Impedance stabilization networks (ISN, or with CISPR 16-1-2 called AAN: asymmetric artificial network) are defined for measuring of conducted common mode disturbances at information technology equipment (ITE) as required in CISPR 22 and CISPR 32. The ISN is placed between the equipment under test (EUT) and auxiliary equipment (AE) or load which are necessary for the operation of the EUT. The ISN establishes the common-mode termination impedance for the EUT’s telecommunications port during measurement and emulates the unsymmetrical contribution (longitudinal conversion loss, LCL) of the connected line. Different ISNs are available in relation to the line category, line numbers and pin-arrangement.

The ISN T4A is designed for measurements on one or two unscreened balanced pairs and consists of one basic network (ISN T400A) with D sub 25 connectors and special adapter sets. A set of adapters consists of LCL adapters to realize the longitudinal conversion loss (LCL)- requirements for the EUT-side in relation to the used cable category (cat. 3, cat. 5) and a connection adapter for the AE-side.