A coded alarm consists of not less than three complete rounds of the number transmitted. Each round will consist of not less than __________ impulses.

• A. 2
• B. 3
• C. 4
• D. 5

Answer: (B)

Coded alarms convey the transmitted number by repeating it in several complete rounds, with each round made up of a sequence of impulses. To ensure the signal is reliably recognized and not confused with noise, there is a documented minimum number of impulses that must appear in every round. That minimum count provides enough pattern to be clearly identified by the receiver and to prevent misreads across rounds. Therefore, the smallest admissible count per round is three impulses. While more impulses per round can be used, the question is asking for the minimum required.