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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2

CHAPTER 9

Ringing and Blocking Oscillators

Introduction

In Section 1 (p5) we saw how the range of a radar target is found by measuring on a c.r.t. the time interval between transmission and reception of a pulse of r.f. energy. The spot begins to move on the c.r.t. screen at the instant the transmitter fires each pulse and moves over a definite path to form a trace. The spot must move at a constant speed and reach the end of the trace after a time determined by the maximum required radar range. Reflected pulses are amplified by the receiver and used either to deflect or brighten the trace at the instant they are received. A simple type A display is illustrated in Fig 1. To ensure accuracy of range measurement we must check that the spot moves at the correct speed. Calibration markers (commonly called 'cal pips' or 'range markers') can be provided to assist in this.

Cal Pips

To calibrate any device means to 'check and correct for any irregularities'. Thus when we check to ensure that the spot is moving along the trace at the correct speed we are calibrating the display.

One method of calibration is to generate a series of very narrow pulses at intervals of exactly one radar mile (10.75 uS), and apply them to the c.r.t. so that they deflect or brighten the trace to give cal pips at the correct intervals along the trace. If the spot is moving at the correct speed


 

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