How do you run EMC precompliance tests?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

Precompliance testing estimates EMC performance before formal testing at an accredited laboratory. Typical tools are a spectrum analyzer or EMI receiver with CISPR bandwidths and detectors, near-field H- and E-field probes, a line impedance stabilization network (LISN) for conducted emissions, a current probe for cable common-mode current, and an antenna for radiated scans in a quiet location or small chamber.^[1]^[2]

How are near-field probes used?

Probes locate sources such as clock lines, switching regulators and poorly decoupled ICs by scanning the board and cables. Near-field readings do not translate directly into far-field compliance, but changes before and after a fix show improvement.^[3]

How are conducted emissions measured?

A LISN (per CISPR 16) provides a defined 50 Ω/50 µH impedance on each power line from 150 kHz to 30 MHz and couples the noise to the analyzer. Use a transient limiter to protect the analyzer input.^[2]

How does cable current predict radiation?

Measuring common-mode current with a clamp-on current probe and applying Paul’s cable-radiation estimate gives a rough field-strength prediction; a few µA at 100 MHz on a 1 m cable can approach Class B limits.^[4]

Frequently asked questions

Do I need a chamber for precompliance?

Not necessarily; probes, LISNs and open-area scans catch most problems, though ambient signals complicate radiated scans.

What margin should precompliance show?

Many teams aim for about 6 dB below limits to cover measurement uncertainty.

Can a spectrum analyzer replace an EMI receiver?

For precompliance, with CISPR bandwidths and quasi-peak detection, often yes.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“EMI/EMC test receiver and precompliance application notes”. Rohde & Schwarz. application note.
“CISPR 16-1-1: Specification for radio disturbance and immunity measuring apparatus and methods — Measuring apparatus”. IEC / CISPR. current edition.
“Electromagnetic Compatibility Engineering”. H. W. Ott, Wiley. 2009.
“Introduction to Electromagnetic Compatibility, 2nd ed.”. C. R. Paul, Wiley. 2006.

Categories: EMC and EMI

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