The spectrum analyzer is a lab instrument. It displays amplitude of signal (strength) as it varies by the signal's frequency. The frequency will show on the horizontal axis and the amplitude will show on the vertical axis.

A spectrum analyzer can be used to work out whether or not wireless transmitters are working in terms of purity of emissions. Output signals at frequencies outside of the intended frequency appear as vertical lines.

A spectrum analyzer can also be used to work out bandwidth of digital or analog signals. The interface of a spectrum analyzer can be connected to a wireless receiver or a PC.

There is more information coming on Spectrum Analyzers and their purposes.