Transponder provides _____ watts to appropriate antenna when responding to interrogations.

• A. 1000 watts
• B. 500 watts
• C. 250 watts
• D. 50 watts

Answer: (B)

When a transponder answers a radar interrogation, it sends back a coded reply with enough strength to be reliably detected by the aircraft’s radar across the intended surveillance range. The output to the antenna is designed to be high enough to cut through noise and headroom variations in range and radar sensitivity, yet not excessive. In practice, the transponder’s power delivered to the antenna during a reply is in the hundreds of watts range. This level provides a stable, observable return for ATC radar without wasting power or causing unnecessary RF interference. If the power were too low, the reply could be missed; if it were much higher, it would be unnecessary and could raise issues with heat and interference.