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2018

There are two kinds of EMC Pre-Compliance tests you can perform – radiated and conducted.  Today, we will review conducted emissions testing – what it is and why it’s important.  For a similar discussion on radiated testing, check out EMC Basics:  What is Radiated Emissions & Immunity Testing?.

 

Conducted emissions tests focus on the unwanted signals that are on the AC mains generated by the device under test (DUT).  Conducted RF emissions are electromagnetic disturbances (noise voltages and currents) that are caused by electrical activity in a DUT and is conducted out of the DUT along its interconnecting cables – for instance, power, signal, or data cables.  Conducted disturbances, in particular, a conductor, can couple directly into another electronic device or component within the same device.  This will provide unwanted signals that could lead to issues, like inaccurate performance.  This type of testing is one of the first group of tests performed in the process for EMC Pre-Compliance, followed by Radiated Emissions testing, Radiated Immunity, and conducted immunity testing.  The general procedure is to connect the appropriate equipment, load the limit, and load the correction factors.

Before we go through the steps to complete the conducted emissions testing process, let’s gather the equipment required.  These are common items that a test bench should have – these include:

 

  • Spectrum Analyzer equipped with EMC pre-compliance measurement software
  • Line impedance stabilization network (LISN) - The LISN is important because it isolates power mains from the DUT, which must have as clean of a signal as possible
  • Limiter
  • DUT

 

Now let’s go through the conducted emissions testing process in seven steps:

 

1.  Set up your test

Connect the signal analyzer to the limiter, LISN, and DUT.  Make sure the cord between the DUT and LISN is as short as possible to avoid the power cord from becoming an antenna.  Measure the signals on the power line with the DUT off.  If you see a signal approaching the established limit lines, you’ll want to set up some additional shielding so that these signals do not interfere with your possible conducted emissions from your DUT.  Shielding isolates components from each other to avoid coupling and interference that unwanted.

 

2.  Select your frequency range

Be sure you are measuring within 150 kHz and 30 MHz, which is the correct bandwidth for this measurement.   This is the corresponding frequency span that meets the CISPR requirement, which is a standard that is used for compliance testing. We will talk more about CISPR in another blog.

 

3.  Load the limit lines and correction factors

 

The two limit lines used for conducted emissions are EN5502 Class A quasi-peak and EN55022 Class A EMI average.  To compensate for measurement errors, add a margin to each limit line.

 

Figure 1:  Scan table where you can select the frequency span needed for the corresponding measurement.

 

Figure 2:  Conducted emissions display with limit lines and margin set

 

4.  Correct  for the LISN and the transient limiter

 

The transient limiter is used to protect the input mixer, basically acting as a filter or attenuator and is used with the LISN.  The correction factors for the LISN and the transient limiter are stored within the signal analyzer and can be easily recalled.  Correction factors adjust the reference plane for the DUT compensate for any loss through cables, space, etc.  Now you are able to view ambient emissions.  During this step, the DUT must be turned off.  If your emissions are above the limit, the cord between the LISN and DUT may need to be shortened.

Most radiated and conducted limits in EMC testing are based on quasi-peak detection mode.  Quasi-peak detectors weigh signals according to their repetition rate, which is done by having a charge rate faster than the discharge rate.  As the repetition rate increases, the quasi-peak detector does not have enough time to discharge completely, resulting in a higher voltage output.

 

The quasi-peak and average of the signals need to be measured and compared to their respective limits.  There are three detectors – Detector 1 will be set to peak, Detector 2 to Quasi-peak, and Detector 3 to EMI average.

 

Figure 3:  Loading correction factor files

 

5.  Locate signals above the limit lines

 

Switch on the DUT to find signals above the limit lines.  This is a good time to check to make sure the input of the signal analyzer is not overloaded by stepping the input attenuator up in value and seeing if they display levels do not change.

 

Figure 4:  Scan and search for signals above the limit lines

 

6.  Measure the Quasi-peak and average of the signals 

 

Most radiated and conducted limits in EMC testing are based on quasi-peak detection mode, which is available in the EMC X application.  Quasi-peak detectors weigh signals according to their repetition rate, which is done by having a charge rate faster than the discharge rate.  As the repetition rate increases, the quasi-peak detector does not have enough time to discharge completely, resulting in a higher voltage output. 

 

The quasi-peak and average of the signals need to be measured and compared to their respective limits.  There are three detectors – Detector 1 will be set to peak, Detector 2 to Quasi-peak, and Detector 3 to EMI average. 

 

Almost there!  We’ve got one more step to go!

 

7.  Review the measurement results 

 

The quasi-peak detector delta to Limit Line 1 & average detector delta to Limit Line 2 should all have negative values.  If there are some measurements that are positive, then there is a problem with conducted emissions from the DUT.  Before redesigning / troubleshooting the DUT with these results, check to ensure there is proper grounding if there are conducted emissions problems.

 

Figure 5: Quasi-peak and average delta to limit - the measurement results

 

Check these tips out for any troubleshooting issues: 

  • If the signals you are looking at are in the lower frequency range of the conducted band (2MHz or lower), you can reduce the stop frequency to get a closer look
  • You can add more data points by changing the scan table
    • The default scan table is two data points per bandwidth, or 4.5 kHz per point

 

To get more data points, change the points per bandwidth to 2.25 or 1.125 to give four or eight points per bandwidth. 

 

For more details on conducted emissions testings, check out the Making Conducted and Radiated Emissions Measurements application note for more information.  Please like, comment, or share!  Stay tuned for the next one!

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.

 

 

 

You have your workspace set up with your oscilloscope, waveform generator, and vector network analyzer. Now all you're missing is some desk space to actually do your work. What if I told you that you could get the same performance from machines half the size of your current setup? Small form factor equipment is a great option for labs where space, cost, or portability are concerns.

 

The P937xA Keysight Streamline Series VNAs are easily controlled via PC.

Figure 1. The P937xA Keysight Streamline Series VNAs are easily controlled via PC.

 

The P937xA is part of Keysight’s Streamline Series, a new family of faceless USB instruments, including vector network analyzers (VNAs), oscilloscopes, and an arbitrary waveform generator (AWG). By moving the user interface (UI) to a computer, we were able to pack our proven hardware into small devices with incredible performance for the price.

 

When you buy instruments, you’re not just buying the hardware. You’re buying into the manufacturer’s ecosystem.

 

In addition to the dependable hardware, the Keysight Streamline Series also comes with our intuitive UI to give you the same experience as full-size instruments. This means that the P937xA has the same SCPI commands, GUI, and measurement science as both our benchtop and modular vector network analyzers. You can also run our common benchtop applications and software upgrades.

 

There are a lot of USB instruments out there now. When shopping for small form factor equipment, it can be hard to see the difference between each vendor when they have somewhat similar specs on paper.

 

Let’s dive into some of these specs and the differences between two of the most popular compact USB vector network analyzers on the market: Keysight’s P937xA and Anritsu’s Shockline MS46122B.

 

In RF measurements, the name of the game is minimizing interference. In today’s wireless world, RF signals and devices must fight all kind of interference. It can feel like the universe is against you when testing RF equipment – and it actually kind of is – thanks to interference from lightning, solar flares, and Earth’s magnetic field.

 

Fortunately for you, modern VNAs are built so precisely that even smaller USB instruments boast impressive specifications. You can see the banner specs of the MS46122B and the P937xA summarized in Table 1 below.

 

Performance / Spec

Keysight P937xA

Anritsu MS46122B1

Min Frequency

300 kHz

1 MHz

Max Frequency

4.5 / 6.5 / 9 / 14 / 20 / 26.5 GHz

8 / 20 / 43.5 GHz

Number of Ports

2 / 4

2

Dynamic Range2 @ 10 Hz IF BW

@4 GHz

115 dB

100 dB

@20 GHz

110 dB

100 dB

Trace Noise

@4 GHz

0.003 dB [1 kHz IF BW]

0.006 dB [10 Hz IF BW]*

Power Range

@4 GHz

-40 to +7 dBm

-20 to +5 dBm

@20 GHz

-40 to +2 dBm

-20 to -3 dBm

Stability dB/deg. C (typical)

@4 GHz

0.02

0.02

IF Bandwidth

10 Hz to 1.2 MHz

10 Hz to 300 kHz

*Performance is characteristic, not typical

1 All Anristu specifications were found in the ShockLine™ Compact Vector Network Analyzers MS46122B datasheet (PN: 11410-00995 Rev. F) on June 20, 2018.

2 Standard (not typical)

Table 1. Keysight P937xA and Anritsu Shockline MS46122B banner specifications.

 

It’s easy to just throw numbers around, so I’m going to explain why you should care about these numbers.

 

Dynamic range, power range, and IF bandwidth are the holy trinity of noise reduction. Flexibility with these specs gives you space to separate your signal from the noise.

 

Dynamic range is the power range of simultaneous input signals that can be accurately measured. This is critical for applications like characterizing filters where the stopband and passband power levels can vary greatly. A wide dynamic range provides more room to set wide IF bandwidth to speed up your measurements.

 

A good power range is essential for characterizing nonlinear devices with a power sweep. It also allows you to run tests without an external power amplifier, saving bench space and keeping your cost of test down.

 

IF bandwidth is one of the most important network analyzer parameters. It offers control over the trade-off between noise reduction and measurement speed. As you can see, the P937xA gives you about a half-order of magnitude more frequency to work with.

 

It sounds great on paper, but how does it look?

 

We all want our products to get to market as fast as possible. An intuitive user interface is critical in speeding up the development process. Easily move through each phase with quick access to common tools and menu options.

 

Note: All Anristu screenshots below were taken on a MS46122B by a Keysight employee on February 21, 2018.

 

User interface of Keysight P937xA vs. Anritsu Shockline MS46122B.

Figure 2. User interface of Keysight P937xA vs. Anritsu Shockline MS46122B.

 

Setting a trigger is one of the most basic needs in making measurements. Having the trigger button right on the main menu of hardkeys makes it so you are always one button press away from the full trigger menu. No need to dig through various menus to set up one of the most critical components of a measurement.

 

Trigger menu on Keysight P937xA vs. Anritsu Shockline MS46122B.

Figure 3. Trigger menu on Keysight P937xA vs. Anritsu Shockline MS46122B.

 

Adding a trace, undoing or redoing an action, or taking a snapshot has never been easier. The P937xA user interface has shortcut icons along the top of the screen for common quick actions.

 

Quick action buttons on Keysight P937xA vs. Anritsu Shockline MS46122B.
Figure 4. Quick action buttons on Keysight P937xA vs. Anritsu Shockline MS46122B.

 

Another helpful capability of the P937xA is the setup wizard. Having all the fundamental steps and parameters in one place makes setup a breeze. There is no need to dive into multiple menus when you have everything in one place.

 

Main parameter setup on Keysight P937xA vs. Anritsu Shockline MS46122B.

Figure 5. Main parameter setup on Keysight P937xA vs. Anritsu Shockline MS46122B.

 

The P937xA also supports context menus with a press and hold (or a right click). These menus give you quick access to different features depending on where you click.

 

Right click quick access menus on Keysight P937xA.

Figure 6. Right click quick access menus on Keysight P937xA.

 

Another feature that will come in handy is the drag and drop for different trace views. This lets you simply drag each trace and place it in a portion of the screen that makes it easier to view the data. This helps make the view more customizable to your specific tests rather than being restricted to a pre-defined menu.

 

Easy drag and drop traces on Keysight P937Xa vs. display options on Anritsu Shockline MS46122B.

Figure 7. Easy drag and drop traces on Keysight P937Xa vs. display options on Anritsu Shockline MS46122B.

 

As we’ve seen, the P937xA’s interface is full of intuitive features to make your measurements easier.

 

In summary, we’ve seen that the P937xA offers excellent measurement capabilities with the same UI you would get from a high-performance benchtop instrument. The P937xA’s stability and very low trace noise mean that once you calibrate it, you can be confident in your measurements. The intuitive user interface ensures you’ll test more efficiently and speed up your development phases. Altogether, the new Keysight Streamline Series USB VNAs pack big performance into a small package so you can fit even more functionality on your bench.

 

Compact form. Zero compromise.

 

Click here to learn more about Keysight’s Streamline Series USB vector network analyzers. Or check out the video demo.