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On November 11th, 2009, the VCCI Council of Japan issued notice describing the restrictions on the use of Impedance Stabilization Network (ISN) to be used for the measurement of telecommunication ports conducted EMI. Although this information is published in the current CISPR standard, the VCCI Council will only begin to deal with the filing of reports on telecommunication port conducted emission from April 2010. Currently, a great deal of confusion abounds on the proper selection of the ISN for telecom measurements. This notice helps to clear up some of that confusion.
As implied, the document describes the acceptable types of ISN, suitable for the measurement of telecom line conducted EMI. Most notably, the document comes with warning notes about using certain types of ISNs with certain quantity of balanced pairs. Get a copy of the notice.