WiFi Interference – MetaGeek Chanalyser and DBx Help!

Warning: I’m not really strong in WiFi so some mistakes or interpretation may occur. Hopefully some WiFi experts will correct me in the comments or email to [email protected]

I’m working  on a badly performing wireless network and getting serious grief. This weekend I packet my MetaGeek WiSpy and downloaded the latest Chanalyser (Mac OSX version!!) and started to analyse the spectrum this morning.

I arrive early and started to analyse the 2.4Ghz spectrum. Then I connected and started a large data transfer (iTunes podcasts). Here is the interface:

Channel under load - Click for Larger


So that looks good to me. The signal is hot because I’m transferring at 6Mb/s in this capture (for testing) which is about as good as it will get on an 802.11b access point. I’m using Cisco AIR-AP1231G-E-K9 which are kind of old but the original intention was to have a best effort guest wireless network built out of the some old kit that was lying around.


Spectrum Analysis 2nd Floor - Click for Larger

So far so good. Can’t see any problems. Spectrum is uncrowded, and the channel I’m using is running at a good strength.

But then, about an hour later I start to see this happening in the spectrum.


Spectrum Interference 1 - Click for Larger Image


See these red spikes across the entire spectrum band ?


Spectrum Interference 2 - Click for Larger Image

And again, but centred in a different frequency.

Spectrum Interference 3 - Click for Larger Image


Those little collection of angry red signal bursts might be the source of a problem. They repeat often and I’m wondering if they are causing the signal dropouts that my wireless users are reporting.


I also used InSSIDer (Mac App Store for USD$6) to help map out the networks use. As you can see there are a lot of networks here. Although Chanalyzer does display the SSID’s I found this even easier to use. The signal strengths look OK to me (but I’m no expert).

InSSIDer interface (Click for Larger)

The EtherealMind View

I’m hoping that someone might recognise this interference and give some hints to possible causes. I’m thinking it could be some sort of wireless reset or beacon, or maybe someone will recognise it as a specific device. The signal seems to be quite specific, happens irregularly but recurs often.

Anyone got any ideas ?

By the way, I’ve already got a lot information from using the Metageek Chanalyzer product to help me analyse my wireless network and solved several problems. It works on my MAC but the Windows version does even more. You can buy the WiSpy DBx (which does 2.4Ghz and 5Ghz ) from their online store. I did try my Air Magnet but found installing the software so painful that I gave up.


The MetaGeek Chanalyser and WiSpy DBx is a demonstration unit that was provided during TechFieldDay Wireless Field Day 1 in Jan 2011 (and the Air Magnet as well). Although I assist in organising some Field Days and a regular attendee/contributor , my opinions and views remain my own. I’m not expected to write or promote any vendors or products that we cover in the event.

My full disclosure statement is here

  • http://www.curtis-lamasters.com/ Curtis LaMasters

    Some things to look for..  Some obvious, some not…

    1) Microwave (2.4 spectrum can get pounded by this)
    2) Wireless ISP near by? (Could bad antenna, broken equipment, or amped)
    3) Motion detectors (security solutions).
    4) City Police/Emergency vehicles.  I’ve seen a few deployments of 2.4 in car for mobile offload.
    5) 2.4 Ghz phones (Land lines)

    Just a few ideas. Probably won’t help. :)

  • David Bulanda

    I think that motion detectors and microwaves are a good bet. I have also seen the wireless security cameras which have their own receivers look similar on metageeks software. It was a few years ago with the classic wispy.

  • Curtis LaMasters

    Greg, did you ever get this worked out?