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.
General Order 40
Radio transmissions in the United States were originally regulated by the Department of Commerce, as authorized by the Radio Act of 1912. The first formal regulations governing broadcasts intended for the general public were adopted effective December 1, 1921. This initially established just two transmitting wavelengths — 360 meters (833 kHz) for "entertainment" broadcasts, and 485 meters (619 kHz) for "market news and weather reports".. The number of broadcasting stations grew dramatically in 1922, reaching over 500 by the end of the year, and the government began making available additional frequencies. By November 1924 a band of frequencies, from 550 to 1500 kHz, had been established, with higher-powered stations, known as "Class B", assigned to the frequencies from 550 to 1070, while lower-powered "Class A" stations were assigned to 1080 to 1500.