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« VIA Rail Adds Wi-Fi to Western Canadian Train Stations | Main | Wee-Fi: Zune for $150, Another WI-Fi Arrest »

August 21, 2007

Wi-Spy Spectrum Analyzers Shows What's in Your Wireless Backyard

To understand what's wreaking havoc on your wireless networks, a spectrum analyzer is key: Sure, you can make guesses. Talk to neighbors. Use Wi-Fi and Bluetooth scanners. But those approaches have limits. What you really need is a spectrum analyzer that can scan the surrounding area across a frequency range and show numerically and graphically what's in the air around you. By moving around with a mobile analyzer, you can pinpoint actual problems, and see displayed over time a moving target as to what's destroying your network's utility.

MetaGeek has two affordable options for desktop Mac OS X, Windows, and Linux analysis, both of which come in the form of a USB stick. When I say affordable, I mean that their units retail for $199 and $399 versus $2,000 and up for full-featured IT management packages and hardware or standalone devices. The two options scan the 2.4 GHz band used for 802.11b/g and one of the bands 802.11n supports. Bluetooth, ZigBee, and cordless phones--among many other devices--also use the band.

The original Wi-Spy debuted over a year ago; the Wi-Spy 2.4x is a more recent entry from June of this year. The differences between the two units were originally software support, with Mac OS X software available just for the original WiSpy at the launch of the newer device. The Wi-Spy 2.4x now has two Mac OS X supporting applications, too, due in part to the programming interface provided by MetaGeek.

MetaGeek has a nice comparison table that explains the difference between the original and 2.4x versions of their product. It boils down to the 2.4x offering greater resolution--it can capture signal strength on a smaller set of frequencies at once--along with higher sensitivity, and an antenna. The antenna can be removed and replaced with others using the same jack style (RP-SMA).

Wispy24I tested both units in my office under Windows Vista and Mac OS X. My office in Seattle's Fremont neighborhood, a mixed retail/office/residential area, has a plethora of Wi-Fi networks. I can see from eight to 14 networks in my office, which is nestled inside a building. I tried turning on a microwave oven adjacent to my office to see what effects that created, too.

Using MetaGeek's own Chanalyzer software, I could watch Bluetooth dancing all over the 2.4 GHz band. Chanalyzer lets you set mark points to track in planar view, in which activity is marked for average and maximum uses across the band, while a live line shows current signal strength. The topgraphic view shows a concentration of activity over time. The spectral view is a moving track that you can replay and change the time dimension on to expand or contract a moment you're viewing. The program lets you "record" a scan, which you can replay in the software. MetaGeek also created a community for sharing scans among those interested in that sort of thing, and has samples you can download and replay in Chanalyzer to show various tests they've performed. (Chanalyzer 2.1 works under Windows. WiSPY-Tools is an independent Linux, BSD, and Mac OS X package with similar features. MetaGeek has a beta of Chanalyzer for Mac that's not currently linked on their Web site.)

Microwave Wispy24The scan above shows the normal environment--fairly congested, and you can see the Bluetooth spikes (by clicking to view the full-size image) as lines that leap up in yellow in the planar view. When I turned on the microwave oven, there was some impact (see at left). In the spectral view, you can see the diagonal green lines between 1 and 2 minutes on the time scale when the microwave was first active; I turned it on again briefly and you can see another set of angry lines. In the topographic view, notice the haze of interference rising above the deeper, thicker red band.

I also experimented with EaKiu, a free and independent Mac OS X software package that supports both the original Wi-Spy, and was updated recently to version 4.0 with Wi-Spy 2.4x support. The package offers some interesting 3D options for visualization, in which you can rotate a continually updating series of receding planes.

I honestly found it tricky to figure out how to test the Wi-Spy models since I had no particular issues facing my rather ugly RF environment at the office, but one fortunately dropped into my lap. Apple recently released its revised model of AirPort Extreme Base Station with Draft N by adding gigabit Ethernet. They also tuned some internal firmware issues to improve speed when network address translation (NAT) was in use. For a review in Macworld magazine, I re-ran the same performance tests that I put the Extreme through in February. In the 5 GHz band, everything was copacetic: terrifically improved speeds due to the gigabit Ethernet removing internal limitations that restricted performance.

Airport Channel Change WispyBut in 2.4 GHz, I was stymied. I could hardly get my N adapters (Intel and Apple) to connect to the base station. With Apple's advice, I turned off Automatic channel selection and chose channel 1. I was seeing kilobits per second throughput when I could connect where I should have seen 30 to 70 Mbps. I fired up the Wi-Spy 2.4x to see what was the matter.

It seemed like I was seeing a lot of energy down at the lower end of the band even when the Extreme wasn't transmitting. I switched to channel 11, and, magically, performance was restored. Now, according to iStumbler, no one is transmitting in channel 1, so there's other ugliness involved. If you look at the Eakiu screen capture (at right), you can see the time sequence moving from newest to oldest on the Z axis (roughly front to back). I switched from channel 1 to 11 right where you see energy levels go down and red (higher dBm signals) disappear on the left, and start to fire up into red on the right. Clearly, something's using that part of the 2.4 GHz band (amateur radio? electronic newsgathering? another licensed purpose? an ugly transmitter?). But without the Wi-Spy, I would have been slightly flummoxed.

The Wi-Spy isn't for every network manager or hobbyist, but it's going to help IT professionals and Wi-Fi busybodies like myself answer a lot of questions that are otherwise lost in the ether.