Skip navigation
All Places > Keysight Blogs > Better Measurements: The RF Test Blog > Blog > Authors nickben

After reading my last blog you’ve been given a brief intro on What are EMC & EMI Measurements and why it is important to measure for to ensure your device is pre-compliant.

 

In this blog we’ll discuss 2 of the 4 EMC pre-compliance tests – radiated tests, emissions and immunity – in more detail.

 

Radiated Testing

Radiated tests, as mentioned in the previous EMC basics blog, entail characterizing unintentional electromagnetic energy release from an electronic device. Radiated tests are the most common EMC test done around the world.

 

Many regulatory bodies across the globe set emission limit standards that all electronic products must meet. Looking at Figure 1 below we see a setup that is commonly seen at a test house, where your product will eventually have to acquire certification from. Your product is placed in a semi-anechoic chamber with an antenna directed at it to capture any phenomena radiating from the device.

 

However, before even sending your device to a test house, it’s important to first do pre-compliance tests of your own. This will not only save you money, but also avoid throwing off your schedule if your device fails at a test house and redesign work is needed. Before we get into how the tests are made, let’s get a better idea of the different kind of radiated tests.

 

Figure 1: Semi-Anechoic chamber where an EMC/EMI test is being conducted with dual antennas. The material of the chamber does not allow signals to leave or enter the room to ensure accurate measurements are made.

 

Radiated Testing - Emissions

Radiated emissions testing can be a bit more complicated than say, conducted emissions testing. This is because radiated tests entail through the air testing, which adds some complexity in how we can accurately measure emissions from a device (Figure 2). The complexity is attributed to the ambient environment, which can interfere with your device under test’s (DUT’s) emissions measurement. So, as part of emissions test, it is important to be able to identify what signals are coming from your device versus the ones coming from the environment. The topic of conflicting ambient signals will be discussed in more detail in a later blog.

 

When testing for radiated emissions, your intention is to determine the electromagnetic energy strength of the emissions that are being output by your device. Most devices usually have some sort of emission, but it is a question of whether those emissions from your device are compliant with the standards set by the regulatory body of your respective region. Pre-compliance testing is done to answer this very question.

 

Figure 2: An example of what emissions and immunity testing entail.

 

Radiated Testing – Immunity

Radiated tests for immunity entail testing the susceptibility of your device to emissions from other surrounding devices (Figure 2). Let’s say you work in a company that designs and manufactures phones. At some point you must determine what these phones’ susceptibility are to the emissions that, let’s say, a nearby laptop may have. Immunity is important to test for because you do not want your device to be accidentally influenced by a neighboring device.

 

Conclusion

Now that you have a better understanding of the types of radiated tests that exist and what they are, knowing how to test for them is the next step. Furthermore, let’s not forget that radiated tests only give you half of the story of EMC pre-compliance testing, as you should also have a good grasp on what conducted tests are – radiated and immunity. This will be discussed in a later blog here on the RF Test blog.

 

For an even more expansive and detailed look into EMC tests, check out the Making Conducted and Radiated Emissions Measurements for more information. Finally, if you enjoyed the blog make sure to give it a like, comment or share! Thanks for reading, and I look forward to seeing you in the next one.

Introduction:

Conceptualizing your next product, designing it, and then releasing it to market are more or less the main phases encountered during a product development cycle. But what if you had gotten as far as finishing your product design only to discover late that you cannot push the product to market, because it didn’t meet some standards set by local regulators. Therefore, testing your product early in the cycle to make sure it works appropriately is just as important as designing it. In this blog we’ll discuss the basics of EMC and EMI pre-compliance – something all electronic products will eventually have to get certified compliance for in a test house. However, compliance testing certification occurs very late in the development process and if you instead did pre-compliance testing earlier on, fixing these problems are easier and less costly (Figure 1).

 

Product Development Cycle including EMI Testing

Figure 1: Pre-compliance testing can uncover problems during earlier stages of development, where solutions are easier and less costly. It can also reduce the risk of design rework and associated schedule delays.

 

What is It

Let’s first figure out the difference between EMC and EMI. EMC and EMI stand for electromagnetic compatibility and electromagnetic interference respectively. EMC, you can say, is the umbrella term whereas EMI is the actual phenomena you will be testing for.

 

All electronic products, whether it be your smartphone or your smart refrigerator, must eventually pass compliance tests in a recognized test house and be certified before they can be brought to market. This certification is required as it demonstrates that your product won’t electromagnetically interfere or be interfered with by any other electronic products in close proximity. To get your device certified, test houses are mainly concerned with making sure your device can pass 4 EMC tests in particular – radiated emissions and immunity tests and conducted emissions and immunity tests.

 

In short, the difference between radiated tests (emissions and immunity) and conducted tests (emissions and immunity) is that the first refers to unintentional release of electromagnetic energy from an electronic device. The latter refers to internal electromagnetic emissions propagated along a power or signal cable, creating noise. Looking at Figure 2 below we see a snapshot of the 4 different tests.

 

EMC Testing, Conducted & Radiated Emissions

Figure 2: Four types of EMC Measurements.

 

The difference between emissions and immunity tests are that the emissions is concerned with the amount of electromagnetic energy emitted from your device while immunity is concerned with how susceptible your device is to electromagnetic energy being emitted from surrounding devices.

 

Why Testing For It Matters

Regulatory bodies, like the FCC in the US, set up standards (CISPR) that devices are tested against. As you would expect, standards vary from one device to another – meaning you would measure the amount of EMI on your smartphone differently than you would military-grade avionic equipment. If you have a good signal analyzer with an EMI application, then you’ll have pre-loaded and configured limits for CISPR and MIL-STD tests that allow you test against these standards quickly. EMI measurements are made to ensure that there is no interference between devices when in operation. When you’ve designed your product, and have it sent off to a test house, the test house will traditionally put your device in an anechoic chamber. An anechoic chamber is used to completely block out signals exiting from within the chamber to outside of it and other signals outside the chamber from entering in it. Within the chamber an antenna is used to test a number of different points on your device. This anechoic chamber setup is similar to the one you see below in Figure 3

 

 EMC Test in an Anechoic Chamber

Figure 3: EMC Test in an Anechoic Chamber. An antenna is directionally pointed at the device under test (DUT).

 

However, simply sending off your product for EMC testing at a certified test house is not the answer. This is because these tests are very expensive to do, and you don’t want to risk having to do design revisions and throwing off your entire schedule. That’s why it’s important to do some due diligence on your end.

 

What’s The Solution

The solution is simple – make sure you conduct your own EMC tests in house (pre-compliance testing) for your device prior to sending it off to a test house for certification (compliance testing). In the off chance that your device doesn’t pass at the test house, it will not only throw off your design cycle and time to market, but also cost you a lot of money.

 

This is where signal analyzers come in handy. Using a signal analyzer, EMI close-field probes and an EMI application, you can conduct your own EMI measurements in house to ensure your device is on track to fulfilling the EMC requirements of the standard that it will be tested against at a test house. You can take a look at Figure 4 below to see some example tools you can equip yourself with to conduct EMC pre-compliance measurements.

 

EMC Testing Tools

Figure 4: A set of tools you can use to conduct your own EMC testing.

 

Conclusion

So, in summary, if you are working towards getting your device to market you definitely need to make sure your device is EMC pre-compliant prior to sending it off to a test house for certification. A signal analyzer with an EMI application and EMI close-field probes are the right tools you need for making sure you can test for EMI accurately. Your design cycle will not only stay on track, but you will also make your manager one happy, and less broke, person.

 

Thanks for taking the time to read this blog, if you enjoyed it feel free to give it a like, comment, and share. Stay tuned for more blogs to come that discusses more about EMC testing. For more in-depth information on EMI conducted and radiated measurements check out the following application note: Making Conducted and Radiated Emissions Measurements.

 

 

 

In the previous edition of The Four Ws, I reviewed the fundamentals of adjacent channel power (ACP). This time I’m discussing the WHAT, WHY, WHEN and WHERE of harmonic distortion measurements. Measuring harmonic distortion will help you validate the proper functioning of your device’s components and, in turn, avoid interference with systems operating in other channels.

 

What is harmonic distortion?

From simple continuous waves (CW) to complex digitally-modulated signals, every real signal has some amount of distortion. One type of distortion to consider is the total harmonic distortion (THD). The THD value indicates how much of your device’s signal distortion is due to harmonics. These harmonics are energies created at various multiples of the frequency of your signal where none previously existed or should exist. This extra energy is frequently caused by nonlinearities in the transfer function of a circuit, component or system. In practical systems, nonlinearities are due to gain compression, transistor switching or source-load impedance mismatches.

 

An 850-MHz signal with obvious harmonics on both sides.

Figure 1: A basic swept measurement made with an X-Series signal analyzer shows an 850-MHz signal with obvious harmonics on both sides.

 

To calculate THD you need to determine the ratio of the sum of the power of all surrounding harmonic components to the power of your device’s fundamental signal:

To calculate THD you need to determine the ratio of the sum of the power of all surrounding harmonic components to the power of your device’s fundamental signal.The resulting THD is stated in dBc.

 

Why and When to measure THD

THD is typically characterized during design validation and troubleshooting when you are confirming that your signal is behaving as expected. Your THD will indicate if your device’s surrounding harmonics will affect your signal quality or interfere with another device.

 

You want the THD to be as low as possible. This implies that your device has a nearly pure signal making it unlikely that it’s harmonics will cause interference. On the other hand, a high THD means that you may need to rework your design because the distortion could negatively affect your signal quality or create interference in other channels.

Measuring THD can also be an effective indicator of overall signal performance. In an amplifier, for example, excessive THD indicates issues like clipping, gain compression, switching distortion, or improper transistor biasing or matching.

 

An example of Where distortion shows up and how you measure it

A simple, real-world example of harmonic distortion is found in audio speakers. Let’s say you’re playing a song from your phone and you hook it up to a speaker. If the speaker’s internal components – amplifiers and filters – give us an accurate reproduction of the song, then the speaker has a low amount of distortion. On the other hand, if the speaker’s internal components give you a misrepresentation of the song then it has a high amount of distortion. Therefore, you want your device’s THD value to be as low as possible to maintain good signal quality.

 

Another issue harmonic distortion can cause is interference with other signals. Since harmonic distortion is unwanted energy at the harmonics (integral multiples) of the fundamental frequency, the distortion can interfere with another device that is operating in the same band as the harmonic. Therefore, a low THD value is also a good indicator that interference is less likely to occur.

 

Seeing your signal’s harmonics can be difficult to observe and measuring them can be quite time consuming if done manually. You’d have to identify all the harmonic power levels, sum them, and then find the ratio to the power of your device’s signal. That is a hassle.

 

However, some signal analyzers provide a built-in measurement that will automatically calculate THD for you. This can shorten your measurement time and ensure an accurate calculation.

 

The built-in harmonics measurement calculates the THD and results for up to 10 individual harmonics.Figure 2. The built-in harmonics measurement on an X-Series signal analyzer quickly calculates the THD for the same 850-MHz signal seen in Figure 1. In addition to THD, the measurement shows results for up to 10 individual harmonics.

 

Using the harmonics measurement shown in Figure 3, you can calculate the total harmonic distortion and the results for up to ten harmonics, automatically.  All you have to do is set the fundamental frequency and the measurement takes care of the rest.

At each cycle, the analyzer performs an accurate zero-span measurement of the device’s signal and each of its harmonics. It calculates the level of each harmonic, as well as the total harmonic distortion of the signal, both of which are shown in dBc. The harmonic distortion measurement used in our example supports signals from simple CW to complex multi-carrier communication signals.

 

Wrapping up

Knowing the total harmonic distortion of your signal can help you evaluate if your device will cause any interference with its own signal or with systems operating in other channels. If you identify troublesome harmonics, you’ll have to rework your design and use something like a filter to tune them out.

THD is just one of nine RF power measurements made easy with PowerSuite, a standard feature on the X-Series signal analyzers. If you’d like to learn more about power measurements, check out the PowerSuite page and the Making Fast and Accurate Power Measurements application note.

 

I hope my fourth installment of The Four Ws provided you with some worthwhile information. Please post any comments – positive, constructive, or otherwise – and let me know what you think. If this post was useful give it a like and, of course, feel free to share.

This week’s post is guest authored by Charlie Slater, Business Development and Operations Manager for Keysight Services.

 

These days, most organizations operate within one of two scenarios: cutting costs while delivering the same topline, or holding costs steady while increasing revenues. The third, less-common scenario is investing more to create a giant leap in output. If you’re in this fortunate group, confidence in future growth usually opens the door to major investments in plant, property and equipment (PPE)—and the “E” in PPE includes test equipment. Optimizing the management of test assets can help you create some semblance of order within the chaos.

 

Uncovering some unexpected side effects of rapid growth

Surprising problems can arise when your organization is moving at high speed. Several months ago I met with a manager in a high-growth company. Our purpose was to plan for onsite delivery of calibration services. When creating such a plan, key baseline information includes the location and condition of all in-hand test assets.

 

As we talked, it became clear that he had incomplete data about his company’s installed base of test equipment. Further discussion revealed the unexpected cause. The company’s engineers had extremely high purchasing authority and pallets of new network analyzers and spectrum analyzers were coming in every day. The manager had virtually no idea what was arriving and limited visibility into what his engineers were actively using or even if the equipment was in working order.

 

Gaining control of test assets and getting more from each one

During chaotic growth, sticking to the basics can help contain spending and restore order to an organization. For the company described above, accurate tracking of all new and existing RF equipment helped get its inventory under control. Today, better monitoring enables compliance with internal and external quality standards, and this includes staying up to date with test-asset calibration.

 

The underlying solution is real-time tools that provide centralized visibility. This enhances productivity by letting managers and engineers find and reassign unused instruments rather than waiting for delivery of new ones.

 

For any organization, real-time monitoring can pinpoint instruments that are underused or idle. In many cases, the most cost-effective way to refresh a languishing-but-viable test asset is an update or upgrade—and new functionality may be just a download away. For hardware upgrades that require installation, the turnaround time is usually shorter than the lead-time for a new instrument.

 

Exploring all three scenarios

To learn more, check out our latest resources, including a white paper about how to best enable 4G to 5G migration and a case study about how one company improved the health of their test assets.

 

Please chime in with any and all comments. How have you tried to optimize your situation? What worked best and why?

As you walk through your lab, take a look at each RF bench. How old are your signal and network analyzers? How often are they kludged together to create one-off measurements? How recently have your engineers bugged you about getting new equipment that can actually test your latest RFIC?

 

I’m here to help you make a stronger case when your team’s success depends on timely access to better RF instruments. This post introduces language, concepts and solutions that will help you influence purchase decisions and improve your chances of getting the right tools at the right time. When you apply these ideas, your newfound business sense may surprise—if not impress—your boss or boss-squared.

 

Understanding your current reality

Day to day, you deal with competing objectives: delivering excellent results while staying within stringent constraints. From a high-level business perspective, there are three ways to do this: cut costs and deliver the same topline; hold costs steady and increase revenues; or invest more to create a giant leap in output. These days, most organizations operate within the first two scenarios while fast-growing companies chase the third.

 

Getting the right tools at the right time (and place)

Whichever situation you face, one of your biggest issues is likely to be test equipment. In fluent “manager speak,” “test assets” are often your organization’s most “underutilized assets.” Why? Because it’s difficult to confidently determine two crucial bits of information: the location of every instrument and how much each one is truly being utilized.

 

For you and your team, easy access to the right tools enables everyone to do their best work and stay on schedule. Applying manager-speak once more: for “technical staff,” “highly available” test equipment can be a “high-leverage asset.”

 

Pushing for better decisions in less time

An accurate view of location and utilization is essential to making credible decisions in less time: Do you need to purchase or rent additional equipment? Is it better to redeploy, upgrade, trade in or sell some of your existing gear?

 

A few basic changes can provide three big benefits: better visibility, improved utilization, and reduced expenses (capital and operating). The starting point is a solution that puts real-time information at your fingertips. Relevant information about test-asset location and utilization is essential to greater availability and improved productivity.

 

Taking the next steps

Being able to make quick, thoughtful decisions on how to best equip your engineers with the right tools is the foundation for a successful organization. To learn more, check out our latest resources to better understand how to drive down your total cost of ownership.

 

Please chime in with any and all comments. How difficult has it been to get the test tools your team needs? What techniques have you used to help make it happen?

Like any RF engineer, there comes a time in your product’s design cycle that you need to test your device to make sure it’s behaving as you expect. There are different ways you can view your device’s signal, which brings us to why measuring signals in the time domain and frequency domain is the same, but not. This is because they both convey the same signal, but in a different way.

 

Figure 1. The time domain of a signal on the left, and the frequency domain of the same signal on the right. The time domain displays a signal in respect to amplitude vs. time whereas the frequency domain displays amplitude vs. frequency.

 

By properly combining spectrum, or a collection of sine waves, you can view the time domain of your signal. It shows your signal’s amplitude versus time. This is typically done using an oscilloscope. Why would you want to view your signal in the time domain, you ask? Basically, a time-domain graph shows how a signal changes with time. This lets you see or visualize instances where the amplitude is different.

 

Viewing your device’s signal in the time domain doesn’t always provide you with all the information you need. For example, in the time domain you can decipher that a signal of interest is not a pure sinusoid, however, you won’t know why. This is where the frequency domain comes in. The frequency domain display plots the amplitude versus the frequency of each sine wave in the spectrum. This may help you discern why your signal isn’t the pure sinusoidal wave you were hoping it to be.

 

Figure 2. Harmonic distortion test of a transmitter, which is most appropriately measured using a spectrum analyzer in the frequency domain.

 

The frequency domain can help identify questions about your signal that you wouldn’t be able to see in the time domain. However, this doesn’t mean that you can just scrap measuring signals in the time domain altogether. The time domain is still better for many measurements, and some measurements are only possible in the time domain. Examples include pulse rise and fall times, overshoot, and ringing.

 

But just like the time domain has its advantages, so does the frequency domain. For one, the frequency domain is better for determining the harmonic content of a signal (as seen in Figure 2). So, those of you in wireless communications who need to measure spurious emissions are better off using the frequency domain. Yet another example is seen in spectrum monitoring. Government regulatory agencies allocate different frequencies for various services. This spectrum is then monitored because it it is critical that each of these services operate at its assigned frequency and stay within the allocated channel bandwidth.

 

While measuring signals in the time domain and frequency domain is similar, it is also very different. Each domain conveys the same signal, but from different perspectives. This enables us engineers to get more insight into how our device is behaving and ultimately develop better products for our customers.

 

To build a stronger foundation in signal analysis that will help you deliver your next breakthrough, check out the Spectrum Analysis Basics app note. Please post any comments - positive, constructive, or otherwise - and let me know what you think. If this post was useful give it a like and, of course, feel free to share.