Narrow-bandwidth television

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Narrow-bandwidth television (NBTV) is a type of television designed to fit into a low-bandwidth channel, in the extreme case using amateur radio voice frequency channels that only range up to a few kilohertz (though channels ranging into a few tens of kilohertz and beyond can also be used). This is in contrast to regular TV systems that use a channel about six megahertz wide. There are two ways to make this work: reduce the scan rate, or reduce the image size. When the scan rate is reduced, this is referred to as slow-scan TV. This article mostly deals with the latter type, where the number of lines in an image may be reduced to just a few dozen.

The earliest mechanical television systems often used narrow channels for sending moving images. Often, the images were only a few dozen lines in size. There is some interest in re-creating some of these old devices, both for the historical perspective and for the technical challenge (see Narrow Bandwidth Television Association). However, narrow-bandwidth TV does not require mechanical TV hardware. Computers and other electronic systems can be used instead.

[edit] Mechanical TV standards

[edit] Nipkow 1884

24 lines. Patent granted but no practical TV transmissions

[edit] WGY, 2XAF, 2XAD

24 lines, 21 fps, progressive scan

[edit] England 1926 (Baird)

30 lines, 5 fps, black-and-white experimental transmissions

[edit] England 1928 (Baird)

30 lines, 5 fps, first experimental colour TV transmissions

[edit] 2XAL New York 1928

48 lines, 7.5 fps, progressive scan

[edit] WRNY New York 1928

36 lines, horizontal progressive scan 48 lines, 10 fps, progressive scan

[edit] Baird, England, 1928-32

30 lines, 12.5 fps, 3:7 vertical aspect ratio, vertical progressive scan, ~70x30 pixels per frame, sound, live TV from studio

[edit] WIBO, WCFL, W9XK (Sanabria) midwest, 1929-32

45 lines, 15 fps, 1:1 aspect ratio, triple interlace scan

[edit] Germany, France, 1930

30 lines, 12.5 fps, 1:1 aspect ratio, horizontal progressive scan

[edit] East coast, 1930-31

48 lines, 15 fps, 6:5 aspect ratio, horizontal progressive scan

[edit] W6XS Los Angeles, 1931

80 lines, 20 fps, progressive scan

[edit] W6XAH Bakersfield, 1931

96 lines, 20 fps, progressive scan

[edit] East coast, 1932

60 lines, 20 fps, 6:5 aspect ratio, horizontal progressive scan

[edit] Berlin 1932

30 lines, 12.5 fps, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images

[edit] Koningswusterhausen 1932

39 lines, 12.5 fps, 4:3 horizontal aspect ratio, ~31x30 pixels per frame, movies

[edit] Doberitz 1932

48 lines, 25 fps, 4:3 horizontal aspect ratio, ~64x48 pixels per frame, sound, talking movies

[edit] Berlin R.P.Z. 1932

60 lines, 25 fps, 4:3 horizontal aspect ratio, ~83x60 pixels per frame, test movies and live images

[edit] Italy 1932

60 lines, 20 fps, 4:3 horizontal aspect ratio, ~45x60 pixels per frame, test movies and live images

[edit] France 1932

60 lines, 12.5 fps, 3:7 vertical aspect ratio, vertical scanning ~35x60 pixels per frame, sound, live images

[edit] Switzerland 1932

30 lines, 16.6 fps, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images

[edit] URSS 1932