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.
Source
KNX Basic Course Documentation — 9 — p. 50
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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