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Using a VNA to Determine Source of Crosstalk

Question asked by sugarglider on Aug 26, 2007
Latest reply on Aug 26, 2007 by sugarglider

I have a question concerning measuring crosstalk between adjacent balanced pair channels. In particular, the DUT I am working with consists of 2 x 100 ohm twisted pair channels. I match the VNA to the DUT using baluns. All ends of both circuits are properly matched, for both common and differential mode, either by the test equipment or by passive terminations. I have access to both the common mode and differential mode ports on the baluns.

I measure crosstalk (near-end and far-end) by making the appropriate connections to the DUT and sweeping S21 across the frequency range of interest. This gives me a plot of crosstalk vs frequency.

Now my question is this - how can I determine where along the channel significant levels of crosstalk are introduced? Or put another way, can I somehow obtain a plot from the VNA which shows the level of crosstalk being induced vs distance from, say, the send end? I use an 8753A VNA which has option 010. I have more modern VNA's but these do not have the time domain option. Will a time domain plot of S21 give me this, or is there some other way?

Thanks in advance for any advice on this.

George G