The signal strength of wireless network access points can vary widely based on position, intervening walls and obstacles, and other factors. Many people are surprised how limited the range of a wireless access point can be, even when there is a short distance and a direct line of sight. Given that some adapters and access points are better than others and that you can also extend the range of your wireless network with wireless extenders, all of these devices benefit from the use of attached antennas.
An antenna can boost the transmission distances of your devices by 20% to 60%, as well as improving both your data transmission throughputs and lowering your error rates. As your signal strength diminishes, wireless devices perform automatic transmission rate fallback. So if your top rated speed is 24 Megabits per second (Mb/s), then as signal strength weakens you will find that your transmission falls through a sequence similar to 12, 6, 3, and 1.5 Mb/s before failing completely.
Antennas are described as either directional or omnidirectional. Directional antennas provide better point to point enhancement, whereas an omnidirectional antenna will boost your signal in all directions, but at a lower level than a directional antenna. Antennas come in several types, and range in price from $40 up to $200. You'll find that antennas have a signal strength booster rating, typically quoted in dBi. At the lower end are 4 and 5-dBi antennas, which are not electronically powered. More powerful antennas can go as high as 12 to 16 dBi.
You can actually build your own antenna from tin cans and parts, as described by by several people on the Internet. One good article by Rob Flickinger on O'Reilly's Web site builds a simple but effective can antenna device and illustrates the necessary components for its construction. The results are as good as you can get from a $150 antenna from a commercial vendor.
Barrie Sosinsky is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.