Spectrum Analyzer. The Best Portable Spectrum Analyzers on the Market
To describe a spectrum analyzer in four words or less, one could say “Portal into another dimension”. If this sounds like science fiction, perhaps it’s no coincidence.The wide range of form factors and features available in modern spectrum analyzers parallels the future world envisioned by fiction writers decades ago.
Today’s wireless, microwave, audio and optical technologies and their countless practical applications are something we often take for granted, and if it’s difficult to imagine our world without this technology, it’s impossible to imagine this technology even existing without the use of spectrum analyzers.
The History of Spectrum Analyzers
In the mid-19th century, the concept of a spectrum analyzer would indeed have seemed like science fiction, since the very nature of electrical and magnetic waves had not yet been discovered. Then, in 1865, James Clerk Maxwell published his revolutionary Dynamical Theory of the Electromagnetic Field, which for the first time accurately characterized the behavior of natural electrical and magnetic waves moving through the airwaves at the speed of light - radio waves. Prior to that time, scientists and practitioners had noticed anomalies such as inadvertent audible transmissions or coincident “sparks” between telegraph stations, but had attributed them to the “ether” or otherwise dismissed them.
In 1885, Heinrich Hertz proved that you could send and receive electrical waves wirelessly, and was bestowed the appropriate honor of having the frequency unit of measure named after him.
What Maxwell had described was like a giant superhighway in the sky, but with no vehicles on the road, no maps and, as yet, no on-ramps. Harnessing this new discovery would take decades.In 1885, Heinrich Hertz proved that you could send and receive electrical waves wirelessly, and was bestowed the appropriate honor of having the frequency unit of measure named after him.
By the 1940’s, Maxwell’s superhighway was becoming super crowded, as the innovation and utilization of radio progressed year after year.Like any other “hidden dimension”, our ability to see and analyze the radio waves was still very limited.The oscilloscope had been developed as a tool to track signal voltage in the time domain by visually plotting the waves on a small CRT display. This instrument had many useful applications in science and engineering, but more innovation was needed to continue the technological evolution.The development of the spectrum analyzer in the early 1960’s was a quantum leap forward.
In a basic sense, anyone who has ever attempted to tune a simple transistor radio has used their ears and fingers to simulate the function of a spectrum analyzer.
In a basic sense, anyone who has ever attempted to tune a simple transistor radio has used their ears and fingers to simulate the function of a spectrum analyzer.As you move the dial through the span of frequencies, you can hear the signal strength and bandwidth of the utilized frequencies (channels), the inherent noise accompanying the signal, as well as the underlying noise floor beneath all channels. If this information were to be transferred to a graphical format, the result would look a lot like the display of a spectrum analyzer.
While the oscilloscope plots the voltage in the y-axis against the time value in the x-axis, the spectrum analyzer graphically tracks the amplitude (signal strength in dB) in the y-axis against the frequency (in Hz or MHz) in the x-axis. Early analyzer features also included adjustability of the span and center-point for the observed frequencies and markers for the frequencies of interest.
The Many Applications of Spectrum Analyzers
Since their humble origins of 50+ years ago, the application and functionality of spectrum analyzers has continued to progress.
The increased use of Wi-Fi and the cell phone revolution have underscored the need for state of the art spectrum analyzer technology in the radio frequency field.
The increased use of Wi-Fi and the cell phone revolution have underscored the need for state of the art spectrum analyzer technology in the radio frequency (RF) field.As telecommunication networks expand, spectrum analyzers are used to determine frequency utilization and interference in a given area.They can also be used to determine the accuracy of a wireless transmitter by comparing the frequencies and bandwidths of an output signal to a received input signal.As we will discuss later, the balance between portability and functionality is extremely important with this type of field application.
RF shielding is required for electronic equipment that will reside in the vicinity of MRI imaging systems, as the electronics can emit unintended signal 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.A spectrum analyzer is an ideal testing tool for either of these scenarios.
The applications of spectrum analyzers in the RF arena alone are as diverse as the signals that travel through the airwaves and beyond.There are many other applications of spectrum analyzers outside the RF arena as well, and the list of applications will no doubt continue to grow.
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.
Although visible light is often perceived as a natural occurrence unrelated to radio frequency waves, they are both 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 spectrum analyzer can be an extremely useful tool for the study of visible, ultraviolet and infrared light sources.
Astronomy, fiber optics and laser technology are just a few of the applications for optical spectrum analyzers.Chemical and biological analysis equipment often includes optical spectral analysis functionality as part of the system.In this way, the reflected optical spectrum of a substance can be “finger-printed” in order to characterize similar substances in future studies.Optical spectrum analyzers require added complexity in order to effectively capture the frequency and intensity of light waves.Since the frequencies are relatively high, the sensitivity needs to be equally high to capture the information accurately.Interferometers might be used to capture the light frequency, while a photodiode can sometimes be used to capture the intensity.
Types of Spectrum Analyzers
The tuning of a radio receiver is probably a very good analogy for the function of a spectrum analyzer because it actually is a lot like a spectrum analyzer in concept and architecture.In their earliest forms, the two circuits were very similar.Only the quality and design of the mixer and oscillator, along with the use of a display rather than a speaker, made the spectrum analyzer more than just a radio receiver.
The original spectrum analyzer design used the superheterodyne principal, invented by Edwin Armstrong in 1918, using a local oscillator to generate a signal that is then 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.
If Armstrong’s superheterodyne design was one small step, then the FFT analyzer was one giant leap.The first use of digital technology in spectrum analyzers, the Fast Fourier Transform (FFT) analyzer is named after the mathematical transform that is used to break the waveform into the various components of its frequency spectrum by converting the signal from the time domain to the frequency domain.Much like the Star Trek transporter disassembling then reassembling the atoms of the crewmen, the FFT analyzer breaks down the signal then reassembles it on the display, with the help of an analog to digital converter.Using this technology also allows for phase information to be captured.Ironically, the man responsible for this breakthrough, Joseph Fourier, had already passed away (1830) before Maxwell had even published his discoveries.
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”.This type of spectrum analyzer also utilizes the FFT transform, but with more processing power, they are able to analyze and store the unabridged history of the signal behavior. 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.
Spectrum Analyzer Functionality
The basic functionality of a spectrum analyzer 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 band width (RBW), video band width (VBW) and sweep time settings are used to control the precision of the measurements and resulting image on the screen.Since the RBW sets that 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 RF spectrum analyzers, 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 or not you are within specification.
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 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 software features include:
- Image 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 product specifications and feature lists.
Spectrum Analyzer Form Factors
Like most electronic instruments of the 1960’s, early spectrum analyzers were a fairly large and heavy piece of equipment that relied on a direct AC power source and generally stayed in one spot. Modern electronics and computer technology have enabled a variety of analyzer form factors to emerge over the last 50 years.Below is a look at the various configurations available today along with how and when they might be used.
Benchtop Spectrum Analyzers
The aforementioned 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 table top.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.Although by definition a benchtop model is designed to remain stationary, some are equipped with battery packs that can make them something of a cross-over into the portable category.
Computer and battery advancements have allowed portable equipment to include functionality that was once reserved for benchtop models.
Portable Spectrum Analyzers
As the number of applications outside the lab for spectrum analyzers increases, portability becomes more important. Fortunately, computer and battery advancements have allowed portable equipment to include more functionality that was once reserved for benchtop models.For this reason, this form factor is now defined more by size (15 lbs. or less) than by quantity or complexity of features.To accommodate varying environmental conditions, portable spectrum analyzers also need to account for screen glare reduction and the ergonomics of the handle and controls.A rugged and sturdy form, able to withstand shipment, vibration and weather conditions is an essential element of the portable form factor which is shared by the handheld category.
Handheld Spectrum Analyzers
The definition of this type of analyzer is fairly 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 considerably. This type of device might be used when the precision or scope of measurements required is fairly low.A handheld spectrum analyzer might be used by a field analyst to study wireless communication interference.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 Analyzers
With the power and flexibility of laptop computers, tablets and even smart phones, 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.
In the 150 years since James Clerk 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 are able to perform a wide variety of measurements for a number of 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 features in compact form factors.
Today, the spectrum analyzer may seem more like an essential tool for a familiar dimension than a portal into a hidden one as history has taught us that the impossible often becomes possible with the right tools in hand.
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