
, 75 µs is used. This applies to both mono
Monaural
Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...
and stereo
Stereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing.
The amount of pre-emphasis that can be applied is limited by 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. They cannot be pre-emphasized as much because it would cause excessive deviation of the FM carrier
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
. Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis; e.g., dbx
Dbx (noise reduction)
dbx is a family of noise reduction systems developed by the company of the same name. The most common implementations are dbx Type I and dbx Type II for analog tape recording and, less commonly, vinyl LPs. A separate implementation, known as dbx-TV, is part of the MTS system used to provide stereo...
in the BTSC
Multichannel television sound
Multichannel television sound, better known as MTS , is the method of encoding three additional channels of audio into an NTSC-format audio carrier.- History :...
TV sound system, or none at all.
FM stereo
In the late 1950s, several systems to add stereoSTEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
to FM radio were considered 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...
. Included were systems from 14 proponents including Crosley, Halstead, Electrical and Musical Industries, Ltd (EMI
EMI
The EMI Group, also known as EMI Music or simply EMI, is a multinational music company headquartered in London, United Kingdom. It is the fourth-largest business group and family of record labels in the recording industry and one of the "big four" record companies. EMI Group also has a major...
), Zenith Electronics Corporation and General Electric. The individual systems were evaluated for their strengths and weaknesses during field tests in Uniontown, Pennsylvania
Uniontown, Pennsylvania
Uniontown is a city in Fayette County, Pennsylvania, southeast of Pittsburgh and part of the Pittsburgh Metro Area. Population in 1900, 7,344; in 1910, 13,344; in 1920, 15,692; and in 1940, 21,819. The population was 10,372 at the 2010 census...
using KDKA-FM
WLTJ
WLTJ , is an Hot Adult Contemporary music format radio station based in Pittsburgh, Pennsylvania. The station, which is owned by Steel City Media, broadcasts with an ERP of 43 kW. Its transmitter is located in Pittsburgh.- History :...
in Pittsburgh as the originating station. The Crosley system was rejected by the FCC because it degraded the signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
of the main channel and did not perform well under multipath RF conditions. In addition, it did not allow for SCA
Subsidiary Communications Authority
Subsidiary Communications Authorization in the United States, and Subsidiary Communications Multiplex Operation in Canada, is a subcarrier on a radio station, allowing the station to broadcast additional services as part of its signal.-Background:"Subsidiary Communications Authorization" is the...
services because of its wide FM sub-carrier bandwidth. 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 USA and later adopted by most other countries.
It is important that stereo broadcasts should 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 in 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) Main channel signal is transmitted as baseband audio
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
in the range of 30 Hz to 15 kHz. The (L−R) Sub-channel signal is modulated onto a 38 kHz double-sideband suppressed carrier (DSBSC) signal occupying the baseband range of 23 to 53 kHz.
A 19 kHz pilot tone, 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. This is transmitted at 8–10% of overall modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
level and used by the receiver to regenerate the 38 kHz sub-carrier with the correct phase.
The final multiplex signal from the stereo generator contains the Main Channel (L+R), the pilot tone, and the sub-channel (L−R). This composite signal, along with any other sub-carriers, modulates the FM transmitter.
The instantaneous deviation of the transmitter carrier frequency due to the stereo audio and pilot tone (at 10% modulation) is
where A and B are the pre-emphasized Left and Right audio signals and
=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.Converting the multiplex signal back into left and right audio signals is performed by a stereo decoder, which is built into stereo receivers.
In order to preserve stereo separation and signal-to-noise parameters, 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.
Stereo FM signals are more susceptible to noise
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
and multipath distortion
Distortion
A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
than are mono FM signals.
In addition, for a given RF level at the receiver, the signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
for the stereo signal will be worse than for the mono receiver. For this reason many FM stereo 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.
Quadraphonic FM
In 1969 Louis DorrenLouis Dorren
Louis Dorren is an American engineer.In 1969 Louis "Lou" Dorren invented the Quadraplex system of single station, discrete, compatible four-channel FM broadcasting. He founded Quadracast Systems, Inc...
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 (cosine quadrature subcarrier) (LF+LR) - (RF+RR) Left minus Right difference signal. This signal's modulation in algebraic sum and difference with the Main channel was used for 2 channel stereo listener compatibility.
- 23 to 53 kHz (sine quadrature 38 kHz subcarrier) (LF+RF) - (LR+RR) Front minus Back difference signal. 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 (cosine quadrature 76 kHz subcarrier) (LF+RR) - (LR+RF) Diagonal difference signal. 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.
- 95 kHz SCA subcarrier, phase-locked to 19 kHz pilot, for reading services for the blind, background music, etc.
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
WWWW-FM
WWWW-FM - "W4 Country" - is a country music radio station based in Ann Arbor, Michigan, broadcasting on 102.9 MHz.-Early years:The 102.9 frequency began operations in or on March 1, 1962 as WOIA and was co-owned with WOIB-AM 1290 in Saline, Michigan. Originally, WOIA and WOIB simulcast a middle of...
(now called WWWW-FM
WWWW-FM
WWWW-FM - "W4 Country" - is a country music radio station based in Ann Arbor, Michigan, broadcasting on 102.9 MHz.-Early years:The 102.9 frequency began operations in or on March 1, 1962 as WOIA and was co-owned with WOIB-AM 1290 in Saline, Michigan. Originally, WOIA and WOIB simulcast a middle of...
) in Ann Arbor/Saline, Michigan
Saline, Michigan
Saline is a city in Washtenaw County in the U.S. state of Michigan. As of the 2010 census, the city population was 8,810.The city is popular for its annual Celtic Festival, which attracts people from all over the United States and its sister cities Brecon, Wales and Lindenberg, Germany...
under the guidance of Chief Engineer Brian Brown.
Other subcarrier services
Renting
Renting is an agreement where a payment is made for the temporary use of a good, service or property owned by another. A gross lease is when the tenant pays a flat rental amount and the landlord pays for all property charges regularly incurred by the ownership from landowners...
ed out. Radio reading service
Radio reading service
A radio reading service or reading service for the blind is a service of many universities, community groups and public radio stations, where a narrator reads books, newspapers and magazines aloud for the benefit of the blind and vision-impaired. It is most often carried on a subcarrier, with...
s for the blind
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
are also still common, and there were experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
s with quadraphonic
Quadraphonic
Quadraphonic sound – the most widely used early term for what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are independent of one another...
sound. If stereo is not on a station, everything from 23 kHz on up can be used for other services. The guard band
Guard band
-Radio and electronic signalling:In radio, a guard band is an unused part of the radio spectrum between radio bands, for the purpose of preventing interference....
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
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
services are now also available. A 57 kHz subcarrier (phase locked
Phase-locked loop
A phase-locked loop or phase lock loop is a control system that generates an output signal whose phase is related to the phase of an input "reference" signal. It is an electronic circuit consisting of a variable frequency oscillator and a phase detector...
to the third harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...
of the stereo pilot tone) is used to carry a low-bandwidth digital Radio Data System
Radio Data System
Radio 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...
signal, providing extra features such as Alternative Frequency (AF) and Network (NN). This narrowband
Narrowband
In radio, narrowband describes a channel in which the bandwidth of the message does not significantly exceed the channel's coherence bandwidth. It is a common misconception that narrowband refers to a channel which occupies only a "small" amount of space on the radio spectrum.The opposite of...
signal runs at only 1187.5 bits per second, thus is only suitable for text. A few proprietary
Proprietary protocol
In telecommunications, a proprietary protocol is a communications protocol owned by a single organization or individual.-Enforcement:Proprietors may enforce restrictions through patents and by keeping the protocol specification a trade secret...
systems are used for private communications. A variant of RDS
Radio Data System
Radio 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...
is the North American RBDS
Radio Data System
Radio 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...
or "smart radio" system. In Germany the analog ARI system was used prior to RDS for broadcasting traffic announcements to motorists (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
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, digital radio
Digital radio
Digital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...
services are being deployed within the FM band rather than using Eureka 147
Digital audio broadcasting
Digital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....
or the Japanese standard ISDB
ISDB
Integrated Services Digital Broadcasting is a Japanese standard for digital television and digital radio used by the country's radio and television stations. ISDB replaced the previously used MUSE "Hi-vision" analogue HDTV system...
. This in-band on-channel
In-band on-channel
In-band on-channel is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency....
approach, as do all digital radio
Digital radio
Digital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...
techniques, makes use of advanced compressed audio
Audio compression
Audio compression may refer to:*Audio compression , a type of lossy compression in which the amount of data in a recorded waveform is reduced for transmission with some loss of quality, used in CD and MP3 encoding, Internet radio, and the like...
. The proprietary iBiquity
IBiquity
iBiquity Digital Corporation is a company formed by the merger of USA Digital Radio and Lucent Digital Radio, with the goal of creating an in-band on-channel digital radio system for the United States and around the world...
system, brand
Brand
The American Marketing Association defines a brand as a "Name, term, design, symbol, or any other feature that identifies one seller's good or service as distinct from those of other sellers."...
ed as "HD Radio
HD Radio
HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals...
", currently is authorized for "hybrid" mode operation, wherein both the conventional analog FM carrier and digital sideband
Sideband
In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing power as a result of the modulation process. The sidebands consist of all the Fourier components of the modulated signal except the carrier...
subcarriers are transmitted. Eventually, presuming widespread deployment of HD Radio
HD Radio
HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals...
receivers, the analog services could theoretically be discontinued and the FM band become all digital.
In the USA services (other than stereo, quad and RDS) using subcarriers are sometimes referred to as subsidiary communications authorisation
Subsidiary Communications Authority
Subsidiary Communications Authorization in the United States, and Subsidiary Communications Multiplex Operation in Canada, is a subcarrier on a radio station, allowing the station to broadcast additional services as part of its signal.-Background:"Subsidiary Communications Authorization" is the...
(SCA) services. Uses for such subcarriers include book/newspaper reading services for blind listeners, private data transmission services (for example sending stock market information to stockbrokers or stolen credit card number blacklists to stores) subscription commercial-free background music services for shops, paging ("beeper") services and providing a program feed for AM transmitters of AM/FM stations. SCA subcarriers are typically 67 kHz and 92 kHz.
Dolby FM
A commercially unsuccessful noise reduction system used with FM radio in some countries during the late 1970s, Dolby FM used a modified 25 µs pre-emphasis time constant and a frequency selective compandingCompanding
In telecommunication, signal processing, and thermodynamics, companding is a method of mitigating the detrimental effects of a channel with limited dynamic range...
arrangement to reduce noise. See: Dolby noise reduction system
Dolby noise reduction system
Dolby NR is the name given to a series of noise reduction systems developed by Dolby Laboratories for use in analog magnetic tape recording. The first was Dolby A, a professional broadband noise reduction for recording studios in 1966, but the best-known is Dolby B , a sliding band system for the...
.
Distance covered by an FM stereo transmission
The range of an FM mono transmission is related to the transmitter RF power, the antenna gain and antenna height. The FCC (USA) publishes curves that aid in calculation of this maximum distance as a function of signal strength at the receiving location.For FM stereo, the maximum distance covered is significantly reduced. This is due to the presence of the 38 kHz subcarrier modulation. Vigorous audio processing improves the coverage area of an FM stereo station.
Adoption of FM broadcasting worldwide
Despite FM having been patented in 1933, commercial FM broadcasting did not begin until 1939, when it was initiated by WRVEWRVE
WRVE is a Hot Adult Contemporary radio station licensed to Schenectady, New York and serving the Capital District and Upper Hudson Valley of New York. It broadcasts at 99.5 FM at 14.5 kilowatts ERP from a transmitter in Guilderland, New York...
, the FM station of General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
's main factory in Schenectady, NY. In countries outside of Europe it took many years for FM to be adopted by the majority of radio listeners.
The first commercial FM broadcasting stations were in the United States, but initially they were primarily used to broadcast classical music to an upmarket listenership in urban areas, and for educational programming. By the late 1960s FM had been adopted by fans of "Alternative Rock" music ("A.O.R. - 'Album Oriented Rock' Format"), but it wasn't 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.
Europe
The medium wave band (known as AM in North America) is overcrowded in Western Europe, leading to interference problems and, as a result, many MW frequencies are suitable only for speech broadcasting.Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
, the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
and particularly Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
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 entertainment to their troopsAmerican Forces NetworkThe American Forces Network is the brand name used by the United States Armed Forces American Forces Radio and Television Service for its entertainment and command internal information networks worldwide...
and for broadcasting cold warCold WarThe Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
propaganda across the Iron curtainIron CurtainThe concept of the Iron Curtain symbolized the ideological fighting and physical boundary dividing Europe into two separate areas from the end of World War II in 1945 until the end of the Cold War in 1989...
. - 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 Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
and Australia were far slower at adopting FM radio than those in either North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
or continental Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
.
Australia
FM started in AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
in 1947 but did not catch on and was shut down in 1961 to expand the television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
band. It was not reopened until 1975. Subsequently, it developed steadily until in the 1980s many AM stations transferred to FM because of its superior sound quality. Today, as elsewhere in the developed world, most Australian broadcasting is on FM, although AM talk stations are still very popular.
New Zealand
Like Australia, New Zealand adopted the FM format relatively late. An experimental FM station, FM 90.7, was broadcast in WhakataneWhakatane
Whakatane is a town in the eastern Bay of Plenty Region, in the North Island of New Zealand, and is the seat of the Bay of Plenty Regional Council. Whakatane is 90 km east of Tauranga and 89 km north-east of Rotorua, at the mouth of the Whakatane River.The town has a population of , with...
in early 1982. Later that year, Victoria University of Wellington
Victoria University of Wellington
Victoria University of Wellington was established in 1897 by Act of Parliament, and was a former constituent college of the University of New Zealand. It is particularly well known for its programmes in law, the humanities, and some scientific disciplines, but offers a broad range of other courses...
's Radio Active began full-time FM transmissions. Commercial FM licences were approved in 1983, with Auckland-based 91FM
Magic 91FM
Magic 91FM or 91FM was a local radio station in Auckland. 91FM began broadcasting on 91.0 FM using the call sign 1MJK in 1983 and was one of the first FM stations to start in Auckland and New Zealand, along with 89 Stereo FM...
and 89FM
89FM (Auckland)
89FM was a local FM radio station in Auckland between 1983 and 1994 and one of the very first radio stations to broadcast on FM in both Auckland and New Zealand. The first FM station in New Zealand was Whakatane station, FM 90.7 in December 1982 but this station was only a temporary summer radio...
being the first to take up the offer. http://www.oldradio.com/archives/international/nzp.html
United Kingdom
In the United KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
began FM broadcasting in 1955, with three national networks carrying the Light Programme, Third Programme and Home Service (renamed Radio 2, Radio 3 and Radio 4 respectively in 1967). 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. 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
Ofcom
Ofcom is the government-approved regulatory authority for the broadcasting and telecommunications industries in the United Kingdom. Ofcom was initially established by the Office of Communications Act 2002. It received its full authority from the Communications Act 2003...
(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 2006, almost 500 such licenses were issued.
Other countries
Most other countries 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.ITU Conferences about FM
The frequencies available for FM were decided by some important conferences of ITUItu
Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...
. 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.
Small-scale use of the FM broadcast band
Consumer use of FM transmitters
In some countries, small-scale (Part 15Part 15 (FCC rules)
Code of Federal Regulations, Title 47, Part 15 is an oft-quoted part of Federal Communications Commission rules and regulations regarding unlicensed transmissions. It is a part of Title 47 of the Code of Federal Regulations , and regulates everything from spurious emissions to unlicensed...
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 becoming less 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 may not. Similar transmitters are often included in satellite radio
Satellite radio
Satellite radio is an analogue or digital radio signal that is relayed through one or more satellites and thus can be received in a much wider geographical area than terrestrial FM radio stations...
receivers and some toys.
Legality of these devices varies by country. The U.S. Federal Communications Commission
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...
and Industry Canada
Industry Canada
Industry Canada is the department of the Government of Canada with responsibility for regional economic development, investment, and innovation/research and development. The department employs 6104 FTEs across Canada....
allow them. Starting on 1 October 2006 these devices became legal in most countries in the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
. Devices made to the harmonised European specification became legal in the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
on 8 December 2006.
FM radio microphones
The FM broadcast band can also be used by some inexpensive wireless microphoneMicrophone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
s, but professional-grade wireless microphones generally use bands in the UHF
Ultra high frequency
Ultra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
region so they can run on dedicated equipment without broadcast interference. Such inexpensive wireless microphones are generally sold as toys for karaoke
Karaoke
is a form of interactive entertainment or video game in which amateur singers sing along with recorded music using a microphone and public address system. The music is typically a well-known pop song minus the lead vocal. Lyrics are usually displayed on a video screen, along with a moving symbol,...
or similar purposes, allowing the user to use an FM radio as an output rather than a dedicated amplifier and speaker.
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 currentCarrier current
Carrier current is a method of low power AM radio transmission that uses the AC electrical system of a building to propagate a medium frequency, AM signal to a relatively small area, such as a building or a group of buildings...
. This is generally considered a form of microbroadcasting
Microbroadcasting
Microbroadcasting is the process of broadcasting a message to a relatively small audience. This is not to be confused with low-power broadcasting....
. As a general rule, enforcement towards low-power FM stations is stricter than AM stations due to issues such as the capture effect
Capture effect
In telecommunication, the capture effect, or FM capture effect, is a phenomenon associated with FM reception in which only the stronger of two signals at, or near, the same frequency will be demodulated....
, 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 espionageEspionage
Espionage or spying involves an individual obtaining information that is considered secret or confidential without the permission of the holder of the information. Espionage is inherently clandestine, lest the legitimate holder of the information change plans or take other countermeasures once it...
and surveillance
Surveillance
Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people. It is sometimes done in a surreptitious manner...
purposes (covert listening device
Covert listening device
A covert listening device, more commonly known as a bug or a wire, is usually a combination of a miniature radio transmitter with a microphone. The use of bugs, called bugging, is a common technique in surveillance, espionage and in police investigations.A bug does not have to be a device...
s 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); most FM radios with analog tuners have sufficient overcoverage to pick up these slightly-beyond-outermost frequencies, although many digitally tuned radios do 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
Pirate radio
Pirate radio is illegal or unregulated radio transmission. The term is most commonly used to describe illegal broadcasting for entertainment or political purposes, but is also sometimes used for illegal two-way radio operation...
activity is broadcast in the FM range, because of the band's greater clarity and listenership, the smaller size and lower cost of equipment.
FM broadcasting by country
- FM broadcasting in AustraliaFM broadcasting in AustraliaFM radio broadcasting started in Australia in 1947 but did not catch on and was shut down in 1961 to expand the television band and not reopened until 1975 when Australia's FM allocation was aligned with most of the rest of the world...
- FM broadcasting in CanadaFM broadcasting in Canada- Domestic FM Networks :FM Broadcasting started just after World War II ended. The Canadian Broadcasting Corporation's first FM outlets were built in Montreal for English and French service , and one each in Toronto, Ottawa and Vancouver....
- FM broadcasting in EgyptFM broadcasting in EgyptFM broadcasting in Egypt began in the 20th century. By the early 1990s, Egypt had only 4 FM stations, but the number increased to 6 by the end of the decade. In 2000, stations moving from the AM band and the introduction of private stations raised the number to 10 stations .All the radio stations...
- FM broadcasting in IndiaFM broadcasting in IndiaThe first FM broadcasting in India was in the year 1977 at Madras.In the mid-nineties, when India first experimented with private FM broadcasts, the small tourist destination of Goa was the fifth place in this country of one billion where private players got FM slots. The other four centres were...
- FM broadcasting in JapanFM broadcasting in JapanThe frequency modulation radio broadcast band in Japan is 76-90 MHz. The 90-108 MHz section is used for television for VHF Channels 1,2 and 3. The narrowness of the Japanese band limits the number of FM stations that can be accommodated on the dial.-Receiver issues:Many Japanese radios are...
- FM broadcasting in NZ
- FM broadcasting in Pakistan
- FM broadcasting in the UKFM broadcasting in the UKFM broadcasting began in the United Kingdom on May 2, 1955 when the BBC started an FM service broadcasting the Light Programme, the Third Programme and the Home Service to the south east of England. There are now over 40 BBC and over 250 commercial FM stations broadcasting in the UK.-BBC :The BBC...
- FM broadcasting in the USAFM broadcasting in the USAFM 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.-History of FM radio in the U.S.:...
FM broadcasting (technical)
- 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...
(related technology) - 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...
- Long-distance FM reception (FM DX)
- Ripping music from FM broadcastsRadio music rippingThe term ripping can also apply to radio. New software, techniques and cloud services now makes it possible to extract the songs played on the radio and digitally save them on separate audio tracks...
- 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...
Lists
- List of broadcast station classes
- Lists of radio stations in North and Central America