Spectrum XT ably tracks down non Wi-Fi sources of interference

By Andrew Garcia  |  Posted 2010-02-01

AirMagnet's Spectrum XT provides an excellent way to track down non-Wi-Fi sources of interference around a corporate wireless network, allowing wireless administrators to more easily identify and locate potential RF problems that could hamper network performance. Support for modern laptop hardware and limited integration with AirMagnet's other tools enhance the overall experience.

With Spectrum XT, AirMagnet (a Fluke Networks company) looked to solve some of the problems that developed over time with its previous-generation spectrum analyzer, AirMagnet Spectrum Analyzer.  The old product, which was based on Cisco's Cognio line of hardware and software, wasn't getting the level of feature enhancements that customers wanted, so AirMagnet wrote new software for use with Spectrum XT. Also, with card bus slots found less commonly in new laptops, Spectrum XT uses a USB-based analysis component instead of a PC Card.

Shipping now, Spectrum XT lists at $2,495, but introductory pricing for ($2,195) will be available through the end of June. At this time, there is no additional discount for current customers of the older AirMagnet Spectrum Analyzer, but AirMagnet officials indicate that they will be rolling out a transition program for those customers within the next few months.

AirMagnet does plan to keep selling the older Cognio-based Spectrum Analyzer product for the time being.

The new USB analysis hardware is a relatively small device (roughly 3.75 by 1.5 by 0.31 inches), with an external antenna connector. The device is too wide to plug directly into a vertically oriented USB slot on a laptop sitting on a desk, but it does come with a foot-long USB extender cable. The included external antenna is omnidirectional and comes with a clip to attach to the top of a laptop panel. The device will also work with an optional directional antenna instead.

Spectrum XT is a 32-bit program and promises to work on Windows 7, Vista and XP. With a small memory footprint (in tests, it typically hovered at about 60MB RAM), the program should work well on modestly horsepowered systems, such as a netbook running Windows XP Home. However, I performed my tests on a Lenovo Thinkpad T400 with a Core2Duo T9400 processor and 2GB of RAM, running Windows XP Professional.

When starting the Spectrum XT, I was immediately presented with several panes of non-Wi-Fi spectrum information for the 2.4GHz band. On the left side of the screen, a channel summary outlines the current, average and maximum FFT (Fast Fourier Transformation), as well as the duty cycle for all 14 channels in the 2.4GHz band. Below that, the Device list details any detected non-Wi-Fi sources of interference, such as cordless phones and microwave ovens. The main panel, meanwhile, shows separate graphs depicting real-time FFT and spectrum density across all the channels.

From a pull-down box at the top left, I could expand my analysis to other frequency bands. I could isolate detections to the lower, middle and upper ranges of the 5GHz bands individually (as well as the 4.9 band), or I could conduct a mixed scan that cycled through all the bands.

Choosing the mixed option will change the default view to show the real-time FFT graphs for the 2.4GHz band and for each segment of 5GHz band. Users can adjust the views to showcase ample other analysis perspectives for each band, however, including channel power, channel duty cycle, interference power and a new event spectrogram view that displays strength of interference of a particular device plotted over time and affected channel.

With Spectrum XT, I could also cull more information about Wi-Fi sources of interference when using the product with a supported Wi-Fi adapter. Armed with the Wi-Fi adapter, I could, from the base screen, detect the number of APs on a given channel, their MAC addresses and the received signal strength.  I could also break down the number of clients and Wi-Fi phones on each channel.

There is also a series of Wi-Fi-specific graphs that can be accessed via the main panel. Among the graphs, I could view channel occupancy (targeting the primary channel and those affected by the transmitter), channel speed (the number of kilobytes sent at a particular connection speed on each channel) and per-channel traffic mix (unicast versus broadcast or multicast). I could also take a more device-centric view of things, identifying the busiest APs in the airspace or those needing the most retries.

I tested in conjunction with a Cardbus-based AirMagnet C1060 802.11 a/b/g/n card; a list of other supported adapters can be found here.  An unsupported adapter will show some basic information about the Wi-Fi environment culled from Windows' built-in Wi-Fi tools.

I liked the new Find Device tool, which somewhat eases the tricky process of tracking down non-Wi-Fi interferers.  Intended to act a little like a Geiger counter would with radiation, the tool displays the current signal strength of the detected interference, constantly refreshing the value. Walking around slowly (AirMagnet recommends a snail's pace of 1meter every 3 to 5 seconds), the dial adjusts according to the detected signal strength, indicating whether I moved away from the interferer (weaker signal) or toward it (stronger signal). There are optional aggravating sound cues to help drive home changes in detected signal strength.

An on-screen dial displays both the current strength detection as well as the maximum detected value during the session, while a timeline plots the signal strength over time. Device finding would be easier with a directional antenna instead of the included omni-directional antenna, however, as users could more easily home in on the direction from which the signal emanates.

The tool can also be used to track down and locate Wi-Fi devices, although other tools are better suited to that activity.

Spectrum XT does integrate with other AirMagnet tools, including AirMagnet WiFi Analyzer PRO and Survey PRO as long as those applications are installed on the same laptop.

In WiFi Analyzer PRO, enabling the connection between the applications adds an RF Spectrum Interferer box to the Interference tab. In tests, this allowed me to view some limited information on non-Wi-Fi sources of interference. While it would be handier to extend the coordination between applications to the visual walkabout tools like in those in Survey PRO--to tie non-Wi-Fi interferer detections to both a place and time on a map in case further analysis is needed after the analysis session--that level of integration is not yet possible.

Spectrum XT supports session recording, allowing the user to capture a trace session and play it back within Spectrum XT at a later time.

Senior Analyst Andrew Garcia can be reached at agarcia@eweek.com. 

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