EMI Troubleshooting: The Need for Close Field Probes
Far field testing has limitations. It cannot identify the source of emissions. Radiated
emissions may come from a USB port, a LAN port, the seam of a shield, a cable, or even a power
cord. Close field testing is the only way to locate the exact source of the emission and is typically
performed using a signal analyzer and close field probe. Close field testing is a relative test, meaning
a comparison of the radiator’s results to the rest of the device’s results can help you address where
redesign work is required. It should be noted that comparing close field test results with EMI standard
test limits is meaningless because a number of factors can affect the test readout, like the probe
position and DUT shape.
Close field EMI testing is a valuable tool in EMC radiated emissions pre-compliance testing. To
perform this testing, a variety of close field probes are used based on their distinct advantages for
locating, evaluating, and troubleshooting potential emission sources.
For a complete EMI test solution, Keysight offers the N9311X-100 close field probe set and X-Series
signal analyzers, combined with the EMI measurement application software. It is a valuable EMI
pre-compliance measurement solution, while offering a range of signal analyzer models to meet
your performance and budget requirements: from the high-performance PXA, through the mid-
performance MXA and EXA, to the very cost-effective CXA.
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