IEC 61000-4-6: Immunity to RF Coupled Onto Cables
How IEC 61000-4-6, which mimics low-frequency radio signals reaching a device through its cables, is performed and why it focuses on cables.
3 min readNovember 9, 2026
Noise Spreads Through Cables Too
Part of the electrical noise a device produces radiates into the air, and part returns to the grid through the power cable. Noise returning to the grid can affect radio receivers and sensitive equipment on the same line.
Conducted emission testing measures this noise, usually between 150 kHz and 30 MHz. In this range the cable is the main path carrying the noise.
What Does a LISN Do?
Grid impedance varies from building to building and even hour to hour. To make the measurement repeatable, a line impedance stabilization network, or LISN, is placed between the device and the grid.
The LISN does two jobs: it presents a standard impedance to the device and keeps noise coming from the grid out of the measurement. The measuring receiver connects to the LISN's measurement port to read the noise the device produces.
How Is the Measurement Made?
The device is placed above the reference ground plane at the distance described in the standard, and excess power cable is bundled in a set way. A quick peak scan is done first, then detailed measurements with quasi-peak and average detectors at frequencies near the limit.
Because radio broadcasts and equipment in the surroundings raise the measurement's noise floor, the test is usually done in a shielded area. That can be the floor of a semi-anechoic chamber or a separate RF shielded room.
Problems and Fixes
The products that most often fail this test are those with switching power supplies. An inadequate input filter, or one placed in the wrong spot on the board, lets noise bypass the filter.
Separating common-mode and differential-mode noise speeds up the fix. Doing this with a LISN and spectrum analyzer during in-house pre-testing is one of the most efficient investments before certification.
Frequently Asked Questions
Can the measurement be made without a LISN?
Indicative measurements can be made with a current probe, but standards-compliant, repeatable results need a LISN.
How are three-phase devices tested?
A LISN is used for each phase or a three-phase LISN is preferred; each line is measured separately.
Are battery-powered devices exempt?
Devices that never connect to the grid usually are, but if they can operate while charging, they are tested with the charger.
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