AP 3302 Pt. 3
Section 2
CHAPTER 11
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.
