CCIR System M, sometimes called 525–line, monochrome NTSC or NTSC-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.
It was also adopted in most of the Americas and Caribbean, 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 on Cambodia and Vietnam (see Color standards section below).
|System(CCIR)||Lines (total)||Lines (visible)||Frame rate (fps)||Channel bandwidth (MHz)||Visual bandwidth (MHz)||Sound offset (MHz)||Vestigial sideband (MHz)||Vision modulation||Sound modulation||Notes|
|M||525||480||29.97 (NTSC color)||6||4.2||+4.5||0.75||Negative||FM||Most of the Americas and Caribbean; Myanmar, Philippines, South Korea, Taiwan (all NTSC-M)|
Cambodia, Vietnam (SECAM-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.
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.
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).