Digital terrestrial television
Digital terrestrial television is a technology for broadcast television in which land-based television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format. DTTV is a major technological advance over the previous analog television, has replaced analog, in common use since the middle of the 20th century. Test broadcasts began in 1998 with the changeover to DTTV beginning in 2006 and is now complete in many countries; the advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, lower operating costs for broadcasters. Different countries have adopted different digital broadcasting standards; the amount of data that can be transmitted is directly affected by channel capacity and the modulation method of the transmission. North America uses the ATSC standard with 8VSB modulation, which has similar characteristics to the vestigial sideband modulation used for analog television.
This provides more immunity to interference, but is not immune to multipath distortion and does not provide for single-frequency network operation. The modulation method in DVB-T is COFDM with either 16-state Quadrature Amplitude Modulation. In general, 64QAM is capable of transmitting a greater bit rate, but is more susceptible to interference. 16 and 64QAM constellations can be combined in a single multiplex, providing a controllable degradation for more important program streams. This is called hierarchical modulation. DVB-T are designed to work in single frequency networks. Developments in video compression have resulted in improvements on the original H.262 MPEG 2 codec, surpassed by H.264/MPEG-4 AVC and more H.265 HEVC. H.264 enables three high-definition television services to be coded into a 24 Mbit/s DVB-T European terrestrial transmission channel. DVB-T2 increases this channel capacity to 40 Mbit/s, allowing more services. DTTV is received either via a digital set-top box, TV gateway or more now an integrated tuner included with television sets, that decodes the signal received via a standard television antenna.
These devices now include digital video recorder functionality. However, due to frequency planning issues, an aerial capable of receiving a different channel group may be required if the DTTV multiplexes lie outside the reception capabilities of the installed aerial; this is quite common in the UK. Indoor aerials are more to be affected by these issues and need replacing. Main articles: List of digital television deployments by country, Digital television transition Afghanistan launched digital transmissions in Kabul using DVB-T2/MPEG-4 on Sunday, 31 August 2014. Test transmissions had commenced on 4 UHF channels at the start of June 2014. Transmitters were provided by GatesAir. Bangladesh had its first DTT service DVB-T2 / MPEG-4 on April 2016 launched by the GS Group; the service is called RealVU. It is done with partnership with Beximco. GS Group acts as a supplier and integrator of its in-house hardware and software solutions for the operator's functioning in accordance with the modern standards of digital television.
RealVu provides more than 100 TV channels in HD quality. The digital TV set-top boxes developed by GS Group offer such functions as PVR and time-shift, along with an EPG. India adopted DVB-T system for digital television in July 1999; the first DVB-T transmission was started on 26 January 2003 in the four major metropolitan cities by Doordarshan. The terrestrial transmission is available in both digital and analog formats. 4 high power DVB-T transmitters were set up in the top 4 cities, which were upgraded to DVB-T2 + MPEG4 and DVB-H standards. An additional 190 high power, 400 low power DVB-T2 transmitters have been approved for Tier I, II and III cities of the country by 2017; the Indian telecom regulator, TRAI, had recommended the I&B to allow private broadcast companies to use the DTT technology, in 2005. So far, the Indian I&B ministry only permits private broadcast companies to use satellite, cable and IPTV based systems; the government's broadcasting organisation Doordarshan had started the free TV service over DVB - T2 to the mobile phone users from February 25 onwards and extended to cover 16 cities including the four metros from April 5, 2016.
Israel started digital transmissions in MPEG-4 on Sunday, August 2, 2009, anal
DirecTV is an American direct broadcast satellite service provider based in El Segundo, California and is a subsidiary of AT&T. Its satellite service, launched on June 17, 1994, transmits digital satellite television and audio to households in the United States, Latin America and the Caribbean, its primary competitors are cable television providers. On July 24, 2015, after receiving approval from the United States Federal Communications Commission and United States Department of Justice, AT&T acquired DirecTV in a transaction valued at $67.1 billion. As of Q1 2017, DirecTV U. S. had 21 million revenues of $12 billion. On November 30, 2016, DirecTV Now, their internet streaming TV service, was launched. In 1953, Howard Hughes created the Howard Hughes Medical Institute, to which he transferred full ownership of Hughes Aircraft. Ostensibly created as a non-profit medical research foundation, HHMI was accused of being used by Hughes as a tax shelter. Following Hughes' death in 1976, HHMI was incorporated in 1977, litigation ensued to determine whether it would be allowed to maintain its interest in Hughes Aircraft.
In 1984, the court appointed a new board for HHMI, which proceeded to sell off Hughes Aircraft to General Motors on December 20, 1985, for an estimated $5.1 billion. General Motors merged Hughes Aircraft with its subsidiary Delco Electronics to create Hughes Electronics Corporation; the new subsidiary was composed of four units: Delco Electronics Company, Hughes Aircraft Company, Hughes Space and Communications Company, Hughes Network Systems. Stanley E. Hubbard founded United States Satellite Broadcasting in 1981 and was a leading proponent for the development of direct-broadcast satellite service in the United States. USSB was awarded five frequencies at the coveted 101-degree west satellite location. Hughes Communications, Inc. was awarded 27 frequencies at the same 101-degree location. After many years, the technology was developed to enable the building of high-power satellites, digital compression standards were developed that allowed multiple digital television channels to be sent through each satellite frequency.
Hughes attempted to create a joint venture with NBC, News Corp. and Cablevision in 1990, to launch the first high-power digital television service called Sky Cable. Failing to do so, the company instead created DirecTV as a separate division and secured an agreement with USSB to build and launch the first high-power direct-broadcast satellite system. DirecTV's name is a portmanteau of "direct" and "TV". Hughes/DirecTV turned to Thomson Consumer Electronics to develop the digital satellite system for the service that would be capable of receiving 175 channels on a small 18-inch dish; these dishes utilized a new generation of smaller, lighter receiver dishes based on military technology introduced by the Global Broadcast System, which predated DirecTV's viability by ten years. Hughes was awarded the contract to build and launch the new high-powered satellites, USSB and DirecTV agreed that the new satellites would carry the two separate programming services: USSB and DirecTV; the USSB and DirecTV programming services were launched on June 17, 1994.
Digital Equipment Corporation provided the hardware for DirecTV, Matrixx Marketing provided customer care via the Matrixx Plus department, DBS Systems created the billing software. In December 1998, DirecTV acquired USSB for $1.3 billion, combined the two satellite services. In 1999, DirecTV acquired PrimeStar, a competitor in the satellite television industry, for $1.83 billion increasing its share of the satellite television market in the US. In September 1996, Hughes purchased 70% of PanAmSat for $3 billion. In 1997, GM transferred it to Delphi Automotive Systems; that same year, Hughes Aircraft was sold to Raytheon for $9.5 billion. Raytheon filed a lawsuit in 1999 accusing Hughes of overstating the value of Hughes Aircraft by $1 billion. A $635.5-million settlement was reached in 2001. In 2000, Hughes Space and Communications was sold to Boeing for $3.75 billion, which it claimed had been overvalued by Hughes. Hughes settled with Boeing for $360 million; these sales left DirecTV, PanAmSat and Hughes Network Systems as the remaining components of Hughes Electronics.
Direct satellite broadcaster were mandated in 1992 to set aside 4% of its channel space for noncommercial educational and informational programming. DirecTV selected C-SPAN, EWTN and the Trinity Broadcasting Network from its current channel lineup plus request additional proposals from other programmers. DirecTV had given PBS Kids, PBS's original application, carriage that did not count against the set aside six weeks before the deadline. DirecTV selected an additional six channels. In 2000, DirecTV introduced the first live in-flight television service for airlines. In September 2000, GM executives, under pressure from GM's shareholders as a result of its poor performance and the greater market worth of Hughes, authorized Hughes executives to begin seeking buyers. In 2001, News Corporation began negotiations to acquire Hughes Electronics in a deal worth $8 billion, which would allow News Corp. to expand its Sky Global Networks satellite television operations into the United States. Negotiations with News Corp. failed, Hughes entered into an agreement on October 28, 2001 to be purchased for $26 billion
Height above average terrain
Height above average terrain, or effective height above average terrain, is a measure of how high an antenna site is above the surrounding landscape. HAAT is used extensively in FM radio and television, as it is more important than effective radiated power in determining the range of broadcasts. For international coordination, it is measured in meters by the Federal Communications Commission in the United States, as Canada and Mexico have extensive border zones where stations can be received on either side of the international boundaries. Stations that want to increase above a certain HAAT must reduce their power accordingly, based on the maximum distance their station class is allowed to cover; the FCC procedure to calculate HAAT is: from the proposed or actual antenna site, either 12 or 16 radials were drawn, points at 2, 4, 6, 8, 10 miles radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station; the altitude of the antenna site, minus the average altitude of all the specified points, is the HAAT.
This can create some unusual cases in mountainous regions—it is possible to have a negative number for HAAT. The FCC has divided the Contiguous United States into three zones for the determination of spacing between FM and TV stations using the same frequencies. FM and TV stations are assigned maximum ERP and HAAT values, depending on their assigned zones, to prevent co-channel interference; the FCC regulations for ERP and HAAT are listed under Title 47, Part 73 of the Code of Federal Regulations. Maximum HAAT: 150 metres Maximum ERP: 50 kilowatts Minimum co-channel separation: 241 km Maximum HAAT: 600 metres Maximum ERP: 100 kilowatts Minimum co-channel separation: 290 km. In all zones, maximum ERP for analog TV transmitters is. In addition, Zone I-A consists of all of California south of 40° north latitude, Puerto Rico and the U. S. Virgin Islands. Zones I and I-A have the most "grandfathered" overpowered stations, which are allowed the same extended coverage areas that they had before the zones were established.
One of the most powerful of these stations is WBCT in Grand Rapids, which operates at 320,000 watts and 238 meters HAAT. Zone III consists of all of Florida and the areas of Alabama, Louisiana and Texas within 241.4 kilometers of the Gulf of Mexico. Zone II is all the rest of the Continental United States and Hawaii. Above mean sea level Above ground level Canadian Radio-television and Telecommunications Commission List of broadcast station classes United States Federal Communications Commission 47 CFR Part 73 Index FCC: Mass Media Calculated Contours FCC: HAAT Calculator "Superpower" Grandfathered FM stations
Local marketing agreement
In North American broadcasting, a local marketing agreement is a contract in which one company agrees to operate a radio or television station owned by another party. In essence, it is a sort of time-buy. Under Federal Communications Commission regulations, a local marketing agreement must give the company operating the station under the agreement control over the entire facilities of the station, including the finances and programming of the station, its original licensee still remains responsible for the station and its operations, such as compliance with relevant regulations regarding content. A "local marketing agreement" may refer to the sharing or contracting of only certain functions, in particular advertising sales; this may be referred to as a time brokerage agreement, local sales agreement, management services agreement, or most a joint sales agreement or shared services agreement. JSAs are counted toward ownership caps for radio stations. In Canada, local marketing agreements between domestic stations require the consent of the Canadian Radio-television and Telecommunications Commission, although Rogers Media has used a similar arrangement to control a U.
S.-based radio station in a border market. The increased use of sharing agreements by media companies to form consolidated, "virtual" duopolies became controversial between 2009 and 2014 arrangements where a company buys a television station's facilities and assets, but sells the license to an affiliated third-party "shell" corporation, who enters into agreements with the owner of the facilities to operate the station on their behalf. Activists have argued that broadcasters were using these agreements as a loophole for the FCC's ownership regulations, that they reduce the number of local media outlets in a market through the aggregation or outright consolidation of news programming, allow station owners to have increased leverage in the negotiation of retransmission consent with local subscription television providers. Station owners have contended that these sharing agreements allow streamlined, cost-effective operations that may be beneficial to the continued operation of lower-rated and/or financially weaker stations in smaller markets.
In 2014 under chairman Tom Wheeler, the FCC began to increase its scrutiny regarding the use of such agreements—particularly joint sales—to evade its policies. On March 31, 2014, the commission voted to make joint sales agreements count as ownership if the senior partner sells 15% or more of advertising time for its partner, to ban coordinated retransmission consent negotiations between two of the top four stations in a market. Wheeler indicated that he planned to address local marketing and shared services agreements in the future; the change in stance prompted changes to then-proposed acquisitions by Gray Television and Sinclair Broadcast Group, rather than use sharing agreements to control them, moved their existing programming and network affiliations to digital subchannels of existing company-owned stations in the market, or a low-power station, relinquished control over the original stations by selling their licenses to third-parties, such as minority-owned broadcasters Due to the FCC's limits on station ownership at the time, local marketing agreements in radio, in which a smaller station would sell its entire airtime to a third-party in time-buy, were widespread between the 1970s and early 1990s.
These alliances gave larger broadcasters a way to expand their reach, smaller broadcasters a means of obtaining a stable stream of revenue. In 1992, the FCC began allowing broadcasting companies to own multiple radio stations in a single market. Following these changes, local marketing agreements fell out of favor for radio, as it was now possible for broadcasters to buy another station outright rather than lease it – consequentially triggering a wave of mass consolidation in the radio industry. However, broadcasters still used local marketing agreements to help transition acquired stations to their new owners; the first local marketing agreement in North American television was formed in 1991, when the Sinclair Broadcast Group purchased Fox affiliate WPGH-TV in Pittsburgh, Pennsylvania. As Sinclair had owned independent station WPTT in that market, which would have violated FCC rules which at the time had prohibited television station duopolies, Sinclair decided to sell the lower-rated WPTT to the station's manager Eddie Edwards, but continued to operate the station through an LMA.
Sinclair's use of local marketing agreements would lead to legal issues in 1999, when Glencairn, Ltd. announced that it would acquire Fox affiliate KOKH-TV in Oklahoma City, Oklahoma from Sullivan Broadcasting. As the family of Sinclair Broadcast Group founder Julian Smith controlled 97% of Glencairn's stock assets and the company was to be paid with Sinclair stock in turn for the purchases, KOKH and Sinclair-owned WB affiliate KOCB would constitute a duo
Fairbanks is a home rule city and the borough seat of the Fairbanks North Star Borough in the U. S. state of Alaska. Fairbanks is the largest city in the Interior region of Alaska. 2016 estimates put the population of the city proper at 32,751, the population of the Fairbanks North Star Borough at 97,121, making it the second most populous metropolitan area in Alaska. The Metropolitan Statistical Area encompasses all of the Fairbanks North Star Borough and is the northernmost Metropolitan Statistical Area in the United States, located 196 driving miles south of the Arctic Circle. Fairbanks is home to the University of Alaska Fairbanks, the founding campus of the University of Alaska system. Though, as of yet, there is not a known permanent Alaska Native settlement at the site of Fairbanks, Athabascan peoples have used the area for thousands of years. An archaeological site excavated on the grounds of the University of Alaska Fairbanks uncovered a Native camp about 3,500 years old, with older remains found at deeper levels.
From evidence gathered at the site, archaeologists surmise that Native activities in the area were limited to seasonal hunting and fishing as fridge temperatures precluded berry gathering. In addition, archeological sites on the grounds of nearby Fort Wainwright date back well over 10,000 years. Arrowheads excavated from the University of Alaska Fairbanks site matched similar items found in Asia, providing some of the first evidence that humans arrived in North America via the Bering Strait land bridge in deep antiquity. Captain E. T. Barnette founded Fairbanks in August 1901 while headed to Tanacross, where he intended to set up a trading post; the steamboat on which Barnette was a passenger, the Lavelle Young, ran aground while attempting to negotiate shallow water. Barnette, along with his party and supplies, were deposited along the banks of the Chena River 7 miles upstream from its confluence with the Tanana River; the sight of smoke from the steamer's engines caught the attention of gold prospectors working in the hills to the north, most notably an Italian immigrant named Felice Pedroni and his partner Tom Gilmore.
The two met Barnette where he convinced him of the potential of the area. Barnette set up his trading post at the site, still intending to make it to Tanacross. Teams of gold prospectors soon congregated around the newly founded Fairbanks. After some urging by James Wickersham, who moved the seat of the Third Division court from Eagle to Fairbanks, the settlement was named after Charles W. Fairbanks, a Republican senator from Indiana and the twenty-sixth Vice President of the United States, serving under Theodore Roosevelt during his second term. In these early years of settlement, the Tanana Valley was an important agricultural center for Alaska until the establishment of the Matanuska Valley Colonization Project and the town of Palmer in 1935. Agricultural activity still occurs today in the Tanana Valley, but to the southeast of Fairbanks in the communities of Salcha and Delta Junction. During the early days of Fairbanks, its vicinity was a major producer of agricultural goods. What is now the northern reaches of South Fairbanks was the farm of Paul J. Rickert, who came from nearby Chena in 1904 and operated a large farm until his death in 1938.
Farmers Loop Road and Badger Road, loop roads north and east of Fairbanks, were home to major farming activity. Badger Road is named for Harry Markley Badger, an early resident of Fairbanks who established a farm along the road and became known as "the Strawberry King". Ballaine and McGrath Roads, side roads of Farmers Loop Road, were named for prominent local farmers, whose farms were in the immediate vicinity of their respective namesake roads. Despite early efforts by the Alaska Loyal League, the Tanana Valley Agriculture Association and William Fentress Thompson, the editor-publisher of the Fairbanks Daily News-Miner, to encourage food production, agriculture in the area was never able to support the population, although it came close in the 1920s; the construction of Ladd Army Airfield starting in 1939, part of a larger effort by the federal government during the New Deal and World War II to install major infrastructure in the territory for the first time, fostered an economic and population boom in Fairbanks which extended beyond the end of the war.
In the 1940s the Canol pipeline extended north from Whitehorse for a few years. The Haines - Fairbanks 626 mile long 8" petroleum products pipeline was constructed during the period 1953-55; the presence of the U. S. military has remained strong in Fairbanks. Ladd became Fort Wainwright in 1960. Fairbanks suffered from several floods in its first seven decades, whether from ice jams during spring breakup or heavy rainfall; the first bridge crossing the Chena River, a wooden structure built in 1904 to extend Turner Street northward to connect with the wagon roads leading to the gold mining camps washed out before a permanent bridge was constructed at Cushman Street in 1917 by the Alaska Road Commission. On August 14, 1967, after record rainfall upstream, the Chena began to surge over its banks, flooding the entire town of Fairbanks overnight; this disaster led to the creation of the Chena River Lakes Flood Control Project, which built and operates the 50-foot-high Moose Creek Dam in the Chena River and accompanying 8-mile-long spillway.
The project was designed to prevent a repetition of the 1967 flood by being able to
Ninilchik is a census-designated place in Kenai Peninsula Borough, United States. At the 2010 census the population was 883, up from 772 in 2000, it is considered an Alaska Native village under the Alaska Native Claims Settlement Act. In the 1970s, villagers formed the Ninilchik Native Association Incorporated; the Ninilchik Traditional Council was established as the government of Alaska Natives in this area. The Alaska Native people of Ninilchik have ancestors of Aleut and Alutiiq descent, as well as some Dena'ina. Many include Russian ancestors, from a couple of men who settled here with their Alutiiq wives and children in 1847, migrants. Russian was spoken in the village for years. Due to the community's isolation, this Russian dialect continued much in its mid-19th century form. With some surviving speakers, it has been studied in the 21st century. Ninilchik is on the west side of the Kenai Peninsula on the coast of Cook Inlet, 38 miles by air southwest of Kenai, 100 miles southwest of Anchorage.
Road access is by the Sterling Highway. By actual road miles it is a distance of 188 miles 44 miles from Homer. According to the United States Census Bureau, the CDP has a total area of 207.2 square miles, of which 0.03 square miles, or 0.01%, are water. Ninilchik first appeared on the 1880 U. S. Census as an unincorporated Creole village. All 53 of its residents were Creole, it returned in 1890 with 81 residents, however the census combined the adjacent locales of the Laida native village and Anchor Point mine along with Treadwell coal mine. There were 53 Creole residents, 16 Natives, 12 Whites. Ninilchik did not return again until 1920, it returned as Ninilchik again in 1930, in every successive census to date. It was made a census-designated place in 1980; as of the census of 2000, there were 772 people, 320 households, 223 families residing in the CDP. The population density was 3.7 people per square mile. There were 762 housing units at an average density of 3.7/sq mi. The racial makeup of the CDP was 82.25% White, 13.99% Native American, 0.52% Asian, 0.13% from other races, 3.11% from two or more races.
0.65% of the population were Hispanic or Latino of any race. There were 320 households out of which 29.4% had children under the age of 18 living with them, 59.4% were married couples living together, 6.9% had a female householder with no husband present, 30.3% were non-families. 23.1% of all households were made up of individuals and 7.8% had someone living alone, 65 years of age or older. The average household size was 2.41 and the average family size was 2.87. In the CDP, the population was spread out with 24.1% under the age of 18, 5.4% from 18 to 24, 26.3% from 25 to 44, 29.5% from 45 to 64, 14.6% who were 65 years of age or older. The median age was 42 years. For every 100 females, there were 110.4 males. For every 100 females age 18 and over, there were 114.7 males. The median income for a household in the CDP was $36,250, the median income for a family was $41,750. Males had a median income of $29,861 versus $22,750 for females; the per capita income for the CDP was $18,463. About 10.4% of families and 13.9% of the population were below the poverty line, including 13.2% of those under age 18 and 7.2% of those age 65 or over.
Before the arrival of Europeans in Alaska, Ninilchik was a Dena'ina Athabaskan lodging area used for hunting and fishing. The name Ninilchik derives from Niqnilchint, a Deni'ana Athabaskan word meaning "lodge is built place"; the first Europeans who permanently settled in the village were Russian colonists who moved there from Kodiak Island in 1847, two decades before the Alaska Purchase in 1867 by the United States. They were Russian Grigorii Kvasnikov, his Russian-Alutiiq wife Mavra Rastorguev, their children, they were soon joined by the Oskolkoff family headed by a Russian man and Alutiiq woman. These were the core families, their descendants, who married Alutiiq, made up most of the village, their dialect of Russian as spoken in the mid-1800s became the primary language spoken in Ninilchik, it survived in that form long past the 1867 Alaska Purchase. A few speakers of the Ninilchik Russian dialect were still alive in 2013. Russian and American linguists are cataloging this isolated dialect.
The 1880 United States Census listed 53 "Creoles" living in Ninilchik in nine extended families. All nine old families of Ninilchik are descendants of the original Kvasnikoff and Oskolkoff families, with numerous marriages to Alaska Natives Alutiiq. In 1896, a school was staffed by Russian Orthodox priests and laymen. Russian Orthodox priests were respected by Alaska Natives because in several areas of southwest Alaska, they had learned indigenous languages and held religious services in those languages. In 1901, the local Russian Orthodox Church was constructed at its current site. In 1911 the first school sanctioned by the U. S. government was known as the Ninilchik School. In 2011 the community celebrated the 100th anniversary of the school. In the 1940s, a number of American homesteaders began to live in the area. In 1949, Berman Packing Company began fish canning operations at Ninilchik. In 1950, the Sterling Highway was completed through the town. A 2007 fir
Ultra high frequency
Ultra high frequency is the ITU designation for radio frequencies in the range between 300 megahertz and 3 gigahertz known as the decimetre band as the wavelengths range from one meter to one tenth of a meter. Radio waves with frequencies above the UHF band fall into the super-high frequency or microwave frequency range. Lower frequency signals fall into lower bands. UHF radio waves propagate by line of sight, they are used for television broadcasting, cell phones, satellite communication including GPS, personal radio services including Wi-Fi and Bluetooth, walkie-talkies, cordless phones, numerous other applications. The IEEE defines the UHF radar band as frequencies between 1 GHz. Two other IEEE radar bands overlap the ITU UHF band: the L band between 1 and 2 GHz and the S band between 2 and 4 GHz. Radio waves in the UHF band travel entirely by line-of-sight propagation and ground reflection. UHF radio waves are blocked by hills and cannot travel far beyond the horizon, but can penetrate foliage and buildings for indoor reception.
Since the wavelengths of UHF waves are comparable to the size of buildings, trees and other common objects and diffraction from these objects can cause fading due to multipath propagation in built-up urban areas. Atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, the attenuation increases with frequency. UHF TV signals are more degraded by moisture than lower bands, such as VHF TV signals. Since UHF transmission is limited by the visual horizon to 30–40 miles and to shorter distances by local terrain, it allows the same frequency channels to be reused by other users in neighboring geographic areas. Public safety, business communications and personal radio services such as GMRS, PMR446, UHF CB are found on UHF frequencies as well as IEEE 802.11 wireless LANs. The adopted GSM and UMTS cellular networks use UHF cellular frequencies. Radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required; when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day.
The length of an antenna is related to the length of the radio waves used. Due to the short wavelengths, UHF antennas are conveniently short. UHF wavelengths are short enough that efficient transmitting antennas are small enough to mount on handheld and mobile devices, so these frequencies are used for two way land mobile radio systems, such as walkie-talkies, two way radios in vehicles, for portable wireless devices. Omnidirectional UHF antennas used on mobile devices are short whips, sleeve dipoles, rubber ducky antennas or the planar inverted F antenna used in cellphones. Higher gain omnidirectional UHF antennas can be made of collinear arrays of dipoles and are used for mobile base stations and cellular base station antennas; the short wavelengths allow high gain antennas to be conveniently small. High gain antennas for point-to-point communication links and UHF television reception are Yagi, log periodic, corner reflectors, or reflective array antennas. At the top end of the band slot antennas and parabolic dishes become practical.
For satellite communication and turnstile antennas are used since satellites employ circular polarization, not sensitive to the relative orientation of the transmitting and receiving antennas. For television broadcasting specialized vertical radiators that are modifications of the slot antenna or reflective array antenna are used: the slotted cylinder, zig-zag, panel antennas. UHF television broadcasting fulfilled the demand for additional over-the-air television channels in urban areas. Today, much of the bandwidth has been reallocated to land mobile, trunked radio and mobile telephone use. UHF channels are still used for digital television. UHF spectrum is used worldwide for land mobile radio systems for commercial, public safety, military purposes. Many personal radio services use frequencies allocated in the UHF band, although exact frequencies in use differ between countries. Major telecommunications providers have deployed voice and data cellular networks in UHF/VHF range; this allows mobile phones and mobile computing devices to be connected to the public switched telephone network and public Internet.
UHF radars are said to be effective at tracking stealth fighters, if not stealth bombers. UHF citizens band: 476–477 MHz Television broadcasting uses UHF channels between 503 and 694 MHz Fixed point-to-point Link 450.4875 - 451.5125 MHz Land mobile service 457.50625 - 459.9875 MHz Mobile satellite service: 406.0000 - 406.1000 MHz Segment and Service examples: Land mobile for private, Australian and Territory Government, Rail industry and Mobile-Satellite 430–450 MHz: Amateur radio 470–806 MHz: Terrestrial television 1452–1492 MHz: Digital Audio Broadcasting Many other frequency assignments for Canada and Mexico are similar to their US counterparts 380–399.9 MHz: Terrestrial Trunked Radio service for emergency use 430–440 MHz: Amateur ra