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. With the amplitude displayed on a logarithmic scale, a wide range of signal behavior can be observed. Spectrum analyzers are commonly used to determine the accuracy of a wireless transmitter. Frequencies and bandwidths of an output signal are compared to the received input.
The spectral components of an RF signal that can be detected using a spectrum analyzer include the dominant frequency, power, distortion, and noise floor. Applications beyond RF include electronic circuit design and test, audio engineering, and fiber optic communications. Advanced digital technology has enabled real-time spectrum analysis to capture transient or elusive events. Programmable test routines, spectrum recording, and intuitive touchscreen displays are now incorporated into compact, handheld spectrum analyzers.
The Importance of Spectrum Analyzers
As the airwaves become more crowded in response to rapidly evolving technology and demand, you simply cannot do your job without a spectrum analyzer.
Spectrum analyzers are used to measure the magnitude of signal input vs. frequency for a given spectrum range. In their earliest incarnation, this functionality distinguished the spectrum analyzer from the oscilloscope by introducing a window into the frequency domain of the signal in addition to the time domain. Today’s spectrum analyzers are a source of detailed insight into signal frequency (in MHz or KHz), amplitude, phase, and modulation behavior.
Inevitable outputs of the wireless revolution have included high spectrum utilization and channel density, diverse interference sources, and a host of duplexing and multiplexing options to squeeze more bandwidth out of airwaves and fiber. The spectrum analyzer remains the best and only test solution for verifying and troubleshooting performance in this complex environment. This need extends from the concept phase for new communication devices to the field testing that guarantees QoE.
Types of Spectrum Analyzers
A spectrum analyzer is similar in concept and architecture to a basic radio receiver. With the addition of an upgraded mixer, oscillator, and graphical display of signal strength, the spectrum analyzer translates radio wave signatures into a quantifiable, visual format. Over the years, spectrum analyzer technology has evolved and improved as the test applications grow in breadth and complexity.
The original spectrum analyzer design used the super-heterodyne principle, invented by Edwin Armstrong in 1918. A local oscillator used to generate a signal is combined with the input signal to translate the frequency. In this ingenious way, the signal frequency tuning can be controlled using the oscillator when it is combined with the input frequency at the circuit’s mixer. In a swept-tuned spectrum analyzer, the oscillator is continuously “swept” through the desired range of frequencies at a constant rate, and this swept band is what appears on the screen.
The first use of digital technology in spectrum analyzers was the Fast Fourier Transform (FFT) analyzer. This technological breakthrough was named after a 19th-century mathematical transform developed by Joseph Fourier. In practical use, the logic is used to process the waveform into the various components of its frequency spectrum by converting the signal from the time domain to the frequency domain. An FFT analyzer breaks down the signal then reassembles it on the display, with the help of an analog to digital converter. This technology also allows phase information to be captured.
Among the limitations of the FFT analyzer are the inherent “blind spots” in time that occur between signal processing cycles. Since processor speeds have increased exponentially, this limitation can be resolved by capturing data continuously, overlapping data collection cycles and analyzing the waveform very quickly so that nothing is missed. Hence the name “real-time analyzer”. Real time spectrum analysis (RTSA) also utilizes the FFT transform, but with more processing power, an unabridged history of the signal behavior can be stored. Transient events or quick blips of signal that may be of importance to the user are always captured when a real-time spectrum analyzer is used.
The Many Applications of Spectrum Analyzers
The increased use of Wi-Fi and the development of 5G have underscored the need for state-of-the-art spectrum analyzer technology in the radio frequency (RF) field. As telecommunication networks expand, spectrum analyzers calculate frequency utilization and interference in each area. A portable spectrum analyzer is also used to determine the accuracy of a wireless transmitter by comparing the frequencies and bandwidths of an output signal to a received input signal.
Cell Tower Installations
Nowhere is the need for advanced RF spectrum analysis more evident than with new cell tower deployments that are expanding the reach of 5G wireless services around the globe. 5G NR technology takes cellular into uncharted territory by utilizing high-frequency bands above 26GHz in the millimeter wave. To optimize 5G bandwidth and coverage, cutting-edge options like time division duplex (TDD) and dynamic spectrum sharing (DSS) must be fully leveraged.
A new 5G cell tower deployment requires miles of cable and dozens of antenna arrays to blend seamlessly with this advanced signal processing capability. All-in-one cell site installation and maintenance test tools address this challenge by combining over the air spectrum analysis with interference testing, fiber and cable validation, and antenna testing capabilities. The OneAdvisor-800 also encompasses an advanced RTSA feature set, including persistence power measurement for higher visibility into TDD performance and intermittent signal behavior.
A policy for most hospitals requires RF shielding for electronic equipment that will reside in the vicinity of MRI imaging systems, as the electronics can emit unintended signals that potentially distort the imaging results. Similarly, electromagnetic compatibility (EMC) is concerned with the unwanted emissions that many types of electrical or electronic devices produce and their influence on existing wireless communication transmissions.
In terms of emissions, it can also impact the cable networks that move information to and from our homes and businesses. Compromised shielding or terminations can lead to interference from escaped signal (egress) disrupting off-air transmissions or leakage into the cable (ingress) interfering with over the wire signals. Handheld, purpose-built spectrum analysis meters such as the OneExpert CATV are ideally suited for rapid, automated testing and troubleshooting in either scenario.WiFi Applications
A spectrum analyzer is an important tool for evaluating WiFi networks as they continue to grow in number and complexity. Crowded WiFi frequency bands ranging from 2.4 GHz to 60 GHz are constantly challenged by interference, channel overlap, and capacity issues. The VIAVI WiFi Advisor uses the power of spectrum analysis to create intuitive spectral views and channel utilization data. Signal strength, RF interference, and utilization for each channel are presented in real time. The WiFi spectrum analyzer also produces metrics and recommendations to optimize WiFi loading and performance.
Although visible light is often perceived as a natural occurrence unrelated to radio frequency waves, both are forms of electromagnetic radiation. Light just happens to become visible at much higher frequencies than those occupied by radio waves. Since light has both inherent frequency and intensity, the electromagnetic spectrum analyzer can be an extremely useful tool for the study of visible, ultraviolet, and infrared light sources.
Optical technology in the telecommunications industry is supported by the power of spectrum analysis. Innovations including dense wave division multiplexing (DWDM) depend upon ongoing wavelength precision and integrity for each individual signal. The OSCA-710 Optical Spectrum Analyzer performs high-speed optical signal-to-noise ratio measurement to characterize and diagnose each DWDM channel while in service. The SmartClass OCC-55/-56 Optical Channel Checkers are an additional, dedicated option for automated CWDM and DWDM power measurement for each wavelength/frequency.Audio Applications
While audio (sound) waves occupy much lower frequencies than radio waves, and travel through the air at a slower speed, the basic premise of frequency versus amplitude is equally applicable in the audio world. Audio engineers might use a spectrum analyzer to compare sound output to input at a live venue, while adjusting the volume levels for various frequencies accordingly and lowering the volume for frequencies creating unwanted feedback or hiss. More scientific applications of audio spectrum analyzers include analysis of the harmonics of an audio signal and the design of ultrasound devices.
Spectrum Analyzer Basics
The basic functionality of a spectrum analysis equipment has changed very little since the earliest models. Once the equipment is powered on and an input has been selected, basic settings consist of selecting the 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. Since the RBW sets the width of the filter that sweeps across the signal, a lower RBW means higher resolution and a more detailed and accurate picture of the signal.
Beyond these basic settings and controls, additional features can typically be placed into one of two categories - practical and nice-to-have. The first commercial spectrum analyzers already incorporated such practical features as span adjustability, frequency markers and sweep time adjustability. Additional features that are highly desirable for almost any type of application include noise markers, peak search, tracking generators and additional input ports for multi-channel analysis.
For an RF spectrum analyzer, inclusion of a demodulator allows the user to “listen” to the signal being analyzed. Spectral masks take the utility of markers to another level by creating an outline for your “acceptable” signal and noise profile, then telling you whether you are within specification. Advanced solutions in the VIAVI CellAdvisor RF Analyzer series also include features such as interference analysis, passive intermodulation (PIM) detection, Bluetooth remote control, and fiber inspection microscopes.
With the current level of computer integration into spectrum analyzer design, most of the nice-to-have features that lend ease of use, programmability and connectivity (through modern interfaces like USB) are more closely tied to software development rather than hardware. The feature sets now available through software are virtually limitless. Some of the more useful and interesting features enabled by advanced software and computing power include:
- Image download and capture to .jpg or .pdf
- Memory and recall features
- Touch screen displays
- Programmable phase noise analysis routines
Like all electronic equipment, functionality and feature sets can vary from the standard issue to the mind-boggling with unlimited combinations in between. Understanding your specific application and what is required to complete your tasks efficiently is a good prerequisite for deciphering specifications of products and feature lists.
Spectrum Analyzer Form Factors
Spectrum analyzers are now available in every conceivable size, shape, and complexity level. For each specific application, VIAVI has developed a breadth of solutions that support a variety of test measurement, maintenance, and troubleshooting activities.Benchtop Spectrum Analyzer
An AC-powered spectrum analyzer is also known as a benchtop model. Some of these benchtop analyzers are designed to be mounted into 19” racks, others are simply designed to sit on a work bench or tabletop. The obvious benefit of this form factor is unlimited size. This allows for greater processing power and infinite space for ports, knobs and buttons that lend greater functional utility.
Since spectrum analyzers in the laboratory environment might be regularly used in conjunction with other equipment like oscilloscopes, the benchtop model is the ideal form factor for hybrid equipment that can function as both spectrum analyzer and oscilloscope, or other similar combinations of products. By definition, a benchtop spectrum analyzer is designed to remain stationary, although some are equipped with battery packs that can make them something of a cross-over into the portable category.
Computer processing, electronics packaging, and battery life improvements have allowed portable equipment (15 lbs. or less) to incorporate functionality that was once reserved for these benchtop models. These advancements have also contributed to a reduced footprint for many benchtop spectrum analyzers used in lab or manufacturing settings. The VIAVI Multiple Application Platform (MAP) series of benchtop analyzers support advanced optical applications including DWDM signal analysis, sensitivity testing, and automated compliance testing.
Portable Spectrum Analyzer
As the number of field applications for spectrum analyzers increase, portability becomes more important. To accommodate varying environmental conditions, portable spectrum analyzers also need to account for screen glare reduction and the ergonomics of the handle and controls.
The CellAdvisor 5G has taken the portable spectrum analyzer category to the next level by combining real-time spectrum analysis in the millimeter wave with 5G beam analysis, fiber verification, and antenna testing capabilities. A rugged and sturdy form and the ability to withstand shipment, vibration, and weather conditions are essential characteristics of the best spectrum analyzer which is shared by the handheld category.
Handheld Spectrum Analyzer
The definition of this type of analyzer is self-evident, since it can be viewed, controlled, and used all while being held in the palm of your hand. Obviously, the weight and space limitations of handheld spectrum analyzers also limit functionality. This type of device might be used when the precision or scope of measurements required is low. Typical uses for the best handheld spectrum analyzer from VIAVI include wireless communication interference tracking and signal location in the field. Regardless of the application, there will always be a trade-off between size and precision. It is up to the user to decide how much accuracy, storage and processing capability is required for the task at hand.
Integrated Spectrum Analyzer
With the power and flexibility of laptop computers, tablets, and even smartphones, it is not surprising that spectrum analyzers now often work in conjunction with these devices. By taking advantage of the adjunct device’s processing, networking, memory, and display capabilities, the “black box” that is now the spectrum analyzer can be dedicated to optimizing accuracy, bandwidth and range. There are many other benefits inherent to this approach since software upgrades and networking of devices can take advantage of the internet, as well as the software and hardware common to any type of computer device.
Who Needs a Spectrum Analyzer?
In the most general sense, a spectrum analyzer can be described as a tool for measuring the power of the spectrum for known and unknown signals. The list of technologies and professions that benefit from this technology continues to grow as the tools become more versatile and compact.
In laboratory and production environments, spectrum analyzers can be used to design, characterize, and test any product generating (or sensitive to) RF, optical, or sound waves of any kind. With the addition of wireless capability into virtually any conceivable device through the internet of things (IoT), the applications are seemingly limitless.
Cell tower deployments are the classic field application for RF spectrum analysis. As the technician pool is strained by the breakneck pace of 5G deployment, versatile, user-friendly portable spectrum analyzers translate to highly efficient installation and confident turn-on. Integrated solutions including the VIAVI OneAdvisor-800 and CellAdvisor 5G can be used to quickly verify cable integrity and isolate loss locations once the tower is erected and fiber is pulled. After construction is completed, the advanced RF spectrum analysis features of these same versatile tools can be used to:
- Validate radio coverage and signal propagation
- Test for over-the-air interference and locate the source(s) with InterferenceAdvisor
- Perform antenna reflection testing and beam validation
Evolution of the Spectrum Analyzer
In the 150 years since James Maxwell gave us our first glimpse into the unlimited potential of the airwaves, the spectrum analyzer has become a truly indispensable tool in the electronics, RF, audio, and optical fields.
Had the spectrum analyzer never been developed, it would not have been possible to analyze the elements of a signal or gauge a circuit’s performance. The laser would have remained the stuff of science fiction, and the telecommunication networks that have become synonymous with modern society could not have existed. Since spectrum analyzers can perform a wide variety of measurements for several different functions, the utility of this innovation cannot be overstated.
Much like the evolution of the radio “superhighway” as the number of applications grew exponentially in the mid-1900’s, the functionality and features available for modern spectrum analyzers have vastly expanded in the past decade, as computer technology continues to enable more capability in compact form factors.
The VIAVI family of RF and optical spectrum analyzers exemplify and accelerate this evolution. Ruggedized, 5G-ready portable spectrum analyzers and purpose-built solutions for every shielding, WiFi, and optical system application provide the key to unlocking the full potential of today’s technology, and bringing invisible interference and performance data into the light.