What is a spectrum analyzer?
A spectrum analyzer is a device that measures the magnitude of an input signal against the frequency within the full range of the instrument[1]. The main use of this device is to measure the power of the spectrum of known and unknown signals[1]. The most common input signal that is measured is electrical, however other signals can be detected like light waves and pressure waves[1]. By understanding the electrical signals, different components can be observed such as the bandwidth and power[1]. To a casual observer, a spectrum analyzer looks like an oscilloscope, and some lab instruments can function as either a spectrum analyzer or oscilloscope[1].
Types
Spectrum analyzers are distinguished by the methods that are used to obtain the signal[2]. There are both swept-tuned and fast Fourier transform based spectrum analyzers.
Swept-tuned: A swept-tuned analyzer uses a super heterodyne receiver to down-convert a portion of the signal to the center frequency of a narrow band-pass filter, whose output power is recorded or displayed as a function of time[2]. By sweeping the receivers center-frequency, the output is also a function of frequency[2]. However, it may miss short-duration events at other frequencies[2].
FFT: An FFT analyzer computes a time-sequence of periodograms. FFT refers to a particular mathematical algorithm used in the process[2]. It is also commonly used in conjunction with a receiver and analog-to-digital converter[2]. The receiver reduces the center-frequency of a portion of the input signal spectrum, but the portion is not swept[2]. The purpose of this receiver is to reduce the sampling rate that the analyzer must contend with[2]. With a low sample rate, FFT analyzers can process all the samples and are able to avoid missing short duration events[2].
References
[1] Composite Materials. [Online]. Available: https://www.gurit.com/Our-Business/Composite-Materials.