On February 17, 2009, all high power over-the-air analog television transmission in the United States will be turned off. Radios, televisions, cell phones, etc. all transmit using different radio frequencies. Check out Radio Waves for a more through discussion on electromagnetic waves. In order for different uses (for instance cell phones and TVs) of radios not to interfere, different uses are assigned to different places in the frequency spectrum. Frequency is the rate at which the wave oscillates up and down. For instance waves with very high frequency oscillate quickly and waves with low frequency oscillate slower. The frequency of a radio transmission is typically measured in the unit Hertz. The unit of Hertz is how many oscillations occur in a second. Thus a 10 Mega Hertz (10MHz) signal oscillates 10,000,000 times a second.

The FCC (a branch of the US government) assigns different portions of the frequency spectrum to different uses. The US people own the entire frequency spectrum for use in the United States and the FCC decides how best to license the frequency for different uses.