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. 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, most narrow-bandwidth TV nowadays uses computers and other electronic systems.

Mechanical TV standards

Nipkow 1884

24 lines. Patent granted but Nipkow did not build a system.

WGY, 2XAF, 2XAD

24 lines, 21 fps, progressive scan

England 1926 (Baird)

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

England 1928 (Baird)

30 lines, 5 fps, first experimental colour TV transmissions

2XAL New York 1928

48 lines, 7.5 fps, progressive scan

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

WIBO, WCFL, W9XK (Sanabria) Chicago, 1929-32

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

Germany, France, 1930

30 lines, 12.5 fps, 3:4 aspect ratio, horizontal progressive scan

New York City, Schenectady, Boston, 1930-31

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

W6XS Los Angeles, 1931

80 lines, 20 fps, progressive scan

W6XAH Bakersfield, 1931

96 lines, 20 fps, progressive scan

New York, Schenectady, Boston, 1932

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

Berlin 1932

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

Königswusterhausen 1932

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

Doberitz 1932

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

Berlin R.P.Z. 1932

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

Italy 1932

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

France 1932

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

Switzerland 1932

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

USSR 1932

30 lines, 12 fps

Belgium 1932

30 lines, 12.5 & 16.6 fps, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, sound, talking movies