Friday, 19 September 2014

Intro To Spectrum Analysers

I've not had time to get to grips with or go through the training on how to use it but, after taking the Spectrum XT home the other day, I certainly found it useful and our team boss asked me to write a little about it.


At home my WiFi kept dropping out. It worked fine on 5GHz but unfortunately Playstations, Chromecasts and my tablet are all only capable of using the 2.4GHz frequency. I had the Wifi Anayzer app (https://play.google.com/store/apps/details?id=com.farproc.wifi.analyzer&hl=en_GB) on my phone and according to that I had a few neighbours on channel 11 and a handful on 6 (with a few in between), so channel 1 for my network seemed perfect. My signal strength seemed strong but first my tablet and then after a while my TV kept disconnecting and struggling to maintain a connection.



We recently purchased the Spectrum XT (http://www.flukenetworks.com/enterprise-network/wireless-network/airmagnet-spectrum-xt) to help with such mysteries and I borrowed it see what it could find.



I found 2 access points on channel 11 and half a dozen on 6 that the adapter could see. It also straight away solved my channel 1 problem.




As you can see in the first picture the duty cycle on channel 1 (as well as 2 and 3) is 100% and is due to a wireless security camera someone nearby has installed that is transmitting all the time. A waste of time using any of these channels then as my access point will stop beaconing and my devices attempting to associate with a duty cycle that high.

Just as I was about to put the laptop away (and move my wireless to channel 6, the least congested) my neighbour must have turned their microwave on, as you can see from the spectrogram in the second picture it caused a fair bit of noise around channel 7 and the ones around it. No wonder all my neighbours are using channel 11.The duty cycle is not high though because the microwave is not close (if it was mine it could be around 50-60%) and they do not continually transmit. If I turned mine on and tried to use the same channel it would probably halve my throughput but would/should still work.


So they mystery of the dropping out connection is solved and, in this case, the best thing is to have multiple access points on the same channel.

Roll on the time when we have 5GHz in every device!

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