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
441-line television system
441 lines, or 383i if named using modern standard, is an early electronic monochrome television system. It was used with 50 interlaced frames per second in France and Germany, where it was an improvement over the previous 180-line system. In the United States it was used by RCA with 60 frames per second from 1938 to 1941. After trials in 375 lines during the Berlin Olympic Games of 1936, by 1937 Germany had introduced a 441 lines with 50 interlaced fields per second television system that replaced the previous 180 lines network relayed by a special Reichspost cable network in the country's main cities; the system's line frequency was 11025 Hz and the broadcast frequencies were 46.0 MHz for vision and 43.2 MHz for sound. Its image aspect ratio was close to 1.15:1. A project began in 1938 involving the National Post and several companies including Bosch, Loewe, Lorenz, TeKaDe and Telefunken that aimed to produce 10,000 units of the television system. However, due to the onset of the Second World War only about 50 devices were installed in military hospitals and various government departments.
The transmitter's aerials in Berlin were destroyed during an Allied Forces' bombing in November 1943, but the station was relayed by a special coaxial cables network to "wide screen" public "TV-rooms" so it carried on this way until 1944. Sample programme on YouTube The Einheitsempfänger is a German TV receiver created in 1939, it could only receive one channel. This allowed for lower prices and would have made difficult the reception of foreign channels, were any of them available; the dimensions of the 1939 receiver were: Case Dimensions: 65 cm x 37 cm x 38 cm Image size / diagonal: 19.5 cm x 22.5 cm / 29 cm. Television programs were for wounded soldiers of the Wehrmacht occupation troops who recovered in the Greater Paris Area hospitals, but they included French-language shows. Broadcasts were monitored in the United Kingdom during the Second World War to gather intelligence information from occupied France; because the 819 lines standard had been adopted in 1948 for the national network, it was due to cease on January 1, 1958.
However, after a long elections coverage night, most of the equipment was destroyed by fire on January 3, 1956. It was decided to indemnify the 3,000 owners of remaining 441 lines sets and to entitle them to reduced rates for their new 819 lines receivers. Since July 1952 the 441 lines transmitter was no longer broadcasting separate programs, but picked up the national network's picture through an 819-441 lines "optical converter"; the line frequency was 11025 Hz with vision broadcast at 46.0 sound at 42.0 MHz. Aerials were independent for audio and vision at the top of the Eiffel tower, both vertically polarized. No gain being obtained from these pre-war basic aerials, the effective radiated power was only the transmitter's peak one, i.e. 30 kW which enabled a good reception in a radius of 100 km around Paris. As displayed in J. M. Frost's WRTH editions at that time, the transmitter's frequencies were listed as channel "F1" or channel "S" in the European Broadcasting Union's official documents.
Replacing pre-war tests in 343 lines, broadcasts using the 441 lines system began in Italy in 1939 with regular services from Rome using 2 kW power and Milan using 400 W power in the frequency band of 40-45 MHz. Broadcasts were discontinued on May 31, 1940; as in France, all technical data – VHF frequencies excepted – were identical to those in use in Germany. Field tests in Los Angeles on various line systems began in 1936, the United States had adopted RCA's 441-line system by 1938; the following year the first pre-built TV receivers were sold on a limited basis in New York City, the new system being publicly launched by NBC during the New York World's Fair in April 1939. Its manufacturers included RCA, General Electric, DuMont, Andrea. Following a decision of the NTSC, the 525-line standard replaced the 441-line standard on July 1, 1941. "World Analogue Television Standards and Waveforms - Line Standards". Archived from the original on 2017-02-11. Retrieved 2017-02-11. Rolf Wigand: Technische Beschreibung des E 1 Eckhard Etzold: Ausführliche Webseite mit vielen Fotos sowie Schaltbild des E 1 http://www.compulink.co.uk/~rrussell/tccgen/manual/tcgen0.html American Early Television Museum: pre-WWII TV-stations in Europe
Television, sometimes shortened to tele or telly, is a telecommunication medium used for transmitting moving images in monochrome, or in color, in two or three dimensions and sound. The term can refer to a television set, a television program, or the medium of television transmission. Television is a mass medium for advertising and news. Television became available in crude experimental forms in the late 1920s, but it would still be several years before the new technology would be marketed to consumers. After World War II, an improved form of black-and-white TV broadcasting became popular in the United States and Britain, television sets became commonplace in homes and institutions. During the 1950s, television was the primary medium for influencing public opinion. In the mid-1960s, color broadcasting was introduced in most other developed countries; the availability of multiple types of archival storage media such as Betamax, VHS tape, local disks, DVDs, flash drives, high-definition Blu-ray Discs, cloud digital video recorders has enabled viewers to watch pre-recorded material—such as movies—at home on their own time schedule.
For many reasons the convenience of remote retrieval, the storage of television and video programming now occurs on the cloud. At the end of the first decade of the 2000s, digital television transmissions increased in popularity. Another development was the move from standard-definition television to high-definition television, which provides a resolution, higher. HDTV may be transmitted in various formats: 1080p, 720p. Since 2010, with the invention of smart television, Internet television has increased the availability of television programs and movies via the Internet through streaming video services such as Netflix, Amazon Video, iPlayer and Hulu. In 2013, 79 % of the world's households owned; the replacement of early bulky, high-voltage cathode ray tube screen displays with compact, energy-efficient, flat-panel alternative technologies such as LCDs, OLED displays, plasma displays was a hardware revolution that began with computer monitors in the late 1990s. Most TV sets sold in the 2000s were flat-panel LEDs.
Major manufacturers announced the discontinuation of CRT, DLP, fluorescent-backlit LCDs by the mid-2010s. In the near future, LEDs are expected to be replaced by OLEDs. Major manufacturers have announced that they will produce smart TVs in the mid-2010s. Smart TVs with integrated Internet and Web 2.0 functions became the dominant form of television by the late 2010s. Television signals were distributed only as terrestrial television using high-powered radio-frequency transmitters to broadcast the signal to individual television receivers. Alternatively television signals are distributed by coaxial cable or optical fiber, satellite systems and, since the 2000s via the Internet; until the early 2000s, these were transmitted as analog signals, but a transition to digital television is expected to be completed worldwide by the late 2010s. A standard television set is composed of multiple internal electronic circuits, including a tuner for receiving and decoding broadcast signals. A visual display device which lacks a tuner is called a video monitor rather than a television.
The word television comes from Ancient Greek τῆλε, meaning'far', Latin visio, meaning'sight'. The first documented usage of the term dates back to 1900, when the Russian scientist Constantin Perskyi used it in a paper that he presented in French at the 1st International Congress of Electricity, which ran from 18 to 25 August 1900 during the International World Fair in Paris; the Anglicised version of the term is first attested in 1907, when it was still "...a theoretical system to transmit moving images over telegraph or telephone wires". It was "...formed in English or borrowed from French télévision." In the 19th century and early 20th century, other "...proposals for the name of a then-hypothetical technology for sending pictures over distance were telephote and televista." The abbreviation "TV" is from 1948. The use of the term to mean "a television set" dates from 1941; the use of the term to mean "television as a medium" dates from 1927. The slang term "telly" is more common in the UK; the slang term "the tube" or the "boob tube" derives from the bulky cathode ray tube used on most TVs until the advent of flat-screen TVs.
Another slang term for the TV is "idiot box". In the 1940s and throughout the 1950s, during the early rapid growth of television programming and television-set ownership in the United States, another slang term became used in that period and continues to be used today to distinguish productions created for broadcast on television from films developed for presentation in movie theaters; the "small screen", as both a compound adjective and noun, became specific references to television, while the "big screen" was used to identify productions made for theatrical release. Facsimile transmission systems for still photographs pioneered methods of mechanical scanning of images in the early 19th century. Alexander Bain introduced the facsimile machine between 1843 and 1846. Frederick Bakewell demonstrated a working laboratory version in 1851. Willoughby Smith discovered the photoconductivity of the element selenium in 1873; as a 23-year-old German university student, Paul Julius Gottlieb Nipkow proposed and patented the Nipkow disk in 1884.
This was a spinning disk with a spiral pattern of holes in it, so each hole scanned a line of the image. Although he never built a working model
180-line television system
180 lines is an early electronic television system. It was used in Germany after on March 22, 1935, using telecine transmission of film, intermediate film system, or cameras using the Nipkow disk. Electronic transmissions using cameras based on the iconoscope began on January 15, 1936 with a definition of 375 lines; the Berlin Summer Olympic Games were televised, using both closed-circuit 375 lines electronic iconoscope-based cameras and 180 lines intermediate film cameras transmitting to Berlin, Munich and Bayreuth via special Reichspost long distance cables in August 1936. In Berlin, twenty-eight public 180 lines television rooms were opened for anybody who did not own a television set. After February 1937 both 180 and 375 lines systems were replaced by a superior 441-line system. Http://www.compulink.co.uk/~rrussell/tccgen/manual/tcgen0.html
Programme Delivery Control
Programme delivery control is specified by the standard ETS 300 231, published by the European Telecommunications Standards Institute. This specifies the signals sent as hidden codes in the teletext service, indicating when transmission of a programme starts and finishes. PDC is used together with StarText, enabling the user to select a programme to record using specially coded teletext programme listings; the combination of features is called PDC/StarText In Germany and some other European countries, the older standard video programming system is in use known as format 2. The two systems do the same thing and most modern VCRs and stand-alone DVD recorders work with both signals. In digital TV, the feature Accurate Recording, based on the PDC specification for analogue recording devices is now used for a DVB-SI event based scheduling system; this was due to the BBC discontinuing the Ceefax service. PDC is transmitted once a second in special packets addressed as magazine 8 and text row 30. Since this row is not displayable it does not interfere with normal pages.
Packet 8/30 has various formats specified by ETSI and PDC is format 2. Each packet 8/30 format 2 has a label number and there can be up to four labels transmitted at a time; each label contains the scheduled start time and date for a programme and flags to indicate the state. Each programme is assigned a label and in general a label will follow this sequence. PRF Set – Prepare for Record; this will get ready. This happens about 40 seconds. PRF Clear – The VCR should be recording. RTI – Record Terminate/Interrupt – Tells the VCR to stop recording; this label is held for 30 seconds. There are complicated rules for the case where a programme is interrupted by another one as in the case of a film with a break for news in the middle. There is a TIMER flag that indicates that there is no valid PDC and that the VCR should use its own timer. Technical specifications and FAQ ETSI standards ETSI EN 300 231 V1.3.1, Specification of the domestic video Programme Delivery Control system ETSI EN 301 775 V1.2.1, Specification for the carriage of Vertical Blanking Information data in DVB bitstreams ETSI TS 102 323 V1.5.1, Chapter 11: "Accurate recording" and Annex A: "Example recorder behaviour" CHARACTERISTICS OF A PROGRAMME DELIVERY CONTROL SYSTEM FOR VIDEO RECORDING "Everything you wanted to know about PDC" "Padding versus Accurate Recording"
In broadcasting, a transposer or translator is a device in or beyond the service area of a radio or television station transmitter that rebroadcasts signals to receivers which can’t properly receive the signals of the transmitter because of a physical obstruction. A translator receives the signals of the transmitter and rebroadcasts the signals to the area of poor reception. Sometimes the translator is called a relay transmitter, rebroadcast transmitter or transposer. Since translators are used to cover a small shadowed area, their output powers are lower than that of the radio or television station transmitters feeding them. Reception of RF signals is sensitive to the size of obstruction in the path between the transmitter and the receiver. Speaking, if the size exceeds the wavelength the reception is interrupted. Since the wavelength is inversely proportional to frequency, it follows than that the higher frequency broadcast is more sensitive to objects between the transmitter and receiver.
If the transmitter and the receiver were at the opposite sides of a hill, MW radio signals may be received, but UHF TV signals won’t be received at all. That’s why translators are employed for VHF and UHF broadcasting. Broadcast station transmitters have the following stages: Audio or video frequency buffer stages Modulator IF stages Mixer RF output stages FM and TV translator stations have the following stages. RF input stages Input mixer; the output stages of both devices are similar. There is no baseband video input to the translator; the translator receives an over-the air RF input signal by means of an antenna, just like a home receiver. Since received signal is modulated there is no need for a modulator. Instead an input mixer or down-converter shifts the radio-frequency signal down to an intermediate-frequency signal. A second mixer shifts the IF signal back up to the TV band output signal frequency. In order to stabilize the output power, the amplification of the input RF signal is automatically controlled by PIN diodes If the frequency of the output signal were to be set equal to the frequency of the input RF signal, the output RF would feed back from the output antenna to the input antenna and the input stage would overload blocking out the translator.
Because of this, the translator output frequency must be different from the input signal frequency. Input and output band-pass filters further isolate the two signals. In North America FM and TV translators were common before satellite broadcasting. With the introduction of satellite broadcasting, some TV translator operators abandoned their stations or switched over to low power TV station licenses because of the higher broadcast quality provided by non-over-the-air input program streams. With the operation of an FM or TV translator being less expensive than the same power full-service station they remained an attractive signal delivery alternative; the transition from the analog NTSC television broadcasting standard to the digital ATSC standard resulted in a resurgence in popularity of TV translator systems in the United States. The introduction of In-band on-channel hybrid analog digital FM technologies provided further opportunities for translator system operators. Broadcast relay station TV transmitters Transmitters Output power of an analog TV transmitter Radial Earth bulge
405-line television system
The 405-line monochrome analogue television broadcasting system was the first electronic television system to be used in regular broadcasting. It was introduced with the BBC Television Service in 1936, suspended for the duration of World War II, remained in operation in the UK until 1985, it was used between 1961 and 1982 in Ireland, as well as from 1957 to 1973 for the Rediffusion Television cable service in Hong Kong. Sometimes called the Marconi-EMI system, it was developed in 1934 by the EMI Research Team led by Sir Isaac Shoenberg; the figure of 405 lines had been chosen following discussions over Sunday lunch at the home of Alan Blumlein. The system used interlacing. In the 405 system the scanning lines were broadcast in two complementary fields, 50 times per second, creating 25 frames per second; the actual image was 377 lines high and interlaced, with additional unused lines making the frame up to 405 lines to give the slow circuitry time to prepare for the next frame. At the time of its introduction the 405-line system was referred to as "high definition" - which it was, compared to earlier systems, although of lower definition than 625-line and standards.
In 1934 the British government set up a committee to advise on the future of TV broadcasting. The committee recommended; the recommendation was accepted and tenders were sought from industry. Two tenders were received: one from the Baird company offering a 240-line mechanical system, the other from EMI offering a 405-line all-electronic one; the Television Committee advised that they were unable to choose between the two systems and that both tenders should be accepted, the two systems to be run together for an experimental period. Broadcasting of the resulting BBC Television Service from its Alexandra Palace site began in November 1936, at first time-sharing broadcasts with the 240-line Baird system; this became the standard for all British TV broadcasts until the 1960s. It soon became apparent that television reception was possible well outside the original intended service area. In February 1938, engineers at the RCA Research Station, Long Island, New York, in the USA, were able to receive the BBC signal 5,000 km away, due to the signal being "bounced" back to earth from the ionosphere.
A few minutes of programming were recorded on 16mm movie film. This is now considered to be the only surviving example of live British television; the images recorded included two of the original three BBC announcers, Jasmine Bligh and Elizabeth Cowell, an excerpt from an unknown period costume drama, the BBC's station identification transmitted at the beginning and end of the day's programmes. The BBC temporarily ceased transmissions on 1 September 1939, the day of the German invasion of Poland, as war was imminent. After the BBC Television Service recommenced in 1946, distant reception reports were received from various parts of the world, including Italy, South Africa, the Middle East, North America and the Caribbean; the BBC lost its monopoly of the British television market in 1954, the following year the commercial network ITV, comprising a consortium of regional companies, was launched. In 1964, the BBC launched its BBC2 service on UHF using only a 625-line system, which older sets could not receive.
For several years BBC1 and ITV transmitted BBC2 the 625-line standard. The introduction of colour on BBC2 in 1967 necessitated an more complex dual-standard set to receive all three channels. In November 1969 BBC1 and ITV started broadcasting in 625-line PAL colour on UHF; as their programming was now produced using the new standard, the 405-line broadcasts served only as a rebroadcast in monochrome for people who did not have the newer receivers. Thereafter, receivers were of a simpler single standard design which could not receive the legacy 405-line transmissions. One reason for the long switchover period was the difficulty in matching the coverage level of the new UHF 625-line service with the high level of geographic coverage achieved with the 405-line VHF service; the last 405-line transmissions were seen on 4 January 1985 in Scotland. This left only the UHF PAL system in operation in the UK; the frequencies used by the 405-line system were left empty, but were sold off. Ireland's use of the 405-line system began in 1961, with the launch of Telefís Éireann, but only extended to two main transmitters and their five relays, serving the east and north of the country.
This was because many people in these areas had 405-line sets for receiving UK broadcasts from Wales or Northern Ireland. Telefís Éireann's primary standard was 625-line; the last 405-line relays, in County Donegal, were turned off in 1982.