Troubleshooting 2.4ghz WiFi with Metageek’s Chanalyzer Pro

I work for a relatively small business comprised of about 120 employees and three locations.  One of the most difficult things about working for a company this size is troubleshooting IT related issues with a limited toolset and budget.

Once such problem was a wireless networking issue that had been irritating me for some time.  We have a set of classrooms, which are frequently used for training classes, presentations, fundraising and various other functions.  Many times, staff and/or visitors need an internet connection for part of their work.

Several times, I brought in wireless access points into the classrooms and connected them to Cat5 ports we have along the walls so people could conveniently connect to the wireless network without having to string around a 50ft Ethernet cable.  This rarely worked.  Most of the time, users would get connected and then suddenly drop off or have their browsing session time out despite Windows claiming they had excellent signal strength and were connected at 54mbps (the limit at the time).  Most of the time, I chalked this up to cheap equipment (I was limited to the Linksys WAP54G at the time) and just ended up wiring their laptop into the Cat5 ports.

Much more recently, we decided to provide a service to low income members of the public on a semi-regular basis.  This service, relies heavily on a web based, database application and we would have to setup and tear down a small extension of our network in these classrooms every two weeks or so.  Having known of the wireless problems I had in the past, I decided to use as small Ethernet switch and just wire all the laptops into our network.

The problem with this, is that with the laptop power cables, printers, paperwork and mice, etc. this became a tangled mess of wiring that gave a sloppy impression and was just a kick or trip away from being taken down and/or possibly yanking some expensive new laptops onto the floor.  This is when I decided I had to figure out what exactly was causing our wireless issue.

My first thought was to blame the construction materials; mostly thick cinder block and some special tiling on the floor for easy cleanup (with some drywall).  After all, concrete/cinder block is known for quickly absorbing wireless signals and causing signal attenuation.  However, I quickly realized that the entire back of the building, which gets heavy wireless use, was constructed of the same material and no one had ever reported the same type of issue there.

I then assumed that there had to be some sort of interference.  Possibly a neighboring business using the same channel I had chosen for the AP in that room.  To check this, I installed two applications; inSSIDer (developed by Metageek) and NetStumbler .  Both applications are popular, free applications that allows a user to get a quick list of the available wireless networks in the area, what channel they are broadcasting on, signal strength and a few other useful bits of data.  So, I loaded these up expecting to see some other network broadcasting on the same channel, but was disappointed when no other outside networks even registered on the lists. In addition, these applications are limited in that they’ll only show you wireless networks, not any source of interference on the 2.4ghz band.

I was now frustrated and essentially just throwing out guesses.  Maybe the fire systems or alarm systems were interfering with it?  Maybe they communicate wirelessly with some controller system?  I checked with our building operations team and maintenance and everyone claimed there wasn’t any type of system communicating wirelessly that might be interfering with the WiFi.

So, I decided I had to try and find some other tool for discovering the source of the problem.  I checked out handheld spectrum scanners, some small tools for mobile devices and a few other options, but I wanted something a bit more robust and future proof (anyone keeping up with the new 802.11 specifications should know that the 2.4ghz is on it’s way out).

After a lot of searching I found myself back at Metageek’s site, looking at their Chanalyzer Pro software (similar in style to inSSIDer but with a lot more power), the WiSpy DBX Spectrum Analyzer (analyzes both bands) and the Device Finder (this is only useful at the 2.4ghz frequency, but relatively inexpensive).  After some thought and price shopping, I bit the bullet and purchased all three directly from their site.

Fast forward a few days, and I’m in the classroom with all software installed and all of our network APs powered off.  The only thing I should see now is whatever is interfering on the 2.4ghz band.  Sure enough, I notice this:


Snapshot of the 2.4ghz spectrum using Metageek’s Chanalyzer Pro.

Not only can I see a live feed of the 2.4ghz spectrum but I can also look at a timeline waterfall to see if the issue is intermittent or static.


Waterfall view.

Clearly, there is something on the 2.4ghz band (something very dense and intense), but what exactly is it?  I moved all over the classroom, using both the WiSpy DBX and the Device Finder, but both seem to fluctuate wildly depending upon where I am in the room.  They do however seem to spike, the closer I move to the parking lot.  I then head outside, to the parking lot, and both the spectrum view and device finder spike as I move farther from the building.  Finally, I spot the likely culprit and walk right up to the base of a light post in the parking lot and look up.  There, bolted to it, are three surveillance cameras.  Another two or three light posts with the same type of cameras are located on different sides of the classrooms.  As I move from one to the next, the same spike moves to another channel.  Still, why are these cameras interfering when the others around the building don’t impact the WiFi?

An e-mail to our vendor and a trip up to the roof with our operations director, and everything is cleared up.  Those three sets of cameras are part of “The Eagle Plus 2.4ghz FM All-Weather Wireless Video System”.  Each beams the video feed directly to receivers placed on the roof, directly over the classrooms.  Had I not travelled out to the parking lot, I may still have figured this out, as Chanalyzer Pro provides common “signatures” of interference sources and can attempt to match the signals you are seeing with those signatures.  You can even set a confidence level and exclude signatures you know it couldn’t be, but on this particular day all I needed was this software and my laptop as I knew there wasn’t going to be an area I couldn’t readily access.

Now that I know the problem, and that the cameras have to stay, we’re going to need to invest in some newer, 5ghz capable hardware, but being able to say with 100% certainty what the problem is makes management more comfortable spending money on a solution and makes my job a lot easier when it comes to troubleshooting WiFi.

I cannot recommend Chanalyzer Pro enough.  You have to give your IT staff the tools they need to solve problems efficiently and this is one of those tools.


About JoeDania83

IT Administrator for a three campus non-profit.
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