1.   A transponder is a device that emits radar signals identifying and locating aircraft for air traffic controllers.

2.   But do they see the radar signals, too?

3.   First of all the radar signal was received and retransmitted by the Viking Lander sitting on the Martian surface.

4.   Nor are the skies above frequented by commercial airlines, which eliminates interfering radar signals.

5.   Similarly, how does a moth perceive the ultrasonic acoustic radar signals of a bat?

6.   The electronic equipment jams enemy radar signals.

7.   The radar signal that reflects back from the airplane is received by the radar dish and is electronically analysed.

8.   The radar signals were sent out in necessarily very powerful pulses, which might have damaged the highly sensitive aerials waiting for the faint returning echoes.

9.   We can think of radar signals as a series of pulses, but each pulse has a so-called carrier frequency.