EMC Question of the Week: March 3, 2025
Two RLCG lumped parameter models for a twisted wire pair transmission line are shown in the figure. One of them uses one R and one L value to model the resistance and inductance per unit length. The other uses separate values of R and L for each wire. The advantage of the second model (using more elements) is that it
- is more accurate
- can model unbalanced lines
- can model common mode voltages
- none of the above
Answer
The best answer is “d.” Both of these RLCG models calculate the same differential-mode propagation on the transmission line, so neither is inherently more accurate. Both models produce the same result whether the transmission line is balanced or unbalanced. Neither of them can be used to calculate the common-mode voltage, current, or any common-mode parameter.
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