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Narrow-bandwidth television (NBTV) is a type of television designed to fit into a channel narrower than the standard bandwidth used for official television standards.
The three predominant worldwide broadcast television standards use either 6 MHz wide channels (as in the Americas and Japan, as ATSC and ISDB-T both use those standards) or 8 MHz (as in most of Europe with DVB-T). Narrow-bandwidth television refers to any method that reduces the bandwidth below that threshold. (These techniques are frequently used in traditional television to allow for multiple digital subchannels on the same bandwidth, but this is not true narrow-bandwidth as the standards do not allow for it, and the extra bandwidth in these cases is usually transferred to another channel.)
There are three ways to reduce the bandwidth of a video signal: reduce the scan rate, reduce the image size, and/or (with digital television) use heavier compression. When the scan rate is reduced, this is referred to as slow-scan TV or, in the most extreme cases when the scan rate is too slow to simulate motion, freeze frame television. With reduced image sizes, this is referred to as low-definition television. In the most extreme cases, the number of lines in an image may be reduced to just a few dozen, and bandwidth reduced to a few tens of kilohertz, within the bandwidth of an amateur radio voice channel. Most narrow-bandwidth TV nowadays uses computers and other electronic systems.
The earliest mechanical television systems often used narrow channels for sending moving images. Often, the images were only a few dozen lines in size.
Name | Details |
---|---|
Nipkow 1884 | 24 lines. Patent granted but Nipkow did not build a system. |
WGY, 2XAF, 2XAD | 24 lines, 21 frame/s, progressive scan |
United Kingdom, 1926 (Baird) | 30 lines, 5 frame/s, black-and-white experimental transmissions |
United Kingdom, 1928 (Baird) | 30 lines, 5 frame/s, first experimental colour TV transmissions [1] |
W3XK, Washington, D.C, 1928 | 48 lines. Oldest television station in the United States. [2] |
2XAL, WRNY "Radio News", New York, 1928 | 48 lines, 7.5 frame/s, progressive scan. Second to broadcast television pictures to the general public, after W3XK in Washington, D.C., [3] [4] [5] [6] [7] [8] |
Baird, United Kingdom, 1928–32 | 30 lines, 12.5 frame/s, 3:7 vertical aspect ratio, vertical progressive scan, ~70x30 pixels per frame, sound, live TV from studio, first outdoor remote broadcasts of the Derby [9] |
W9XAA/WCFL, W9XAO/WIBO, W9XAP/WMAQ (Western Television / Sanabria), Chicago, 1928–33 | 45 lines, 15 frame/s, 1:1 aspect ratio, triple interlace scan. Live TV from studio. (Above transmissions: Picture station / sound station) [10] |
W9XK/WSUI, Iowa City, Iowa (Used Western Television/Sanabria system), 1933–39 | 45 lines, 15 frame/s, 1:1 aspect ratio, triple interlace scan. Includes sound on WSUI. Educational TV pioneer. Live TV from studio. [10] |
Germany, France, 1930 | 30 lines, 12.5 frame/s, 3:4 aspect ratio, horizontal progressive scan |
New York City, Schenectady, Boston, 1930–31 | 48 lines, 15 frame/s, 6:5 aspect ratio, horizontal progressive scan |
W6XAO Los Angeles, 1931 | 80 lines, 20 frame/s, progressive scan |
W6XAH Bakersfield, 1931 | 96 lines, 20 frame/s, progressive scan |
New York, Schenectady, Boston, 1932 | 60 lines, 20 frame/s, 6:5 aspect ratio, horizontal progressive scan |
Berlin 1932 | 30 lines, 12.5 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images |
Königs Wusterhausen 1932 | 39 lines, 12.5 frame/s, 4:3 horizontal aspect ratio, ~31x30 pixels per frame, movies |
Doberitz 1932 | 48 lines, 25 frame/s, 4:3 horizontal aspect ratio, ~64x48 pixels per frame, sound, talking movies |
Berlin R.P.Z. 1932 | 60 lines, 25 frame/s, 4:3 horizontal aspect ratio, ~83x60 pixels per frame, test movies and live images |
Italy 1932 | 60 lines, 20 frame/s, 4:3 horizontal aspect ratio, ~45x60 pixels per frame, test movies and live images |
France 1932 | 60 lines, 12.5 frame/s, 3:7 vertical aspect ratio, vertical scanning ~35x60 pixels per frame, sound, live images [11] |
Switzerland 1932 | 30 lines, 16.6 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images |
USSR 1932 | 30 lines, 12 frame/s |
Belgium 1932 | 30 lines, 12.5 & 16.6 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, sound, talking movies |
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.
Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative advancement and represented the first significant evolution in television technology since color television in the 1950s. Modern digital television is transmitted in high-definition television (HDTV) with greater resolution than analog TV. It typically uses a widescreen aspect ratio in contrast to the narrower format (4:3) of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit up to seven channels in the same bandwidth as a single analog channel, and provides many new features that analog television cannot. A transition from analog to digital broadcasting began around 2000. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards:
NTSC is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170.
Television (TV) is a telecommunication medium for transmitting moving images and sound. Additionally, the term can refer to a physical television set rather than the medium of transmission. Television is a mass medium for advertising, entertainment, news, and sports. The medium is capable of more than "radio broadcasting," which refers to an audio signal sent to radio receivers.
Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the characteristics of the human visual system.
Progressive scanning is a format of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence. This is in contrast to interlaced video used in traditional analog television systems where only the odd lines, then the even lines of each frame are drawn alternately, so that only half the number of actual image frames are used to produce video. The system was originally known as "sequential scanning" when it was used in the Baird 240 line television transmissions from Alexandra Palace, United Kingdom in 1936. It was also used in Baird's experimental transmissions using 30 lines in the 1920s. Progressive scanning became universally used in computer screens beginning in the early 21st century.
Color television or colour television is a television transmission technology that includes color information for the picture, so the video image can be displayed in color on the television set. It improves on the monochrome or black-and-white television technology, which displays the image in shades of gray (grayscale). Television broadcasting stations and networks in most parts of the world upgraded from black-and-white to color transmission between the 1960s and the 1980s. The invention of color television standards was an important part of the history and technology of television.
Broadcasttelevision systems are the encoding or formatting systems for the transmission and reception of terrestrial television signals.
Mechanical television or mechanical scan television is an obsolete television system that relies on a mechanical scanning device, such as a rotating disk with holes in it or a rotating mirror drum, to scan the scene and generate the video signal, and a similar mechanical device at the receiver to display the picture. This contrasts with vacuum tube electronic television technology, using electron beam scanning methods, for example in cathode-ray tube (CRT) televisions. Subsequently, modern solid-state liquid-crystal displays (LCD) and LED displays are now used to create and display television pictures.
The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting. The number of television lines influences the image resolution, or quality of the picture.
The concept of television is the work of many individuals in the late 19th and early 20th centuries. The first practical transmissions of moving images over a radio system used mechanical rotating perforated disks to scan a scene into a time-varying signal that could be reconstructed at a receiver back into an approximation of the original image. Development of television was interrupted by the Second World War. After the end of the war, all-electronic methods of scanning and displaying images became standard. Several different standards for addition of color to transmitted images were developed with different regions using technically incompatible signal standards. Television broadcasting expanded rapidly after World War II, becoming an important mass medium for advertising, propaganda, and entertainment.
A number of experimental and broadcast pre World War II television systems were tested. The first ones were mechanical based and of very low resolution, sometimes with no sound. Later TV systems were electronic.
A field-sequential color system (FSC) is a color television system in which the primary color information is transmitted in successive images and which relies on the human vision system to fuse the successive images into a color picture. One field-sequential system was developed in 1940 by Peter Goldmark for CBS, which was its sole user in commercial broadcasting. The Federal Communications Commission adopted it on October 11, 1950, as the standard for color television in the United States. Its regular broadcast debut was on June 25, 1951. However, a few months later, CBS ended color broadcasting on October 20, 1951. In March 1953, CBS withdrawn its color system as a standard, creating an opening for all-electronic color systems from other manufacturers.
The technology of television has evolved since its early days using a mechanical system invented by Paul Gottlieb Nipkow in 1884. Every television system works on the scanning principle first implemented in the rotating disk scanner of Nipkow. This turns a two-dimensional image into a time series of signals that represent the brightness and color of each resolvable element of the picture. By repeating a two-dimensional image quickly enough, the impression of motion can be transmitted as well. For the receiving apparatus to reconstruct the image, synchronization information is included in the signal to allow proper placement of each line within the image and to identify when a complete image has been transmitted and a new image is to follow.
High-definition television (HDTV) describes a television or video system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since at least 1933; in more recent times, it refers to the generation following standard-definition television (SDTV). It is the standard video format used in most broadcasts: terrestrial broadcast television, cable television, satellite television.
441-line is the number of scan lines in some early electronic monochrome analog television systems. Systems with this number of lines were used with 25 interlaced frames per second in France from 1937 to 1956, Germany from 1939 to 1943, Italy from 1939 to 1940, Japan in 1939, as well as by RCA in the United States with 30 interlaced frames per second from 1938 to 1941. Broadcasts were planned in Finland for 1940, but eventually cancelled due to World War II. Some experiments with a similar system were carried out on the USSR in the 1930s.
CCIR System B was the 625-line VHF analog broadcast television system which at its peak was adopted by more than one hundred countries, either with PAL or SECAM colour. It is usually associated with CCIR System G for UHF broadcasts.
CCIR System G, also known as the "Gerber Standard", is an analog broadcast television system used in sixty countries around the world for UHF channels. System G is generally associated with System B for VHF.
Telechrome was the first all-electronic single-tube color television system. It was invented by well-known Scottish television engineer, John Logie Baird, who had previously made the first public television broadcast, as well as the first color broadcast using a pre-Telechrome system.
375-line corresponds to two different electronic television systems, both using 375 scan lines. One system was used in Germany after 1936 along with the 180-line system, being replaced in a few years by the superior 441-line system. It was also tested in Italy around the same time.