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Encyclopedia > FM Radio

FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity sound over broadcast radio. individually-donated time and energy direct government payments or operation indirect government payments, such as radio and television licenses grants from foundations or business entities selling advertising or sponsorship public subscription or membership fees charged to all owners of TV sets or radios, regardless of whether they intend to receive... By the mid 20th century humans had achieved a level of technological mastery sufficient to leave the surface of the planet for the first time and explore space. ... Edwin Howard Armstrong Edwin Howard Armstrong (December 18, 1890 - March 31, 1954) was an American electrical engineer and inventor. ... When used in supervisory signaling in telephony, the term frequency-change signaling has been used to describe frequency modulation. ... High fidelity or hi-fi reproduction is a quality standard that means the reproduction of sound or images is very faithful to the original. ...


Broadcast bands

The original FM broadcast band in the United States in the early-1940s was on 42-50 MHz with 0.2 MHz channel spacing. This band was abandoned after World War II and is now allocated to a seldom-used two-way communications service. // Events and trends World War II was a truly global conflict with many facets: immense human suffering, fierce indoctrination, and the use of new, extremely devastating weapons such as the atomic bomb. ... Combatants Allies: Poland, United Kingdom, Soviet Union, France/Free France, United States, China, Canada, India, Australia, New Zealand, South Africa, Greece,Norway and others Axis Powers: Germany, Italy, Japan, Bulgaria, Finland, Romania, Hungary, Burma, Slovakia Casualties Military dead: 17 million Civilian dead: 33 million Total dead: 50 million Military dead...

The name "FM band" is misleading, since one can transmit FM on any frequency within the VHF range. All of these bands mentioned are in the VHF band which extends from 30MHz to 300MHz.

Throughout the world, 87.5-108 MHz (or some portion thereof, in the U.S. is 88.1-107.9 MHz) is used as a broadcast band, with one very notable exception: Japan, which uses its own unique 76-90 MHz band with 0.1 MHz channel spacing.

The frequency of an FM broadcast station (more strictly its assigned nominal center frequency) is usually an exact multiple of 100 kHz. In most of the the Americas and Caribbean only odd multiples are used. In Italy, multiples of 50 kHz are used. The Americas (sometimes referred to as America) is the area including the land mass located between the Pacific Ocean and the Atlantic Ocean, generally divided into North America and South America. ... Central America and the Caribbean (detailed pdf map) The Caribbean (Spanish: Caribe; French: Caraïbe; Dutch: Caraïben; Portuguese: Caribe or Caraíbas) is a region of the Americas consisting of the Caribbean Sea, its islands (most of which enclose the sea), and the surrounding coasts. ...

The bandwidth of an FM transmission is normally somewhat wider than these figures, and depends on whether stereo is used and the manner in which the peak deviation is regulated. In the UK, for example, broadcast licences specify that the nominal bandwidth of the transmission is 270 kHz.

In many countries the minimum spacing for stations intended to serve overlapping areas is 400 kHz.

In the former Soviet republics, and some Eastern Bloc nations, an additional older band from 65.9 to 74 MHz is also used. Assigned frequencies are multiples of 30 kHz. This older band, sometimes referred to as the OIRT band is slowly being phased out in many countries. Headquarters Minsk, Belarus Member states 11 member states 1 associate member Working language Russian Executive Secretary Vladimir Rushailo Formation December 21, 1991 Official website http://cis. ... A map of the Eastern Bloc. ... The International Radio and Television Organisation (official name in French: Organisation Internationale de Radiodiffusion et de Télévision or OIRT), more often called Intervision (Russian Интервидение, Polish Interwizja), was an East European network of radio and television broadcasters established in 1946 with the primary purpose of exchanging productions between its members. ...

Technical characteristics

Pre-emphasis and de-emphasis

Random noise 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. NOiSE is a one volume manga created by Tsutomu Nihei as a prequel to his acclaimed ten-volume work, Blame!. It offers some rather sketchy information concerning the Megastructures origins and initial size, as well as the origins of Silicon life. ... Familiar concepts associated with a frequency are colors, musical notes, radio/TV channels, and even the regular rotation of the earth. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... All signals are comprised of a whole range of different frequencies added up together. ... In communications, transmission is the act of transmitting electrical messages (and the associated phenonomena of radiant energy that pass through media). ...

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, 75 µs is used. This applies to both mono and stereo transmissions. In physics and engineering, the time constant, usually denoted by the Greek letter Ï„ (tau), characterizes the frequency response of a first-order, linear time-invariant (LTI) system. ... A resistor-capacitor circuit (RC circuit), or RC filter or RC network, is one of the simplest analogue infinite impulse response electronic filters. ... Monaural (often shortened to mono) sound reproduction is single-channel. ... Symbol for stereo Stereophonic sound, commonly called stereo, is the reproduction of sound, using two independent audio channels, through a pair of widely separated speaker systems, in such a way as to create a pleasant and natural impression of sound heard from various directions as in natural hearing. ...

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 program-dependent variable pre-emphasis (e.g. J.17) or none at all.) A carrier wave, or carrier is a waveform (usually sinusoidal) that is modulated (modified) to represent the information to be transmitted. ...

FM stereo

The Zenith-GE pilot tone multiplex system was added to FM radio in the early 1960s to allow FM stereo. Zenith Electronics Corporation is a manufacturer of televisions in the USA. It was the inventor of the modern remote control, and it introduced HDTV in North America. ... GE redirects here; for other uses, see GE (disambiguation). ... In telecommunication, a pilot is a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes. ... In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... The outrageously crowded Woodstock festival epitomized the popular antiwar movement of the 60s. ...

It is important that stereo broadcasts should be compatible with mono receivers. For this reason, the left (L) and right (R) channels are matrixed into sum (M) and difference (S) signals, i.e. M=(L+R)/2 and S=(L−R)/2. A mono receiver will just use the M signal. A stereo receiver will matrix the M and S signals to recover L and R: L=M+S and R=M−S.

The M signal is transmitted as baseband audio in the range 30 Hz to 15 kHz. The S signal is amplitude-modulated onto a 38 kHz suppressed carrier to produce a double-sideband suppressed carrier (DSBSC) signal in the range 23 to 53 kHz. A schematic representation of hearing. ... Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. ...

A 19 kHz pilot tone, at exactly half the 38 kHz subcarrier frequency and with a precisely defined phase relationship to it, is also generated. This is transmitted at 8-10% of overall modulation level and used by the receiver to regenerate the 38 kHz subcarrier with the correct phase. In telecommunication, a pilot is a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes. ... Modulation is the process of varying a carrier signal, typically a sinusoidal signal, in order to use that signal to convey information. ... A subcarrier is separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. ...

The final multiplex signal from the stereo generator is the sum of the baseband audio (M), the pilot tone, and the DSBSC subcarrier (S). This multiplex, along with any other subcarriers, modulates the FM transmitter. A stereo generator is an electronic device designed to encode stereophonic information for transmission over radio or television. ...

Converting the multiplex signal back to left and right is performed by a stereo decoder, which is built into stereo receivers.

It is normal practice to apply pre-emphasis to the left and right channels before matrixing, and to apply de-emphasis at the receiver after matrixing.

Other subcarrier services

The subcarrier system has been further extended to add other services. Initially these were private analog audio channels which could be used internally or rented out. Radio reading services for the blind are also still common, and there were experiments with quadraphonic sound. If there is no stereo on a station, everything from 23kHz on up can be used for other services. The guard band around 19kHz (±4kHz) 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. Rent can refer to: Renting, a system of payment for the temporary use of something owned by someone else. ... A radio reading service or reading service for the blind is a service of many public radio stations, where a narrator reads newspapers and magazines aloud for the benefit of the blind and vision-impaired. ... This article or section does not cite its references or sources. ... In the scientific method, an experiment (Latin: ex-+-periri, of (or from) trying), is a set of actions and observations, performed in the context of solving a particular problem or question, to support or falsify a hypothesis or research concerning phenomena. ... Quadraphonic sound uses four channels in which speakers are positioned at all four corners of the listening space, reproducing signals that are independent of each other. ...

Digital services are now also available. A 57kHz 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 Alternate 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 digital system is one that uses discrete numbers, especially binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (an analog system). ... In electronics, a phase-locked loop (PLL) is a closed-loop feedback control system that maintains a generated signal in a fixed phase relationship to a reference signal. ... In acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. ... Radio Data System, or RDS, is a standard for sending small amounts of digital information using conventional FM radio broadcasts. ... AF, Alternate frequencies. ... Narrowband (narrow bandwidth) refers to a signal which occupies only a small amount of space on the radio spectrum -- the opposite of broadband or wideband. ... In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ... The term text has multiple meanings depending on its context of use: In language, text is a broad term for something that contains words to express something. ... Proprietary indicates that a party exercises private ownership, control or use over an item of property, usually to the exclusion of other parties. ...

The United States is the only country attempting to put digital radio onto FM rather than using EUREKA 147 like most other countries (including Canada), or ISDB like Japan. This in-band on-channel approach results in highly-compressed audio, and blocks any opportunity for new stations to broadcast. The proprietary iBiquity system, branded as "HD Radio", uses subcarriers and extends out somewhat into the sidebands. The hybrid digital (hence "HD") system can later take the bandwidth used by the current analog stereo system, and eventually go all-digital, though this would shut out every existing analog radio. This article needs to be cleaned up to conform to a higher standard of quality. ... Eureka 147 is a protocol for digital radio broadcasting originally developed in Europe, but now being deployed in many countries around the world. ... Integrated Services Digital Broadcasting (ISDB) is the digital television (DTV) and digital audio broadcasting (DAB) format. ... In-band on-channel (IBOC) is a method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency. ... Audio compression is a form of data compression designed to reduce the size of audio data files. ... iBiquity 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 (IBOC) digital radio system for the United States. ... In marketing, a brand is a collection of feelings toward an economic producer. ... HD Radio is an in-band on-channel (IBOC) digital radio system created by iBiquity for broadcasting via existing FM and AM radio stations. ... In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing energy as a result of the modulation process. ... In biology, hybrid has three meanings. ...

Non-broadcast uses

Consumer use of FM transmitters

In some countries, small-scale (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 becoming less and 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. In the U.S., Part 15 is an often-quoted section of Federal Communications Commission (FCC) rules and regulations, regarding unlicensed transmissions. ... A digital audio player (DAP) is a device that stores, organizes and plays digital music files. ... For the meaning of cassette in genetics, see cassette (genetics). ... A satellite radio or subscription radio (SR) is a digital radio that receives signals broadcast by communications satellite, which covers a much wider geographical range than terrestrial radio signals. ...

Legality of these devices varies by country; while the FCC in the US and Industry Canada allow them, the United Kingdom's Ofcom prohibits them as an intrusion on licensed broadcasting. The Department of Industry, also referred to as Industry Canada, is the department of the government of Canada with responsibility for regional economic development, investment, and innovation/research and development. ... The Office of Communications, usually known as Ofcom, is the UKs communications regulator. ...

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 recieving 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 beyond-outermost frequencies, although many digitally-tuned radios do not. Espionage is the practice of obtaining information about an organization or a society that is considered secret or confidential (spying) without the permission of the holder of the information. ... Surveillance is the monitoring of behavior. ... A bug is the common name for a covert listening device, usually a combination of a miniature radio transmitter with a microphone. ...

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, due to the band's greater clarity and listenership. The term pirate radio lacks a specific universal interpretation. ...

See also

FM broadcasting in the USA began in the 1930s. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... AM radio is radio broadcasting using Amplitude Modulation. ... AM stereo is any of a number of mutually-incompatible techniques for broadcasting two_channel audio in the mediumwave band in a manner that is compatible with receivers designed for standard amplitude modulation. ... This is the list of broadcast station classes. ... The pre- and early history of radio is the history of technology that produced instruments that use radio waves. ... This article is a list of radio stations that are scattered on Earth. ... Radio Data System, or RDS, is a standard for sending small amounts of digital information using conventional FM radio broadcasts. ... TV DX and FM DX are two terms, customarily grouped together, that mean distant reception of TV and FM radio stations, respectively. ...

External links

  • U.S. Patent 1941066
  • An Introduction to FM MPX
  • Stereo for Dummies Many graphs that show waveforms at different points in the FM Multiplex process
  • Listen to Live FM Radio Tune a number of FM radios around the world and get live audio (Pay Site)
  • CIA Factbook list of stations worldwide

  Results from FactBites:
FM Query -- FM Radio Technical Information -- Audio Division (FCC) USA (517 words)
Please refer any comments or suggestions on the FM Query to Dale Bickel, dale.bickel@fcc.gov.
Only FM records with current engineering data will be retrieved.
FM List provides faster response for larger inquiries.
FM broadcasting - Wikipedia, the free encyclopedia (658 words)
FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity sound over broadcast radio.
FM radio is distributed primarily through broadcast reception of FM radio signals, although it is also possible to distribute FM signals via cable FM, either by using an adapter to plug analogue cable wires directly into an FM receiver, or through the use of television channel allocations on a digital cable service.
The Zenith-GE pilot-tone multiplex system was added to FM radio in the early 1960s to allow FM stereo.
  More results at FactBites »



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