Frame rates, picture resolution, and audio modulation are discussed extensively in the pages on broadcast television systems and analog television. Because the luminance (luma, monochrome picture) and chroma (color added to the monochrome image) are delivered as one signal, NTSC video is composite video. The term "composite" means that the signal contains two types of information: a luminance component and a color component.
NTSC is an acronym for "National Television System Committee". This system was developed by the U.S. Federal Communications Commission in 1953 for use with standard-definition televisions (SDTV). In 1975, the FCC required that all broadcast signals be converted to the NTSC format to enable them to be received by older televisions as well as more modern ones. After many years of broadcasting in the NTSC format, most U.S. stations have moved to high-definition television (HDTV), which uses different frequencies than SDTV does. However, some stations remain in the NTSC format because they cannot afford to move to HDTV or for other reasons.
Television sets made after 1991 are capable of displaying both SDTV and NTSC signals. However, if you try to watch an old black and white TV show on a digital set, it will look pretty bad because the signal has been compressed for storage on disk.
The System M television transmission, which has 30/1.001 (roughly 29.97) interlaced frames of video per second, uses NTSC color encoding. Each frame is made up of two fields of 262.5 scan lines each, for a total of 525 scan lines. The viewable raster is made up of 486 scan lines. Therefore, one-half of the scan lines are not visible.
An average person can see about 50 meters in good daylight conditions, but it's difficult to see clearly beyond that distance. In general, the farther away something is, the less detail you will be able to see it with the naked eye. This is true even with things like mountains and trees which seem far away yet contain their own unique details at various distances.
Nighttime viewing is also limited because darkness decreases visual sensitivity. At night, people can see only objects that are bright enough to reflect light into the eye. This means that even distant objects must be lit by a light source otherwise they will be invisible during the dark hours.
In conclusion, the human eye is capable of seeing up to 100 meters in clear weather under ideal lighting conditions but only 50 meters in poor lighting or at twilight.
A composite video signal is a single transmission that contains the chrominance (color) and luminance (brightness) components of a video signal, as well as sync information, on a single cable. A composite video transmission, unlike an RF signal, does not need to be demodulated in order to be interpreted by a video display. The receiver portion of your television or VCR can detect the presence of sync pulses in the signal and adjust its internal timing circuitry to match those pulses. From then on, the video signal will be displayed in synchronism with the color burst.
Sync pulses are short, high-amplitude signals that occur at fixed intervals throughout the transmission channel. They allow the receiver to keep time without reference to another source such as a clock. There are two types of sync pulses used in composite video: horizontal and vertical. The frequency of these pulses varies according to the standard being followed. For example, the NTSC standard uses a 14.318 MHz horizontal sync pulse, while the PAL standard uses a 15.625 MHz horizontal sync pulse. These pulses are transmitted along with the chroma subcarrier on Channel 3 of a typical composite video signal.
The chroma subcarrier is a sound carrier that is added to the composite video signal to carry the color information. It operates at 4.5 MHz for NTSC and 5 MHz for PAL. Since it's only 4 kHz wide, it has more room between samples than the audio range of voice or music recording devices.