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# Note for Radar System - RS By Anju A Chandran

• Note
• Electronics and Communication Engineering
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Anju A Chandran
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Figure-1      The Chronometer: A chronometer is a clock that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation. When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage is necessary for navigation, lacking electronic or communications aids. The first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval (and later aerial) navigation and enabling the Age of Discovery and Colonialism to accelerate. Figure 2 shows the Chronometer. Figure-2 Department of Electronics & Communication, DIET, Rajkot BE Sem 8, 181103, Lecture B.1 Page 2

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 The Sextant:  A sextant is an instrument used to measure the angle between any two visible objects.  Its primary use is to determine the angle between a celestial object and the horizon which is known as the object's altitude.  Using this measurement is known as sighting the object, shooting the object, or taking a sight and it is an essential part of celestial navigation.  The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart.  Figure 3 shows the Sextant. Figure-3  The Theodolite:  A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes.  Theodolites are used mainly for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology.  A modern theodolite consists of a movable telescope mounted within two perpendicular axes—the horizontal or trunnion axis, and the vertical axis.  When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc.  Figure 4 shows the Theodolite. Figure-4 Department of Electronics & Communication, DIET, Rajkot BE Sem 8, 181103, Lecture B.1 Page 3

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 Magellan circumnavigated the Globe in the early sixteenth century with the aid of listed instruments.  In eighteenth century the Chronometer, a very accurate clock, was produced.  With the chronometer the navigator was able to determine his longitude by noting the transit time.  Navigation became science as well as art.  In twentieth century, electronics entered the field.  Time signals were broadcast by which the Chronometers could be corrected.  Direction finders and other navigational aids which enable the navigator to obtain a fix using entirely electronic aids were developed and came into extensive use.  Our aim is to study about all navigational aids which employ electronics in some way.  To start with a brief account of other methods of navigation. Other Reading: 1. http://en.wikipedia.org/wiki/Compass 2. http://en.wikipedia.org/wiki/Chronometer 3. http://en.wikipedia.org/wiki/Sextant 4. http://en.wikipedia.org/wiki/Theodolite Department of Electronics & Communication, DIET, Rajkot BE Sem 8, 181103, Lecture B.1 Page 4