Cable decoders, also known as cable descramblers and cable boxes, are devices used to control the television signals provided by cable companies. These little black boxes may seem mysterious, but they're relatively simple devices. Understanding the basics of cable decoders will let you communicate with the cable company more easily should you encounter problems with your decoder. It also will help you grasp what the decoder can and cannot do with your signal.
When your TV signal comes through your coaxial cable into your home, the data is compressed so that it can travel quickly. The data takes up so little space that the cable company can send you data for hundreds of channels at once. Unfortunately, your television isn't equipped to decompress the data and sort it out. Without a decoder, you can't make out a picture on the television screen. A cable decoder thus is like an interpreter between the cable company and your television. It decodes the data and arranges it for you based on the channel you've selected. Once decoded, your television can make sense of the data for the channel and you see a picture. Therefore, the most basic function of a decoder is data decompression.
You need at least two coaxial cables for a cable decoder to work. One hooks the decoder to the cable connection on your wall. The other connects the box to your television. With this arrangement, the decoder can decompress the cable data before it reaches your television and then send it forward to the set.
Because a cable decoder works like a middle man and is able to send decompressed data to only one television station at a time, you'll need multiple boxes if you want to watch different channels on multiple televisions, as indicated by Comcast.
Power and Viewing
The decoder is responsible for providing decompressed video and audio data to your television. If you turn the cable box off, you won't be able to watch any stations because the television itself isn't able to decompress the data. This means that you must run two devices--the decoder and your TV set--simultaneously any time you want to watch a cable program. Do not make the mistake of thinking that your television isn't working properly just because the decoder isn't getting power.