Spokane is a city in Spokane County in the state of Washington in the northwestern United States. It is located on the Spokane River west of the Rocky Mountain foothills in eastern Washington, 92 miles south of the Canada–US border, 18 miles from the Washington–Idaho border, 228 miles east of Seattle along Interstate 90. Known as the birthplace of Father's Day, Spokane's official nickname is the "Lilac City". A pink, double flower lilac variety known as'Syringa Spokane' is named for the city, it is the seat of Spokane County and the economic and cultural center of the Spokane Metropolitan Area, the Spokane–Coeur d'Alene combined statistical area, the Inland Northwest. The city, along with the whole Inland Northwest, is served by Spokane International Airport, 5 miles west of downtown Spokane. According to the 2010 Census, Spokane had a population of 208,916, making it the second-largest city in Washington, the 101st-largest city in the United States; the first people to live in the area, the Spokane tribe, lived off plentiful game.
David Thompson explored the area with the westward expansion and establishment of the North West Company's Spokane House in 1810. This trading post was the first long-term European settlement in Washington. Completion of the Northern Pacific Railway in 1881 brought settlers to the Spokane area; the same year it was incorporated as a city with the name of Spokane Falls. In the late 19th century and silver were discovered in the Inland Northwest; the local economy depended on mining and agriculture until the 1980s. Spokane hosted the first environmentally themed World's Fair at Expo'74. Many of the downtown area's older Romanesque Revival-style buildings were designed by architect Kirtland Kelsey Cutter after the Great Fire of 1889; the city features Riverfront and Manito parks, the Smithsonian-affiliated Northwest Museum of Arts and Culture, the Davenport Hotel, the Fox and Bing Crosby theaters. The Cathedral of Our Lady of Lourdes is the seat of the Roman Catholic Diocese of Spokane, the city is the center of the Mormon Spokane Washington Temple District.
The Cathedral of St. John the Evangelist represents the Anglican community. Gonzaga University was established in 1887 by the Jesuits, the private Presbyterian Whitworth University was founded three years and moved to north Spokane in 1914 In sports, the Gonzaga Bulldogs collegiate basketball team competes at the Division I level. Professional and semi-professional sports teams include the Spokane Chiefs in junior ice hockey, the Spokane Indians Minor League Baseball team located in nearby Spokane Valley; as of 2010, Spokane's only major daily newspaper, The Spokesman-Review, had a daily circulation of over 76,000. The first humans to live in the Spokane area were hunter-gatherer societies that lived off plentiful fish and game; the Spokane tribe, after which the city is named, are believed to be either their direct descendants, or descendants of people from the Great Plains. When asked by early white explorers, the Spokanes said their ancestors came from "up North." Early in the 19th century, the Northwest Fur Company sent two white fur trappers west of the Rocky Mountains to search for fur.
These were the first white men met by the Spokanes, who believed they were sacred, set the trappers up in the Colville River valley for the winter. The explorer-geographer David Thompson, working as head of the North West Company's Columbia Department, became the first European to explore the Inland Empire. Crossing what is now the Canada–US border from British Columbia, Thompson wanted to expand the North West Company further south in search of furs. After establishing the Kullyspell House and Saleesh House trading posts in what are now Idaho and Montana, Thompson attempted to expand further west, he sent out two trappers, Jacques Raphael Finlay and Finan McDonald, to construct a fur trading post on the Spokane River, which flows west from Lake Coeur d'Alene to the Columbia River, trade with the local Indians. This post was established in 1810, at the confluence of the Little Spokane and Spokane rivers, becoming the first enduring European settlement of significance in what became Washington state.
Known as the Spokane House, or "Spokane", it was in operation from 1810 to 1826. Operations were run by the British North West Company and the Hudson's Bay Company, the post was the headquarters of the fur trade between the Rocky and Cascade mountains for 16 years. After the latter business absorbed the North West Company in 1821, the major operations at the Spokane House were shifted north to Fort Colville, reducing the post's significance. In 1836, Reverend Samuel Parker visited the area and reported that around 800 Native Americans were living in Spokane Falls. A medical mission was established by Marcus and Narcissa Whitman to cater for Cayuse Indians and hikers of the Oregon Trail at Walla Walla in the south. After the Whitmans were killed by Indians in 1847, Reverend Cushing Eells established Whitman College in their memory setting up the first church in Spokane. In 1853, two years after the establishment of the Washington Territory, the first governor, Isaac Stevens, made an initial effort to make a treaty with Chief Garry and the Spokanes at Antoine Plantes' Ferry, not far from Millwood.
After the last campaign of the Yakima Indian War, the Coeur d'Alene War of 1858 was brought to a close by the actions of Col. George Wright, who won decisive victories agai
Kirkland is a city in King County, United States. A suburb east of Seattle, its population was 88,630 in a 2017 census estimate, which made it the sixth largest city in the county and the twelfth largest in the state; the city's downtown waterfront has restaurants, art galleries, a performing arts center, public parks, a collection of public art bronze sculptures. Kirkland was the original home of the Seattle Seahawks. Warehouse chain Costco had its headquarters in Kirkland. While Costco is now headquartered in Issaquah, the city is the namesake of its "Kirkland Signature" store brand; the land around Lake Washington to the east of Seattle was first settled by Native Americans. English settlers arrived in the late 1860s, when the McGregor and Popham families built homesteads in what is now the Houghton neighborhood. Four miles to the north people settled near what is now called Juanita Bay, a favored campsite of the Natives because a wild potato, "wapatos", thrived there; the Curtis family arrived in the area in the 1870s, followed by the French family in 1872.
The Forbes family homesteaded what is now Juanita Beach Park in 1876, settled on Rose Hill in 1877. Additional people settled in the area, by the end of the 1880s, a small number of logging and boat-building communities were established. In 1886, Peter Kirk, a British-born enterprising businessman seeking to expand the family's Moss Bay steel production company, moved to Washington after hearing that iron deposits had been discovered in the Cascade mountain range. Other necessary components such as limestone, needed in steel smelting, were available in the area. Further yet, a small number of coalmines had been established nearby in Newcastle and train lines were under construction. Plans were underway to build the Lake Washington Ship Canal. Kirk realized that if a town were built near the water it would be a virtual freshwater port to the sea, as well as help support any prospective mill. At the time, Kirk was not a U. S. could not purchase any land. Leigh S. J. Hunt owner of the Seattle Post-Intelligencer, offered to partner with Kirk and buy the necessary real estate.
Under their new venture, the Kirkland Land and Development Company and Hunt purchased thousands of acres of land in what is now Kirkland's downtown in July 1888. Kirk and his associates started the construction of a new steel mill soon after, named Moss Bay Iron and Steel Company of America. After founding the city of Kirkland in 1888 one of the earliest on the Eastside at the time, Kirk's vision of a "Pittsburgh of the West" was beginning to take form. Construction soon commenced on several substantial brick homes and business blocks that would house and serve the steel mill employees. However, the Seattle, Lake Shore and Eastern Railway, purchased by Tacoma-based Northern Pacific, had now refused to construct a rail line to the lake; this would, after all, have a negative impact on Tacoma, furiously competing with Seattle as the dominant Puget Sound seaport. The ensuing financial issues and numerous obstacles took a toll on Kirk, running out of investors. Hunt was in debt from the purchase of land.
The plans continued and the steel mill was completed in late 1892 on Rose Hill. Financial issues arose and due to the Panic of 1893 the mill subsequently closed without producing any steel. In spite of everything, Kirk was determined not to give up on his namesake town, Kirkland was incorporated in 1905 with a population of 532. A final attempt at a steel mill in Kirkland was planned by James A. Moore in 1906, his company, the Northwestern Iron & Steel Company paid $250,000 in cash for a 1,500-acre site but the mill never materialized. This came at the heels of the Pacific Steel Company, incorporated earlier in 1906 by J. F. Duthie, William Calvert and L. S. Cragin; this company soon amounted to nothing. In 1900 the Curtis family made a living operating a ferry-construction business on Lake Washington. Along with Captain John Anderson, the Curtises were among the first to run ferries in the area. Leschi, first operated on December 27, 1913, was the original wooden ferry to transport automobiles and people between the Eastside and Madison Park until her retirement in 1950.
The ferry operations ran nearly continuously for 18 hours each day. The construction of the first Lake Washington floating bridge in 1940, made ferry service unprofitable and led to its cancellation. Subsequent years saw wool warship building become the major industries; the first woolen mill in the state of Washington was built in Kirkland in 1892. The mill was the primary supplier of wool products for the Alaska Gold Rush prospectors and for the U. S. military during World War I. By 1917, after the completion of the Lake Washington Ship Canal, the construction of ocean-going vessels had become a major business. By 1940, the thriving Lake Washington Shipyard had constructed more than 25 warships during World War II for the U. S. Navy, on what is now Carillon Point. Since the incorporation of Kirkland in 1905, the city has grown to 12 times its original geographic boundaries, nearly doubling in size during the 1940s and 1960s; the Kirkland Historical Annexation Areas Map provides a history of Kirkland's expansion by Annexation.
Kirkland consolidated with the neighboring town of H
FM broadcasting is a method of radio broadcasting using frequency modulation technology. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. Theoretically wideband AM can offer good sound quality, provided the reception conditions are ideal. FM radio stations use the VHF frequencies; the term "FM band" describes the frequency band in a given country, dedicated to FM broadcasting. Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions: In the former Soviet republics, some former Eastern Bloc countries, the older 65.8–74 MHz band is used. Assigned frequencies are at intervals of 30 kHz; this band, sometimes referred to as the OIRT band, is being phased out in many countries.
In those countries the 87.5–108.0 MHz band is referred to as the CCIR band. In Japan, the band 76–95 MHz is used; the frequency of an FM broadcast station is an exact multiple of 100 kHz. In most of South Korea, the Americas, the Philippines and the Caribbean, only odd multiples are used. In some parts of Europe and Africa, only multiples are used. In the UK odd or are used. In Italy, multiples of 50 kHz are used. In most countries the maximum permitted frequency error is specified, the unmodulated carrier should be within 2000 Hz of the assigned frequency. There are other unusual and obsolete FM broadcasting standards in some countries, including 1, 10, 30, 74, 500, 300 kHz. However, to minimise inter-channel interference, stations operating from the same or geographically close transmitter sites tend to keep to at least a 500 kHz frequency separation when closer frequency spacing is technically permitted, with closer tunings reserved for more distantly spaced transmitters, as interfering signals are more attenuated and so have less effect on neighboring frequencies.
Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave. With FM, frequency deviation from the assigned carrier frequency at any instant is directly proportional to the amplitude of the input signal, determining the instantaneous frequency of the transmitted signal; because transmitted FM signals use more bandwidth than AM signals, this form of modulation is used with the higher frequencies used by TV, the FM broadcast band, land mobile radio systems. The maximum frequency deviation of the carrier is specified and regulated by the licensing authorities in each country. For a stereo broadcast, the maximum permitted carrier deviation is invariably ±75 kHz, although a little higher is permitted in the United States when SCA systems are used. For a monophonic broadcast, again the most common permitted. However, some countries specify a lower value for monophonic broadcasts, such as ±50 kHz. Random noise has a triangular spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest audio 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 audio frequencies in the receiver reduces the high-frequency noise; these processes of boosting and reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively. The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 µs time constant is used. In the Americas and South Korea, 75 µs is used; this applies to both stereo transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing; the use of pre-emphasis becomes a problem because of the fact that many forms of contemporary music contain more high-frequency energy than the musical styles which prevailed at the birth of FM broadcasting. Pre-emphasizing these high frequency sounds would cause excessive deviation of the FM carrier. Modulation control devices are used to prevent this.
Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis. Long before FM stereo transmission was considered, FM multiplexing of other types of audio level information was experimented with. Edwin Armstrong who invented FM was the first to experiment with multiplexing, at his experimental 41 MHz station W2XDG located on the 85th floor of the Empire State Building in New York City; these FM multiplex transmissions started in November 1934 and consisted of the main channel audio program and three subcarriers: a fax program, a synchronizing signal for the fax program and a telegraph “order” channel. These original FM multiplex subcarriers were amplitude modulated. Two musical programs, consisting of both the Red and Blue Network program feeds of the NBC Radio Network, were transmitted using the same system of subcarrier modulation as part of a studio-to-transmitter link system. In April 1935, the AM subcarriers were replaced with much improved results.
The first FM subcarrier transmissions emanating from Major Armstrong's experimental station KE2XCC at Alpine, New Jersey occurred in 1948. These transmissions consisted of two-cha
Redmond is a city in King County, United States, located 16 miles east of Seattle. The population was 64,291 in a 2017 census estimate. Redmond is recognized as the home of Microsoft and Nintendo of America. With an annual bike race on city streets and the state's only velodrome, Redmond is known as the "Bicycle Capital of the Northwest". Native Americans have lived in the Redmond area for over 10,000 years, based on artifacts discovered at the Redmond Town Center archaeological site and Marymoor Prehistoric Indian Site; the first European settlers arrived in the 1870s. Luke McRedmond filed a Homestead Act claim for land next to the Sammamish Slough on September 9, 1870, the following year Warren Perrigo took up land adjacent to him; the rivers and streams had so many salmon that the settlement was named Salmonberg. More settlers came, with the establishment of the first post office in 1881, the name of the community was changed to Melrose; the new name was derived from Melrose House, which upset McRedmond.
After becoming postmaster, he petitioned to have the name changed to Redmond in 1883. The abundant forests and fish of Redmond provided jobs for loggers and fishermen and with those jobs came demand for goods and services, bringing in merchants; the logging industry expanded in 1889 when Seattle Lake Shore & Eastern Railway built a station in the center of town. The first plat for Redmond was filed on May 11, 1891, encompassing much of the area now known as downtown. After reaching the necessary population of 300, Redmond was incorporated on December 31, 1912. Redmond experienced an economic downturn in the 1920s. Prohibition forced saloons to close; the forests were declining after heavy logging. The deforested land was suitable for farming. Agriculture became Redmond's primary business; when the U. S. entered shipyard jobs and other wartime work came to Redmond. After the war, Redmond's expansion began in earnest; the city expanded over thirty times larger in area through annexations between 1951 and 1967.
From 1956 to 1965, Redmond was bordered by the town of East Redmond, formed by rural homeowners and dissolved by the Washington Supreme Court. The completion of the Evergreen Point Floating Bridge across Lake Washington in 1963 allowed Redmond to flourish as a suburb of Seattle. In 1978, the U. S. Census Bureau proclaimed Redmond the fastest growing city in the state. Many technology companies made the city their home, the increasing population demanded more retail shops. Redmond underwent a commercial boom during the 1990s, culminating in 1997 with the opening of Redmond Town Center, a major regional shopping center on the site of a long-defunct golf course. In recent years the city has been experiencing growing pains as a result of its rapid expansion in the areas of urban sprawl and traffic congestion. During rush hour it can take upwards of 2 hours to travel from the beginning of SR-520 at Avondale Road to Downtown Seattle, a mere 18 miles away; these problems are being mitigated by the expansion of SR-520 and the Evergreen Point Floating Bridge, as well as the planned light rail service via the East Link Extension from Seattle to Redmond to open in 2023.
Redmond is bordered by Kirkland to the west, Bellevue to the southwest, Sammamish to the southeast. Unincorporated King County lies to the east; the city's urban downtown lies just north of Lake Sammamish. Overlake, the city's second urban center, is to the west of Lake Sammamish; the Sammamish River runs north from the lake along the west edge of the city's downtown. Redmond is located at 47°40′10″N 122°07′26″W. According to the United States Census Bureau, the city has a total area of 16.94 square miles, of which, 16.28 square miles is land and 0.66 square miles is water. Redmond, like most of the Pacific Northwest, has a mild climate for its latitude, but still gets all four seasons. Summers tend to be warm and dry, with low rainfall and sunny or sunny from June to September. Winters tend to be wet, with November being the rainiest month. Snowfall is uncommon, with the most common cold air being in a form of a high pressure system, driving out the rains from the area. However, snowfall is not as rare as in other cities like Seattle near the moderating effects of Puget Sound.
The average warmest month is August. The highest recorded temperature was 105 °F on July 29, 2009. On average, the coolest month is January; the lowest recorded temperature was −7 °F in January 1950. The maximum average precipitation occurs in December. According to a 2015 estimate, the annual median income for a household in the city was $99,586; the average home value in 2014 was $649,000. As of the census of 2010, there were 54,144 people, 22,550 households, 13,890 families residing in the city; the population density was 3,325.8 inhabitants per square mile. There were 24,177 housing units at an average density of 1,485.1 per square mile. The racial makeup of the city was 65.2% White, 1.7% African American, 0.4% Native American, 25.4% Asian, 0.2% Pacific Islander, 3.2% from other races, 4.0% from two or more races. Hispanic or Latino of any race were 7.8% of the population. There were 22,550 households of which 32.4% had children under the age of 18 living with them, 51.4% were married couples living together, 6.9% had a female householder with no husband present, 3.3% had a male householder with no wife present, 38.4% were non-families.
29.6% of all households were made up of individua
Seattle metropolitan area
The Seattle metropolitan area is an urban conglomeration in the U. S. state of Washington that includes Seattle and its surrounding satellites and suburbs. It includes the three most populous counties in the state—King and Pierce—and is considered a component of the greater Puget Sound region; the United States Census Bureau defines the metropolitan area as the Seattle–Tacoma–Bellevue, WA Metropolitan Statistical Area. With an estimated population of 3,867,046 as of 2017, it is the 14th largest Metropolitan Statistical Area in the United States, with half of Washington's population; as defined by the United States Census Bureau, the Seattle metropolitan area is made up of the following: Seattle–Bellevue–Everett metropolitan division King County: Seattle and its immediate vicinity Snohomish County: north of Seattle Tacoma metropolitan division Pierce County: south of SeattleBased on commuting patterns, the adjacent metropolitan areas of Olympia and Mount Vernon, along with a few smaller satellite urban areas, are grouped together in a wider labor market region known as the Seattle–Tacoma–Olympia Combined Statistical Area known as the Puget Sound region.
The population of this wider region is 4,686,536—roughly two-thirds of Washington's population—as of 2017. The Seattle CSA is the 12th largest CSA, the 13th largest primary census statistical area in the country; the additional metropolitan and micropolitan areas included are: Bremerton–Silverdale metropolitan area Kitsap County: west of Seattle, separated from the city by Puget Sound. The racial makeup of the MSA were as followed: White: 71.9% Black or African American: 5.6% American Indian and Alaskan Native: 1.1% Asian: 11.4% Pacific Islander: 0.8% Two or more races: 5.3% Some other race: 3.8% Hispanic or Latino: 9.0% In 2010 the median income for a household in the MSA was $63,088 and the median income for a family was $76,876. The per capita income was $32,401. According to the Pew Research Center's 2014 U. S. Religious Landscape Study, the Seattle metropolitan area's religious affiliation is as follows: Christian: 52% Protestant Christian: 34% Catholic Christian: 15% Other Christian: 3% Non-Christian faiths: 10% Buddhist: 2% Hindu: 2% Judaism: 1% Islam: Less than 1% Other faiths: 4% Unaffiliated: 37% Don't Know: 1% Major Seattle Tacoma Bellevue EverettOther Seattle–Tacoma International Airport Paine Field Boeing Field Harvey Airfield Renton Municipal Airport U.
S. Route 2 Interstate 5 State Route 7 State Route 9 State Route 16 State Route 18 Interstate 90 State Route 99 U. S. Route 101 State Route 202 Interstate 405 State Route 520 State Route 522 Interstate 605 Interstate 705 Sound Transit, buses, light rail in Puget Sound area Community Transit, buses in Snohomish County except Everett King County Metro, buses in King County Pierce Transit, buses in Pierce County Everett Transit, bus service in the city of Everett Intercity Transit, bus service in Thurston County Mason Transit Authority, bus service in Mason County Seattle Streetcar, streetcar service in the city of Seattle
In electronics and telecommunications, a transmitter or radio transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, applied to the antenna; when excited by this alternating current, the antenna radiates radio waves. Transmitters are necessary component parts of all electronic devices that communicate by radio, such as radio and television broadcasting stations, cell phones, walkie-talkies, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, spacecraft, radar sets and navigational beacons; the term transmitter is limited to equipment that generates radio waves for communication purposes. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not called transmitters though they have similar circuits; the term is popularly used more to refer to a broadcast transmitter, a transmitter used in broadcasting, as in FM radio transmitter or television transmitter.
This usage includes both the transmitter proper, the antenna, the building it is housed in. A transmitter can be a separate piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver; the term transmitter is abbreviated "XMTR" or "TX" in technical documents. The purpose of most transmitters is radio communication of information over a distance; the information is provided to the transmitter in the form of an electronic signal, such as an audio signal from a microphone, a video signal from a video camera, or in wireless networking devices, a digital signal from a computer. The transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, called the carrier signal; this process is called modulation. The information can be added to the carrier in several different ways, in different types of transmitters. In an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude.
In a frequency modulation transmitter, it is added by varying the radio signal's frequency slightly. Many other types of modulation are used; the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as cell phones, walkie-talkies, garage door openers. In more powerful transmitters, the antenna may be located on top of a building or on a separate tower, connected to the transmitter by a feed line, a transmission line. Electromagnetic waves are radiated by electric charges undergoing acceleration. Radio waves, electromagnetic waves of radio frequency, are generated by time-varying electric currents, consisting of electrons flowing through a metal conductor called an antenna which are changing their velocity or direction and thus accelerating. An alternating current flowing back and forth in an antenna will create an oscillating magnetic field around the conductor.
The alternating voltage will charge the ends of the conductor alternately positive and negative, creating an oscillating electric field around the conductor. If the frequency of the oscillations is high enough, in the radio frequency range above about 20 kHz, the oscillating coupled electric and magnetic fields will radiate away from the antenna into space as an electromagnetic wave, a radio wave. A radio transmitter is an electronic circuit which transforms electric power from a power source into a radio frequency alternating current to apply to the antenna, the antenna radiates the energy from this current as radio waves; the transmitter impresses information such as an audio or video signal onto the radio frequency current to be carried by the radio waves. When they strike the antenna of a radio receiver, the waves excite similar radio frequency currents in it; the radio receiver extracts the information from the received waves. A practical radio transmitter consists of these parts: A power supply circuit to transform the input electrical power to the higher voltages needed to produce the required power output.
An electronic oscillator circuit to generate the radio frequency signal. This generates a sine wave of constant amplitude called the carrier wave, because it serves to "carry" the information through space. In most modern transmitters, this is a crystal oscillator in which the frequency is controlled by the vibrations of a quartz crystal; the frequency of the carrier wave is considered the frequency of the transmitter. A modulator circuit to add the information to be transmitted to the carrier wave produced by the oscillator; this is done by varying some aspect of the carrier wave. The information is provided to the transmitter either in the form of an audio signal, which represents sound, a video signal which represents moving images, or for data in the form of a binary digital signal which represents a sequence of bits, a bitstream. Different types of transmitters use different modulation methods to transmit information: In an AM transmitter the amplitude of the carrier wave is varied in proportion to the modulation signal.
In an FM transmitter the frequency of the carrier is varied by the modulation signal. In an FSK transmitter, which transmits digital data, the frequency of the carrier is shifted between two frequencies which represent the two binary digits, 0 and 1. Many oth
A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance over dipole antennas—or omnidirectional antennas in general—when greater concentration of radiation in a certain direction is desired. A high-gain antenna is a directional antenna with a narrow radiowave beam width; this narrow beam width allows more precise targeting of the radio signals. Most referred to during space missions, these antennas are in use all over Earth, most in flat, open areas where no mountains lie to disrupt radiowaves. By contrast, a low-gain antenna is an omnidirectional antenna with a broad radiowave beam width, that allows the signal to propagate reasonably well in mountainous regions and is thus more reliable regardless of terrain. Low-gain antennas are used in spacecraft as a backup to the high-gain antenna, which transmits a much narrower beam and is therefore susceptible to loss of signal.
All practical antennas are at least somewhat directional, although only the direction in the plane parallel to the earth is considered, practical antennas can be omnidirectional in one plane. The most common types are the Yagi antenna, the log-periodic antenna, the corner reflector antenna, which are combined and commercially sold as residential TV antennas. Cellular repeaters make use of external directional antennas to give a far greater signal than can be obtained on a standard cell phone. Satellite Television receivers use parabolic antennas. For long and medium wavelength frequencies, tower arrays are used in most cases as directional antennas; when transmitting, a high-gain antenna allows more of the transmitted power to be sent in the direction of the receiver, increasing the received signal strength. When receiving, a high gain antenna captures more of the signal, again increasing signal strength. Due to reciprocity, these two effects are equal—an antenna that makes a transmitted signal 100 times stronger will capture 100 times as much energy as the isotropic antenna when used as a receiving antenna.
As a consequence of their directivity, directional antennas send less signal from directions other than the main beam. This property may be used to reduce interference. There are many ways to make a high-gain antenna. Horn antennas can be constructed with high gain, but are less seen. Still other configurations are possible—the Arecibo Observatory uses a combination of a line feed with an enormous spherical reflector, to achieve high gains at specific frequencies. Antenna gain is quoted with respect to a hypothetical antenna that radiates in all directions, an isotropic radiator; this gain, when measured in decibels, is called dBi. Conservation of energy dictates. For example, if a high gain antenna makes a 1 watt transmitter look like a 100 watt transmitter the beam can cover at most 1⁄100 of the sky. In turn this implies that high-gain antennas must be physically large, since according to the diffraction limit, the narrower the beam desired, the larger the antenna must be. Antenna gain can be measured in dBd, gain in Decibels compared to the maximum intensity direction of a half wave dipole.
In the case of Yagi type aerials this more or less equates to the gain one would expect from the aerial under test minus all its directors and reflector. It is important not to confuse dBd. Gain is dependent on the number of elements and the tuning of those elements. Antennas can be tuned to be resonant over a wider spread of frequencies but, all other things being equal, this will mean the gain of the aerial is lower than one tuned for a single frequency or a group of frequencies. For example, in the case of wideband TV antennas the fall off in gain is large at the bottom of the TV transmitting band. In the UK this bottom third of the TV band is known as group A. Other factors may affect gain such as aperture, efficiency; these factors are easy to improve without adjusting other features of the antennas or coincidentally improved by the same factors that increase directivity, so are not emphasized. High gain antennas are the largest component of deep space probes, the highest gain radio antennas are physically enormous structures, such as the Arecibo Observatory.
The Deep Space Network uses 35 m dishes at about 1 cm wavelengths. This combination gives the antenna gain of about 100,000,000, making the transmitter appear about 100 million times stronger, a receiver about 100 million times more sensitive, provided the target is within the beam; this beam can cover at most one hundred millionth of the sky, so accurate pointing is required. Use of high gain and Millimeter-