• 
• 
• 

 1 of 3

Gallery

Banish your Wi-Fi woes

Posted on 15 Mar 2010 at 16:05

Paul Ockenden explains how to get the best out of your Wi-Fi connection

These enable you to see actual physical RF activity, rather than just the data that happens to percolate through your typical wireless chipset. There’s a simple version known as Wi-Spy 2.4i, which uses an internal antenna and costs around £60 from the official UK distributor Crownhill.

The device I have is the Wi-Spy 2.4x, the next model up in the range, which has better frequency resolution and also an RP-SMA-connected external antenna that gives far better reception (and enables you to plug in a higher-gain antenna should you need it). It comes with more fully featured software, too. The Wi-Spy 2.4x costs £121 from Crownhill.

Other Wi-Spy models cover the 900MHz band – useful if you want to track RFID or cordless phones – and the 5GHz band. Although the latter is used by some Wi-Fi kit (802.11a and certain variants of 802.11n), it’s a far less crowded band with hardly any other competing activities, so I’d recommend Wi-Spy 2.4x as the best choice for most people.

All these Wi-Spy devices come with software called Chanalyzer. A “lite” version is supplied with Wi-Spy 2.4i and a full-fat version called Chanalyzer 3 with the more expensive analysers. I’ll just consider the latter here.

It offers three main views called spectral, topographic and planar. Spectral is a waterfall view across the whole 2.4GHz band, using colour to pick out the relative signal strength at each point in time. This is excellent for troubleshooting intermittent problems, since it highlights devices that are perhaps emitting only short bursts of noise.

The topographic view plots frequency versus amplitude, with colour used to identify how often a particular co-ordinate is recorded; leave it running for a while and it will give a good indication of the typical local network conditions.

Planar view also plots frequency versus amplitude, but this time showing the maximum, average and real-time values. The topographic and planar views work well together to show instantaneous activity as well an historic fingerprint.

The feedback from Chanalyzer is amazing, graphically illustrating, for example, that if you’re using 802.11n with its 40MHz channel-width option turned on, you’re wiping out a huge chunk of the Wi-Fi spectrum. It also clearly shows interference from nearby microwave ovens, which interestingly isn’t only on the 2.45GHz frequency (close to Wi-Fi channel 9) you’ll see written on the nameplate of your oven; most microwaves seem to splat interference across all channels.

For anyone who’s responsible for Wi-Fi within an enterprise, or for installing wireless networks for SME or domestic clients, I reckon Wi-Spy is a must-have tool.

Leave it running for a couple of minutes and you’ll easily identify the channels with the least RF pollution. Run it over a number of hours and it will identify and help you solve intermittent problems.

Download a year of Paul Ockenden's Mobile & Wireless columns by heading to our Free Downloads site