Spectrum Analyzers 101: What It Is And How To Use It

A laboratory will often have several pieces of equipment lying around, each with specific uses and functionalities. Although each apparatus is generally important, some have more use than others during specific projects. That's often the case with spectrum analyzers when it comes to any project that involves radio frequencies.

What Does A Spectrum Analyzer Do?

As the name suggests, a spectrum analyzer is an apparatus that can detect and analyze the radio frequency (RF) spectrum. Its appearance is similar to an oscilloscope-it has a monitor on one side and a set of buttons on the other side. The monitor displays the strength of the RF waves, while the controls allow you to perform various tasks, like recording detected signals.

What Can Spectrum Analyzers Tell You?

Although the visuals of its monitor are roughly the same each time, scientists and engineers can extract numerous metrics from a single snapshot or image. Here's a list of those metrics:

Amplitude units
Antenna input immunity
Frequency resolution
Harmonic current emission
Modulated signal width
Noise
Occupied bandwidth
Radiated emission
Resolution bandwidth
Signal strength
Spurious signal
Sweep time
Volume level

There's rarely ever a scenario where these metrics will be vital all at the same time. However, each of these metrics can provide valuable insights depending on the project or application.

Applications Of Spectrum Analyzers

Wireless devices Wi-Fi and cellular networks use radio frequencies to send signals between different devices. As technology advances, radio waves become more commonplace.

So far, engineers and scientists have used spectrum analyzers for the following applications:

1. Research And Development

During research and development, scientists and engineers must test various metrics concerning the project. Doing so can help solve tough problems that have been a bottleneck to the team.

The metrics may vary from one project to another.

In the case of projects that involve circuits or systems that generate RF signals, the development team must be able to see the details of the output signals. Examples of such projects include:

Internet of Things (IoT) devices and systems
RADAR
Traditional radio
Mobile networking systems

In these projects, the development team must be able to measure metrics, like noise, modulated signal width, and spurious signals. With these pieces of data, the team can troubleshoot problems and optimize the product's performance, allowing them to move to production more quickly.

Even during production, there are bound to be problems with the device, perhaps, because a previous measurement didn't hold up. Again, a spectrum analyzer can be a big help.

2. Inspection And Compliance Testing

Before a company can release a product that generates electromagnetic signals to the market, it must pass the electromagnetic compatibility (EMC) testing and get a certification. It's a requirement for markets in countries like the US, China, New Zealand, and Korea. Basically, it's a test to ensure the system or equipment performs satisfactorily and doesn't produce electromagnetic disturbances that may cause harm in the electromagnetic environment.

Examples of equipment that shouldn't encounter electromagnetic disturbances include:

Medical equipment that can endanger patients in the event that it malfunctions
Electronics bought by the masses, like smartphones, computers, and laptops
Automotives with electromagnetic features that can cause accidents when dysfunctional
Industrial equipment that handles, manages, or controls heavy machinery and robotics
Control systems responsible for the security of an organization

It goes without saying that when these products ever go rogue or malfunction, they can bring harm to both human lives and property, hence the EMC compliance. Non-compliance can lead to charges. Although they're designed to ensure consumer safety, EMC tests have proven to be an excellent step to optimize an equipment's performance and quality. However, keep in mind that every industry will have its own set of rules and guidelines for EMC compliance.

Nevertheless, a spectrum analyzer should prove to be helpful since some analyzers have features specifically designed for EMC testing. These may include its ability to detect the following:

Amplitude unit
Antenna input immunity
Frequency resolution
Harmonic current emission
Radiated emission
Resolution bandwidth
Sweep time

Because of this, spectrum analyzers are viewed as an essential component of EMC testing.

3. Telecommunications

A spectrum analyzer can detect and analyze every source of signal from a radio wave input. That includes both the dominant and background signals. For that reason, it's a valuable device for detecting signal sources that might interfere with the primary communication signal.

Furthermore, one of the metrics a spectrum analyzer can measure is occupied bandwidth, a measure of how wide a signal can spread. If the bandwidth is too wide, it's likely to spread outside the target channel and may interfere with other channels it wasn't meant to reach.

As a result, the network performance may drop significantly. That's why the occupied bandwidth must be kept at the required limit, and spectrum analyzers are a big help in making sure of that.

4. Music

Although they're not the same type of frequency, just like radio waves, audio waves also have their own spectrum. That's why spectrum analyzers, specifically the ones designed to detect audio, can help deconstruct an audio signal. These devices display real-time visuals of incoming audio signals. Sound engineers use visuals to study and analyze the harmonics of audio.

Apart from these four, there are other applications of spectrum analyzers. After all, they have a vast array of features, so some of those are bound to be used for unorthodox applications.

Moreover, it's worth noting that spectrum analyzers come in different types.

Different Types Of Spectrum Analyzers

When it comes to performance, there are two main types of spectrum analyzers. The third type you'll see in this section doesn't differ in performance, but, instead, in functionality.

Here's a look at the first type.

1. Swept-Tuned Spectrum Analyzer

Swept-tuned spectrum analyzers were developed in 1960 and were the first type of analyzer invented. They have similar functionality to radio receivers in that you must input the necessary details to select a frequency, much like how you choose a channel with your radio.

Upon choosing a frequency, the analyzer begins to produce images of the radio signal. It's best used for repetitive or steady signals since it can't analyze frequencies in real time. For that, you must use the second type of spectrum analyzer.

2. Real-Time Spectrum Analyzer

As the name suggests, a real-time spectrum analyzer displays images of various frequencies in real-time. It doesn't require you to pick a frequency as it's able to detect every signal in a given time period. It can distinguish between signals, including the low-level signals that are being drowned by the higher-level ones. Real-time spectrum analyzers are typically more expensive than swept-tuned analyzers due to their superior performance and larger array of features.

3. Audio Spectrum Analyzer

An audio spectrum analyzer is a device that focuses mainly on the audio spectra rather than the radio spectra. And, as stated earlier, it's primarily used to study and analyze harmonics.

In order to choose the most suitable type, you must first evaluate your specific needs and your purpose for buying the device. Also, keep in mind that while the real-time spectrum analyzer generally has superior performance to its counterpart, that doesn't necessarily mean it'll always be the better option between the two. In some cases, less is better.

Different Forms Of Spectrum Analyzers

In addition to the type of spectrum analyzer according to functionality, it also comes in different forms. Each form offers different ways to access the system. Here's a look at each form:

1. PXI Spectrum Analyzers

A spectrum analyzer refers to a physical, electronic device most of the time. However, it can also take the form of a card that you can insert into a PXI rack. It has the basic function of a spectrum analyzer, although it doesn't have as many features. Think of it as the budget version.

2. USB Spectrum Analyzers

A USB spectrum analyzer works exactly as you might imagine. It comes in the form of a USB drive, and you can access the system by plugging it into a computer. It's more affordable and cost-effective as it uses the existing resources of a computer to which it's connected.

Upon plugging the USB into a computer, you'll gain access to a system that allows you to perform various tasks a regular spectrum analyzer can do, although it's a bit limited.

USB spectrum analyzers have more features than PXI analyzers, but they're still lacking compared to the traditional version of spectrum analyzers. However, it depends on the brand. Low-end USB analyzers come with only the most basic features. They don't offer the real-time functionality that most analyzers do. However, a high-end USB spectrum analyzer may offer real-time operation. Put simply, it has the benefits of being cheaper, smaller, and more portable, but it also has the disadvantage of not being as efficient or accurate as its benchtop counterpart.

3. Handheld Spectrum Analyzers

A handheld spectrum analyzer has a similar appearance to a smartphone, albeit a bit larger and chunkier. It performs better than USB analyzers, but can't compare to its benchtop counterpart. This form of the device is designed specifically for measuring radio or electromagnetic transmissions while you're in the field. Its main selling point is its portability, as it's relatively small and lightweight. It also uses a battery that you can charge regularly.

4. Portable Spectrum Analyzers

Portable spectrum analyzers have the same selling point as handheld analyzers. They're not as portable as the handheld version, and they have a similar appearance to the traditional benchtop spectrum analyzer. However, they're a bit smaller, lighter, and have a handle at the top. They're used in a similar manner as handheld analyzers-to detect and analyze transmissions while in the field. However, they typically have slightly better performance than the handheld version.

Just like the handheld version, portable spectrum analyzers are also battery-powered.

5. Benchtop Spectrum Analyzers

Benchtop spectrum analyzers have the best performance out of these five forms. They're heavy, with a weight of more or less 30 pounds, and are the size of an average-sized radio. Unlike the previous two versions, you must plug them into an AC power during operation, meaning you must leave them in the lab. However, there are companies that offer battery packs for these devices.

In addition to their weight, benchtop spectrum analyzers are also generally more expensive than their other counterparts. Part of it might be due to the extra utilities they have that can't be found in other versions, like the fans or vents that dissipate heat generated by such devices during operation.

As you can see, the performance of a spectrum analyzer is often inversely proportional to its portability. It's up to you which of these two factors you want to prioritize.

How Do You Use A Spectrum Analyzer?

To start with, you must first get a spectrum analyzer. Although you can get it from any marketplace you want, it's best to look for a reliable supplier.

Unfortunately, there are no pre-defined guidelines on how you can use a spectrum analyzer. It depends on numerous factors. But, to start with, you must answer the following questions:

What type of spectrum analyzer are you using?
For what purposes do you want to use the device?
What specific metric do you intend to analyze?
In what form is your spectrum analyzer?

Thankfully, the basic concept of a spectrum analyzer is the same across different types and purposes. Here's a look at the five elements that you must know to use an analyzer:

1. Display

The display consists of two axes. The horizontal axis corresponds to the frequency, while the vertical axis corresponds to the amplitude, so it shows you the amplitude of each frequency.

2. Frequency

There are four controls you must know about in order to use a spectrum analyzer at its most basic level. Keep in mind that these four controls are typically located on the right side of the device.

The first control or button is frequency. It allows you to set the frequency that you want to monitor closely. You can set it by clicking the button that corresponds to frequency and typing in the appropriate number on the keypad.

3. Span

Once you've entered a frequency, you can move on to the span button. This control allows you to set the width of each of the frequency bands you see in the display. Again, you can set its value using the numeric keypad or the rotary control. It's common practice to reduce the span values if you want to close in on the gaps you want to see or monitor.

4. Amplitude/Reference Level

The reference level controls the vertical axis in the device's display. It must be adjusted according to what you want to achieve, meaning there's no correct answer as to whether you must increase or decrease its value. However, when it's too low, the signal may vanish as it blends into the noise levels. 20dB is the minimum adjustment for the reference level.

5. Resolution Bandwidth

The resolution bandwidth is similar to the span. The lower its value, the higher the resolution of the display and the more you can see. However, it's a control you must adjust only when you see the signal's final filter. The downside to a low bandwidth is it takes more time to scan frequencies.

While there are several other things you must know to perform in-depth operations using a spectrum analyzer, these basics should be sufficient for the most part.

Wrapping Up

Spectrum analyzers might look intimidating, but they have numerous uses. You can use it to work on a product, troubleshoot network problems, and more. Moreover, it's completely learnable, although you must first understand how it works before you get started with the actual hands-on practice. Thankfully, with this guide, you should be able to touch up on both the theory and practice part of the learning process.