Liam Heurtau Yr: 12
The first function of a television set is to select a channel (or frequency range) to output. This is done by the part of the television set called the tuner. The television tuner works the same way a radio tuner works. Out of the many incoming signals the television tuner picks out one channel's frequency and outputs encoded audio and video information into a fixed frequency. The tuner always outputs in the same frequency, often called the intermediate frequency. It is only the picture information encoded in that frequency that changes. So, if the user selects channel 2, the picture encoded in the electromagnetic waves corresponding to channel 2 is picked and encoded by the tuner using the intermediate frequency. The TV tuner has a channel selector to move up and down the spectrum of incoming frequencies. Because the tuner always outputs the same, its output signal can be amplified easily. Now the signal is large enough to be processed. A sound detector retrieves sound out of the amplified intermediate frequency signal, directs it to a sound amplifier and then to a speaker. On a black and white television a video detector receives amplified frequency and sends the luminance information to the picture tube. Luminance is the amount of light in each dot on the screen. For a colour television, the video detector extracts another signal called chrominance. Chrominance is simply the colour of each dot of the image without the intensity (or luminance). But, the colour picture tube needs the intensity of red, green, and blue as signals. Given both the chrominance and luminance signals, a special converter circuit can recreate the intensity of red, green, and blue in each dot.