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.
Reference distance
Real-world calculations can also be done by including data from digital topographical maps, typically along 12 or 16 radials, and including the specifications from the radiation pattern for a directional antenna. However, this does not fit the definition of a reference in this sense, even though it determines the actual broadcast range of a station. This actual range is used in the reserved band in the U.S., while the reference distance is used for commercial radio stations.