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# Using 4395A to obtain characteristic impedance vs. frequency

Question asked by jpbledsoe001 on Jun 14, 2011
Latest reply on Aug 4, 2011 by Tisfurs
I used a 4395A to obtain impedance data over a range of frequencies for an unknown length of shielded-twisted-pair cable:

1. Impedance with the other end open and
2. Impedance with the other end shorted

Then, I tried to estimate Zo at each frequency using sqrt(L/C). However, both real and imaginary data have positive values at some frequencies and negative values at other frequencies. At first I thought the open-circuit imaginary values should all be negative because of the parallel capacitance. Then, I noticed some of the open-circuit imaginary values are positive in sign. Ditto with the short-ckt imaginary values and real values for both short and open-ckt cases.

How should I treat the negative versus positive values of R and X for both open and short-ckt cases?

Again, my goal is to find Zo across a range of frequencies. It would be great to obtain Zo in the form of R + jX.

Can the 4395A do all the math (post-processing I've been struggling with in Excel due to the sign issue) and provide Zo versus frequency in a data file?

Thanks,

Jeff