What is a Spectrum Analyzer?

A spectrum analyzer is a widely used test device that measures and plots signal power (amplitude) over a selected frequency range. In the most general sense, it is a tool for measuring the power and frequency for known and unknown signals. A variety of products have been developed to evaluate a wide range of network and signal behavior. The frequencies and bandwidths of output signals can also be compared to the received input. 

Spectral components observed with a spectrum analyzer include the dominant frequency, harmonics, power, distortion, and noise floor. Common applications include radio frequency (RF) signal analysis, electronic circuit design and test, audio engineering, and fiber optic network activation and maintenance. Advanced digital technology enables a real-time spectrum analyzer to capture transient or elusive events. Programmable test routines, spectrum recording, and intuitive touchscreen displays are hallmarks of the latest generation of handheld instruments.  

Technology has gradually evolved since the first swept-tuned analyzers emerged over 100 years ago. The digital architecture that enabled the Fast Fourier Transform (FFT) analyzer ultimately led to true real time spectrum analysis (RTSA) with no sampling gaps or ‘blind spots’ in time. The form factors and types of spectrum analyzer now available include every conceivable size, shape, and complexity level. For each specific application, VIAVI has developed a breadth of solutions to support test, maintenance, and troubleshooting activities.  

Benchtop
AC-powered analyzers for lab and manufacturing environments are typically designed for a standard 19” rack or tabletop installation for larger equipment. The benefits and features of benchtop models include higher computing power and available real estate for modules, ports, knobs, buttons, and displays. A full spectrum analyzer in the lab is frequently used in conjunction with an oscilloscope or other high-end equipment.

Portable
As the number of applications multiply, portability and durability gain importance. A portable spectrum analyzer is usually battery operated or rechargeable, under 15 lbs., and optimized for use in the field. Compact spectrum analyzers are often ruggedized, incorporating features such as screen glare reduction, weather-proofing, and integrated handles.

Handheld
A new class of small spectrum analyzer that can fit in the palm of your hand has become a reality. Despite advancements in internal design and component performance, these ultra-compact units are not typically required to be high performance tools and so are limited with respect to feature sets, frequency range, and accuracy. Typical uses for a handheld spectrum analyzer include wireless communication interference tracking and signal location in the field.

Integrated
The processing power, memory, and display capabilities of laptop computers, tablets, and smartphones can be made to work in conjunction with modern spectrum analyzers. Advanced measurement features can then be dedicated to optimizing accuracy, bandwidth, and range. This versatility signals a new class of analyzers with the integrated device’s connectivity also leveraged for software upgrades, reporting, and storage.  

The list of applications utilizing the best spectrum analyzer technology continues to grow as the tools become more versatile and compact. In laboratory and production environments, they can be used to design, characterize, and test any product generating (or sensitive to) RF, optical, or sound waves. With wireless capability added to virtually any device through the internet of things (IoT), the applications for field testing are limitless.

Optical Spectrum Analysis: Since light has both inherent frequency and intensity, a spectrum analyzer is the perfect tool for the study of optical spectra and power from numerous light sources. Optical networks in the telecommunications industry are enabled and supported by the capabilities of spectrum analysis. Optical transmission technologies including dense wave division multiplexing (DWDM) and reconfigurable optical add-drop multiplexers (ROADM) depend on wave form precision and integrity that must be verified.  

• Manufacturing Test practices have evolved for a wide range of optical components and systems. General purpose tools are used to design, test, and manufacture passive components, source lasers, and amplifiers. High resolution optical spectrum analysis (OSA) test modules quantify and diagnose fine wavelength features for products like modulated DWDM transmission systems and complex optical sources.  
• Field Test applications for optical spectrum analyzers continue to expand as the DWDM, C-band transmission, and tight channel spacing previously seen only in high-speed metro/longhaul fiber deployments find their way into access networks. At speeds of up to 800Gb/s per channel, optical signal to noise ratio (OSNR) is a valuable test metric for service providers, contractors, and network equipment manufacturers (NEMs) to assess the performance of all optical channels simultaneously or troubleshoot live network issues.

RF Spectrum Analysis: The increased use of Wi-Fi and the rollout of 5G have highlighted the need for state-of-the-art technology in the radio frequency (RF) field. As telecommunication networks expand, spectrum analyzers assess the frequency utilization, interference, and accuracy of wireless transmission and interference.  

• Cell Tower Installations are a classic field application for RF spectrum analysis. 5G NR technology takes cellular into uncharted territory by utilizing high-frequency bands above 26GHz in the millimeter wave. Cutting-edge 5G transmission modes like time division duplex (TDD) require persistence spectrum analysis features for characterization and troubleshooting. All-in-one cell site installation and maintenance test tools combine over the air spectrum analysis with interference testing, fiber validation, and antenna testing capabilities.  
• RF Shielding is required for many electronic devices in the vicinity of hospitals and other venues with RF-sensitive equipment such as MRI imaging systems. Electromagnetic compatibility (EMC) is concerned with unwanted emissions that influence existing wired and wireless communications. A purpose-built cable spectrum analyzer or meter can detect escaped signals (egress) and signal leakage into wired cable networks (ingress).
• WiFi Applications continue to grow in number and complexity. Crowded WiFi frequency bands ranging from 2.4 GHz to 60 GHz are challenged by interference, channel overlap, and capacity issues. The power of spectrum analysis can be used to assess signal strength, channel utilization, and RF interference in real time. These useful metrics help operators to optimize their WiFi loading and performance. 

What does a spectrum analyzer measure? 
The spectrum analyzer working principle is used to measure the magnitude (power) of signal input vs. the frequency (wavelength) over a given spectrum range. Visibility into the frequency domain vs the time domain of the signal distinguishes these devices from oscilloscopes. They also provide detailed insight into the signal to noise ratio (SNR), phase, and modulation behavior.

What is the basic functionality? 
Learning how to use a spectrum analyzer is similar in concept to using a basic radio receiver. With the addition of an upgraded mixer, oscillator, and graphical display of the signal strength, wave signatures are translated into a quantifiable, visual format. Over the years, technology has evolved and improved to support more industries and applications. Despite this progress, the basic functionality and display have remained similar.  

How do you use a spectrum analyzer? 
Usage has changed very little since the earliest models. Once the equipment is powered on and an input has been selected, basic settings include center frequency, span width, and reference levels for the amplitude (y-axis). The resolution bandwidth (RBW), video bandwidth (VBW) and sweep time settings are used to control the precision of the measurements and resulting image on the screen.  

Features 

• Basic features: Control the measurement parameters and determine how the data is analyzed and presented to the user. Digital technology and cloud connectivity continue to enable more diverse and useful features. Simply asking, “what is a spectrum analyzer used for?” in a given application is a good way to sort through the volume of available products and feature lists.  
• Common Features: The first commercial spectrum analyzers already incorporated practical features like span adjustability, frequency markers, and sweep time settings. Additional features that are helpful for almost any type of application include noise markers, peak search, tracking generators, and additional input ports for multi-channel analysis.
• Advanced Features: Include demodulators for RF spectrum analyzers that allow the user to “listen” to the signal being analyzed. Spectral masks and programmable phase noise analysis simplify setup and standardize test routines. Advanced features sets also include persistence spectrum analysis, interference analysis, and software enabled features such as touch screen displays, image capture and recall, test process automation (TPA), and cloud connectivity.

What is a network analyzer vs spectrum analyzer? 
Although both are widely used in the electronics and RF industries, there are key differences between them. While a spectrum analyzer measures the behavior and variation of radio or light waves, a network analyzer is used to characterize the response of components like transistors, filters, and mixers within a pre-configured RF circuit. This type of network analyzer is also separate in form and function from the powerful network monitoring and data analysis solutions used to capture, store, and analyze computer network packet data.  

How have spectrum analyzers evolved? 
In the 150 years since James Maxwell gave us our first glimpse into the unlimited potential of radio airwaves, the spectrum analyzer has become an important tool in the electronics, RF, audio, and optical fields. The explosion of new features and functionality over the past decade is on par with the advancement experienced in the mid-1900’s, when FFT-based models created the distinction of analogue swept vs real time spectrum analyzer. Automated workflows, high-definition color graphics, and multi-function capabilities within compact devices have led to higher levels of performance and success.