Wireless Network Administration: Wavelength and Antennas

A term related to frequency is wavelength. Radio waves travel at the speed of light. The term wavelength refers to how far the radio signal travels with each cycle. For example, because the speed of light is roughly 300,000,000 meters per second, the wavelength of a 1-Hz radio wave is about 300,000,000 meters. The wavelength of a 2-Hz signal is about 150,000,000 meters.

As you can see, the wavelength decreases as the frequency increases. The wavelength of a typical AM radio station broadcasting at 580 KHz is about 500 meters. For a TV station broadcasting at 100 MHz, it’s about 3 meters. For a wireless network broadcasting at 2.4 GHz, the wavelength is about 12 centimeters.

It turns out that the shorter the wavelength, the smaller the antenna needs to be in order to adequately receive the signal. As a result, higher frequency transmissions need smaller antennas. You may have noticed that AM radio stations usually have huge antennas mounted on top of tall towers, but cell phone transmitters are much smaller and their towers aren’t nearly as tall.

That’s because cell phones operate on a higher frequency than do AM radio stations. So who decides what type of radio gets to use specific frequencies?