A coded alarm requires not less than three complete rounds of the transmitted number. Each round not less than how many impulses?

• A. One impulse
• B. Two impulses
• C. Three impulses
• D. Four impulses

Answer: (C)

In coded alarm signaling, a round is a complete transmission of the coded number, and the system repeats that round to ensure reliability. Each round needs a clear, distinct pattern so the receiver can recognize and count it correctly. Having at least three impulses in a round provides a definite rhythm and separation from noise, making it easy to identify where a round starts and ends. Because the signal must be repeated not less than three times, the minimum total pattern is three rounds with three impulses per round, totaling nine impulses. Using more impulses per round would still meet the requirement, but the minimum per round is three.