RF Spectrum Analysis with Metageek
This week I wanted to talk about the first vendor to present at Wireless Tech Field Day, Metageek. I have had one of their Wi-Spy 2.4x products for several years as my good friend Douglas Haider @wifijedi (Go visit his blog, the link is just there on the right!) gave me it when he had been given an extra one. I used it for a while mainly to learn what different RF signatures looked like and to troubleshoot customer problems. I found Ryan and Trent from Metageek to be well, geeks like me and their presentation was liked by all at WFD. They started off with a presentation about how and why Metageek got started then launched into going over the capabilities of their products. I won’t go much into their presentation here as it has been covered very well by some of the other delegates at WFD, this page at Revolution Wi-Fi provides a good list of all the articles.
My main intent in writing this was to highlight Metageek as a learning tool to learn RF spectrum analysis. The reason for this is that I know many of you will not have the money to purchase the Air Magnet product or even (if you can still get one) the Cisco Cognio product and may be very well asking yourself if you will be able to get the job done and learn what you need to know with Metageek’s Wi-Spy. I would say most definitely yes to this question and what’s more even though you may later be able to purchase one of the other companies products you will still find the Wi-Spy to be incredibly useful in your job as a WLAN engineer.
The difference between Wi-Spy’s approach to Spectrum Analysis and the other manufacturers was described by Ryan of Metageek as that Wi-Spy takes little snapshots quickly across the spectrum to build its view of what the RF signal looks like whereas the others take larger chunks or bites of data to see what is there. There are advantages to both approaches in that you get slightly different views on what is going on in the RF world. Primarily what you are doing in using a spectrum analyzer is looking at a pictoral representation of a signal that you can’t see with your own eyes. Products like Wi-Spy use colors to highlight different interpretations of the data and also waveforms so that you can get some idea of the patterns that regularly show up in this type of RF data.
If you look at the above screenshot of Chanalyzer Pro you will see right away, even without knowing what is being represented, that there is a large amount of RF data in the center of the screen. This was me turning on a microwave in order to show how this affects the RF signal. If you look a bit closer at the top, you will see this data is being represented in a slightly different way. Imagine that the center graph is you looking down at a waterfall of this RF data going by. The graph at the top is a slice of the data below turned horizontally so you can pick out more easily the relative energy levels of the signals and see the patterns of RF data. I have overlayed some other aspects onto the top graph so you can, for example, pick out the SSIDs but this is the essence of spectrum analysis, to be able to pick out patterns from the RF and use those patterns to have an idea of what type of device might be interfering with the Wi-Fi signal. Metageek has designed their products so that you can quickly see the patterns and start to recognize them and even provides ‘signatures’ to help you learn. This is very powerful.
More than likely, if you either have a Wi-Spy or purchase one to learn about spectrum analysis, you will get the free version of Chanalyzer that comes with the product. As you can see in the screenshot above it has that same powerful visual representation of the RF data that its bigger sibling does. The advantage of the Pro version is that it allows you to quickly move back and forth across a large set of data and find the interesting bits to look at and that it includes a screen that represents duty cycle. Duty cycle is a representation of how busy a particular frequency is and how much a signal is using that frequency. By the way, if you just want a quick free product to look at the Wi-Fi signals around you then you can’t go wrong with InSSIDer, shown below. To me graphs are so much nicer to look at than Netstumbler lists of AP signal strength.
As you can see a very important component of becoming a WLAN engineer is learning how the RF spectrum works. We use the unlicensed bands of 2.4GHz and 5GHz for our day to day WLAN communications and as such these frequencies are quite often used by other devices. Anyone who runs a wireless network in a hospital will be quite familiar with those areas where the 2.4GHz band just will not work and its usually due to some medical device that is needed and has been in the hospital for a number of years. You may also have heard that the 2.4GHz band is becoming crowded. Products such as Metageek’s Wi-Spy and Chanalyzer give you a way to see the RF spectrum as you may never have seen it before.
I had not been able to really work with Chanalyzer Pro before Wireless Tech Field Day and I must admit it was an oversight on my part. The presentation Metageek gave to us was at just the right level. It showed me why I should use Wi-Spy in addition to the tools I already have and what the technical differences were between the way Metageek approaches spectrum analysis and how almost everyone else does it. Even if you can only afford to purchase the Wi-Spy 2.4i you will gain a great deal of knowledge as to what different patterns of interference looks like in the RF world and you can begin to gain a wider vision of the world of RF.
I am a strong believer that one day wireless networks will become so ubiquitous that anyone learning to be a network engineer will also need to learn about WLANs as part of their study. In order to really understand wireless networks you need to understand RF and spectrum analysis. It’s fun for me to sit and watch a screen showing microwave interference such as you saw above (while the microwave heats the water so much it goes all over the place). I also have a lot of fun tracking down what a mysterious signal is that is interfering with my network. This is part of the fun of being a WLAN engineer, you actually get to become part detective in your job. Pretty soon you will be so good at it you can go take the Certified Wireless Analysis Professional (CWAP). I will be myself pretty soon and I am looking forward to proving that I have that level of knowledge about wireless networks.
source: wifikiwi
