AP 3302 Pt. 3
Section 1
CHAPTER 2
Basic Requirements Of A Pulse-Modulated Radar System
Secondary radar may also be used as a navigational aid. In this role the interrogator is carried in the aircraft and the transponder is a radar beacon on the ground. The signals transmitted by the transponder when interrogated by the aircraft equipment are used by the aircraft to provide information on the range and bearing of the beacon. In this way a required landing ground may be located.
The operation is basically the same in each case. The block diagram of a typical system is shown in Fig 14. Each pulse from the interrogator is picked up by the transponder aerial and passed to the receiver where it is amplified and converted to a d.c. pulse. This pulse triggers the modulator which produces a waveform to switch the transponder transmitter on and off. A coding unit may be used to regulate the duration of the transponder pulse, this pulse being radiated back to the interrogator where it is used to provide the required information about the 'target'.
