EMI Debugging with Spectrum Analyzers
Precompliance, as well as debugging tests, are most commonly done with the help of a spectrum analyzer or an oscilloscope. The approach and diagnostic techniques of oscilloscopes were discussed in the last article.
This article’s focus is on spectrum analyzers. With built-in CISPR detectors, they offer advanced functions that can simplify EMI debugging. For debugging and locating emission sources using a spectrum analyzer, the R&S®FPC1000 (187-3723) and R&S®FPC1500 (187-3725) spectrum analyzers offer outstanding performance. Together with the R&S®HZ-17 near-field probe set, this is an excellent solution used for locating the source and EMI debugging. The R&S®HZ-16 preamplifier improves measurement sensitivity up to 3 GHz, with approx. 20 dB gain and a noise figure of 4.5 dB.
Benefits & Limitations
The R&S®FPC1500 spectrum analyzer is an affordable, multipurpose instrument. Providing features of a spectrum analyzer, a signal generator and a network analyzer, it is perfect for EMI precompliance measurements. Besides, the instrument is suitable for general development, debugging and verification of electronic designs. A spectrum analyzer offers EMI-specific detectors (quasi-peak, CISPR-average), can easily measure very low amplitudes and high frequencies. Besides, the instruments offer longer gapless recording and wide dynamic ranges for detecting small signals in the vicinity of large signals. Another benefit is the availability of a dual-logarithmic axes display and a documentation PC software. However, a spectrum analyzer is not as versatile and more expensive compared to an oscilloscope.
Radiated & Conducted Emissions
By testing radiated emissions, you measure the electromagnetic field strength of unintentional emissions generated by your products. These emissions are inherent to any electrical circuit. The R&S®FPL high-end as well as the R&S®FPH handheld spectrum analyzers are a good choice for locating the source of unwanted emissions.
EMI measures comprise not only radiated emissions but also conducted emissions propagating towards the mains supply. In order to test conducted emissions, you can use the R&S®FPC1000 and the R&S®FPC1500 spectrum analyzers to analyze the level of RF energy coupled to the mains supply. This, however, requires the RF signal to be separated from the mains supply and stabilized to 50 Ω. This is achieved using a line impedance stabilization network.