Windows XP Unwired

Understanding Radio Waves

Most of the wireless technologies mentioned in the last section make use of radio waves. Wi-Fi, GPRS, GPS, and Bluetooth all utilize radio waves to transmit signals.

Radio Wave Basics

Put simply, a radio wave is an electromagnetic wave. It can propagate through a vacuum, air, liquid, or even solid objects. It can be depicted mathematically as a sinusoidal curve as shown in Figure 1-5.

Figure 1-5. A sine wave representing a radio wave

The distance covered by a complete sine wave (a cycle) is known as the wavelength . The height of the wave is called the amplitude . The number of cycles made in a second is known as the frequency. Frequency is measured in Hertz (Hz), also known as cycles per second. So, a 1 Hz signal makes a full cycle once per second. You should be familiar with this unit of measurement: if your new computer operates at 2 GHz, the internal clock of your CPU generates signals at roughly two billion cycles per second.

Tip

Note that frequency is inversely proportional to the wavelength — the longer the wavelength, the lower the frequency; the higher the frequency, the lower the wavelength. The wavelength of a 1 Hz signal is about 30 billion centimeters, which is the distance that light travels in one second. A 1 MHz signal has a wavelength of 300 meters.

Modulating Radio Waves

The sine wave carries data. To receive the transmission (such as audio or ...