What indicates a properly functioning two-wire line?

• A. Continuous, clear audio with no excessive noise when speaking; the line remains complete during talk.
• B. Intermittent buzzing noise regardless of speaking.
• C. The line shows occasional crackling only when other lines are active.
• D. The line is loud but with delay.

Answer: (A)

In a two-wire line, the signal path must stay a continuous, closed circuit while you talk. When the line is working properly, speech comes through clearly and steadily with no extra noise, and the line remains complete without drops. That uninterrupted, clean audio shows the line is properly terminated and not suffering from open circuits or high resistance.

If you hear buzzing that appears regardless of whether you’re speaking, that points to a fault such as a loose connection or a nearby short. Crackling that only happens when other lines are active suggests cross-talk or poor shielding, not a healthy pair. A loud signal with delay indicates the line is loading or capacitively coupled in a way that slows or distorts transmission. So the best indication of a properly functioning two-wire line is continuous, clear audio with the line remaining complete during talk.