What does the use of two frequencies in secondary radar transactions eliminate?

• A. Clutter caused by direct reflections
• B. Signal loss due to rain
• C. Multipath interference
• D. Noise from the power supply

Answer: (C)

Using two frequencies in secondary radar transactions helps prevent multipath interference. Multipath occurs when the transmitted signal reaches the receiver via more than one path, creating ghost echoes or distorted ranges and bearings. In secondary radar, the interrogation and the reply use two distinct frequencies, so a true target’s response must align properly on the expected paired frequencies. A spurious path or reflection is unlikely to produce a consistent, correctly-timed reply on both frequencies, allowing the system to discriminate against these false echoes. The other options relate to clutter from direct reflections, rain-induced signal loss, or internal electrical noise, which aren’t specifically mitigated by simply using two frequencies.