Spectrum Analyzer

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].

Form Factor

Benchtop: This spectrum analyzer can be plugged into AC power, which is generally meant for a lab environment[3].  Benchtop spectrum analyzes have historically offered better performance and specifications than the portable or handheld versions[3]. They also normally have multiple fans to dissipate the heat produced by the processor[3]. Due to their architecture, bench top spectrum analyzers typically, weigh more than 30 pounds[3]. Some also offer optional battery packs, which allow them to be used away from AC power[3]. 

Portable: This form factor is useful for nay applications where the spectrum analyzer needs to be taken outside to make measurements or simply carried when in use[3]. Portable spectrum analyzers are usually battery powered, clearly viewable in different environments, and is very light at about 15 pounds[3].

Handheld: This version of the spectrum analyzer is useful for applications where the device has to be very small and light[3]. Handheld analyzers offer limited capabilities compared to its larger versions[3]. They often consume very little power, are battery-powered, and is very small and light[3].

References

[1] Composite Materials. [Online]. Available: https://www.gurit.com/Our-Business/Composite-Materials.