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EMI Debugging & Pre-compliance Tests: Oscilloscope or Spectrum Analyzer?

Different test equipment for EMI tests

EMI debugging revolves around a simple idea – to have a convenient and affordable setup that can be used during product design for verification and early detection of po­tential problems. Each step of the product development process requires continuous EMI testing that can be performed by different types of test equipment. Most commonly debugging and pre-compliance tests are done with the help of a spectrum analyzer or an oscilloscope with near-field probes.

Oscilloscope versus spectrum analyzer

Oscilloscopes together with spectrum analyzers offer a wide range of diagnostic techniques that can be helpful during any stage of the product developmental cycle – ensuring that the product successfully passes full EMC compliance testing, making it ready for market on time, without investing in additional equipment.

If you are looking to perform EMI pre-compliance tests up to 3 GHz, Rohde & Schwarz offers a portfolio of instru­ments dedicated to cost-efficient EMI testing and debug­ging. The instruments tackle EMI problems from various perspectives. Each instrument category offers a different approach and diagnostic techniques that can complement each other at different stages of the product development cycle.

What are the advantages of using oscilloscopes?

Oscilloscopes are typically already available at the R&D engineer’s bench. Therefore oscilloscopes are often considered as an economically sensible tool. Their ability to perform EMI debugging tasks provides a more cost-effective solution that eliminates the need for additional equipment. State-of-the-art oscilloscopes are ideal tools for EMI debugging because they are able to transform signals from the time domain into the frequency domain (by fast Fourier transform (FFT)). The combination of synchronized time domain and frequency domain analysis with advanced triggers allows quick insight into EMI problems. Besides, EMI debugging with an oscilloscope enables correlation of interfering signals with time domain events. Oscilloscopes can easily detect electromagnetic interference from electronic circuits with high speed and accuracy. The basic working principle of an oscilloscope is to capture sig­nals when the input signal exceeds a specific trigger value, which helps to capture the peaks of the noise signal.

What are the advantages of using spectrum analyzers?

Spectrum analyzers are commonly used in pre-compliance test setups. With built-in CISPR detectors, they offer ad­vanced functions that can simplify EMI debugging. Compared to the use of an oscilloscope, it is much more cost-intensive and a spectrum analyzer is not as versatile. However, there are also some important benefits using a spectrum analyzer. A spectrum analyzer can easily measure very low amplitudes and high frequencies. Spectrum analyzers offer longer gapless recording and provide wide dynamic ranges for detecting small signals in the vicinity of large signals. Besides, spectrum analyzers offer EMI-specific detectors (quasi-peak, CISPR-average). Apart from that, there is a dual-logarithmic axes display available.

Rohde & Schwarz is a high-tech company that thrives on innovation. To maintain its high quality standards, Rohde & Schwarz keeps almost the entire value chain within the company while the majority of products are developed in Germany. The Munich based technology group develops, produces and sells a wide range of electronic capital goods for industry and government customers with a focus on solutions that contribute to a safer and connected world.

28 Jan 2020, 14:17