Common Mode Choke Saturation Measurement with LISN

The saturation characteristics of common mode chokes are tricky to measure directly. Using LISN, engineers can assess how 60Hz line current affects attenuation. An oscilloscope monitors line voltage on channel A, with 2ms/div and triggering at AC peaks. Current flow at the peak may reduce filter efficiency. DMRN connects LISN to channel B of the oscilloscope, matched to 50Ω. In linear range, emission increase is 6–10dB. 
Saturation boosts emissions, with full saturation possibly exceeding 40dB. The degradation factor, peak/minimum emission, quantifies the line current’s impact on filtering. Typical good filters have factors of 2–4. Influences include inductance drop from 60Hz current and rectifier behavior. Flugan used this principle to lower ballast conduction emissions.