Narrow-bandwidth television
Encyclopedia
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 to eight megahertz wide.
, or reduce the image size. When the scan rate is reduced, this is referred to as slow-scan TV
. With the latter type, 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. However, most narrow-bandwidth TV nowadays uses computer
s and other electronic
systems.
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
designed to fit into a low-bandwidth channel, in the extreme case using amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
voice frequency
Voice frequency
A voice frequency or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech.In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz...
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 to eight megahertz wide.
Design
There are two ways to make this work: reduce the scan rateFrame rate
Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
, or reduce the image size. When the scan rate is reduced, this is referred to as slow-scan TV
Slow-scan television
Slow-scan television is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.A technical term for SSTV is narrowband television...
. With the latter type, the number of lines in an image may be reduced to just a few dozen.
The earliest mechanical television
Mechanical television
Mechanical television was a broadcast television system that used mechanical or electromechanical devices to capture and display video images. However, the images themselves were usually transmitted electronically and via radio waves...
systems often used narrow channels for sending moving images. Often, the images were only a few dozen lines in size. However, most narrow-bandwidth TV nowadays uses computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s and other electronic
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
systems.
Mechanical TV standards
| 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) |
| 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. |
| 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 |
| W6XS 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 |
| Königswusterhausen 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 |