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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2


Timebase Principles


In Section 1 we saw some of the ways in which received information is displayed on a radar indicator. The type of display we use is determined by the job which the equipment is designed to do, but no matter how complicated the display may seem it is always built up by one spot of light moving rapidly over the screen of the c.r.t. (Fig 1).

In this chapter we are going to learn how the spot is made to move in the required manner. Before we do so however we shall recall a few essential facts about the action of a c.r.t. (see AP 3302 Part lB p 515).

Any c.r.t. can be divided into four main parts. These, together with their function, are illustrated in Fig 2. If the c.r.t. uses electric fields for deflecting and focusing the electron beam, we have an electrostatic c.r.t. A magnetic c.r.t. uses external coils to provide focusing and deflection. Some c.r.t.s use a combination of electrostatic focusing and magnetic deflection.

Controls are also provided so that the appearance of the picture on the screen may be adjusted. These include:


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