CCIR System M
Introduction Analog TV systems global map, with System M in red.CCIR '''System M''', sometimes called '''525–line''', monochrome '''NTSC''', '''NTSC-M''', or '''CCIR-M''', is the analog broadcast television system approved by the FCC (upon recommendation by the National Television Systems Committee - NTSC) for use in the United States since July 1, 1941, replacing the 441-line TV system introduced in 1938.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.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).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:* 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-MACFile:Ntsc channel.svg|Radio spectrum of a System M television channel with NTSC colorFile:VHF Usage.svg|Plan showing VHF frequency ranges for ITU Systems
Color standards Television color encoding by nation; Brazil (PAL-M) and all green countries (NTSC) are based on monochrome System M.===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  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, 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