3.6 Introduction to Spectrum Analyzers

3.6 Introduction to Spectrum Analyzers

Spectrum analyzers are extremely useful tools for characterizing and analyzing a variety of devices and systems. Using an external Continuous Wave or CW source, the most common measurements performed on a spectrum analyzer are measurements of frequency, power, harmonic content, modulation, spurs, and noise. Given the capability to measure these quantities, you can determine total harmonic distortion, occupied bandwidth, signal stability, output power, intermodulation distortion, power bandwidth, carrier-to-noise ratio, and a host of other measurements.

When testing non-linear devices such as amplifiers or mixers, it is important to understand how these create distortion products and what these distortion products look like. Understanding the characteristics of noise and how a noise signal looks compared to other types of signals can also help you in analyzing your device/system. It is easy to get a trace on the display, but it is much more difficult to interpret results than with a network analyzer. Furthermore, understanding the important aspects of a spectrum analyzer for measuring all of these types of signals will help you make more accurate measurements and give you confidence that you are interpreting the results correctly [1] [2]. Spectrum analyzer specifications will help you determine if a particular instrument will make the measurements you need to make, and how accurate the results will be.

This section discusses the major components inside the analyzer and why they are important including the spectrum analyzer specifications that are important for your application and how to achieve the best accuracy. Many of the issues discussed are described and illustrated in more detail in [1] [2]

This section is divided into the following subsections:

3.6.1 Operation

IF Filter Detector
Video Filter Input
Attenuator
IF Gain
Front Panel Operation

3.6.2 Understanding Specifications & How They can Affect Your Measurements

3.6.2.1 Accuracy

Frequency Readout Accuracy
Relative Amplitude Accuracy Absolute
Amplitude Accuracy Improving
Overall Uncertainty

3.6.2.2 Resolution

RBW
Selectivity
Residual FM
Noise Sidebands

3.6.2.3 Sensitivity/DANL

RF Input Attenuator Setting
IF filter (RBW)
VBW
Video filtering vs. Video Averaging

3.6.2.4 Distortion

3.6.2.5 Dynamic Range

3.6.3 Calibrating A Spectrum Analyzer for Absolute Power Measurements

3.6.4 References


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