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.
City of license
While becoming less meaningful over the decades, stations are still required to post a public file somewhere within 25 miles of the city, and to cover the entire city with a local signal. In the United States, a station's transmitter must be located so that it can provide a strong signal over nearly all of its "principal community" (5 mV/m or stronger at night for AM stations, 70 dbuV for FM, 35 dbu for DTV channels 2-6, 43 dbu for channels 7-13 and 48 dbu for channels 14+), even if it primarily serves another city. For example, American television station WTTV primarily serves Indianapolis; however, the transmitter is located farther south than the other stations in that city because it is licensed to Bloomington, 50 miles south of Indianapolis. In some cases, such as Jeannette, Pennsylvania-licensed WPCW 19, the FCC has waived this requirement; the station claimed that retaining an existing transmitter site 25.6 miles southeast of its new community of license of Jeannette would be in compliance with the Commission's minimum distance separation requirements (avoiding interference to co-channel WOIO 19 Shaker Heights). Another extreme example of a station's transmitter located far from the city of license is the FM station KPNT, formerly licensed to Ste. Genevieve, Missouri and transmitting from Hillsboro, but serving the St. Louis and Metro East market to the north. In 2015, the station was allowed by the FCC to move their city of license to Collinsville, Illinois and have a transmitter in St. Louis proper with a power decrease.