Back in my hardware engineering days, I used an oscilloscope to examine signals on circuit boards showing the signal’s amplitude (strength) and phase over time. This is also known as the “time domain” information of a signal.
How cool would it be to be able to “see” your WiFi 2.4 GHz and 5 GHz frequency space? The problem is that with a scope, you can only see what is happening at a given frequency such as looking at gate on a chip clocked at 1 GHz.
To look at a broader frequency spectrum at a glace (802.11 channels 1 through 11 for instance) we need to convert time domain information into frequency domain information using a mathematical technique known as Fast Fourier Transformation (FFT). This is precisely what a spectrum analyzer does and coincidently, is a technique often used to sweep for bugs across a wide range of frequencies.
In your wireless network, those “bugs” could be rogue WiFi devices, other wireless devices occupying the same frequencies, or just plain old spurious interference. Bluetooth, cordless phones, and microwave ovens are some of the obvious offenders, but don’t overlook devices like x10 wireless cameras that also use this open and unlicensed space.
It’s all the latter junk that we can’t see even with wireless site surveying and mapping tools, that can seriously degrade the performance of WiFi or halt it altogether. The ultimate pre-deployment site survey is to sweep the 802.11 frequencies in your environment to see how quiet or noisy it is, allowing you to eliminate problems up front, pick the optimal channels, size and orient antennas, and so forth. Once the wireless infrastructure is deployed, the spectrum can then be continuously monitored.
Think of it like monitoring your RF air quality. Perhaps we need an industry standard RF smog index or perhaps an air quality combo tool for places like LAX. Stay tuned tomorrow for more smog, er, blog on spectrum analysis.