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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2


Frequency-Dividing & Counting Circuits

Between E and A however the diode resistance increases sharply and a trigger pulse applied during this time ‘locks’ the circuit before point A is reached. The circuit shown is triggered by every fifth input pulse, giving a count-down ratio of 5:1. Very high count-down ratios of up to 40:1 may be achieved with this circuit.

Counting Circuits

Counting circuits have two main uses in radar:

a.      As a means of measuring the pulse repetition frequency of a circuit, ie the number of regular pulses occurring per second.

b.      As a means of counting the number of random pulses which have occurred over a given period of time.

A number of circuits have been devised for these applications, including bistable multi-vibrators and gas discharge valves, but the most usual circuit arrangement uses diodes.


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