What does the vertical axis of a spectrum analyzer display?

• A. Duration
• B. Time
• C. Amplitude
• D. Frequency

Answer: (C)

In a spectrum analyzer, you’re looking at how much energy the signal has at each frequency. The vertical axis represents the amplitude (or magnitude) of those spectral components, usually shown in decibels relative to a reference. The horizontal axis is the frequency axis, spanning the spectrum you’re examining. So the vertical axis is about how strong each frequency component is, not about how long the signal lasts or when it occurs. Duration or time would belong to time-domain measurements, and frequency belongs on the horizontal axis, not the vertical.