Question

Why does radiated external noise not disturb the KNX signal in symmetrical transmission?

Answer

D — Because the noise hits both wires with the same polarity, it does not change the voltage difference the device evaluates

Correct: Radiated noise affects both wires with the same polarity and so has no effect on the evaluated difference.

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All proposed choices (exam context)

A.The device filters out all AC and keeps only the DC
B.A shield connected to PE absorbs the noise before it reaches the wires
C.The noise is always at a different frequency and is simply ignored
D.Because the noise hits both wires with the same polarity, it does not change the voltage difference the device evaluates✓

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