[TowerTalk] Measuring Common Mode Choke with Anritsu VNA

[Paul Christensen]

>"So why strive for measurement accuracy that has little direct relevance to most real-world installations?"

For me, the answer is in understanding the measurement limitations in order to determine what's "good enough."  Without understanding the limitation, then we are in a guessing game with ourselves.  

I think it's more important to know why a DUT measures as it does rather than seek a specific Z value.  At a minimum, we should be able to answer: (1) why SRF changes with the number of turns through a ferrite core; (2) why complex Z is important and not only Z magnitude; (3) why small distributed capacitance affects measurement accuracy, particularly as F increases; (4) and why physical layout is important and what means can be employed to minimize the adverse effects to CM choking resistance in its operating environment (e.g., placed inside a metal enclosure.)       

So, if one elects to use S11 instead of S21, and understands the above, then achieving a less than ideal result can lead to a "good enough" outcome. 

Paul, W9AC