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 displays a total of 525 lines of video (with 480 carrying visible image information) at 30 frames per second using 6 MHz spacing between channel numbers, and is used for both VHF and UHF channels. Video is amplitude modulated.
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 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.
Further information: Broadcast television systems § ITU identification scheme
Some of the important specifications for System M are listed below:
|System(CCIR)||Lines (total)||Lines (visible)||Frame rate (fps)||Channel bandwidth (MHz)||Visual bandwidth (MHz)||Sound offset (MHz)||Vestigial sideband (MHz)||Vision modulation||Preemphasis||Sound modulation||Color Standards|
|M||525||480||29.97 (NTSC color)||6||4.2||+4.5||0.75||Negative||75 μs||FM||NTSC-M|
|30 (original/PAL color)|
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 called 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.
Main article: 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.
Main article: SECAM
Between 1970 and 1991 a variation of the SECAM color system, known as SECAM-M, was used in Cambodia and Vietnam (Hanoi and other northern cities).