For most of us, Wi-Fi has become our preferred way to connect our Macs to other networked devices and the Internet. However, most of us also have times when those connections slow down or fail altogether. When that happens, however, there are several things you can do to diagnose and (ideally) fix the problem.
Signal and noise
The thing to remember about Wi-Fi is that it's a form of radio: Signals are passed to and from your Mac and your router (and any other networked devices) by transmitters and receivers at both ends tuned to the same frequency. While the information being sent might be digital in nature, the medium it rides on is analog. As such, the ability to transmit and receive data via Wi-Fi is dependent on two things: the strength of the signal between those transmitters and receivers; and the volume of interference — unusable "noise" — from other devices using that same frequency.
The analogy is to listening to the radio in your car: Sometimes, the signal gets weaker as you drive farther away from the station's transmitter. Other times, even if the signal is crisp and strong, you might hear two different stations — one you want to listen to, one you don't — on the same channel; that's noise.
Your Mac's ability to maintain a good Wi-Fi connection is a function of both of these signal types: If the signal from your router to your computer is too weak or if there's too much noise from competing signals, then — as with your car radio — your Mac will lose its ability to make sense of what it's "hearing."
You can see all this activity in real-time using OS X's built-in Wireless Diagnostics utility (/System/Library/CoreServices/Applications/). Open this utility and choose Utilities from the Window menu. In the panel that then appears, open the Performance tab. You should see two graphs: One showing the signal and noise levels, another showing the ratio of the two (a common way to determine relative strength). (The levels measured in that first graph are negative because they're based on the logarithms of values between 0 and 1, and such logarithms are negative.)
In general, for the signal measurement you want to see values of -10 to -70 dBm (decibel-milliwatts); for noise, -80 to -100 dBm. As the levels of the signal and of the noise get closer to one another, your wireless connection will begin dropping data packets and requiring that they be resent. This will slow down data transmission, and potentially cause your Mac to drop its connection altogether.
The power of place
If you are having problems with your Wi-Fi connection, and you've checked Wireless Diagnostics, the numbers there (and the radio analogy above) should give you some clues about how to fix the problem. One of the most fundamental things you can do is change the position of your Mac, your router, or both.
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