To understand the mechanism behind wireless Internet cards, you first have to grasp how the wireless Internet itself works. Rather than transmitting data through a phone line, digital subscriber line (DSL) or high-speed cable, a wireless Internet network transmits data the same way that radios and cell phones do: radio waves.
A WiFi hot spot, usually a wireless router or access point, first receives information from the Internet the old-fashioned way: through wires. It then translates that data from the binary form (the computer code of 1s and 0s) into radio waves. Next it broadcasts those radio waves into the surrounding area. Wireless signals typically travel between 75 feet and 150 feet (23 meters and 46 meters). In a wide open area with no obstacles, however, they have been known to transmit up to 1,000 feet (305 meters) and, with optimal conditions, even a mile (1.6 kilometers) [source: Wi-Fi Alliance]. More on those optimal conditions in a little bit.
Wireless Internet cards within the range of the radio signal pick it up using a tiny antenna and translate it back into binary code for your computer to read. The process also works in the opposite direction, with the card translating your computer's information into radio waves to send to the router, where it is put back into binary form and sent to the Internet over the wires.
The radio communication used by wireless networks is slightly different from that of radios and cell phones. For instance, wireless Internet cards are designed to work at higher frequencies to handle more data -- typically either 2.4 gigahertz or 5 gigahertz. In addition, the cards and the routers can communicate on one of three different frequency channels. In cases where many people are using the wireless signal, like an airport crowded with business travelers, the cards and the routers can also jump between channels to reduce interference.
Wireless cards operate under networking standards that are a variation of the basic 802.11 standard. These standards were developed by the Institute of Electrical and Electronics Engineers to differentiate between the various technologies. The 802.11b and 802.11g standards are the most common, while the faster 802.11n, which was recently released, is not as widespread.
Although WiFi radio signals have some benefits over regular radio signals, they are still subject to interference by physical obstacles. Interference happens when a signal is hampered by distance or a physical obstacle. For instance, microwaves and many cordless phones operate in the same frequency used by some WiFi networks, so you might notice a slowdown in your service if you're trying to warm your latte while you sign on. Likewise, if you move to another room or if an elephant comes to stand between you and the hot spot, the signal could be lost.
Don't worry if you don't have your own wireless network at home or at work. You can purchase prepaid wireless Internet cards in the U.S. from companies such as T-Mobile, which allow you access to all the T-Mobile hot spots. This can get kind of pricey, though, so you may want to kick in the cash to set up your own network or find a local spot that advertises a free Wi-Fi connection.
If you're overwhelmed by computer acronyms, brace yourself. On the next page, you'll learn the difference between PCI, PCMCIA (PC) and WCF cards.