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.
SATEL
The operation range of a radio modem varies depending on the transmission power, antenna gain and mast height, and environment. In rural areas a 1 W radio modem with a line-of-sight radio link may range over 20 km and even up to 50 km in exceptionally amicable environments. In dense metropolitan areas, a corresponding range may vary from several kilometers to over 10 km. With a 10 W radio modem, a range of up to 80 km can be reached in favorable environments. By using radio modem repeaters, much broader areas can be covered.