LISNs

Line Impedance Stabilization Network (LISN) is a specialized RF impedance network used in electromagnetic compatibility (EMC) testing to measure conducted emissions from electrical and electronic devices. It is placed between the equipment under test (EUT) and the mains supply to provide a defined RF impedance and a stable measurement port for an EMI receiver, enabling repeatable assessments of RF noise that travels onto the power lines.

A LISN typically consists of a mains inlet, a network that presents a controlled RF impedance to the EUT, and a measurement path that connects to an EMI receiver. It isolates RF signals on the mains from the laboratory power network while presenting a known impedance to the measurement port, usually 50 ohms, over the test frequency range. The unit usually includes shielding, protective earth connections, and standard connectors for line, neutral, and the measurement port. The RF path is filtered to prevent RF from propagating back into the power source while allowing the EMI receiver to capture the EUT’s emissions.

In practice, LISNs are used to measure conducted emissions in accordance with standards such as CISPR 16-1-2 and its national adoptions (for example EN 55022). The EMI receiver is connected to the LISN’s measurement port, and measurements are made for line-to-ground and line-to-line emissions over the specified frequency range, typically from about 9 kHz up to 30 MHz. Results are reported as voltage levels on the LISN port and compared with regulatory limits.

There are single-phase and multi-line LISNs for different test configurations, with variations including calibration ports and different impedance networks. Proper calibration and adherence to the relevant standard are essential for accurate, repeatable results.