Narrow-bandwidth television (NBTV) is a type of
television
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...
designed to fit into a channel narrower than the standard
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
used for official television standards.
The three predominant worldwide broadcast television standards use either 6
MHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
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
Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative adva ...
) use heavier
compression
Compression may refer to:
Physical science
*Compression (physics), size reduction due to forces
*Compression member, a structural element such as a column
*Compressibility, susceptibility to compression
* Gas compression
*Compression ratio, of a ...
. When the scan rate is reduced, this is referred to as
slow-scan TV
Slow-scan television (SSTV) is a picture transmission method, used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.
A literal term for SSTV is narrowband television. Analog broadcast tel ...
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
Low-definition television (LDTV) refers to TV systems that have a lower screen resolution than standard-definition TV systems. The term is usually used in reference to digital TV, in particular when broadcasting at the same (or similar) resol ...
. 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
Electronic may refer to:
*Electronics, the science of how to control electric energy in semiconductor
* ''Electronics'' (magazine), a defunct American trade journal
*Electronic storage, the storage of data using an electronic device
*Electronic co ...
systems.
Mechanical TV standards
The earliest
mechanical television
Mechanical television or mechanical scan television is a television system that relies on a mechanical scanning device, such as a rotating disk with holes in it or a rotating mirror drum, to scan the scene and generate the video signal, and a si ...
systems often used narrow channels for sending moving images. Often, the images were only a few dozen lines in size.
See also
*
History of television
*
List of experimental television stations
This page is a list of the experimental television stations before 1946. After 1945 (in the United States) the television frequencies were opened up to commercialization and regular broadcasts began. Regular broadcast television start dates vary wi ...
*
Moving image formats
This article discusses moving image capture, transmission and presentation from today's technical and creative points of view; concentrating on aspects of frame rates.
Essential parameters
The essential parameters of any moving image sequence a ...
*
Prewar television stations
This is a list of pre-World War 2 television stations of the 1920s and 1930s. Most of these experimental stations were located in Europe (notably in the United Kingdom, France, Germany, Italy, Poland, the Netherlands, and Russia), Australia, Can ...
*
Television systems before 1940
*
PXL-2000
The PXL2000 is a toy camcorder produced by Fisher-Price in 1987. Designed for maximal economy, it records extremely low-resolution monochrome video and audio, all to compact audio cassette.
It was on the market for one year with about 400,000 ...
References
External links
W9XK Experimental Television at the University of IowaThe Narrow Bandwidth Television Association
{{Video formats
History of television
Television transmission standards