November 29, 2011, 2:55 PM — When you set up a Wi-Fi network, whether using access points (base stations) from Apple or another vendor, you're usually playing a guessing game. Where should I put a base station to get the best coverage and performance? Or multiple base stations? Apple provides some tools to help, including the somewhat hidden Wi-Fi Diagnostics program (buried in /System/Library/CoreServices/), but using them requires some expertise, as well as keeping your eye on ever-changing signal-strength numbers. NetSpot bypasses the technical in favor of the visual. This free site-survey software is a remarkable aid in laying out even a small-home network, using a Mac laptop as your survey tool.
You start with a map of a single floor, which you either draw using a few primitive graphics tools or load as an image file which is used as the background. You give the map a scale in meters or feet by marking the distance between two known points. Finally, you mark the region of the map that represents the area you're going to scan.
With the map ready, you simply walk the area with your laptop. At any position, clicking the corresponding location on the map tells NetSpot to perform an on-the-spot scan of any and all Wi-Fi signals it can find. You can mark as many spots as you want--the more you mark, the better your results, especially in a house or office that has dead areas due to a poor network layout, or thick walls, furniture, or appliances that block Wi-Fi signals. I tested by mapping most corners and doorways.
When you click the Stop Scan button, NetSpot draws a color-spectrum heat map in which the indigo end of the spectrum represents the weakest (or no) signal-to-noise ratio (SNR, the measure of how much information may be carried, a rough gauge of throughput), and the red end represents the strongest. This is a bit confusing, as a typical user might think of green as best, yellow as moderate, and red as worst. A scale at the bottom of the finished map at least helps you calibrate your head.
Instead of SNR, you can view your site's raw signal-level or noise-level heat map using the Visualize pop-up menu, or choose to see the signal-to-interference ratio, a different measure that can be useful if there are lots of nearby networks. Also available is an oddball but useful access-point-counting visualization that lets you view only regions in which base stations' signals overlap. (You can tweak this last option to show only regions in which a minimum number of routers overlap.)