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Date: 29th November 2011     

Use Lion's secret Wi-Fi Diagnostics utility

Wireless networking is the the best invention since the TV remote and it makes life so much easier for computers, tablets, mobile phones and other devices to communicate without the need for cables. Put a wireless router anywhere in your home or office and you can connect to it and get on the internet using a Wi-Fi enabled device from anywhere. It's like magic, except when it doesn't work. Sometimes we are plagued with poor connections and drop-outs, but fortunately there is a Wi-Fi Diagnostics tool in OS X Lion that can help to solve your problems. It's hidden though, so you probably don't even know it's there. Its output might be meaningless too, so here's a guide to using this hidden secret utility.

To start the app, open a new Finder window and click the hard disk drive in the left panel under Devices. Go to the System folder, then Library and finally CoreServices. Scroll down to the bottom of the window and double click Wi-Fi Diagnostics.app.

Four options are offered when the app starts and the most useful on is the first - Monitor Performance. Choose this and the main part of the window shows a live scrolling chart of the signal and noise strengths. The orange signal line shows how strong the Wi-Fi signal is and it varies a little over time so it's quite jagged. The green noise line shows the amount of interference and this can be from other wireless devices and nearby electrical equipment. The signal line should be as high up the chart as possible and the noise line should be as low down as possible. A good Wi-Fi network should have a big gap between the signal strength and background noise.

Wi-Fi Diagnostics

There are some figures at the top and you can see the channel used by the wireless router. Routers can use any one of around a dozen different channels and if you have problems with a poor wireless connection you should try a different channel. You can find more information about selecting wireless channels here.

The signal and noise columns show the signal strength and the noise, and both of these are useful. However, you need to understand how they work. Notice that they are negative values and have a minus sign in front of them. Count backwards like this: 5 4 3 2 1 0 -1 -2 -3 -4 -5. It is obvious that 4 is bigger than 2, but also notice that -4 is smaller than -2. In other words -2 is a bigger number than -4. If you can get your head around that, you can understand the figures.

You want the signal to be as strong as possible, which means a big number. In the screen shot the signal strength is -53 and a value of -50 would be bigger and -40 would be bigger still. The closer to zero the signal strength is, the better your Wi-Fi will be (-53 is pretty average, so use it as a guide when looking at your own).

For the best possible wireless connection you want as little noise (interference) as possible, so you want the noise figure to be small. In the screen shot it is -96. A value of -100 would be better and -110 better still, but -90 would be worse because it's a bigger number which means more noise.

Working with negative numbers can be confusing!

So how do we get a better wireless network? The position of the wireless router and the computer or device affects the signal strength and noise. The signal weakens as the distance between the two increases, so make sure they are close together. Walls and floors reduce the signal strength too, so position the router somewhere in the middle of the house or office rather than in a corner out of the way. Place the router away from other electrical equioment, so don't hide it behind the TV for example. Place it on a desk or table with plenty of free space around it. (Routers get quite warm and need the space to keep cool too.)