Difference between revisions of "Radio Frequencies, Bands, and Channels"

Revision as of 12:33, 4 June 2015

Radio frequency transmissions are divided up into contiguous bands for different purposes. These groupings are usually due to the different physical characteristics or behavior of radio waves at different frequencies (more on this below). To understand the properties of different radio waves, let's first calculate the wavelength of some typical radio frequencies found in each of the main broadcast bands. As explained above, this is performed by dividing the speed of light by the frequency of interest:

• Band: MF — Medium Frequency — AM (amplitude mall/ago/0 Radio Band (535-1705 kHz)

Channel: AM Radio — 1120 kHz 300 million meters/sec ÷ 1120 thousand cycles /sec = 268 meters (880 feet)

• Band: VHF — Very High Frequency FM Viequeney moduilatiaii) Radio Band (88-108 MHz)

Channel: FM Radio — 98.1 MHz 300 million meters/sec = 98.1 million cycles/sec = 3 meters (10 feet)

• Band: VHF — Very High Frequency — Television Band (54-216 MHz)

Channel: VHF TV, Channel 8-183 MHz 300 million meters/sec ÷ 183 million cycles/sec = 1.64 meters (5 feet)

• Band: UHF — Ultra High Frequency — Television Band (470-806 MHz)

Channel: UHF TV, Channel 40 — 629 MHz 300 million meters/sec ÷ 629 million cycles/sec = 0.48 meters (19 inches)

• Band: SHF — Super High Frequency — Broadcasting Satellite Ku Band (11-14 GHz)

Channel: Direct Broadcast Satellite, Transponder 30 — 12.647 GHz 300 million meters/sec ÷ 12.647 billion cyclesfsec = 2.37 centimeters (1 inch)

As this summary of the Electromagnetic Spectrum illustrates, the wavelengths of different broadcast bands vary quite a bit, from hundreds of feet to an inch or less. Because of these differing wavelengths, there are major physical differences in the design of antenna types used to transmit and receive signals in different bands. The amplitudes (or power) of these signals also greatly influence the design and size of these antennas.

Each radio band is divided into individual channels, and each of these channels includes a range of frequencies. The range of frequencies included in a channel from lowest to highest is known as the channel's batidwidin. (The term may also refer to any particular range of frequencies, not just those in RF.) For simplicity, however, a channel is often identified by its reizterfrequency, so that only one numerical value (rather than two) will have to be cited when referring to a particular channel. If the center frequency is given and the channel bandwidth is known, the upper and lower frequency limits of the channel can be easily derived. For example, a channel with a 2 kHz (2,000 Hz) bandwidth centered at 100 kHz occupies the spectrum between 99 kHz and 101 kHz.

The UHF and SHF bands have further subdivisions, with bands that are used for terrestrial radio links, satellite links, and for satellite broadcasting. These include the L, Cyan, X, Ku, IC, and Ka bands, with frequencies ranging from about 1 GHz to 40 GHz.

United States Frequency Allocations Chart

The United States Department of Commerce, National Telecommunications and Information Administration - Office of Spectrum Management released this chart to the public in 2003. This is an enormous chart that would make an excellent poster to hang on your wall. It is very detailed. Click the icon below for a direct link to the file.