Wireless spectrum analysis typically falls into two camps: free open-source software such as NetStumbler or Kismet, and ultrapricey hardware-software combo products like the Grasshopper. This leaves a huge gap between those who have the time to play with open-source stuff and those who have the budget to play with proprietary tools.
MetaGeek is charging head-first into this gap with its Wi-Spy product line of inexpensive (sub-$800) spectrum analysis products. In April, eWEEK reviewed MetaGeek Wi-Spy 2.4x, an earlier product that only covered the 2.4GHz band. The Wi-Spy DBx retains the power and ease of use of its predecessor while adding improved software and coverage for the 5GHz band.
The vast majority of businesses-and homes-are already using a WLAN or are planning on installing a one. With so many networks and devices out there, the airwaves are getting jammed. Organizations need to perform site surveys to plan a WLAN and then regularly scan the airwaves to look for unauthorized or rogue access points. In addition, there are many sources of interference, such as microwaves and some cordless phones, which can degrade performance or outright block WLAN traffic. Wireless administrators are constantly on the lookout for new ways to solve these problems.
Wi-Spy DBx is a small USB device that can scan the radio frequency range from 2.400GHz to 2.495GHz and 5.170GHz to 5.815GHz (complete coverage of 802.11a/n), with a resolution of 328KHz. It can detect signals in the amplitude range of -115 dBm to -6.5 dBm with a resolution of 0.5 dBm. The Chanalyzer visualization software includes a device signature library that allows a user to determine what is creating interference.
The first thing I noticed about Wi-Spy DBx is that it uses an industry-standard antenna connector (RP-SMA) that enhances the flexibility of the device because the antenna can be replaced with another for greater directionality and gain. For example, by using a series of adapters, I was able to connect an 18 dBi omnidirectional antenna, which allowed me to pick up dozens of WLANs in my New York neighborhood. I ultimately decided that the best way to troubleshoot with the Wi-Spy DBx was to start with the monster antenna to do a wide scan and then move to the smaller supplied antenna to pinpoint interference.
Testing Wi-Spy DBx with Chanalyzer 3.2
I began by downloading the newest version of Chanalyzer, the Chanalyzer 3.2 beta, from the MetaGeek Web site. Software installation was wizard-driven and took less time to install than to download. I tested the Wi-Spy DBx on two PCs, a Windows Vista 64-bit PC with an Intel Core 2 Quad with 8GB of RAM, an overclocked Nvidia 8800GT video card and a 1TB hard drive; and a much lesser 1.1GHz Mobile Pentium III laptop with 768MB RAM and a 40GB hard drive running Windows XP Pro Service Pack 3.
While performance on both was more than acceptable, the desktop blazed through visualization while the laptop was noticeably slower. The advantage of the laptop is that it also has an 802.11b NIC (network interface card) from which Chanalyzer can read SSID (service set identifier) information.
It took a little while to get acclimated to the Chanalyzer interface; thankfully the help section is well-written and informative. There are three ways to view data: Spectral View, which shows noise over time in a waterfall view; Topographic View, which aggregates the entire session into a single display that shows overall use of the spectrum; and Planar View, which shows the current, average and maximum amplitudes plotted against their frequency. You can show a single or multiple views at once.
The trick is to collect data for 15 minutes to 24 hours and then try to identify the devices utilizing various frequencies. To get started quickly, open the help section and view Troubleshoot, Interference Identification. I arranged all three views on the screen at once and could very quickly see the background level of transmissions and peaks of utilization (amplitude > -65 dBm) at 5394.2, 5400.1, 5649.6MHz, with a bunch of smaller peaks (amplitude between -90 and -85 dBm). Serendipitously, I received a phone call and answered with my Uniden 5.8GHz cordless and a new peak appeared at 5810.1MHz.
The Wi-Fi Channel report provides a performance grade for each channel based on the detected duty cycle and other measures of signal quality. I could tell very quickly which channels would be better for WLAN deployment as well as how interference from specific devices affected performance.
A great new feature is the ability to install Wi-Spy DBx at a remote site and still access it. This is done by installing the MetaGeek Recon software on the computer with the Wi-Spy DBx unit, making that machine Internet-accessible and opening the appropriate port. I was able to do this easily on the laptop and access it from Chanalyzer on my desktop.
Overall, Wi-Spy DBx is a great tool for those looking to troubleshoot WLAN interference quickly, easily and inexpensively.
Matthew D. Sarrel is executive director of Sarrel Group, an IT test lab, editorial services and consulting company in New York City.