120 Ohm Cabling

A not so common question these days is whether the DSP-4x00, DTX or DSX CableAnalyzers can measure 120 Ω cabling. The answer is yes, but don't expect Return Loss to pass. This is because the DSP-4x00, DTX CableAnalyzer and DSX CableAnalyzer are IEC 61935-1 compliant, which requires the testers to be terminated with a 100 Ω circuit. Going from 100 Ω in the tester to 120 Ω cabling will cause a significant reflection of the signal (Return Loss).
 
There was a conflict in the standards between ISO/IEC 11801:2002 and IEC 61156-5. ISO/IEC 11801:2010 clarified this better with:

ISO/IEC 11801:2010

9.2.2.3 Characteristic impedance
Refer to 6.3.10 of IEC 61156-5:2009, measured according to 6.3.10.1.1 of IEC 61156-1:2007, on a standard length of 100 m. The nominal impedance shall be 100 Ω.