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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

(Fig 2a) the cal pips line up exactly with the mile markings on the fixed range scale. If they do not line up (Fig 2b and c) the circuits which control the spot movement (i.e. the timebase circuits) need to be adjusted.

In Fig 2 the maximum range of the equipment is shown as only five miles and cal pips at intervals of one mile range are convenient for calibrating the display. If the maximum range is 100 miles, 100 cal pips along a few inches of trace would be confusing; it is then more convenient to have markers at, say, 10-mile intervals.

Many radar equipments have more than one range. Thus when switching from one range to another the time intervals between cal pips must also be changed to avoid cluttering up the display with too many cal pips at the longer ranges.

In the type A display the cal pips deflect the trace to give blips. In intensity-modulated displays the cal pips are applied to the control grid or the cathode of the c.r.t. to produce bright spots on the screen. In a p.p.i. display, where the trace is rotating, the bright spots form calibration rings on the face of the c.r.t. (Fig 3).

Cal pips can also be used to measure the pulse duration of a square wave (Fig 4). The wave-form being examined and the cal pips are applied together to an oscilloscope. The period and pulse duration of the waveform are then found simply by counting the cal pips. Knowing the time interval between successive cal pips, the other factors follow.


 

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