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.