How to Use Spectrum Analyzers: A Beginner's Guide

Spectrum analyzers are essential tools in the field of electrical engineering and signal processing. They allow us to visualize and analyze the frequency content of signals, making them invaluable in a wide range of electronic disciples such as audio engineering, wireless communication, and law enforcement surveillance. 

In this beginner's guide, we will demystify spectrum analyzers and provide you with a step-by-step approach to using them effectively. 

What is a Spectrum Analyzer?

A spectrum analyzer provides a graphical representation of signal amplitudes versus frequency, helping users to identify and analyze the different frequency components in a signal. This ability can help you monitor signals, troubleshoot, and analyze frequency.

The x-axis of the spectrum analyzer represents the frequency range being analyzed, typically spanning from low frequencies to high frequencies. The y-axis represents the amplitude or power level of the signal at each frequency point.

By plotting the amplitude or power levels of various frequencies, a spectrum analyzer allows users to visually identify and analyze different frequency components present in a signal, giving users valuable insights. 

Making Basic Measurements 

Spectrum analyzers' basic measurements allow you to understand the characteristics of a signal, including its amplitude, frequency components, and harmonic content. They form the foundation for more advanced analysis and troubleshooting tasks using spectrum analyzers.

Some of the basic measurements are:

1. Measuring signal amplitude and power:

• The spectrum analyzer helps you understand the signal's magnitude and variations across different frequencies by measuring a signal's amplitude or power level. This measurement indicates the strength or intensity of the signal at a specific frequency. 

2. Identifying frequency components

• One of the primary functions of a spectrum analyzer is to help you visually identify peaks or spikes that represent specific frequencies present in the signal. This lets you determine the dominant frequencies or frequency ranges within the analyzed signal.

3. Detecting and analyzing harmonics

• Harmonics are whole number multiples of the fundamental frequency in a signal. Spectrum analyzers are effective tools for detecting and analyzing harmonics, as they can reveal additional frequency components that occur at these multiples, helping you find harmonic distortion or harmonic content. 

 

Parts and Their Functions

Here are the core components and features you'll commonly find in a spectrum analyzer. Remember that different models may vary in their specific implementation and capabilities, designed for particular applications.

• Input Section: The input section of a spectrum analyzer consists of connectors to accept various types of input signals, such as coaxial connectors or input probes. It also includes filters and attenuators to control the signal levels and prevent distortion.
• Mixer: The mixer combines the input signal with a local oscillator signal to shift the frequency spectrum to a lower frequency range called the intermediate frequency (IF). This process enables easier signal processing and analysis.
• IF Section: The IF section includes amplifiers, filters, and detectors to extract the amplitude information of the frequency components. For example, the Rigol DSA832E's innovative digital IF design provides high-precision amplitude readings, exceptional measurement speed, and the ability to measure smaller signals. 
• Display: The display section presents the frequency spectrum graphically, typically on a screen or monitor, showing the amplitude of the frequency components, allowing users to interpret the signal characteristics visually. The Rigol DSA800 family features a widescreen display, compact design, and easy-to-use interface, making it ideal for benchtop or field apps in RF and wireless testing and production.
• Controls and User Interface: Spectrum analyzers have controls and a user interface for adjusting settings such as frequency range, span, resolution bandwidth, and amplitude scale. They also include markers for precise frequency measurements, trace averaging for reducing noise, and various display options for better visualization.
• Additional Features: Advanced spectrum analyzers may offer features such as built-in tracking generators (to analyze the frequency response of components), modulation analysis capabilities, signal modulation options, and connectivity options for data transfer and remote control.

How to Configure Your Spectrum Analyzer

Remember that the right settings depend on the specific signal you are analyzing, and the information you aim to extract from the spectrum is important. 

Get creative, experiment with different settings, and consider the characteristics of the signal you are working with to find the correct settings. 

Here are some considerations when conjuring your analyzer:

1. Selecting an input source: Analog VS Digital 

• The analog input is best if you're analyzing continuous waveforms or analog RF signals. Connect the analog signal directly to the spectrum analyzer.
• The digital input option is best if you're working with digital signals like communication systems or data transmission networks. 

2. Setting the frequency range and span

• Specify the frequency range in which you want the spectrum analyzer to measure signals to calculate the right frequency band for your analysis.
• The span determines the width of the frequency window displayed on the spectrum analyzer's screen so that you can focus on specific frequency ranges. 

3. Adjusting resolution bandwidth and video bandwidth

• Set the resolution bandwidth (RBW) to define the width of the frequency bin (the specific segment or interval analyzed). 
• Choosing a smaller RBW provides finer frequency resolution, allowing you to distinguish closely spaced frequency components. But remember, this may also increase measurement time. 
• Determine the video bandwidth (VBW) to specify the bandwidth of the video filtering applied to the displayed spectrum. This affects the spectrum analyzer's ability to capture and display signal amplitude variations accurately. 
• Opting for a smaller VBW can improve amplitude accuracy, but it may result in slower updates on the display.

Spectrum Analyzers VS Vector Network Analyzer

While spectrum analyzers focus on amplitude and frequency characteristics, vector network analyzers (VNAs) provide detailed insights into signals' magnitude and phase characteristics. VNAs testing is used across automotive, medical, telecommunications, and other industries. 

They measure electrical networks' complex impedance, transmission, reflection, and scattering parameters, such as radars, antennas, cellular networks, and Wi-Fi. The Siglent SVA 1015x, for instance, is a great option for broadcast and RF device testing with its wide frequency range. 

VNAs work by injecting a known test signal into the device being tested and analyzing the response to learn about the behavior of the network.

The key difference between a spectrum analyzer and a vector network analyzer are:

1. Spectrum analyzers focus on analyzing signals' amplitude and frequency content, while VNAs provide both amplitude and phase information.
2. Spectrum analyzers are often used for general signal analysis, whereas VNAs are designed for detailed network characterization and analysis.

If your projects can benefit from both, there are testing instruments that are both spectrum and vector network analyzers. You can also add modules that allow your devices to do both types of measurements. 

Best Practices and Tips

By following these best practices and understanding key concepts related to spectrum analyzers, you can optimize your measurement accuracy, reliability, and overall effectiveness.

1. Proper grounding and shielding considerations:

• Ensure to properly ground and shield the spectrum analyzer and the device tested to ensure accurate measurements and minimize interference. Follow best practices for grounding, use appropriate cables and connectors, and consider the electromagnetic environment in which conducting the measurements.

3. Understanding the dynamic range and noise floor 

• Dynamic range refers to the difference between the strongest and weakest signals a spectrum analyzer can accurately measure. Selecting a spectrum analyzer with an appropriate dynamic range for your application is important. 
• Also, understanding the noise floor, which represents the inherent noise in the measurement system, helps determine the minimum detectable signal level. Check out this fantastic video by Linus Tech Tips to see different types of testing equipment in action.

2. Interpreting and documenting measurement results

• When using a spectrum analyzer, it is crucial to interpret the measurement results accurately. Understand the units and scaling used in the display, identify peaks or significant frequency components, and analyze the amplitude or power levels in relation to the frequency. 
• Documenting measurement settings, results, and any relevant observations ensures traceability and facilitates analysis and troubleshooting in the future.

Using spectrum analyzers is a valuable skill for engineers, technicians, and hobbyists working with electronic signals. While they may initially appear complex, remember to practice and experiment. With time, you'll become adept at analyzing and manipulating signals using spectrum analyzers, unlocking a new world of possibilities for your projects.