Ultra high frequency
Ultra High Frequency (UHF) is a electromagnetic radiation. Especially its frequency is between 300 MHz and 3 GHz (3,000 MHz). Because of short wavelength, UHF has strong directivity and it has small area. UHF is commonly used for television signals. It is strong enough to be protected from other signal, but because of its strong directivity, receiving error by an obstacle occurs more. Hence it needs sensitive sensors.
Uses[change | change source]
UHF frequencies have higher attenuation from atmospheric moisture and benefit less from 'bounce', or the reflection of signals off the ionosphere back to earth, when compared to VHF frequencies. The frequencies of 300–3000 MHz are always at least an order of magnitude above the MUF (Maximum Usable Frequency). The MUF for most of the earth is generally between 25–35 MHz. Higher frequencies also benefit less from ground mode transmission. However, the short wavelengths of UHF frequencies allow compact receiving antennas with narrow elements; many people consider them less ugly than VHF-receiving models
United States[change | change source]
On December 29, 1949 KC2XAK of Bridgeport, Connecticut became the first UHF television station to operate on a regular daily schedule.
In the United States, UHF stations (broadcast channels above 13) originally gained a reputation for being more locally owned, less polished, less professional, less popular, and for having a weaker signal than their VHF counterparts (channels 2–13). The movie UHF, starring Weird Al Yankovic, parodied this phenomenon.
However, with the emergence of additional broadcast television networks ( Fox, UPN, WB, and PaxThe PAX Network PAX TV PaxNet or simply PAX is a cable television network formed in 1998. PAX, which is owned by Paxson Communications, shows family-oriented programming. Its programming contains little or no sex, violence or strong language. Unlike most), the concentration of media ownershipConcentration of media ownership is a commonly used terms among media critics, policy makers, and others to characterize ownership structure of media industries. Media ownership is said to be concentrated usually in one or more of the following ways., and the proliferation of cable televisionCable television or Community Antenna Television CATV (and often shortened to 'cable') is a system of providing television, FM radio programming and other services to consumers through fixed coaxial cables, rather than by the older and more widespread rad, digital televisionDigital television DTV uses digital modulation and compression to broadcast video, audio and data signals to television sets.
Introduction A major use of DTV can be to carry more channels on the same amount of bandwidth. Another can be high-definition pro, and DSSDigital Satellite System (DSS) or Direct Broadcast Satellite (DBS is a technology to deliver a television or audio signal digitally, directly from an orbiting satellite to a consumer's one- to three-foot-diameter dish at the consumer's home or business. in the 1990sCenturies: 19th century 20th century 21st century Decades: 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s 2020s 2030s 2040s Years: Events and trends Computers, technology Explosive growth of the Internet; decrease in the cost of computers and other techn, the distinction between UHF and VHF stations has virtually disappeared in the United States. Most HDTV stations (those using the ATSC television standard) broadcast their over-the-air signal in the UHF band.
United Kingdom[change | change source]
In Britain, UHF television began with the launch of BBC2 in 1964, using a 625-line system (which had higher resolution, and therefore required greater bandwidth, than the existing 405-line system). BBC1 and ITV soon added their own 625-line services on UHF (British channels 21 to 69), and PAL colour was introduced on UHF only in 1967– 1969. VHF was phased out by 1986. Today all British terrestrial television channels (analog and digital) are on UHF. A drawback to this is the very large number of small relay transmitters needed to fill in gaps in the main transmitters' coverage, which would not have been necessary with a VHF system due to its different propagation characteristics.