Conducted Emission Testing: What Is a LISN and Why Use It?
Conducted emission testing, which measures the noise devices send back to the grid through their power cable, and the LISN that is essential to it.
3 min readNovember 10, 2026
Preparation
The product is placed on the insulating table on the turntable in the worst-case operating mode representing real use. Cables are arranged as the standard describes, and auxiliary equipment is kept outside the chamber where possible.
Before measuring, the chamber's noise floor is checked. This scan, taken with the product off, prevents signals from the environment being mistaken for the product's own.
The Pre-Scan
The first step is a fast peak scan. The turntable is turned to a few angles and the antenna is positioned at different heights in horizontal and vertical polarization. The aim is to quickly find frequencies approaching the limit.
Suspect frequencies found in the pre-scan go on a list. Since measuring the whole frequency range in detail would take hours, only these frequencies move on to the next step.
Maximization and Final Measurement
At each listed frequency, the turntable is rotated through a full turn and the antenna height is scanned to find the position of maximum emission. Small changes to cable layout can also be tried at this stage.
The final measurement is made at this worst-case position with a quasi-peak or average detector and compared with the limit. The report shows the measured value, the limit and the margin for each frequency.
Conditions for a Reliable Result
For this process to be meaningful, the chamber must be validated by NSA measurement and antennas and cables must be calibrated. A result found in an unvalidated chamber may not match the certification lab's result.
The same steps apply to teams doing pre-tests; only the time is shortened. A SAC-3 chamber lets you do all these steps in-house.
Frequently Asked Questions
How long does a radiated emission test take?
Usually several hours per product; operating modes and the number of frequency ranges add time.
Is measurement software essential?
Manual measurement is possible, but automation software greatly shortens scanning, maximization and reporting.
Who decides which mode the product is tested in?
The manufacturer defines the realistic operating mode that produces the most emission and writes it into the test plan.
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