Your application will determine which instrument you should use. By Allen Montijo, Agilent Technologies, Colorado Springs, CO Signal characteristics that are difficult to see in the time domain frequently become visible in the frequency domain. The classic example is a square wave, which appears as the sum of many harmonics in the frequency domain. In effect, a spectrum analyzer is a bank of narrowband filters, each tuned to a different frequency at regular intervals.
Spectrum analyzers have the widest frequency range of all the instruments.
They can analyze signals from tens of hertz into the hundreds of gigahertz over a wide dynamic range. A spectrum analyzer sweeps across a frequency range, effectively applying a series of narrowband filters to a CW signal. EMI engineers also use these instruments to perform precompliance EMI scans. Because they measure only one frequency band at a time, spectrum analyzers have three main drawbacks. First, they can measure only steady-state signals, so they are impractical for measuring transient events.