EMC Question of the Week: March 5, 2018

Twisting the wires in a wire pair carrying differential-mode signals,

1. reduces differential-mode EM coupling to the circuit
2. reduces common-mode EM coupling to the circuit
3. increases the characteristic impedance
4. all of the above

Answer

The best answer is "a." Twisting a wire pair reduces differential-mode magnetic field coupling, because voltages coupled to successive twists will have alternating polarities. The same is true for differential-mode currents induced by electric field coupling.  

Twisting a wire pair generally has very little effect on the common-mode noise coupling or the characteristic impedance. 

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