I have a cabel model for Spectre in form of an S parameter file.  Interestingly, it inverts at DC but not at higher frequencies.  The lowest frequency tabulated in the file is 10MHz.
Another interesting behavior is that if I feed into the line a DC unbalanced pattern (average = 20mV), out comes a DC balanced one.  Why?

What I am after is, whether my cable amplifies the DCD  from the input to the output.

What am I missing here?  How realistic is the shown transient response, if the DC response is clearly wrong?

Zoltan