Question

A simple technique called the “body fade” helps with locating these things. Individuals searching for these things might use a three-element quad or yagi with a high front-to-back ratio and look for “nulls” and “peaks”. Though it was originally invented to detect lightning strikes, a system nicknamed “huff-duff” displays the location (15[1])of these things on an oscilloscope. A sport known as “fox hunting” combines orienteering with finding these (-5[1])things. During World War II, Robert (-5[1])Watson-Watt was tasked to determine if the Nazis could use one of these things as a “death ray”, which eventually led to the (*) Chain Home project. The task of finding the bearing to one of these things is simply called “direction finding”, which along with GPS is often used (-5[1])by aircraft or ships for navigation. For 10 points, antennas are used to detect signals produced by what things through amplitude or frequency modulation? ■END■ (10[3])

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