NTSC
The United States Federal Communications Commission convened the National Television System Committee in 1940 to resolve conflicts between competing companies. These corporations argued over how to introduce a nationwide analog television system that would work for everyone. The committee issued its first technical standard for black-and-white television in March 1941. This standard relied on a 1936 recommendation by the Radio Manufacturers Association. Technical advancements using vestigial sideband techniques allowed engineers to increase image resolution significantly. The NTSC selected 525 scan lines as a compromise between different corporate proposals. RCA wanted to use 441 scan lines, which was already used by their NBC TV network. Philco and DuMont pushed for higher numbers between 605 and 800 lines instead. The final recommendation set a frame rate of 30 frames per second. Each frame consisted of two interlaced fields containing 262.5 lines each. Engineers also defined an aspect ratio of 4:3 for the picture display. They chose frequency modulation for the sound signal to ensure clear audio transmission.
In January 1950, the committee reconstituted itself to standardize color television systems. The FCC briefly approved a 405-line field-sequential color TV standard developed by CBS in October 1950. A third line-sequential system from Color Television Inc. was also considered during these deliberations. The CBS system proved incompatible with existing black-and-white sets because it used a rotating color wheel. It reduced the number of scan lines from 525 to 405 and increased the field rate to 144. Legal action by rival RCA kept commercial use off the air until June 1951. Regular broadcasts lasted only a few months before the Office of Defense Mobilization banned all color set manufacturing in October. This ban occurred ostensibly due to the Korean War. CBS rescinded its system in March 1953 after realizing it could not succeed commercially. The FCC replaced it on December 17 of that year with an NTSC color standard. Several companies including RCA and Philco helped develop this new compatible standard. The first publicly announced network broadcast using the compatible color system aired on the 30th of August 1953. NBC's Kukla Fran and Ollie episode was viewable in color only at headquarters. The first nationwide viewing happened on January 1 with the Tournament of Roses Parade.
Color information entered the black-and-white image through a subcarrier frequency of 3.579545 MHz. Engineers chose this specific frequency so horizontal line-rate modulation components fell between luminance signal components. Chrominance signals could be easily filtered out of the luminance signal on new sets. Existing sets would see minimal visibility of the added color data. Frequency divider circuit limitations required constructing the subcarrier as a composite from small integers. The calculation involved multiplying 5 times 7 times 9 MHz then dividing by 8 times 11. Horizontal line rate dropped to 15,734 lines per second from 15,750 lps. Frame rates reduced to approximately 29.970 fps from 30 fps. These changes amounted to just 0.1 percent but were tolerated by existing TV sets. Red green and blue primary signals weighted into a single luma signal designated Y prime. Color-difference information encoded into chrominance signals carried only color information. Black-and-white receivers displayed NTSC color signals by ignoring the chroma signal entirely. Early sets did not filter chroma out causing crawling dot patterns in saturated areas. Orange-blue color information transmitted on I signal at 1.3 MHz bandwidth. Purple-green color information encoded on Q signal at 0.4 MHz bandwidth. Two signals amplitude modulated 3.58 MHz carriers 90 degrees out of phase with each other.
Analog broadcasts largely phased out with the advent of digital television standards. NTSC broadcasters in the U.S. faced an FCC requirement to shut down analog transmitters by the 17th of February 2009. The shutdown date moved later to June 12 of that year for full compliance. Low-power and Class A stations plus translators had until 2015 to cease operations. An FCC extension allowed some Channel 6 stations to operate until the 13th of July 2021. Canadian analog TV transmitters in markets not subject to mandatory 2011 transitions shut down by the 14th of January 2022. Innovation Science and Economic Development Canada set this schedule in 2017. Most countries using NTSC or other analog standards switched to newer digital systems. North America parts of Central America and South Korea adopted ATSC standards instead. Japan adopted standards different from ATSC for their own needs. Most over-the-air NTSC transmissions in the United States ended on the 12th of June 2009. By the 31st of August 2011, similar shutdowns occurred in Canada and most other NTSC markets. At least four different digital standards now exist worldwide replacing the old analog infrastructure.
NTSC color encoding almost invariably used with CCIR System M across many regions. NTSC-N originally proposed in the 1960s as a 50 Hz broadcast method for System N countries. Paraguay Uruguay and Argentina chose PAL before adopting NTSC-N proposals. In 1978 Apple II Europlus reintroduced it as NTSC 50 combining 625-line video with 3.58 MHz color. Atari ST running PAL software used this system since monitors could not decode standard PAL colors. NTSC 4.43 transmits an NTSC color subcarrier of 4.43 MHz instead of 3.58 MHz. Output viewable only by TVs supporting the system like most PAL sets. OSKM began broadcasting from Moscow experimental TV studio in January 1960. This version adapted NTSC to European D/K 625/50 standard seven years before modified SECAM adoption. About 4,000 TV sets produced in four models remained non-commercially available. Reception problems sometimes degraded color accuracy causing ghosting or phase changes on the colorburst. Vacuum-tube electronics through the 1960s led to technical issues requiring tint controls. Video professionals jokingly referred to NTSC as Never The Same Color due to inconsistencies. Some stations transmitted TV Guide On Screen data on VBI lines 11 through 18.
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Common questions
When did the United States Federal Communications Commission convene the National Television System Committee?
The United States Federal Communications Commission convened the National Television System Committee in 1940 to resolve conflicts between competing companies. The committee issued its first technical standard for black-and-white television in March 1941.
What date did the FCC replace the CBS color system with an NTSC color standard?
The FCC replaced the incompatible CBS system on December 17 of that year with an NTSC color standard. Several companies including RCA and Philco helped develop this new compatible standard which aired publicly on the 30th of August 1953.
Why did engineers reduce the frame rate from 30 fps to approximately 29.970 fps in NTSC color systems?
Engineers reduced the frame rate to accommodate a subcarrier frequency of 3.579545 MHz so horizontal line-rate modulation components fell between luminance signal components. This change amounted to just 0.1 percent but were tolerated by existing TV sets to ensure compatibility.
On what date did most over-the-air NTSC transmissions end in the United States?
Most over-the-air NTSC transmissions in the United States ended on the 12th of June 2009 following an FCC requirement to shut down analog transmitters. The shutdown date moved later to June 12 of that year for full compliance after originally being set for the 17th of February 2009.
Which countries adopted NTSC-N proposals instead of PAL before the 1960s?
Paraguay Uruguay and Argentina chose PAL before adopting NTSC-N proposals. NTSC-N was originally proposed in the 1960s as a 50 Hz broadcast method for System N countries.