By Becky Waring If you’re suffering from poor Wi-Fi performance, dropouts, or dead zones despite having the latest and greatest router, it’s time to check your airwaves. Metageek’s inexpensive Wi-Spy spectrum analyzers will root out rogue access points, interfering neighbors,cordless phones, and more — giving you back control over your Wi-Fi net.

So many channels, but still no place to go

There are 11 channels in the 2.4GHz Wi-Fi spectrum (up to 14 outside the U.S.) and a whopping 23 in the 5GHz band. Moreover, most newer routers automatically choose by default the best available channel. So why do we still have so many Wi-Fi problems?



Ask Steve Jobs — his keynote iPhone 4 demonstration (reported in a June 7 InfoWorld story) failed epically due to interference from the hundreds of Novatel MiFis and similar portable wireless access points in the audience. The problem is simply too many devices fighting for too little bandwidth.

Of the 11 channels available in the most-commonly used spectrum — 2.4GHz — only three (1, 6, and 11) are non-overlapping; they don’t interfere with each other when used simultaneously. Fire up your laptop and look at the list of Wi-Fi networks within range. When was the last time you saw only three or fewer SSIDs (network names) listed?

In my Berkeley house, which has only one neighbor within 20 feet in any direction (most are 30 to 40 feet away), I typically see 11 to 15 SSIDs in my Wi-Fi network list. Most have very weak signals that I probably couldn’t connect to with any reliability — which means they probably don’t interfere much. But at least three have usable signal strength, sufficient to actively compete with my access point.

The obvious solution is to move to the 5GHz band, which has more channels and far-fewer occupants. But this band can have coverage problems: its higher frequency needs more power to cover a given area, and most 5GHz routers don’t deliver those extra watts. And because many wireless clients (notebooks, wireless printers, and so forth) have only 2.4GHz transceivers, you’ll end up with a dual-band router anyway.

To help you choose the clearest channel in either band, network scanners such as Metageek’s free inSSIDer software (see Figure 1) can show which channels are taken by nearby routers, as well as the routers’ relative signal strengths. InSSIDer (information page) is the best free tool out there by far, and it provides a valuable grade that measures network quality over time.


Figure 1. InSSIDer shows a list of nearby Wi-Fi networks, plotting their channels and signal strengths on a graph in the lower-right corner of the window. This figure shows many nets competing for channel 1 — and only a couple of nets using channels 6 and 11.

That’s fine if all you had to worry about was competing routers. But in the real world, many other devices use the 2.4GHz and 5GHz bands: cordless phones, Bluetooth devices, wireless speakers, baby monitors, remote control cars, car alarms, microwave ovens, wireless video, and surveillance systems come to mind. None of these devices is revealed by your Wi-Fi adapter or scanning tools such as inSSIDer. For a complete survey of competing radio activity, you need to add an additional piece of hardware.

Get spectrum analysis at a bargain price

To fully troubleshoot Wi-Fi issues caused by non–Wi-Fi sources, you need a radio-spectrum analyzer — a device typically associated with scientists, radio geeks, and network administrators and costing U.S. $2,000 and up. These enterprise-level analyzers come from companies such as Fluke Networks, Cisco Systems, and Berkeley Varitronics, and they’re designed for organizations with really big Wi-Fi networks: hotels, university campuses, office complexes, convention centers, and the like. As you might suspect, the complexity of these tools matches their price.

At its heart, however, spectrum analysis is pretty straightforward. In small-network settings, all you really need for troubleshooting is a picture of what signals are bouncing around your home or office, plotted by frequency and amplitude (strength). This information will let you identify and locate radio sources so you can understand what’s affecting your wireless network.

This is exactly what Metageek’s Wi-Spy USB dongles (info page) are designed to do. These low-cost devices, shown in Figure 2, put spectrum-analysis tools into the hands of anyone with a more-earthly budget of $99 to $599 and the ability to read a graph. Although the first Wi-Spy came out in 2006, it was crude compared to today’s offerings, which now include 5GHz support and far-more advanced software.

The current product line has three models, the $99 Wi-Spy 2.4i, the $199 Wi-Spy 2.4x, and the $599 Wi-Spy DBx. (The 2.4i and DBx are shown in Figure 2.) The 2.4x and DBx add finer signal resolution and an external antenna for better reception. The DBx model also adds 5GHz support.


Figure 2. The Wi-Spy 2.4i and Wi-Spy DBx. The DBx adds 5GHz support and an external antenna for better reception.

Although I tested the top-of-the-line Wi-Spy DBx, most small-network troubleshooters can get by for now with the 2.4x model (or even the 2.4i, if you’re on a tight budget). At this time, there are just not that many products competing for the 5GHz band — the 2.4x gives you the most bang for your buck. These are the only spectrum analyzers in this price range, I know of.

Metageek’s secret sauce? Its software

Although the Wi-Spys are excellent devices, it’s the Chanalyzer software that makes them sing. Windows automatically installed the Wi-Spy DBx, when I plugged the device into my PC. I then installed and fired up Chanalyzer 4 to see what creatures lurked in the 2.4GHz band.

Chanalyzer 4 (info page) is new and is included with both the Wi-Spy 2.4x and DBx. The low-end Wi-Spy 2.4i comes with the more-limited Chanalyzer Lite (info page).

For network troubleshooters who need more-extensive analysis tools, Metageek offers its $499 Chanalyzer Pro software. It adds features which can help you identify conflicting devices and track them down.

Chanalyzer has three graphical views, as shown in Figure 3:

• Topographic. This view, shown at the top of Figure 3, is the main graph of spectral activity. It plots the signal strength (amplitude) of radio activity on the vertical axis against frequency along the horizontal axis. Wi-Fi channels 1–11 are also labeled along this axis. The more activity recorded over time for a given frequency, the brighter the colors get; the longer you let the program run, the more densely filled the graph becomes.
  
  
• Planar. The planar view can be plotted on top of the topographic data or separately. It shows single lines representing the average, maximum, and real-time values of frequency versus amplitude. This instantaneous view is great for troubleshooting when viewed together with the historical data.
  
  
• Spectral. This view, shown in the middle of the screen, plots activity across the entire frequency band (2.4 or 5GHz) against time on the vertical axis, using color to indicate relative signal strength. The plot moves downward in a waterfall as time passes. A burst of activity manifests itself as brighter colors (representing, for example, the downloading of a file from the Web). Background levels of activity are also displayed. Using this view, you can easily see the effect of turning radio sources, such as a cordless phone or microwave, on and off.
  

Figure 3. The Chanalyzer 4 software showing all three views: topographic, planar, and spectral.

You can run the scans for hours or even days and record the results for later playback and study. When troubleshooting a problematic site, you want at least 24 hours of activity as a baseline.

In my location, two things became evident as I started scanning. First, there were several competing networks around channel 1 (which I also saw by using inSSIDer). Second, there was a mysterious spike to the left of channel 1 (more visible when we zoomed in on the graph). Using Metageek’s handy library of spectral signatures, I easily identified it as a cordless phone. (You can upload your own spectral recordings to share with other users.)


Figure 4. Some common spectral signatures: a Wi-Fi access point, a microwave oven (wow!), a cordless phone, and a wireless video system.

Sure enough, when I checked with my neighbors, they had a 2.4GHz cordless-phone system. I would never have discovered this if not for Wi-Spy. (Cordless phone users can change channels easily, which can make them hard to pin down over time. One solution is to ditch the 2.4GHz models for those using DECT 6.0, which operates at 1.9GHz.)

One of the coolest new features in Chanalyzer 4 is the ability to overlay Wi-Fi network information on the topographic view and to see a list of networks below the graphs. Essentially, the functions of inSSIDer are now built into Chanalyzer, making problems easier to diagnose and report.


Figure 5. You can now toggle Wi-Fi network labels on and off in Chanalyzer 4′s topographic view.

Use Wi-Spy to map your network landscape

Another great way to use Chanalyzer is to walk around a room or house with it and see how things change on the graphs. You can find dead zones, locate devices that might be unexpected sources of interference, and find the best physical location for your router.

One of my favorite Wi-Fi stories is about the Berkeley professor who kept her router in the living room, on a low stand just behind her TV. It also happened to be next to a wall, behind which were the kitchen sink and granite countertops. She couldn’t get reception anywhere but the living room. She couldn’t understand why — the router had worked fine in her previous house. I moved the router four feet (up to a shelf above the TV and above the kitchen counter line), and voilà, whole-house coverage!

Plumbing, stone, ceramic tile, water tanks, metal, and so on are all physical barriers to Wi-Fi that are easily avoided with proper placement.

You can easily plot the results of your placement changes with Ekahau’s cool HeatMapper (download page), a site-survey application that creates heat maps — geographical signal-strength charts.

With HeatMapper, you can load a floor plan into the program, then walk around clicking points on the map as you pass them — thus logging Wi-Fi signal data at each location. When you’re finished, you’ll get a nice map showing the coverage and strength of your access point in a color-banded topographic view.

With a little upfront planning and airwave investigation using tools such as Wi-Spy and HeatMapper, you can achieve far-better average throughput on your Wi-Fi net, eliminate most dropouts, measurably improve productivity, and prevent countless headaches.

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Becky Waring is the former editor of NewMedia Magazine and has written for PC World, Macworld, Wired, Upside Magazine, Technology Review, CNET, and many other outlets.

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