The same page with parallax. Page 852. [C16: from Gk, from paralellos (italic) PARALLEL + epipedon (italic) plane surface, from EPI- + pedon (italic) ground]
Radio waves are electromagnetic radiation, usually referring to frequencies 300 GHz and below. Higher frequencies of electromagnetic radiation are things like visible light, x-rays, and gamma rays.
Question for you: how does a radar detect its own return signals while sending high-energy outbound signals? I think of an analogy like shouting really loudly over and over but never hearing whether anyone acknowledges you because you can't over the sound of your own voice. Does the Doppler effect of a detected object change the frequency enough for the radar to distinguish? Or, perhaps the in/out signals are brief enough as to be out of phase so that a computer can tell them apart? How did it work with early radar systems? Great video! 👍
Great question! And I love the analogy! You’re absolutely right that trying to “shout and listen” at the same time doesn’t work very well. In fact, trying to transmit a high-power RF pulse while the sensitive receiver circuit is active could destroy it. For that reason, your basic monostatic radar system uses a “duplexer” to switch the antenna between transmitting or receiving, so it’s only in one mode at any given time. After transmitting a pulse, the radar needs to wait sufficiently long to listen for return signals before transmitting again. This period is called the Pulse Repetition Interval (PRI).
@@barronstone To add to Barron’s comments, some less basic radars will transmit and receive at the time, known as Continuous Wave (CW) radars. They do this by spatially separating the transmitting and receiving elements. A basic example of this is MIT’s Coffee Can Radar design, where one coffee can monopole antenna is used as a transmitter and another as a receiver, about half a foot apart from one another. More advanced examples are phased array radars where different elements will be transmitting and receiving at the same time. These phased arrays will send out ‘chirps’, where the continuous wave steps up and down different frequencies over time (known as a Frequency Modulated Continuous Wave radar). For military applications this is used in Non-Cooperative Target Recognition (NCTR).
