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In telecommunications, frequency modulation (FM) conveys information over a carrier wave 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.In addition, it is used to send signals into space.This technique, known as FM synthesis, was popularized by early digital synthesizers and became a standard feature for several generations of personal computer sound cards.An audio signal (top) may be carried by an AM or FM radio wave.The top diagram shows the modulating signal superimposed on the carrier wave.Edwin Armstrong presented his paper: "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation", which first described FM radio, before the New York section of the Institute of Radio Engineers on November 6, 1935.Frequency modulation is also more robust against simple signal amplitude fading phenomena.FM receivers employ a special detector for FM signals and exhibit a phenomenon called capture effect, where the tuner is able to clearly receive the stronger of two stations being broadcast on the same frequency.An FM signal can also be used to carry a stereo signal: see FM stereo.However, this is done by using multiplexing and demultiplexing before and after the FM process, and is not part of FM proper.The rest of this article ignores the stereo multiplexing and demultiplexing process used in "stereo FM", and concentrates on the FM modulation and demodulation process, which is identical in stereo and mono processes.This gives FM another advantage over other modulation schemes that require linear amplifiers, such as AM and QAM.If , the modulation is called narrowband FM, and its bandwidth is approximately 2fm.FM signal increases, but the spacing between spectra stays the same.If the frequency deviation is held constant and the modulation index increased, the bandwidth stays roughly the same, but the spacing between spectra decreases.Implementation
One common method of generating the FM signal is to feed the information signal into the input of a VCO.Miscellaneous
Note that frequency modulation can be regarded as a special case of phase modulation where the carrier phase modulation is the time integral of the FM modulating signal.This page was last modified 13:14, 22 January 2008.Adoption of FM broadcasting worldwide
3.Consumer use of FM transmitters
4.Broadcast bands
The original FM broadcast band in the United States until 1946 was on 42 to 50 MHz with 0.This band was abandoned after World War II and is now allocated to fixed, mobile, and land mobile radio services.It is effectively shorthand for 'frequency band in which FM is used for broadcasting'."UKW," which stands for "Ultrakurzwellen" in German, meaning "ultra short wave", is still widely used in Germany.Broadcast bands around the world
Throughout the world, the broadcast band is 87.In the former Soviet republics, and some Eastern Bloc nations, an additional older band from 65.The frequency of an FM broadcast station (more strictly its assigned nominal centre frequency) is usually an exact multiple of 100 kHz.For more information on FM frequency allocations, see FM broadcast band.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.This applies to both mono and stereo transmissions and to baseband audio (not the subcarriers).Oscar Bonello demonstrates in his March 2007 AES paper.The individual systems were evaluated for their strengths and weaknesses.The Halstead system was rejected due to lack of high frequency stereo separation and reduction in the main channel signal to noise ratio.The (L+R) Main channel signal is transmitted as baseband audio in the range of 30 Hz to 15 kHz.SCA), modulates the FM transmitter.Converting the multiplex signal back into left and right audio signals is performed by a stereo decoder, which is built into stereo receivers.Stereo FM signals are more susceptible to noise and multipath distortion than are mono FM signals.The baseband layout is as follows:
50 Hz to 15 kHz Main Channel (Sum of all 4 channels) (LF+LB+RF+RB) signal, for Mono FM listening compatibility.RF+RB) Left minus Right 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.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.Hz 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.Other subcarrier services
The subcarrier system has been further extended to add other services.Radio reading services for the blind are also still common, and there were experiments with quadraphonic sound.If Stereo on a station, everything from 23 kHz on up can be used for other services.Hz) must still be maintained, so as not to trigger stereo decoders on receivers.Radio Data System signal, providing extra features such as Alternative Frequency (AF) and Network (NN).This narrowband signal runs at only 1187.The proprietary iBiquity system, branded as "HD Radio", uses subcarriers and extends out somewhat into the sidebands.SCA subcarriers are typically 67 kHz and 92 kHz.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.Ironically, this shift has transformed AM into the "alternative band" that FM once was.Particularly in Germany after World War II, the best available medium wave frequencies were used by the Allied occupation forces both for broadcasting entertainment to their troops and for broadcasting cold war propaganda across the Iron curtain
The regional structure of German broadcasting meant that the few remaining AM frequencies available for civilian domestic broadcasting fell far short of the number required and the broadcasters looked to FM as an alternative.Public service broadcasters in Ireland and Australia were far slower at adopting FM radio than those in either North America or continental Europe.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.In 2006 almost 500 such licenses were issued.FM started in Australia 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.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 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.The milestone of those conferences is the Stockholm agreement of 1961 among 38 countries.Starting on 1 Oct 2006 these devices became legal in most countries in the European Union.This is generally considered a form of microbroadcasting.FM broadcast band for such operations is that the receiving equipment would not be considered particularly suspect.This page was last modified 20:30, 21 January 2008.All text is available under the terms of the GNU Free Documentation License.Your Multimedia Internet Clients can now..Great Sounding Web Address WWW.Sites and audience profiles by federation.Best of all, they really understand what we want and what we need.BoingBoing
Boing Boing attracts more than 2 million unique visitors to its site each month, and has over 3.AdRants, ad exec veteran Steve Hall's blog, posted an article to the effect that if Boing Boing covers your ad campaign, it's gone viral.Named 'Best of the Web 2006' by BusinessWeek.In a 2006 article, The New Yorker described Boing Boing as "a technology blog that is read by geeks the world over."Deal Of The Week
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