Building Wireless Community Networks

Antenna Characteristics and Placement

While I am not a radio frequency (RF) engineer, I have had a lot of practical experience setting up 802.11b networks. There isn’t nearly enough room here for a full examination of the nuances of radio frequency communications. For more authoritative sources, be sure to check out the great resources in Appendix A—notably, the fantastic publications put out by the American Radio Relay League (AARL), an association of amateur radio operators. Radio is an entire field of study unto itself.

Antenna selection has a tremendous impact on the range and usability of your wireless network. Ironically, the design of almost every external 802.11b card puts the antenna in the worst possible orientation: sideways and very close to the laptop (or desktop). In this position, the radiation pattern is almost straight up and down! Not only does this drive half your signal into the table, it leaves your poor, underpowered radio susceptible to interference from the computer itself.

The one notable exception to this state of affairs is Apple’s built-in AirPort card. They’ve thought enough to include an internal antenna connector that runs up the LCD panel. This is an excellent design with much better range, although it does preclude adding an external antenna. It looks like IBM is the first to play copycat with their i Series ThinkPads as well.

You will see a tremendous difference in signal strength by attaching a small omnidirectional external antenna to your client ...