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KFRC

KFRC

KFRC is an FM broadcast radio station in San Francisco, California in the United States, which began broadcasting as an AM station in 1924. Since 1991, the station has been broadcasting on 99.7 MHz FM, but for over 80 years, the station had served the community on 610 kHz AM until 2005. The famous callsign letters were sequentially issued, as was common when KFRC signed on the air in 1924. They did not stand for "Frisco", nor did they stand for "Known For Radio Clearness," though this was the slogan used when the station first signed on with 50 watts of power. Broadcasts had been heard over a much larger area than had been anticipated. Another slogan KFRC used in its early days was "Keep Forever Radiating Cheer".

Early history

The beginning of KFRC was largely due to the efforts of its first manager, Harrison Holliway. As a child, he was a ham radio buff, and by 1920, he was operating his own amateur station, 6BN. For a time, Harrison was on the air every day with 6BN, broadcasting record programs "for the sheer pleasure of it". He also worked as a part-time newspaper reporter, covering high school sporting news for the San Francisco Call. Beginning in 1920, Holliway attended Stanford University. During the summer of 1924, Holliway was working at a radio shop called the Radio Art Corporation in San Francisco. A Western Electric salesman called on the owners, Jim Threlkeld and Thomas Catton, and sold them on the idea of starting a new radio station (and of course, buying a Western Electric transmitter). And so, KFRC was born, and Holliway became the manager. KFRC went on the air on September 24, 1924 with speeches by local dignitaries, followed by a program with concert, symphony and dance orchestras. Although the signal was only 50 watts, reception proved exceptionally good. It was heard on the U.S. Atlantic Coast, and across the Pacific Ocean as far away as New Zealand. In the following years, Holliway interviewed such personalities as baseball great Rogers Hornsby, French-Canadian heavyweight boxer Jack Renault, and actors William S. Hart, Douglas Fairbanks, Jr., and John Barrymore. Harry "Mac" McClintock who hosted a daily children's program, later wrote the hit song "Big Rock Candy Mountain".

Don Lee networks

In 1926, KFRC was purchased by Don Lee, who was the wealthy California distributor for Cadillac automobiles. He is said to have had "a personal habit of doing everything in grand style." His family owned the station for 25 years. In 1927, he purchased KHJ in Los Angeles, and in 1929, both stations became affiliated with William S. Paley's Columbia Broadcasting System (CBS). Jack Benny's announcer Don Wilson began his radio career at KFRC. Others included Ralph Edwards, Art Van Horn, and Mark Goodson, who later went on with partner Bill Todman to create many radio and television game and quiz shows. Other personalties associated with KFRC during the Don Lee era were Art Linkletter, Mel Venter, Bea Benaderet, Harold Peary, Morey Amsterdam, Juanita Tennyson, Merv Griffin, and John Nesbitt. Don Lee died in 1934 and his son took over management. KFRC (and sister KHJ in Los Angeles) switched to the new Mutual Broadcasting System on December 29, 1936.

1950s and 1960s: Bill Drake era

In 1949, RKO-General acquired KFRC. Like most radio stations during the 1950s, KFRC lost ratings and share to television. In the mid-1960s, KFRC changed to a Top 40 rock and roll music format, and quickly became the dominant station in the region with that format through the 1970s, featuring the tight, carefully programmed sound developed programmer, Bill Drake, formerly of cross-town rival, KYA. It entered its second "golden era," which coincided with San Francisco’s Summer of Love.

1970s and 1980s: Dr. Don Rose, Magic 61

From 1973 until 1986, Dr. Don Rose (July 5, 1934–March 30, 2005) was a memorable radio personality on KFRC. With earlier experience at WQXI (AM) in Atlanta, Georgia, and WFIL in Philadelphia, he was known for his corny one-liners, wacky sound effects, and good heart. With Dr. Don as anchor, KFRC was voted "Station of the Year" four times by Billboard Magazine. He was considered by many to be the king of radio in the Bay Area during the last decade of AM's musical dominance. With the decline of the Top 40 format by the mid 1980s, KFRC's programming was changed to feature a 1940s big band format, and was known as "Magic 61".

1990s: adding FM

In the 1990s, KFRC changed to a nostalgia format by playing the rock hits of the 60's and 70's, recreating the successful Bill Drake years. When, in 1980, KFRC sold off its money-losing FM station at 106.1 (to become KMEL, it soon became clear that the owners had made a mistake. This was corrected in 1991 with the purchase of the station at 99.7. The frequency for many years had been KNBC, and later KYUU and KXXX. Under KFRC, the FM signal at 99.7 was simulcast (which means broadcast together) with the popular AM station at 610. The oldies format proved very successful in the Bay market.

Current events, heritage

In 2005, the owners, Infinity Broadcasting (CBS), announced the sale of the AM station, which was anticipated to receive new call letters. The sale price was reported to be $35 million. The oldies format of KFRC AM and FM was scheduled to continue on the FM frequency. The sale of the AM station came about as a result of Viacom's purchase of CBS' Sacramento television affiliate, KOVR. Because KFRC's strong 5,000 watt AM signal from the Berkeley Marina was heard as a local station not only in San Francisco, but in Sacramento as well, the FCC required Infinity to sell either one of its Sacramento stations or a Bay Area station that had Sacramento as part of its city-grade coverage. Gerry Cagle, who programmed KFRC in the early eighties, and now writes for MusicBiz.com, commented in 2005: :"KFRC wasn't a position on the dial. It was a place in the hearts of the many professionals who worked there to build and continue a legacy unmatched in radio. It was also a place in the hearts of the listeners who made it important in their lives. 610 means nothing. 'KFRC San Francisco with the Best Music!' will live forever in that magical place we all go when we think about the good things of the past." [http://www.tangentsunset.com/sfradiohistory2.htm] Infinity sold the AM station to Family Stations, the owners of KEAR 106.9 FM, a Christian radio station. Shortly thereafter, Family Stations sold their FM station to Infinity. On April 29, 2005, Family Stations began simulcasting the signal of their FM station on 610 AM. The Oakland Athletics baseball team, which was the only sports tenant the past few years on the AM side, negotiated with Family Stations to have their games broadcast until the end of the 2005 baseball season. On September 5, 2005, KFRC-FM, the only oldies outlet in San Francisco moved their format ahead ten years switching to a '70s & '80s music format. The legendary KFRC call letters left the AM band on October 17, 2005, when the KEAR call letters were transferred from 106.9 FM to 610 AM. Meanwhile, 106.9 FM became KIFR, and is now an FM talk station owned by Infinity.

External links

- [http://www.kfrc.com/ KFRC official website]
- [http://users.adams.net/~jfs/kfrc1.htm The History of KFRC San Francisco and the Don Lee Networks]
- [http://www.sfmuseum.org/hist3/kfrc.html Virtual Museum of the City of San Francisco, KFRC webpage]
- [http://www.doctordonrose.com/index1.html Dr. Don Rose fan website]
- [http://www.tangentsunset.com/sfradiohistory.htm Tangent Sunset San Francisco Bay Area Radio History]
- [http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/09/05/DDGFNEHK1N1.DTL KFRC switches from oldies to music of 1970s and '80s], from the San Francisco Chronicle
- [http://www.bayarearadio.org/schneider/kfrc1.shtml The History of KFRC Radio]
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Frequency modulation

Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave. (Contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.) In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. Digital data can be represented by shifting the carrier frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Normal (analog) TV sound is also broadcast using FM. A narrowband form is used for voice communications in commercial and amateur radio settings. The type of FM used in broadcast is generally called wide-FM, or W-FM. In two-way radio, narrowband narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space. FM is also used at intermediate frequencies by most analog VCR systems, including VHS, to record the luminance (black and white) portion of the video signal. FM is the only feasible method of recording to and retrieving from magnetic tape without extreme distortion, as video signals have a very large range of frequency components -- from a few hertz to several megahertz. FM is also used at audio frequencies to synthesize sound. 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.

Applications in radio

sound card Edwin Armstrong presented his paper: [https://michael.industrynumbers.com/fm.pdf "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 requires a wider bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against interference. Frequency modulation is also more robust against simple signal amplitude fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission: hence the term "FM radio" (although for many years the BBC insisted on calling it "VHF radio", which is quite logical, since commercial FM broadcasting uses a well-known part of the VHF band; in certain countries, expressions referencing the more familiar wavelength notion are still used in place of the somewhat mysterious modulation technique name). FM receivers inherently exhibit a phenomenon called capture, where the tuner is able to clearly receive the stronger of two stations being broadcast on the same frequency. Problematically, however, frequency drift or lack of selectivity may cause one station or signal to be suddenly overtaken by another on an adjacent channel. Frequency drift typically constituted a problem on very old or inexpensive receivers, while inadequate selectivity may plague any tuner. 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.

Theory

If the signal to be transmitted is :

x_m(t)\,

which is restricted in amplitude to be :

\left| x_m(t) \right| \le 1 \,

and the sinusoidal carrier is :

x_c(t) = A \cos (2 \pi f_c t)\,

where f_c is the carrier's base frequency in hertz and A is an arbitrary amplitude, the carrier will be modulated by the signal as in :

x_c(t) = A \cos \left( 2 \pi \int_^ f(\tau)\, d \tau \right) = A \cos \left( 2 \pi \int_^ \left[ f_c + f_\Delta x_m(\tau) \right] \, d \tau \right)

:where,

f(t) = f_c + f_\Delta x_m(t)

In this equation, f(t) is the instantaneous frequency of the oscillator and f_Δ is the frequency deviation, which represents the maximum shift away from f_c in one direction, assuming x_m(t) is limited to the range ±1. Although it may seem that this limits the frequencies in use to f_c ± f_Δ, this neglects the distinction between instantaneous frequency and spectral frequency. The frequency spectrum of an actual FM signal has components extending out to infinite frequency, although they become negligibly small beyond a point. For a simplified case, the harmonic distribution of a sine wave signal modulated by another sine wave signal can be represented with Bessel functions - this provides a basis for a mathematical understanding of frequency modulation in the frequency domain. A rule of thumb, Carson's rule states that nearly all the power of a frequency modulated signal lies within a bandwidth of :

2(f_\Delta +f_m)\,

where f_Δ is the peak deviation of the instantaneous frequency f(t) from the center carrier frequency f_c (assuming x_m(t) is in the range ±1) and f_m is the highest modulating frequency of x_m(t). 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. Frequency-shift keying refers to the simple case of frequency modulation by a simple signal with only discrete states, such as in Morse code or radio-teletype applications. Manchester encoding may be regarded as a simple version of frequency shift keying, where the high and low frequencies are respectively double and the same as the bit rate, and the bit transitions are synchronous with carrier transitions. When used in supervisory signaling in telephony, the term frequency-change signaling has been used to describe frequency modulation. The phrase frequency-modulated, an adjective, should have a hyphen when used attributively.

Modulation Index

As with other modulation indices, in AM this quantity indicates by how much the modulated variable varies around its unmodulated level. For FM, it relates to the variations in the frequency of the carrier signal: :

h = \frac = \frac \

With a tone-modulated FM wave, if the modulation frequency is held constant and the modulation index is increased, the (non-negligible) bandwidth of the 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.

External links

- http://www.rfcafe.com/references/electrical/frequency_modulation.htm
- http://www.fas.org/man/dod-101/navy/docs/es310/FM.htm Category:Radio modulation modes ko:주파수 변조 ja:周波数変調

Radio station

A radio station is a sound broadcasting service. Traditionally, radio stations have broadcast through the air via radio waves (a form of electromagnetic radiation), sent through a transmitter and antenna. Today, many if not most stations broadcast via cable FM, local wire networks, satellite, or the Internet as well as (or instead of) atmospheric broadcasting. Stations can be linked in radio networks to broadcast a common program, either in syndication or simulcast, or both. Broadcasting program material in real time is known as live broadcasting. As technology for sound recording improved, an increasing proportion of broadcast programming used pre-recorded material. A current trend is the automation of radio stations. Some stations now operate without direct human intervention by using entirely pre-recorded material sequenced by computer control (see Voice-tracking). Radio stations are of several types. The best known are the AM and FM stations, including both commercial and public or nonprofit varieties. Non-commercial college and university radio stations are found throughout the developed world. The earliest radio stations were simply radio telegraph systems, and did not carry audio. The first known audio transmission that could be called a broadcast occurred on Christmas Eve in 1906, and was made by Reginald Fessenden. While many early experimenters attempted to create systems similar to radiotelephone devices where only two parties were meant to communicate, there were others who intended to transmit to larger audiences. Charles Herrold started broadcasting in California in 1909 and was carrying audio by the next year. For the next decade, radio tinkerers had to build their own radio receivers. KDKA AM of Pittsburgh, Pennsylvania (owned by Westinghouse) started broadcasting as the first "commercial" radio station on November 2, 1920. The commercial sense of the station came from the type of license—they didn't start airing advertisements until a few years later. The first broadcast was the results of the U.S. presidential election, 1920. Many historians base KDKA's status as "first" on the fact that commercially-produced radio receivers weren't available until that time. However, by that standard, many believe that other stations should count, as at least one smaller manufacturer with their own station was making radios by the time KDKA was licensed. AM stations were developed first. AM refers to amplitude modulation, a mode of broadcasting radio waves, and occurs on North American airwaves in the mediumwave frequency range of 530 to 1700 kHz (known as the "standard broadcast band"). The band was expanded in the 1990s by adding nine channels from 1620 to 1700 kHz. Channels are spaced every 10 kHz in the Americas, and generally every 9 kHz everywhere else. Europe also uses the longwave band. FM refers to frequency modulation, and occurs on VHF airwaves everywhere (except Japan) in the frequency range of 88 to 108 MHz. Japan uses the 74 to 90 MHz band. FM stations are much more popular in economically developed regions, such as Europe and the United States, especially since higher sound fidelity and stereo broadcasting became common in this format. The digital radio stations are now emerging, first in Europe (the U.K. and Germany), and later in the United States. The European system is named DAB, for Digital Audio Broadcasting, and uses the public domain EUREKA 147 system. In the United States, the IBOC system is named HD Radio and owned by a private company, a consortium called iBiquity. It is expected that for the next 10 to 20 years, all these systems will co-exist, while by 2015 to 2020 digital radio may predominate, at least in the developed countries. Many other non-broadcast types of radio stations exist. These include:
- base stations for police, fire and ambulance networks
- military base stations
- dispatch base stations for taxis, trucks, and couriers
- emergency broadcast systems
- amateur radio stations

External links

- [http://search.fcc.gov/query.html?qt=radio+station&col=fccall+edocs+digest&ht=0&qp=&qs=&qc=&pw=100%25&ws=0&la=en&qm=0&st=1&nh=10&lk=1&rf=0&oq=&rq=0&si=0&Submit+search+request.x=8&Submit+search+request.y=9 In the United States, See FCC]
- category:broadcast engineering ja:ラジオ放送局

California

California is a state located on the west coast of the United States. It is by far the most populous state in the U.S., as well as the most physically diverse, with the highest and the lowest points in the lower 48 states located within 150 miles of each other. If California were an independent nation, it would have the sixth largest economy in the world (after the rest of the U.S., Japan, Germany, Britain and France; see economy of California). The state's official nickname is "The Golden State" in reference to California's 1849 Gold Rush. California's U.S. postal abbreviation is CA, and its Associated Press abbreviation is Calif. As one of the most demographically diverse states in the nation, California is a dominant force in American culture as well as the nation's economy. It has some of the nation's largest cities, including Los Angeles, San Diego, San Jose, and San Francisco, and is responsible for many legal and technological innovations. The entire region originally known as California was composed of the Mexican peninsula now known as Baja California and much of the land in the current states of California, Nevada, Utah, Arizona and Wyoming, known as Alta California. In these early times, the boundaries of the Sea of Cortez and the Pacific coast were only partially explored and California was shown on early maps as an island. The name comes from Las sergas de Esplandián (Adventures of Splandian), a 16th century novel, by Garci Rodríguez de Montalvo, where there is an island paradise called California. (For further discussion, see: Origin of the name California.)

History

:Main articles: History of California, History of California (20th century) The first European to explore parts of the coast was the Portuguese João Rodrigues Cabrilho in 1542. The first to explore the entire coast and claim possession of it was Francis Drake in 1579. Beginning in the late 1700s, Spanish missionaries set up tiny settlements on enormous grants of land in the vast territory north of Baja California. The missions played a dominant role in the decimation of California's indigenous population. Upon Mexican independence from Spain, the chain of missions became the property of the Mexican government, and they were quickly dissolved and abandoned. In 1846, at the outset of the Mexican-American War, the California Republic was founded and the Bear Flag was flown, which featured a golden bear and a star. The Republic came to a sudden end, however, when Commodore John D. Sloat of the United States Navy sailed into San Francisco Bay and claimed California for the United States. Following the war, the region was divided between Mexico and the United States. The Mexican portion, Baja (lower) California was later divided into the states of Baja California and Baja California Sur. The western part of the U.S. portion, Alta (upper) California, was to become the state of California. In 1848, the Spanish-speaking population of distant upper California numbered around 4,000. But after gold was discovered, the population burgeoned with Americans and a few Europeans in the great California gold rush. In 1850, the state was admitted to the Union of the USA. During the American Civil War, popular support in California was divided 70% for the South and 30% for the North, and although California officially entered on the side of the North, many troops went east to fight for the Confederacy CSA. At first, travel between the far Pacific West to the eastern population centers was time-consuming and dangerous, requiring either long ocean voyages, or difficult transcontinental passages. A more direct connection came in 1869 with the completion of the first transcontinental railroad. After this rail link was established, hundreds of thousands of Americans came west, where new Californians were discovering that land in the state, if irrigated during the dry summer months, was extremely well suited to fruit cultivation and agriculture in general. Citrus, oranges in particular, was widely grown, and the foundation was laid for the state's prodigious agricultural production of today. During the early 20th century, migration to California accelerated with the completion of major transcontinental highways like the Lincoln Highway and Route 66. In the period from 1900 to 1965 the population grew from fewer than one million to become the most populous state in the Union. From 1965 to the present, the population demographic changed radically and became one of the most diverse in the world. The state is generally liberal-leaning, technologically and culturally savvy, and a world center of engineering businesses, the film and television industry and, as mentioned above, American agricultural production.

Law and government

California is governed as a republic, with three branches of government, the executive branch consisting of the Governor of California and the other independently elected constitutional officers, the legislative branch consisting of the Assembly and Senate, and the judicial branch consisting of the Supreme Court of California and lower courts. The state also allows direct participation of the electorate by referendum, recall, and ratification. The Governor of California and the other state constitutional officers serve four-year terms and may be re-elected only once. The California State Legislature consists of a 40 member Senate and 80 member Assembly. Senators serve four year terms and Assembly members two. The terms of the Senators are staggered so that half the membership is elected every two years. The Senators representing the odd-numbered districts are elected in years evenly divisible by four, i.e., presidential election years. The Senators from the even-numbered districts are elected in the intervening even-numbered years, in the gubernatorial election cycle. California's legislature is organized in such a way that the party caucus leaders wield great power and can usually speak on behalf of their caucuses. Many important legislative decisions are thus not made on the floor of the legislature but in back-room deals by the "Big Five", which comprises the governor and the Democratic and Republican leaders of each chamber. For the 2005–2006 session, there are 48 Democrats and 32 Republicans in the Assembly. In the Senate, there are 25 Democrats and 15 Republicans. The current Governor is the Republican Arnold Schwarzenegger, whose current term lasts through January 2007. Schwarzenegger was only the second person in the history of the United States to be put into office by a recall of a sitting governor (the first was the 1921 recall of North Dakota Governor Lynn J. Frazier). Schwarzenegger replaced Governor Gray Davis (1999–2003), who was removed from office by the October 2003 California recall election. The state's capital is Sacramento. During California's early history under European control, the capital was successively located in Monterey (1775–1849), San Jose (1849–1851), Vallejo (1852–1853), Benicia (1853–1854), and San Francisco (1862). The capital moved to Sacramento temporarily in 1852 when construction on a State House could not be completed in time in Vallejo. The capital's final move to Sacramento was on February 25, 1854 where it has been permanently, except for a four-month temporary move in 1862 to San Francisco, due to severe flooding in Sacramento. California's giant judiciary is the largest in the United States (with a total of 1,600 judges, while the federal system has only about 840). It is supervised by the seven Justices of the Supreme Court of California. Justices of the Supreme Court and Courts of Appeal are appointed by the Governor, but are subject to retention by the electorate every 12 years. Judges of the trial courts, the Superior Courts in each county, may be appointed by the Governor or elected directly by the voters, depending on when the vacancy occurs. Superior Court judges serve six-year terms, after which they may run for re-election. Unlike the retention elections for Supreme Court and Court of Appeal justices, Superior Court judges run for re-election in open races, in which other qualified candidates may run as challengers. California's legal system is explicitly based on English common law but carries a few features from Spanish civil law. Capital punishment is a legal form of punishment and the state has the largest "Death Row" population in the country. At the national level, California is represented by two senators and 53 representatives, as of 2005. It has 55 electoral votes in the U.S. Electoral College. (As California is the most populous state in the Union, its counts of Congressmen and Presidential Electors are, of course, also the largest.) The two U.S. Senators from California are Democrats Dianne Feinstein and Barbara Boxer. 33 Democrats and 20 Republicans represent the state in the U.S. House of Representatives. While California is among the most Democratic and liberal states in the nation because of the large concentration of voters in populous areas, much of California is politically very conservative, notably the Central Valley, the Inland Empire, Orange and San Diego counties, and most inland, eastern, and rural areas. Democratic bastions are mostly coastal and include the entire San Francisco Bay Area, Los Angeles, Salinas, Santa Barbara, and Imperial County. The state has supported Democrats in the last four presidential elections. In 2004, Republican President George W. Bush received a majority of votes in more than half the state's 58 counties, but still lost California's 55 electoral votes to John Kerry, who won 54.3% of the popular vote, by a margin of 10 percentage points. See also: List of California Governors, U.S. Congressional Delegations from California, List of California counties, List of California ballot propositions

Geography

California borders the Pacific Ocean, Oregon, Nevada, Arizona, and the Mexican state of Baja California. The state has strikingly beautiful natural features, including an expansive central valley, tall mountains, hot deserts, and hundreds of miles of scenic coastline. With an area of 411,000 km² it is the third largest state in the U.S and larger than Germany in size. Most major cities cling to the cool seacoast along the Pacific, notably Los Angeles, San Francisco, San Jose, Santa Ana/Orange County, and San Diego. However, the capital, Sacramento is in the Central Valley. California has extremely varied geography. In the center of the state lies the Central Valley, a huge, fertile valley bounded by the coastal mountain ranges in the west, the granite Sierra Nevada to the east, the volcanic Cascade Range in the north and the Tehachapi Mountains in the south. Mountain-fed rivers, dams, and canals provide water to irrigate the Central Valley. With dredging, several of these rivers have become sufficiently large and deep that several inland cities, notably Stockton, California, are seaports. The hot, fertile Central Valley is California's agricultural heartland and grows a large portion of America's food, yet near freezing temperatures are not uncommon during winter which sometimes wipe out portions of crops. The bottom part of the valley, which is part desert, is known as the San Joaquin Valley while the upper half is known as the Sacramento Valley. In the center and east of the state are the Sierra Nevada (meaning Snowy Range in Spanish), containing the highest peak in the contiguous lower 48 states, Mount Whitney, at 14,505 feet (4421 m). Also located in the Sierra are the world famous Yosemite National Park and a deep freshwater lake, Lake Tahoe, the largest lake in the state by volume. To the east of the Sierra are Owens Valley and Mono Lake, an essential seabird habitat. To the west is Clear Lake, California's largest freshwater lake by area. The Sierra Nevada receives arctic temperatures in the winter and holds several dozen small glaciers, including the most southern glacier in the United States (Palisade Glacier). California has about 35% of its total surface area covered by forests. California's diversity of pine species is unmatched by any other state. Though other states have a higher percentage of their land area covered by forests, in terms of total area, California contains more forestland than any other state except Alaska. Most of the forest is found in 2 places. First, in the northwestern part of the state and along the western slope of the Sierra Nevada. Smaller forests, mainly consisting of oaks, can be found along the coast ranges of California closer to the coast, and also in the foothills of the Sierra Nevada. Smaller areas of pine forests can be found in the San Gabriel and San Bernardino mountains of Southern California and also in the mountain areas of Central San Diego Country. Deserts in California make up about 25% of the total surface area. In the south lie the Transverse Ranges and a large salt lake, the Salton Sea. The south-central desert is called the Mojave. To the northeast of the Mojave lies Death Valley, which contains the lowest, hottest point in North America. The lowest point of Death Valley and the peak of Mount Whitney are less than 200 miles apart. The hiking trek between the two points has been attempted, several times, most notably by Lee Bergthold. Indeed, almost all of southeastern California is arid, hot desert, with the Coachella Valley routinely experiencing extreme high temperatures during the summer. Finally, along the densely-populated but long California coast lie a number of major metropolitan areas, including San Francisco Bay, Los Angeles, and San Diego. Climates near the Pacific Ocean are remarkably moderate compared with inland climates. Winter temperatures never reach freezing (snow is unheard of) and summer temperatures rarely reach above the high 80's Fahrenheit (27 °C). California is famous for its earthquakes, due partly to the presence of the San Andreas Fault. While more powerful earthquakes in the United States have occurred in Alaska and along the Mississippi River, California earthquakes are notable in their frequency and location in highly populated areas. Some people believe, eventually, a huge earthquake will result in the splitting of coastal California from the continent, either to sink into the ocean or form a new landmass. The fact that this scenario is completely implausible from a geologic standpoint does not lessen its acceptance in public conventional wisdom, or its exploitation by the producers of science fiction and fantasy media. Notable movies in which the possible destruction of much of California by an earthquake includes the titles Earthquake, A View to a Kill, Escape from L.A. and Superman. California is also home to several volcanoes, some active such as Mammoth Mountain. Other volcanoes include Lassen Peak, which erupted from 1914 and 1921, and Mount Shasta.

Climate

Different regions of California have very different climates, depending on their latitude, elevation, and proximity to the coast. Most of the state has a Mediterranean climate, with rainy winters and dry summers. The influence of the ocean generally moderates temperature extremes, creating warmer winters and substantially cooler summers, and the cold oceanic California Current offshore often creates summer fog near the coast. As one moves away from the coast, the climate becomes more continental, with colder winters and markedly hotter summers. The temperature gradient between immediate coast and low-lying inland valleys in the north is about 7 °F (4 °C) in winter, coast being warmer, and in summer roughly 25 °F (14 °C) but opposite. In the south, the figures are approximately 4 and 23 °F (2 °C and 13 °C), respectively; however 4 °F and 35 °F (2 °C and 20 °C) between Santa Barbara and Death Valley. Westerly winds from the ocean also bring moisture, and the northern parts of the state generally receive higher rainfall than the south. California's mountain ranges influence the climate as well: moisture-laden air from the west cools as it ascends the mountains, dropping moisture; some of the rainiest parts of the state are west-facing mountain slopes. Northwestern California has a temperate climate with rainfall of 15–40 inches (400–1000 mm) per year. The Central Valley has a Mediterranean climate, but with greater temperature extremes than the coastal areas; parts of the valley are often filled with thick fog, similar to that found in the coastal valleys. The high mountains, including the Sierra Nevada, have a mountain climate with snow in winter and mild to moderate heat in summer. On the east side of the mountains is a drier "rain shadow." California's desert climate regions lie east of the high Sierra Nevada and southern California's Transverse Ranges and Peninsular Ranges. The low deserts east of the southern California mountains, including the Imperial and Coachella valleys and the lower Colorado River, are part of the Sonoran Desert, with hot summers and mild winters; the higher elevation deserts of eastern California, including the Mojave Desert, Owens Valley, and the Modoc Plateau, are part of the Great Basin region, with hot summers and cold winters. Death Valley, in the northern portion of the Mojave Desert on the east side of the state, is the hottest spot on the Western Hemisphere, with high temperatures over 120 °F common in the summer. The highest temperature in the Western Hemisphere, 134 °F (56.6 °C), was recorded in Death Valley on July 10, 1913. Temperatures of 130 °F or higher have been recorded as recently as 2005. The 24-hour average July temperature in Death Valley is 101 °F (38 °C) (1961--1990 standard).

Ecology

Ecologically, California is one of the richest and most diverse parts of the world, and includes some of the most endangered ecological communities. California's diverse geography, geology, soils and climate have generated a tremendous diversity of plant and animal life. The State of California is part of the Nearctic ecozone, and spans a number of terrestrial ecoregions, and is perhaps the most ecologically diverse state in the United States. California has a rather high percentage of endemic species. California endemics include relict species that have died out elsewhere, including the redwoods and the Catalina Ironwood (Lyonothamnus floribundus). Many other endemics originated through differentiation or adaptive radiation, whereby multiple species develop from a common ancestor to take advantage of diverse ecological conditions. California's great abundance of species of California lilac (Ceanothus) is an example of adaptive radiation. Many California endemics have become endangered, as urbanization, logging, overgrazing, and the introduction of exotic species have encroached on their habitat. Furthermore, California is home to the largest trees in the world, the Giant Sequoias. California's native grasses were perennials, which stayed green year-round in most of the state's subclimates. After European contact, these were generally replaced by invasive species of European annual grasses; and, in modern times, California's hills turn a characteristic golden brown in summer and fall. California's nickname The Golden State is in reference to the California Gold Rush, and not to the golden brown summer hillsides as is sometimes stated.

Economy

California Gold Rush California Gold Rush] California has the fifth largest economy in the world. It is responsible for 14% of the United States' gross domestic product (GDP). The gross state product (GSP) is about $1.5 trillion ($1,500,000,000,000, as of 2004), making it greater than that of every other U.S. state, and most countries in the world (by Purchasing Power Parity). The predominant industry, more than twice as large as the next, is agriculture, (including fruit, vegetables, dairy, and wine). This is followed by aerospace; entertainment, primarily television by dollar volume, although many movies are still made in California; and light manufacturing including computer hardware and software, and the mining of borax. Per capita personal income was $33,403 as of 2003, ranking 12^th in the nation. Per capita income varies widely by geographic region and profession. The Central Valley has the most extreme contrasts of income, with migrant farm workers making less than minimum wage. While some coastal cities include some of the wealthiest per-capita areas in the U.S., notably San Francisco and Marin County, the non-agricultural central counties have some of the highest poverty rates in the U.S. The high-technology sectors in Northern California, specifically Silicon Valley, in Santa Clara and San Mateo counties, are currently emerging from economic downturn caused by the dot.com bust, which caused the loss of over 250,000 jobs in Northern California alone. Recent (Spring 2005) [http://uclaforecast.com economic data] indicates that economic growth has resumed in California, although still slightly below the national annualized forecast of 3.9%. The international boom in housing prices has been most pronounced in California, with the median property price in the state rising to about the half-million dollar mark in April 2005.

Demographics

Population

As of 2004 California had a population of 35,893,799. The state had 9,400,000 foreign-born residents (26.5% of the population), of which an estimated 2,209,000 were illegal aliens (illegal aliens accounted for nearly one-fourth of the foreign-born population and 6.2% of the total state population). California is the most populous state—more than 12 percent of Americans live in the state. California's population is larger than all but 33 countries; more populated than Canada.

Racial and Ancestral Makeup

The Census Bureau considers race and Hispanic origin to be two separate categories. Hispanics must not only select "Hispanic"; they must also select a race such as White or Asian, or, simply "some other race." This makes interpreting Census data difficult. Thus, for the sake of simplicity, the data below does consider Hispanic origin to be its own category. It therefore shows only non-Hispanic members of each group: non-Hispanic Whites, non-Hispanic Eskimos, non-Hispanic people of two or more races, etc. For more information on race and the Census, see [http://en.wikipedia.org/wiki/Race_%28U.S._Census%29 here].


	2000 Census [http://www.census.gov/popest/states/asrh/tables/SC-EST2003-03/SC-EST2003-03-28.pdf]	2003 Estimate [http://www.census.gov/popest/states/asrh/tables/SC-EST2003-03/SC-EST2003-03-28.pdf]
White	47.4%	45.2%
Hispanic/Latino	32.4%	34.3%
Asian	11.0%	11.4%
Black	6.5%	6.3%
Two or More Races	1.9%	1.9%
Native American and Inuit	0.5%	0.5%
Native Hawaiian and Other Pacific Islander	0.3%	0.3%

California lacks a majority ethnic group. It is the third minority-majority state, after Hawaii and New Mexico. Non-Hispanic Whites are still the largest group, but are no longer a majority of the population due to high levels of immigration in recent years. Hispanics make up over one-third of the population; in order, other groups are Asians, Blacks, and Native Americans. Because of high levels of immigration from Latin America, especially Mexico, and higher birth rates among the Hispanic population, Hispanics are predicted to become a majority in the state around 2040. California has the second-largest Asian population (percentage-wise) of any state, Hawaii having the largest. The largest ancestries in California are Mexican (25%), Filipino, German, Irish, and Asian. Mexicans and Chicanos predominate in Southern California, the Central Valley, Salinas, and parts of the San Francisco Bay area. Irish and German ancestries are dominant in the eastern Sierra Nevada, the far north, and the North Coast. San Francisco has the greatest concentration of Asians in the continental United States, with Chinese numerous in San Francisco, Alameda, and Santa Clara counties and Filipinos particularly numerous in San Mateo county.

Languages

As of 2000, 60.5% of California residents age 5 and older speak English at home and 25.8% speak Spanish. Chinese is the third most spoken language at 2.6%, followed by Tagalog at 2.5% and Vietnamese at 1.3%. The indigenous languages of California number more than one hundred, but most are in danger of language death, despite revitalization efforts. Since 1986, the California Constitution has specified English as the common and official language of the state. The politics of language, particularly concerning language policy regarding the teaching and official use of immigrant languages is a major political issue in the state.

Religion

The religious affiliations of the people of California:
- Christian – 75%
- Protestant – 38%
- Baptist – 8%
- Presbyterian – 3%
- Methodist – 2%
- Lutheran – 2%
- Other Protestant or general Protestant – 23%
- Roman Catholic – 34%
- Other Christian – 3%
- Jewish – 2%
- Other Religions – 3%
- Non-Religious – 20% As with many other western states, the percentage of California's population identifying themselves as "non-religious" is comparatively high in relation to the rest of the U.S.

Important cities and towns

Image:Sacramento from Riverwalk.jpg|Sacramento Image:DowntownLosAngeles.jpg|Los Angeles Image:Sandiego.arp.750pix.jpg|San Diego Image:Lightmatter sanfrancisco.jpg|San Francisco Image:SanJoseDowntownIMG016elf wb.jpg|San Jose Image:Long Beach, CA at night.jpg|Long Beach Image:La2-oakland.jpg|Oakland Image:Anaheimdland.jpg|Anaheim The state of California has 478 cities, the majority of which are within one of the large metropolitan areas. 68% of California's population lives in its two largest metropolitan areas, Greater Los Angeles and the San Francisco Bay Area.
- Population greater than 10,000,000 (urbanized area)
- Los Angeles/Long Beach (Greater Los Angeles)
- Population greater than 5,000,000 (urbanized area)
- San Francisco/Oakland/San Jose/Santa Rosa (San Francisco Bay Area)
- Population greater than 2,500,000 (urbanized area)
- San Diego
- Orange County
- Inland Empire (Riverside/San Bernardino)
- Population greater than 1,000,000 (urbanized area)
- Fresno
- Sacramento
- Population greater than 500,000 (urbanized area)
- Bakersfield
- Stockton
- Oxnard/Ventura (Ventura County)
- Population greater than 250,000 (urbanized area)
- Visalia/Tulare/Porterville (Tulare County)
- Modesto
- Salinas/Monterey (Monterey County)
- Santa Barbara/Goleta/Santa Maria (Santa Barbara County)
- Palmdale/Lancaster (Antelope Valley)
- Indio/Palm Springs (Coachella Valley) For a list of important suburbs within the above areas, see List of urbanized areas in California (by population).

25 wealthiest places in California

Thanks to the state's powerful economy, certain California cities are among the wealthiest on the planet. The following list is ranked by per capita income: 1 Belvedere, California - Marin County - $113,595
2 Rancho Santa Fe, California - San Diego County - $113,132
3 Atherton, California - San Mateo County - $112,408
4 Rolling Hills, California - Los Angeles County - $111,031
5 Woodside, California - San Mateo County - $104,667
6 Portola Valley, California - San Mateo County - $99,621
7 Newport Coast, California - Orange County - $98,770
8 Hillsborough, California - San Mateo County - $98,643
9 Diablo, California - Contra Costa County - $95,419
10 Fairbanks Ranch, California - San Diego County - $94,150
11 Hidden Hills, California - Los Angeles County - $94,096
12 Los Altos Hills, California - Santa Clara County - $92,840
13 Tiburon, California - Marin County - $85,966
14 Sausalito, California - Marin County - $81,040
15 Monte Sereno, California - Santa Clara County - $76,577
16 Indian Wells, California - Riverside County $76,187
17 Malibu, California - Los Angeles County - $74,336
18 Del Monte Forest, California - Monterey County - $70,609
19 Piedmont, California - Alameda County - $70,539
20 Montecito, California - Santa Barbara County - $70,077
21 Palos Verdes Estates, California - Los Angeles County - $69,040
22 Emerald Lake Hills, California - San Mateo County - $68,966
23 Loyola, California - Santa Clara County - $68,730
24 Blackhawk-Camino Tassajara, California - Contra Costa County - $66,972
25 Los Altos, California - Santa Clara County - $66,776
Note: Marin County ranks as the wealthiest county in the United States based on per capita personal income.

Education

Image:Berkeley glade afternoon.jpg|UC Berkeley Image:Stanford campus aerial photo.jpg|Stanford Image:USC Bovard Auditorium enh.jpg|USC Image:RHall.JPG|UCLA Image:Tower Hall and MDA.JPG|San Jose State Image:UCSD_lib1024.jpg|UC San Diego Image:Millikan Library.jpg|Caltech Image:Csulb pyramid.jpg|CSU Long Beach California's public educational system is supported by a unique constitutional amendment that requires 40% of state revenues to be spent on education. The preeminent state university is the University of California, which employs more Nobel Prize winners than any other institution in the world and is considered one of the finest public higher-education systems in the country. The nine general UC campuses are in Berkeley, Los Angeles, San Diego, Davis, Santa Cruz, Santa Barbara, Irvine, Riverside, and Merced. The University of California, San Francisco, teaches only graduate health-sciences students, and the Hastings College of Law, also in San Francisco, is one of UC's four law schools. The UC system is intended to accept students from the top 12.5% of college-bound students, and provide most graduate studies and research. The University of California also administers federal laboratories for the Federal Department of Energy: Lawrence Livermore National Laboratory, Lawrence Berkeley National Laboratory, and Los Alamos National Laboratory. The California State University system provides education for teachers, the trades, agriculture and industry. With over 400,000 students, the CSU system is the largest university system in the United States. It is intended to accept most college-bound high-school students, while carrying out some research, especially in applied sciences. Lower-division course credits are frequently transferable to the University of California. The California Community Colleges system provides vocational education, remedial education, and continuing education programs. It awards certificates and associate degrees. It also provides lower division general-education courses, whose credit units are transferable to the CSU and UC systems. It is composed of 109 colleges organized into 72 districts. The system serves a student population of over 2.9 million. Notable private universities include Stanford University, the University of Southern California (USC), and the California Institute of Technology (Caltech) (which administers the Jet Propulsion Laboratory for NASA). California has hundreds more private colleges and universities, including many religious and special-purpose institutions. This leads to many unique entertainment and educational opportunities for residents. For example, Southern California, with one of the highest densities of post-secondary institutions in the world, has a very large base of classically trained vocalists that compete in large choir festivals. Near Los Angeles, there are numerous art and film institutes, including the CalArts Institute. Public secondary education consists of high schools that teach elective courses in trades, languages and liberal arts with tracks for gifted, college-bound and industrial arts students. They accept students from roughly age 14 to 18, with mandatory education ceasing at age 16. In many districts, junior high schools or middle schools teach electives with a strong skills-based curriculum, for ages from 11 to 13. Elementary schools teach pure skills, history and social studies, with optional half-day kindergartens beginning at age 5. Mandatory full-time instruction begins at age 6. The primary schools are of varying effectiveness. The quality of the local schools depends strongly on the local tax base, and the size of the local administration. In some regions, administrative costs divert a significant amount of educational monies from instructional purposes. In poor regions, literacy rates may fall below 70%. One thing they all have in common is a state mandate to teach fourth grade students about the history of California, including the role of the early missions; most schools implement this by requiring students complete a multiple medium project.

Sports

California's large population has helped to make it home to many professional sports teams, including fifteen major professional sports league franchises, far more than any other state. However, since the re-location of the Los Angeles Raiders and Los Angeles Rams in the 1990s, it could be argued that no one city is able to lay claim to a "Grand Slam" (i.e. having a team in each of the four leagues) unless Oakland, San Francisco and San Jose are counted as being in a single metropolitan area.

Major league teams

Major League Baseball
- Los Angeles Angels of Anaheim
- Los Angeles Dodgers
- Oakland Athletics
- San Diego Padres
- San Francisco Giants National Basketball Association
- Golden State Warriors
- Los Angeles Clippers
- Los Angeles Lakers
- Sacramento Kings National Football League
- Oakland Raiders
- San Diego Chargers
- San Francisco 49ers National Hockey League
- Anaheim Mighty Ducks
- Los Angeles Kings
- San Jose Sharks

Other teams

Arena Football League
- San Jose Sabercats
- Los Angeles Avengers Major League Soccer
- Club Deportivo Chivas USA
- Los Angeles Galaxy
- San Jose Earthquakes Women's National Basketball Association
- Los Angeles Sparks
- Sacramento Monarchs

Transportation

Sacramento MonarchsCalifornia's vast terrain is connected by an extensive system of freeways, expressways, and highways, all maintained by Caltrans and patrolled by the California Highway Patrol, except for the numbered expressways in Santa Clara County which were built and maintained by the county itself. Californians typically take to the roads for their commutes, errands, and vacations, giving California's cities a reputation for severe traffic congestion. Almost all California highways are non-toll roads. Notable exceptions are any major bridges. As for air travel, Los Angeles International Airport and San Francisco International Airport are major hubs for trans-Pacific and transcontinental traffic. There are about a dozen important commercial airports and many more general aviation airports throughout the state's 58 counties. California also has several important seaports. The giant seaport complex formed by the Port of Los Angeles and the Port of Long Beach in Southern California is the largest in the country and responsible for handling about a fourth of all container cargo traffic in the United States. The Port of Oakland handles most of the ocean containers passing through Northern California. Port of Oakland ]] Intercity rail travel is provided by Amtrak. Los Angeles and San Francisco both have subway networks, in addition to

Amplitude modulation

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. (Contrast this with frequency modulation, in which the frequency of the carrier is varied; and phase modulation, in which the phase is varied.) AM is commonly used at radio frequencies and was the first method used to broadcast commercial radio. The term "AM" is sometimes used generically to refer to the AM broadcast (mediumwave) band (see AM radio).

Applications in radio

AM radio A basic AM radio transmitter works by first DC-shifting the modulating signal, then multiplying it with the carrier wave using a frequency mixer. The output of this process is a signal with the same frequency as the carrier but with peaks and troughs that vary in proportion to the strength of the modulating signal. This is amplified and fed to an antenna. An AM receiver consists primarily of a tunable filter and an envelope detector, which in simpler sets is a single diode. Its output is a signal at the carrier frequency, with peaks that trace the amplitude of the unmodulated signal. Unlike other modulation techniques, this is all that is needed to recover the original audio. In practice, a capacitor is used to undo the DC shift introduced by the transmitter and to eliminate the carrier frequency by connecting the signal peaks. The output is then fed to an audio amplifier. The fact that signals can be decoded using very simple equipment is one of the primary advantages of amplitude modulation. This was especially important in the early days of commercial radio, when electronic components were still quite expensive. This simplicity and affordability helped make AM one of the most popular methods for sending voice and music over radio during the 20th century. the 20th century, with the recovered audio fed directly to an earphone.]] AM radio's main limitation is its susceptibility to atmospheric interference, which is heard as static from the receiver. The narrow bandwidth traditionally used for AM broadcasts further limits the quality of sound that can be received. Since the 1970s wideband FM has been preferred for musical broadcasts, due to its higher audio fidelity and noise-suppression characteristics.

Forms of AM

In its basic form, amplitude modulation produces a signal with power concentrated at the carrier frequency and in two adjacent sidebands. Each sideband is equal in bandwidth to that of the modulating signal and is a mirror image of the other. Thus, most of the power output by an AM transmitter is effectively wasted: half the power is concentrated at the carrier frequency, which carries no useful information (beyond the fact that a signal is present); the remaining power is split between two identical sidebands, only one of which is needed. To increase transmitter efficiency, the carrier can be removed (suppressed) from the AM signal. This produces a reduced-carrier transmission or double-sideband suppressed carrier (DSSC) signal. If the carrier is only partially suppressed, a double-sideband reduced carrier (DSRC) signal results. DSSC and DSRC signals need their carrier to be regenerated (by a beat frequency oscillator, for instance) to be demodulated using conventional techniques. Even greater efficiency is achieved—at the expense of increased transmitter and receiver complexity—by completely suppressing both the carrier and one of the sidebands. This is single-sideband modulation, widely used in amateur radio due to its efficient use of both power and bandwidth. A simple form of AM often used for digital communications is on-off keying, a type of amplitude-shift keying by which binary data is represented as the presence or absence of a carrier wave. This is commonly used at radio frequencies to transmit Morse code, referred to as continuous wave (CW) operation.

Example

Suppose we wish to modulate a simple sine wave on a carrier wave. The equation for the carrier wave of frequency

\omega_c

, taking its phase to be a reference phase of zero, is :

c(t) = C \sin(\omega_c t)

. The equation for the simple sine wave of frequency

\omega_m

(the signal we wish to broadcast) is :

m(t) = M \sin(\omega_m t + \phi)

, with

\phi

its phase offset relative to

c(t)

. Amplitude modulation is performed simply by adding

m(t)

C

. The amplitude-modulated signal is then :

y(t) = (C + M \sin(\omega_m t + \phi)) \sin(\omega_c t)

The formula for

y(t)

above may be written :

y(t) = C \sin(\omega_c t) + M \frac - M \frac

The broadcast signal consists of the carrier wave plus two sinusoidal waves each with a frequency slightly different from

\omega_c

, known as sidebands. For the sinusoidal signals used here, these are at

\omega_c + \omega_m

and

\omega_c - \omega_m

. As long as the broadcast (carrier wave) frequencies are sufficiently spaced out so that these side bands do not overlap, stations will not interfere with one another.

A more general example

:This relies on knowledge of the Fourier Transform. The discussion of the figure may prove more useful for a quicker understanding. Consider a general modulating signal

m(t)

, which can now be anything at all. The same basic rules apply: :

\,y(t) = [C + m(t)]\cos(\omega_c t)

. Or, in complex form: :

y(t) = [C + m(t)]\frac

Taking Fourier Transforms, we get: :

|Y(\omega)| = \piC\delta(\omega - \omega_c) + \fracM(\omega - \omega_c) + \piC\delta(\omega + \omega_c) + \fracM(\omega + \omega_c)

, where

\delta(x)

is the Dirac delta function — a unit impulse at

x

— and capital functions indicate Fourier Transforms. This has two components: one at positive frequencies (centered on

+\omega_c

) and one at negative frequencies (centered on

-\omega_c

). There is nothing mathematically wrong with negative frequencies, and they need to be considered here — otherwise one of the sidebands will be missing. Shown below is a graphical representation of the above equation. It shows the modulating signal's spectrum on top, followed by the full spectrum of the modulated signal. spectrum This makes clear the two sidebands that this modulation method yields, as well as the carrier signals that go with them. The carrier signals are the impulses. Clearly, an AM signal's spectrum consists of its original (2-sided) spectrum shifted up to the carrier frequency. The negative frequencies are a mathematical nicety, but are essential since otherwise we would be missing the lower sideband in the original spectrum! As already mentioned, if multiple signals are to be transmitted in this way (by frequency division multiplexing), then their carrier signals must be sufficiently separated that their spectra do not overlap. This analysis also shows that the transmission bandwidth of AM is twice the signal's original (baseband) bandwidth — since both the positive and negative sidebands are 'copied' up to the carrier frequency, but only the positive sideband is present originally. Thus, double-sideband AM is spectrally inefficient. The various suppression methods in Forms of AM, can be seen clearly in the figure — with the carrier suppressed there will be no impulses and with a sideband suppressed, the transmission bandwidth is reduced back to the original, baseband, bandwidth — a significant improvement in spectrum usage. An analysis of the power consumption of AM reveals that DS-AM with its carrier has an efficiency of about 33% — very poor. The forms of AM with suppressed carriers are found to be 100% power efficient, since no power is wasted on the carrier signal which conveys no information.

Modulation index

As with other modulation indices, in AM, this quantity indicates by how much the modulated variable varies around its 'original' level. For AM, it relates to the variations in the carrier amplitude and is defined as: :

h = \frac

. So if

h=0.5

, the carrier amplitude varies by 50% above and below its unmodulated level, and for

h=1.0

it varies by 100%.

References

- Newkirk, David and Karlquist, Rick (2004). Mixers, modulators and demodulators. In D. G. Reed (ed.), The ARRL Handbook for Radio Communications (81st ed.), pp. 15.1–15.36. Newington: ARRL. ISBN 0-87259-196-4. Category:Radio modulation modes ko:진폭 변조 ja:振幅変調

1991

1991 (MCMXCI) is a common year starting on Tuesday of the Gregorian calendar.

Events

January

- January 2 - Sharon Pratt Dixon is sworn in as mayor of Washington, DC becoming the first black woman to lead a city of that size and importance.
- January 4 - The United Nations Security Council votes unanimously to condemn Israel's treatment of Palestinians.
- January 10 - SA State Govt forced to bail out State Bank.
- January 11 - The Soviets storm Vilnius to stop Lithuanian independence.
- January 12 - Gulf War: The U.S. Congress passes a resolution authorizing the use of military force to liberate Kuwait.
- January 13 - The Soviet Union troops assault the Vilnius TV tower in Lithuania and kill 14 unarmed civilians, many more are injured.
- January 13 - Soccer stampede and fight at Johannesburg, South Africa - 42 dead.
- January 14 - Three PLO guerilla chiefs assassinated in Tunis.
- January 16 - US serial killer Aileen Wuornos confesses to the murders of six men.
- January 17 - Operation Desert Storm begins.
- January 17 - Gulf War: The air strikes against Iraq begin.
- January 17 - Gulf War: Iraq fires 8 Scud missiles into Israel.
- January 17 - Harald V becomes King of Norway on the death of his father, Olav V.
- January 18 - Eastern Airlines shuts down after 62 years citing financial problems.
- January 26 - The Somalian president Siad Barre flees his compound in Mogadishu.
- January 29 - Siad Barre is succeeded by Ali Mahdi Muhammad.

February

February.]]
- February 4 - The Baseball Hall of Fame votes to ban Pete Rose.
- February 5 - A Michigan court bars Dr Jack Kevorkian from assisting in suicides.
- February 7 - Haiti's first democratically-elected president, Jean-Bertrand Aristide, is sworn in.
- February 7 - The IRA launches a mortar attack on 10 Downing Street during a cabinet meeting.
- February 9 - Voters in Lithuania vote for independence.
- February 11 - UNPO, the Unrepresented Nations & Peoples Organization, forms in the Hague, Netherlands.
- February 13 - Gulf War: Two laser-guided "smart bombs" destroy an underground bunker in Baghdad killing hundreds of Iraqis. Iraqi officials claim that the bunker was a bomb shelter but United States military intelligence identified it as a military facility.
- February 15 - The Visegrad Agreement, establishing cooperation to move toward free-market systems, is signed by the leaders of Czechoslovakia, Hungary and Poland.
- February 16 - Gulf War: American and British war planes bomb the suburbs of Baghdad, injuring at least 11 civilians and killing three others.
- February 22 - Gulf War: Iraq accepts a Russian proposed cease fire agreement. The US rejects the agreement, but said that retreating Iraqi forces would not be attacked if they left Kuwait within 24 hours.
- February 23 - Gulf War: Ground troops cross the Saudi Arabian border and enter Kuwait, thus starting the ground phase of the war.
- February 23 - Thailand: General Sunthorn Kongsompong leads a bloodless coup d'état, deposing Prime Minister Chatichai Choonhavan.
- February 25 - Gulf War: An Iraqi Scud missile hits an American military barracks in Dhahran, Saudi Arabia killing 28 US Marines.
- February 26 - Gulf War: On Baghdad radio, Iraqi leader Saddam Hussein announces the withdrawal of Iraqi troops from Kuwait. Iraqi soldiers set fire to Kuwaiti oil fields as they retreat.
- February 27 - Gulf War: Kuwait is liberated, and a ceasefire is declared, after 100 hours of ground fighting. Iraq accepts the terms of the ceasefire, which call for the country to disarm.

March

- March-April - Iraqi forces suppress rebellions in the southern and northern parts of the country, creating a humanitarian disaster on the borders of Turkey and Iran
- March 1 - Ballistic Missile Submarine USS-Lafayette (now ex-Lafayette) starts to be deactivated
- March 1 - Ethan-Allen-class submarine USS-Sam Houston (now ex-Sam Houston SSBN-609) starts to be deactivated
- March 1 - Clayton Keith Yeutter finishes as the United States Secretary of Agriculture, under the George H. W. Bush administration
- March 3 - An amateur video captures the beating of Rodney King by Los Angeles police officers.
- March 3 - Latvia and Estonia vote to become independent of the Soviet Union
- March 4 - Vermont celebrates its bicentennial statehood.
- March 4 - Most primitive form of World Wide Web is put online.
- March 9 - Massive demonstrations are held against Slobodan Milošević in Belgrade. Two people are killed and tanks are in the streets
- March 10 - Gulf War: Operation Phase Echo - 540,000 American troops begin to leave the Persian Gulf
- March 11 - A curfew is imposed on black townships in South Africa after fighting between rival political gangs killed 49.
- March 13 - The United States Department of Justice announces that Exxon has agreed to pay $1 billion for the clean-up of the Exxon Valdez oil spill in Alaska.
- March 14 - After 16 years in prison for allegedly bombing a pub in an Irish Republican Army attack, the "Birmingham Six" are freed when a court determines that the police fabricated evidence
- March 15 - Four Los Angeles, California