Red Seal Electrician Practice
Signalling and communicationQuestion 42 of 1506

A long run carries a serial signal. Why is a differential voltage signal better than a signal referenced to common ground?

  1. It raises the signal voltage above the noise level by a fixed amount at the sender
  2. Noise on both wires is ignored; only the difference counts
  3. It turns the signal into a sine wave, which needs no receiver at all
  4. It ties each wire to ground so that any noise drains away to earth
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Correct answer: Noise on both wires is ignored; only the difference counts

The differential receiver rejects noise that is common to both wires.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 14.4: Electrical Signal Types

Practice signalling and communication

Questions last reviewed: 18 October 2026