Narrow-bandwidth television


Narrow-bandwidth television 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 or 8 MHz. Narrow-bandwidth television refers to any method that reduces the bandwidth below that threshold.

Design

There are three ways to reduce the bandwidth of a video signal: reduce the scan rate, reduce the image size, and/or 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.
NameDetails
Nipkow 188424 lines. Patent granted but Nipkow did not build a system.
WGY, 2XAF, 2XAD24 lines, 21 frame/s, progressive scan
England 1926 30 lines, 5 frame/s, black-and-white experimental transmissions
England 1928 30 lines, 5 frame/s, first experimental colour TV transmissions
2XAL New York 192848 lines, 7.5 frame/s, progressive scan
Baird, England, 1928-3230 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, Chicago, 1928-3345 lines, 15 frame/s, 1:1 aspect ratio, triple interlace scan. Live TV from studio.
W9XK/WSUI, Iowa City, Iowa, 1933-3945 lines, 15 frame/s, 1:1 aspect ratio, triple interlace scan. Includes sound on WSUI. Educational TV pioneer. Live TV from studio.
Germany, France, 193030 lines, 12.5 frame/s, 3:4 aspect ratio, horizontal progressive scan
New York City, Schenectady, Boston, 1930-3148 lines, 15 frame/s, 6:5 aspect ratio, horizontal progressive scan
W6XAO Los Angeles, 193180 lines, 20 frame/s, progressive scan
W6XAH Bakersfield, 193196 lines, 20 frame/s, progressive scan
New York, Schenectady, Boston, 193260 lines, 20 frame/s, 6:5 aspect ratio, horizontal progressive scan
Berlin 193230 lines, 12.5 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images
Königs Wusterhausen 193239 lines, 12.5 frame/s, 4:3 horizontal aspect ratio, ~31x30 pixels per frame, movies
Doberitz 193248 lines, 25 frame/s, 4:3 horizontal aspect ratio, ~64x48 pixels per frame, sound, talking movies
Berlin R.P.Z. 193260 lines, 25 frame/s, 4:3 horizontal aspect ratio, ~83x60 pixels per frame, test movies and live images
Italy 193260 lines, 20 frame/s, 4:3 horizontal aspect ratio, ~45x60 pixels per frame, test movies and live images
France 193260 lines, 12.5 frame/s, 3:7 vertical aspect ratio, vertical scanning ~35x60 pixels per frame, sound, live images
Switzerland 193230 lines, 16.6 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images
USSR 193230 lines, 12 frame/s
Belgium 193230 lines, 12.5 & 16.6 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, sound, talking movies