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Radio Signals
Radio transmissions are a form of electromagnetic energy, as are X-rays, infrared and visible light; each type differs from the others due to its characteristic frequencies. Radio waves have frequencies ranging from a few thousand hertz to a few hundred gigahertz. The frequency of light waves is about 100 terahertz, or about 1,000 times that of the highest radio frequencies. X-rays have much higher frequencies still, about 1,000 times that of light. Radio waves are a convenient form of communication because they move at the speed of light and carry information at low cost over long distances.
Interference Prevention
One of the main goals of frequency allocation is the prevention of radio interference. Without regulation, two or more radio stations in the same town might broadcast in the same frequency. A radio receiver tuned to that frequency would pick up all of them as an unintelligible mishmash of sound. One broadcaster might boost his transmission power to overwhelm the signals of competing stations. The FCC issues licenses for all radio transmission equipment, making sure that frequencies don't interfere and power levels remain reasonable. They also establish standards for computers and other electronic equipment so unintended radio-frequency "noise" doesn't compromise legitimate broadcasts.
Radio Frequency Uses
The FCC has allocated frequencies for many different groups in addition to commercial broadcasters. Frequencies have been set aside for boat and aircraft communication and navigation, police and fire departments and ham radio enthusiasts. Scientists doing research using radio telescopes have their own frequency allocations, as do organizations such as NASA. The FCC governs the use of satellite frequencies used for weather, telephone communications and the military. Frequencies are also allocated for low-power radio uses such as wireless telephones, cell phones and Wi-Fi data networks.
Allocation Patterns
The FCC allocates the radio spectrum as "bands" or ranges of frequencies. For example, the allocation for AM radio ranges from 535 kHz to 1,605 kHz. Many allocations are more complex, such as those set aside for amateur broadcasting; amateur bands include 1.8 to 1.9 MHz, 3.5 to 4.0 MHz, 7.0 to 7.3 MHz and 50 to 54 MHz. Although many bands are reserved for a single use, others can have multiple uses; for example, the 435 kHz to 495 kHz band is approved for maritime mobile communication and aeronautical navigation.
Ongoing Allocation Challenges
Although many commercial radio broadcasting frequencies have not changed in several decades, new technologies have made the radio spectrum a dynamic environment. For example, in 2009, television broadcasters switched from traditional analog to digital signals. Doing so freed up the band between 698 MHz to 806 MHz, which the FCC reallocated to state and local public safety.