Overview

Government agencies divide the radio frequency spectrum into frequency bands that are authorized for specific uses defined geographic regions (such as a city). In the United States, the responsibility for allocating the radio wave portion of our electromagnetic spectrum belongs to the Federal Communications Commission (FCC). The government's interest in this responsibility is multi faceted. This includes defense interests, public safety, business operations, and the benefit of the general public.

Table 1.1 shows the typical categorization of frequency bands and types of use. The very lowest frequencies (ELF) are able to communicate through water. Because low frequency signals bend with the Earth, they are commonly used for ship communications. Medium frequency signals are used for land based radio (AM and FM) broadcasts. Very high frequency signals are commonly used for television and cellular communication. Because microwave signals travel best directly between points (line of sight), they are commonly used by point-to-point microwave and satellite communication systems. When the electromagnetic waves reach high enough frequencies, they obtain the properties of light (such as infrared).