Narrow-bandwidth television

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.)

Design

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.

Mechanical TV standards

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
England 1926 (Baird) 30 lines, 5 frame/s, black-and-white experimental transmissions
England 1928 (Baird) 30 lines, 5 frame/s, first experimental colour TV transmissions
2XAL New York 1928 48 lines, 7.5 frame/s, progressive scan
Baird, England, 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
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)[1]
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. [1]
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
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
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See also

References
  1. "Early Chicago Television, Mechanical Tv, Ua Sanabria". Hawestv.com. Retrieved 2010-03-02.
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