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.
Radio 390
Radio 390 was named after the station's wavelength, so listeners would know where to tune. The actual wavelength was 388 metres (773 kHz), but 390 was easier to remember. Like its neighbour, Radio City, Radio 390 took advantage of the fort's layout by erecting a 250-foot vertical mast on an inner tower, guyed to three of the outer towers. This, with additional elevation from the height of the towers, gave a stable and efficient antenna, better than ship-based stations, ensuring coverage of southern England with only a 10 kilowatt transmitter. For advertisers, the station claimed 35 kilowatts.