Wi-Spy Spectrum Analyzer
February 03, 2006
You probably wont find a smaller or less expensive way to analyze your surroundings for radio interference.
Pros: Inexpensive; simple software; displays information about non-Wi-Fi devices
Cons: Doesn't read 5 GHz band, no external antenna support
If it seems like your Wi-Fi network isn't working quite as well as you expected, there's a good chance the problem is due to some form of interference. You probably know about the myriad devices around the typical home (like microwave ovens, baby monitors, and many cordless phones) that can interfere with WLANs, but there are also equally potent and less obvious sources of interference, including Bluetooth devices and other nearby WLANs (which won't show up in your WLAN client utility unless they're set to broadcast an SSID).
Since interference problems can manifest themselves in many ways and can be either chronic or intermittent, they can be difficult to pinpoint. If you're lucky, you may be able to correlate a drop in performance (or perhaps even a complete loss of signal) with the phone ringing or someone nuking a burrito. But without a spectrum analyzer to sniff the air, confirming the presence of interference, finding a remedy can remain elusive.
The Wi-Spy will work with any notebook or desktop PC with USB 2.0 or 1.1 ports, though the included software utility requires Windows 2000 or XP with Microsoft's .NET Framework 1.1 installed. A Mac OS X version of the utility is under development for late Spring release, and there is also a third-party Linux utility available, though it doesn't have all the capabilities of the Windows version.
Installing the Wi-Spy is quick and easy: you plug it in, and within about a minute you're ready to go. The Wi-Spy device gets recognized by Windows as a generic HID (Human Interface Device, like a mouse) so you don't have to install any special drivers for it. The software utility can be installed on your system, but you have the option of running it directly from the CD, which can be very convenient when you're using a system other than your own. (As it turns out, running the utility directly from the CD didn't actually work for us; it resulted in an exception error, which MetaGeek says was due to a DLL that was inadvertently omitted from the disc. Corrected discs should be shipping with the product by the time you read this, however.) Indeed, the fact that the software ships on a business card-sized mini CD instead of a standard full-size one makes carrying it around much easier.
Looking for Air Pollution
Fire up the Wi-Spy software, and you're presented with an analysis graph that immediately begins reporting RF spectrum data in real time. You can view any combination of current data, average, and maximum traces, and can configure the graph's X-axis to display the 2.4 GHz wireless spectrum either by frequency range (2400 to 2483 MHz) or by the 11 user-selectable channels available. In the latter mode, selecting a particular channel highlights its frequency boundaries, so you can see when and how different channels overlap each other. Because Wi-Spy reports signals from any 2.4 GHz device and not just Wi-Fi, you'll be able to spot any RF activity that could be interfering with your wireless network.
In addition to viewing current data, you can use Wi-Spy to record data to a file and play it back later. You can play recordings in real time or at an accelerated rate. Since Wi-Spy can continue to collect and display current data while you're playing back a recording, it's easy to compare historical data to current readings. Wi-Spy comes with several reference recordings that can help you identify the telltale RF signatures of items like a microwave or cordless phone (both the single-channel and higher-interference frequency-hopping variety).
There are lots of ways to customize the look of the graphs to personal needs or taste -- you can customize the color of each item and choose from a number of different line types. There are also customizable keyboard shortcuts to quickly hide or display individual data points, and analysis graphics can be printed to about a half-dozen file formats or copied to the clipboard for embedding into other documents.
In addition to the analysis view, Wi-Spy offers a spectrogram view so you can see how the RF data being gathered changes over time. The 2D spectrogram can display anything from two minutes to 24 hours of past data, though whenever you change the time scale, the spectrogram resets and you lose the data you've accumulated up until that point.
Although there's a lot to like about the Wi-Spy, there are a couple of limitations. First, the Wi-Spy only sees the 2.4 GHz band, so it won't work with 802.11a networks (then again, there's a lot less interference to worry about up at 5 GHz). The Wi-Spy can't use an external antenna, although MetaGeek says it's developing a Wi-Spy that supports one, and that should be available this summer.
Aside from the aforementioned shortcomings, there are a few other admittedly minor nits to pick. The Wi-Spy doesn't come with a cap, which leaves the USB connector exposed and vulnerable to dirt and damage. The plastic shell also lacks a built-in loop, which precludes you from attaching a lanyard for wearing the device (or at least more easily finding it at the bottom of a crowded bag). Finally, in an ideal world, the Wi-Spy would come with a small amount of built-in memory to hold the software, making the device fully self-contained.
Of course, when all is said and done, the Wi-Spy, like any spectrum analyzer, is an informational tool. While it can identify problems, it can't explicitly address the issue of interference -- that part is up to you. That may not always be easy, since not every potential source of interference is under your control (especially if you live in dense quarters like an apartment complex). But Wi-Spy is cheap, small, and easy enough to use that it can be a major step towards compensating or eliminating interference with your WLAN.