Evaluating the strength of your AirPort network

Reader Dwayne Ahern has a question about the strength of his Wi-Fi network. He writes:

I have an AirPort Extreme Base Station in my home office, and I’m not sure I’ve positioned it in the best place for good reception around the house. As I walk around with my MacBook Air, I see the Wi-Fi fan in the menu bar drop a bit in some places, but that seems like a pretty rough estimate. Is there a way I can get a better idea of how strong the signal is?

There is, but it requires math.

Before I outline that math, let’s give credit where it’s due: A person going by the name Tesserax has written a helpful guide on optimal base station placement. In that guide he spells out the following steps.

On your MacBook Air, hold down the Option key, click the Apple menu, and choose System Information. In the resulting System Information window, select Wi-Fi under the Network heading. Locate the Signal/Noise entry and make a note of what follows it: –41dBm / –88dBm, for example.

You then use the formula Signal – Noise = Signal strength. So, using our example above, –41 – (–88) = 47. (If, like me, you are math challenged, you can simply turn the figures into positive numbers and write the formula as Noise – Signal = Signal strength or, using our example, 88 – 41 = 47.)

Locating your base station's signal/noise ratings

Swell. And so what exactly does that mean? According to Tesserax, you want a signal that’s 25dB and above. Specifically, the guidelines say:

  • 40+dB = Excellent signal
  • 25dB to 40dB = Very good signal
  • 15dB to 25dB = Low signal
  • 10dB to 15dB = Very low signal
  • 5dB to 10dB = Little or no signal

In our example, we’re getting wonderful reception at 47dB.

If you find that you’re not getting stellar reception, it’s time to try moving the base station to see if that helps. If it doesn’t, you could change channels in case some other nearby wireless device is interfering with your base station’s signal.

To do that, launch the AirPort Utility, select your base station, and click Edit. In the sheet that appears, select the Wireless tab and click the Wireless Options button. In the resulting Wireless Options sheet, you’ll see at least one Channel pop-up menu; normally it’s set to Automatic, but you can change it. If possible, learn about the channels that your other devices—your wireless phone, for example—are using, and choose a channel far away from the one that the potentially interfering device is on.

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