How Wi-Fi Cards Function

Step into any café, and you'll find countless people tapping away at their laptops. It may seem like everywhere you go—from university campuses and libraries to coffee shops like Starbucks and fast-food spots like McDonald's—offers wireless internet, and you're right. Currently, 241,506 Wi-Fi hotspots span across 134 nations, and some of these hotspots cover entire cities [source: JiWire].

These hotspots typically connect to the broader internet network via wires or cables and then transmit the internet signal wirelessly to individual computers through radio frequencies. Many personal computers receive this signal using a wireless internet card, a compact device roughly the size of a credit card.

Wi-Fi, everywhere. Explore more laptop images.

Wireless Internet cards, also known as Local Area Network (LAN) cards, are a type of adapter card that enhances your computer's functionality. Other adapter cards can support teleconferencing, boost audio systems, or transfer photos from a digital camera.

Wireless Internet cards come in various types for laptops, desktops, and PDAs. Many computers come with one already installed, but they can also be bought affordably, self-installed, or easily inserted into a slot on the side of the computer.

The growing number of Wi-Fi hotspots has made wireless Internet cards even more sought after. Originally used mostly in homes or businesses for multiple users to share an internet connection, they are now a must-have for anyone with a computer, particularly as entire cities go wireless. For further details, check out How Municipal Wi-Fi Works.

In this article, you'll discover how wireless Internet cards communicate with hotspots to access the internet. You’ll also explore the different types of wireless cards and what to consider when purchasing one, so you can check your e-mail while enjoying a soy latte.

Learn how a device no larger than your hand can detect a signal from hundreds of feet away in the next section.

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Wireless Internet Overview

To comprehend how wireless Internet cards function, you need to first understand how wireless Internet works. Unlike traditional methods like phone lines, digital subscriber lines (DSL), or high-speed cable, wireless Internet networks send data through radio waves, similar to how radios and cell phones transmit signals.

A Wi-Fi hotspot, usually a wireless router or access point, initially receives data from the Internet in the traditional manner: through wired connections. It then converts this information from binary form (the computer language of 1s and 0s) into radio waves. These waves are then broadcast to the surrounding area. Wireless signals typically range between 75 and 150 feet (23 to 46 meters), but in clear areas with no obstructions, they can reach up to 1,000 feet (305 meters), and under ideal conditions, even up to a mile (1.6 kilometers) [source: Wi-Fi Alliance]. More on those ideal conditions soon.

Wireless Internet cards within the radio signal's range capture the signal using a small antenna, converting it back into binary code for your computer to process. The reverse process also occurs, with the card turning your computer’s data into radio waves to send to the router, where it is transformed back into binary and transmitted to the Internet via wires.

The radio communication used by wireless networks differs slightly from that of radios and cell phones. For example, wireless Internet cards are designed to operate at higher frequencies to handle more data—typically 2.4 gigahertz or 5 gigahertz. Additionally, cards and routers communicate using one of three frequency channels. In areas with heavy traffic, like airports full of business travelers, cards and routers can switch between channels to reduce interference.

Wireless cards follow networking standards that are variations of the basic 802.11 standard. These standards, developed by the Institute of Electrical and Electronics Engineers, distinguish between different technologies. The 802.11b and 802.11g standards are the most common, while the faster 802.11n, which was introduced more recently, is not yet as widespread.

While Wi-Fi radio signals offer some advantages over regular radio signals, they are still vulnerable to interference from physical obstacles. Interference occurs when a signal is blocked by distance or physical barriers. For example, microwaves and many cordless phones operate on the same frequency as some Wi-Fi networks, so you might notice a slowdown in service if you're trying to heat your latte while connecting. Similarly, if you move to another room or if an elephant happens to stand between you and the hotspot, the signal may be lost.

If you don’t have your own wireless network at home or work, don’t worry. You can purchase prepaid wireless Internet cards in the U.S. from companies like T-Mobile, which grant access to all T-Mobile hotspots. However, this can become costly, so you may want to consider investing in your own network or finding a local spot that offers free Wi-Fi.

If you're confused by computer abbreviations, get ready for more! On the next page, you'll discover the differences between PCI, PCMCIA (PC), and WCF cards.

Wireless Internet Cards for Laptops, Desktops, and PDAs

If you’ve ever browsed the adapter card section at a computer store, you know how many different types there are. Cards labeled PCI refer to a specific communication language between the card and the computer's central processor. PCI stands for Peripheral Component Interconnect, an industry standard describing how connected devices communicate with the computer through a central path called the bus.

PCI network adapters come in various shapes and sizes known as form factors. Two common types are the mini PCI, a wireless network card embedded within a laptop, and the PCI wireless adapter card used for desktops. Since a desktop’s bus is inside the machine, desktop wireless Internet cards must be installed inside, and most desktops come with one preinstalled. If you’re after an external adapter, look for one that connects via USB.

Other terms you might come across include the PC Card or ExpressCard labels. While PCI wireless network adapters communicate through the computer's bus, PC Card adapters simply slide into a side slot, making them especially common in laptops due to their slim profile. The newer ExpressCard technology is gradually replacing PC Card adapters.

The PC Card and ExpressCard names come from PCMCIA, the Personal Computer Memory Card International Association, which created a standard network adapter using the PC form factor. These cards are sometimes labeled as PCMCIA cards. Regardless of what they're called, they all slide into a laptop's side slot, typically sticking out slightly to improve signal reception and transmission with their built-in WiFi antennas.

You can also find USB keys that serve as wireless adapters. These devices, which look like the memory sticks or flash drives you plug into a USB port on your computer, are growing in popularity as a convenient option.

Another type of wireless Internet card is available for PDAs. For those not yet using a BlackBerry, there’s WCF. Wireless CompactFlash cards, similar to PC Cards, slot into the side or back of a PDA and enable Internet connectivity.

The variety of wireless Internet cards doesn’t end there. Read on to discover even more differences.

Comparing Wireless Internet Connection Cards

When purchasing a wireless Internet card, there are a few key factors to consider, such as the networking standard the card uses. For example, 802.11b, once the most common WiFi standard, operates in the 2.4-gigahertz range and supports a data transfer rate of 11 megabits per second. The term bandwidth refers to how much data can be transferred in a set amount of time, and the higher the number, the faster the transfer rate. Thus, 802.11g and 802.11n, which support data speeds of 54 and 140 megabits per second, respectively, will allow you to stream video much faster than the older, slower 802.11b standard.

It's essential to pay attention to the networking standard of the card you purchase to ensure it works with your other wireless devices. For example, if your home network operates on the 2.4-gigahertz frequency, and you purchase a card that only supports the 5-gigahertz range, it won’t work. However, if you buy a card that’s WiFi-certified for the same frequency and features (such as encryption codes) as the other devices you're using, you're good to go. Alternatively, you can opt for a dual-band card, which works across both frequency bands and is compatible with all WiFi-certified products.

Additionally, be sure to check the card's data transfer rate, coverage range, and the operating system it supports. You'll also want to decide whether you prefer a card with an external or internal antenna. Finally, security is a crucial factor. Wireless networks are more vulnerable to hacking than wired networks, so taking extra precautions is necessary. The Wi-Fi Alliance recommends connecting only through a trusted provider that employs encryption technologies. If you have your own network, use WiFi-certified products that support WiFi Protected Access (WPA) to ensure your security.