This gallery is also a TechRepublic article.
NetStumbler is an excellent free tool for performing WLAN site surveys (note that NetStumbler is not useful for penetration or security testing, but that's not in the scope of this article). It won't give you all the polished reports, and it takes a little extra work to come up with the results. However, with a little help from this tutorial and our downloadable Excel Macro tool, this is an excellent free solution.
First, you simply walk around the building with a laptop running NetStumbler on a predetermined path with sampling points where you want to measure the RF signal levels.You will need a simple floor plan with selected sampling points along the path that you're going to walk but before you start walking, you must start NetStumbler and make sure you see live Access Points to make sure NetStumbler is working correctly.