TV signal and how it works

Television is one of the most influential inventions of our time. Via the TV, we receive news, information, movies and other types of video directly into our homes. However, have you ever wondered how the television works? How we get hundreds channels at home for free? Surprisingly, the TV structure is quite simple and the process of transformation of the TV signal into picture too.





Black and White TV signal





Black and white TV sets have a screen that is coated with a substance called white phosphor. An electron beam "draws" the image as it moves across the white phosphor one line at a time. To visualize the whole picture the electron beam has to go in a "raster scan" mode. This is achieved by using magnetic coils powered by the electronic circuit. In this mode, the beam moves horizontally from the upper left corner to the right. Then it turns back to the left side diagonally to reach the second horizontal line. When the beam reaches the lower right corner, it turns back directly to its original point or the upper left corner. When the beam moves horizontally it is on, but when it flies back diagonally it is off, because it would leave a trail on the screen. There are two terms referring to the electron beam. The first is the horizontal retrace and is used to note the movement of the beam to the left side, whilst the vertical retrace is used to mark the movement from the bottom to the top. In order to achieve different colors such as white, gray and black, the intensity of the beam is altered as it moves from left to right and thus different shades appear. Our mind accepts the image as one, because of the miniature distance between the rows. Usually these rows are around 480.





Color TV signal





The color TV signal works in almost the same way as the black and white TV signal. The difference comes from the addition of a chrominance signal to the normal black and white signal. The black and white TVs neglect this signal, whilst the color TV decodes both the chrominance signal and the intensity signal in order to modulate three different color beams. Most of the TVs are using an interlacing method as they paint the screen. This method allows the screen to be painted 60 times per second. However, the beam paints only half of them as it paints over row, thus painting the whole screen in two phases. There is an alternative method to the interlacing. It is known as progressive scanning and allows the screen to be painted 60 times per second. This method is used in the PC monitors as it reduces flicker.





If you would like to get HD TV signal, please visit this amazing Danish website. To find out how you can get proper TV signal, click here.