Defining Analog TV Signals
The majority of television signals coming into homes are still analog. Analog TV signals reach homes through over-the-air broadcast TV, by traditional cable TV systems, and by satellite.
In North America, an analog system known as NTSC has been in place for decades. (The standard is more than 60 years old, having been developed in the 1940s!) In fact, it hasn’t been changed or updated since the advent of color television in the 1960s. Although the NTSC system is capable of producing a surprisingly good picture under ideal circumstances, its analog nature makes it susceptible to various kinds of interference and signal degradation. Consequently, the picture can be downright awful by the time it gets to your television, which is why the TV world is slowly turning digital.
Analog television displays a maximum of 480 scan lines (525 total, but you can’t see them all because some are used for things such as closed captioning), displays 30 frames (60 fields) per second, and is an interlaced system.
Just as the NTSC standard is common in North America (and Japan), a couple of other standards — known as PAL and SECAM — are common in other parts of the world. Unless you have a special TV designed for the purpose, you can’t tune in to PAL broadcasts with an NTSC TV or NTSC with a PAL TV. This is one reason why you can’t buy videotapes in many parts of the world and use them in the United States.
Television is undergoing some radical changes. Like most other devices before it, the television is beginning to make the leap from the analog to the digital world. Unlike many of those devices, however, TV has been making the leap in a series of agonizingly slow steps.