I sometimes have a need for a spectrum analyzer to troubleshoot wireless microphones and the RF environment in which I run them. The cost had precluded getting one. There is a way to get some of the functions inexpensively. I purchased a software defined radio USB stick (NooElect R820T) from Amazon for 16 bucks, plugged it in, and downloaded free software from sdrsharp.com. This provides many of the functions of a legit SA. Limitations: No calibrated anything, a frequency range of 25 MHz to 1700 MHz, and a maximum screen sweep of 2 MHz. It is not a Rohde and Schwartz and will lie to you (like any other SA) if you set it up improperly. For 16 bucks, it's wonderful. Here are two of my Vega wireless:
