Technical Insights > RF + Microwave

4 EMC Compliance Testing Tips for a Quick, Painless Experience

2020-01-23  |  5 min read 

What is EMC Compliance testing? 

Electromagnetic compatibility (EMC) testing measures a device’s response to electromagnetic environments. The device must meet standards for emissions and measurement time. Most EMC Compliance testing is done by a third-party company, but it is possible to do your own pre-compliance tests to know where you stand before sending your device out for costly tests.  

EMC Compliance testing chamber.

Below, I’ll explain what the best measurement practices are for EMC compliance. 

  1. Use Time Domain Scan. 


    By using time domain scan, you can increase the number of devices you test by reducing your overall scan time and headaches. Less time wasted + more devices tested = higher revenue. Although testing standards require measurements to meet specific time lengths (dwell time), some scans currently take hours to complete. Using a time domain scan can shrink that test time to minutes. 

    Real Time Scan application.

    How does it work?  

    Our N9048B EMC receiver uses something called high-overlap fast Fourier transforms (FFT) to include multiple resolution bandwidths at the same time. This saves measurement time by ensuring regulatory dwell time only applies once for all data in the acquisition bandwidth, which can reach upwards of 10 MHz. Using a swept or stepped frequency domain scan, dwell time is added for each measurement, which adds up quickly. Where frequency scans take up to 250 seconds, time domain scan can take 2 or less. Now, let’s say you need to make 144 scans. 144 scans at 250 seconds each leads to ten hours of testing. However, 144 scans at 2 seconds each is closer to 5 minutes of testing. 

  2. Use a wide acquisition bandwidth. 

    Wide Acquisition bandwidth to reduce dwell time.


    When using a wider acquisition bandwidth, fewer frequency steps are required. When a receiver makes steps in frequency, the local oscillator (LO) inside must also change frequency. This adds time to your measurements as the LO relocks onto the new frequency.  

    What’s the catch? 

    Time-domain scan acquisition bandwidths must also take RF and microwave preselector bandwidths into account. Preselector filters band-limit RF energy that reaches the receiver’s first mixer. This allows for better dynamic range. However, when FFT acquisition bandwidth grows too wide, FFT amplitude vs. Frequency effects add to the preselector amplitude and frequency response. It’s important to choose a receiver that finds a balance in the size of acquisition bandwidth that ensures fast scanning without hurting FFT amplitude accuracy. 

  3. Use a high degree of FFT overlap. 


    Certain standards, such as CISPR 16-1-1:2010 and MIL-STF-461, require a high level of amplitude accuracy. Engineers achieve this by overlapping FFTs in the time domain by up to 90%. This overlap ensures that no impulsive signals are lost between FFT periods. When this happens, a receiver may misreport the amplitude as lower than expected or lose the signal completely.   

    Non-overlapped FFT bands, leading to possible signal loss.

    Highly overlapped FFTs that can more reliably capture impulsive signals and accurately measure amplitude.

  4. Select the right receiver. 


    When choosing an EMC receiver, designers must consider speed, overload protection, and measurement sensitivity. Time-domain scans paired with wide acquisition bandwidths allow for high speeds, but this also widens preselector bandwidth. A wide preselector bandwidth reduces dynamic range, allowing impulsive energy to reach the first mixer of the receiver. This lost overload protection can be prevented by adding input attenuation at the cost of sensitivity. Finding a balance between speed, overload protection, and sensitivity is hard to find, but Keysight’s N9048B PXE EMC receiver makes it easy. By combining narrow RF preselection filters, overload protection, fast time domain scanning, and a new and improved 350 MHz bandwidth, the N9048B allows shorter, more accurate tests. The gapless signal capture created by high-overlap FFTs and a frequency range from 2 Hz – 44Ghz ensure no signals are left behind. 

    How Keysight can help: 

    Use the N9048B for analog demodulation, basic IQ analysis, or as a military EMI receiver. The possibilities are endless when your receiver meets CISPR 16-1-1 and MIL-STD-461 standards. 

Keysight's N9048B Signal Analyzer for EMC Compliance Testing

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