Telecommunication
The other meaning of the term "channel" in telecommunications is seen in the phrase communications channel, which is a subdivision of a transmission medium so that it can be used to send multiple streams of information simultaneously. For example, one radio station can broadcast radio waves into free space at frequencies in the neighborhood of 94.5 MHz (megahertz) while another radio station can simultaneously broadcast radio waves at frequencies in the neighborhood of 96.1 MHz. Each radio station would transmit radio waves over a frequency bandwidth of about 180 kHz (kilohertz), centered at frequencies such as the above, which are called the "carrier frequencies". Each station in this example is separated from its adjacent stations by 200 kHz, and the difference between 200 kHz and 180 kHz (20 kHz) is an engineering allowance for the imperfections in the communication system.
Satellite radio
Ground stations transmit signals to the satellites which are 35,786 kilometers (22,236 miles) above the Equator in Clarke belt orbits. The satellites send the signals back down to radio receivers in cars and homes. This signal contains scrambled broadcasts, along with meta data about each specific broadcast. The signals are unscrambled by the radio receiver modules, which display the broadcast information. In urban areas, ground repeaters enable signals to be available even if the satellite signal is blocked. The technology allows for nationwide broadcasting, so that, for instance US listeners can hear the same stations anywhere in the country.