What main feature distinguishes primary radar from secondary radar?

• A. Primary radar uses signals reflected off surfaces
• B. Secondary radar requires active transponders
• C. Primary radar has a longer range
• D. Secondary radar is less accurate

Answer: (B)

The distinguishing feature of primary radar is that it relies on radio waves that are transmitted from the radar system, which then reflect off objects, such as aircraft or terrain, back to the radar receiver. This fundamental principle allows primary radar to detect the presence and location of objects within its operational range without requiring those objects to emit any response.

On the other hand, secondary radar operates differently; it relies on active transponders present on the aircraft. These transponders respond to queries or signals sent by the radar system and send back specific information, such as altitude and identification. This interaction not only enhances the detection capability but also provides additional data that is not available through primary radar alone.

While primary radar can have a longer range, depending on its design and operating frequency, that is not the defining characteristic that sets it apart from secondary radar. Similarly, the accuracy of secondary radar is typically higher because it receives specific information directly from the aircraft, making option B the main feature that differentiates the two types of radar systems.