CCIR System M,[1][2][3] sometimes called 525–line, monochrome NTSC, NTSC-M, or CCIR-M,[4][5] is the analog broadcast television system approved by the FCC (upon recommendation by the National Television Systems Committee - NTSC)[6] for use in the United States since July 1, 1941,[7][8] replacing the 441-line TV system introduced in 1938.[8] System M comprises a total of 525 interlaced lines of video, of which 486 contain the image information, at 30 frames per second. Video is amplitude modulated and audio is frequency modulated, with a total bandwidth of 6 MHz for each channel, including a guard band.[9]
It was also adopted in the Americas and Caribbean; Myanmar, Philippines, South Korea, Taiwan and Japan (here with minor differences, informally referred to as System J). System M doesn't specify a color system, but NTSC (NTSC-M) was normally used, with some exceptions: NTSC-J in Japan, PAL-M in Brazil and SECAM-M in Cambodia, Laos and Vietnam (see Color standards section below).
The letter M designation was attributed by the ITU at the 1961 Stockholm meeting (see ITU identification scheme).[10]
In 1965, Thailand decided to replace System M with 625-line CCIR System B which started in 1967 and adopted PAL in the same year. [11]
Since 2015, System M is being replaced by digital broadcasting, in countries such as the Americas, Japan, South Korea, Taiwan and the Philippines.
Specifications
Some of the important specifications for System M are listed below:[12]
- Lines (total): 525
- Lines (visible): 486
- Frame rate: 29.97 Hz (NTSC color), 30 Hz (monochrome and PAL-M color)
- Channel bandwidth: 6 MHz
- Visual bandwidth: 4.2 MHz
- Sound offset: +4.5 MHz
- Vestigial sideband: 0.75 MHz
- Vision modulation: Negative
- Preemphasis: 75 μs
- Sound modulation: FM
- Color standards: NTSC-M, NTSC-J, PAL-M, SECAM-M, Clear-Vision, B-MAC
Radio spectrum of a System M television channel with NTSC color
Plan showing VHF frequency ranges for ITU Systems
Color standards
NTSC-M and NTSC-J
Strictly speaking, System M does not designate how color is transmitted. However, in nearly every System M country NTSC is used for color television. This combination is called NTSC-M, but usually simply referred to as "NTSC", because of the relative lack of importance of black-and-white television. In NTSC-M and Japan's NTSC-J, the frame rate is offset slightly, becoming 30⁄1.001 frames per second, usually labeled as the rounded number 29.97.
PAL-M
The main exception to System M's being paired with NTSC color is Brazil, where PAL color is used instead, resulting in the PAL-M combination unique to that country. It is monochrome-compatible with other System M countries, but not compatible with other PAL countries, which use 625-line based systems.
SECAM-M
Between 1970 and 1991 a variation of the SECAM color system, known as SECAM-M, was used in Cambodia,[13] Laos, and Vietnam (Hanoi and other northern cities).
References
See also
- NTSC — dominant color system used with System M, so much so that System M is often referred to as "NTSC". Much of the information in the NTSC article is actually about System M.
- Broadcast television systems — explains other types of television system standards
- Multichannel television sound — usual method for adding stereo to System M and System N audio carriers
- Pan-American television frequencies