A spectrum analyzer is a type of electronic test equipment. It is used to determine what frequencies are being produced by a specific circuit, and the amplitude of each frequency component. The display screen on the spectrum analyzer will show a plot of the results as a function of amplitude against frequency.

The vertical axis is calibrated to record the amplitude, while the horizontal axis is calibrated to record the frequency. Because of the large range of amplitudes that can be recorded, it is best to have the data represented in a logarithmic scale instead of a linear. This will ensure that all values are represented.

The graphic representation of sound has come quite a ways from the early days of focusing beams of light onto a mirror. This crude method of analyzing sound was used until Hermann von Helmholtz developed the earliest spectrum analyzer. By developing a series of hollow glass spheres with calibrated resonance frequencies, Helmholtz developed a way to detect frequencies.

The glass spheres would vibrate when stimulated by the correct frequency, which could be heard by placing the spheres up to the ear. Although Helmholtz's analyzer worked, it was awkward to use, and it didn't allow for the information to be displayed graphically. Today's spectrum analyzers, like those made by Tektronix, are easy to use and display a graphic representation so the information can be properly analyzed.