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Analog TV signals consist of video on AM waves and audio on FM waves. NTSC, PAL, and SECAM are the most popular analog standards. Analog broadcasts have an aspect ratio of 4:3 and are subject to interference. Analog technology is being replaced by digital technology worldwide, which offers higher resolutions, non-interlaced signals, and a 16:9 aspect ratio.
An analog TV signal consists of a video signal broadcast on AM radio waves and an audio signal broadcast on FM waves. Analog technology is currently being replaced by digital technology all over the world.
In the United States, black-and-white analog TV broadcasts were standardized in 1941 by the National Television System Committee (NTSC), later followed by an updated color standard in 1953. NTSC has been adopted by North America, Central America, and from parts of South America, Japan and other nations. Other parts of the world have developed the analog standards Phase Altering Line (PAL) and Sèquentiel Couleur Avec Mèmoire (SECAM). Less popular standards have also been developed.
Analog broadcasts have an aspect ratio of 4:3 or an almost square configuration. An NTSC signal has 525 scan lines, although only 486 make up the visible raster. The remaining lines contain sync and vertical retrace information. The lines are painted in two passes on an analog screen, each pass painting every other line, interweaving the passes to create a flicker-free image. The frame rate is 30 frames per second, resulting in an effective frame rate of 29.97 frames per second.
A PAL analog TV signal comes in many versions, including B/G/H/I/D/M and PAL Nc. Most are 625 scan lines, interlaced, at 25 frames per second, although audio carrier frequencies differ between standards. PAL M, like NTCS, uses 525 scan lines and 29.97 frames per second. Brazil uses PAL M, while other types of PAL are used in most of South America, Australia, China and other territories, again noting that digital broadcasting is replacing this technology at varying rates, regionally.
The SECAM standard was developed in France and has also evolved over the years into different flavors. It also uses 625 scan lines, with the exception of its M version, which like PAL M and NTSC has 525 scan lines. SECAM was used in France, Africa, Russia and other parts of the world, although many territories migrated to PAL in the 1990s.
An analog TV signal is subject to interference which can cause unwanted effects such as ghosting and snow. The distance from the transmitter and the topographical factor intervened in the clarity of the signal.
An analog television is quite heavy for its size due to the lead-lined vacuum chamber that houses the scanning mechanism known as a cathode ray tube (CRT). This mechanism converts the broadcast signal into a moving image by firing electrons at the back of the television phosphor screen many times per second to recreate each frame of information. Analog TV has a deep footprint, takes up a large amount of space, and emits a fair amount of radiation compared to digital TVs.
Analog television broadcasting is a legacy technology, although it continues to be used in territories that have not yet transitioned to digital standards. Digital technologies use less bandwidth to deliver more signal information, resulting in the capability for higher resolutions, non-interlaced signals, and a 16:9 aspect ratio (similar to a movie screen in configuration). Other benefits of digital TV include the ability to broadcast at lower resolutions that are still superior to analog TV, making room for more channels to be broadcast within the same assigned frequency band.
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