2-2
SYNCHRONIZER FUNCTION
The specific function of the synchronizer is to produce TRIGGER PULSES that start the transmitter,
indicator sweep circuits, and ranging circuits.
Timing or control is the function of the majority of circuits in radar. Circuits in a radar set
accomplish control and timing functions by producing a variety of voltage waveforms, such as square
waves, sawtooth waves, trapezoidal waves, rectangular waves, brief rectangular pulses, and sharp peaks.
Although all of these circuits can be broadly classified as timing circuits, the specific function of any
individual circuit could also be wave shaping or wave generation. The operation of many of these circuits
and associated terms were described in detail in NEETS, Module 9, Introduction to Wave-Generation and
Wave-Shaping Circuits.
Q1. What is the purpose of the synchronizer in a radar system?
Q2. What is the purpose of the majority of circuits in a radar system?
SYNCHRONIZER OPERATION
Radar systems may be classified as either SELF-SYNCHRONIZED or EXTERNALLY
SYNCHRONIZED systems. In a self-synchronized system, the timing trigger pulses are generated in the
transmitter. In an externally synchronized system, the timing trigger pulses are generated by a MASTER
OSCILLATOR, which is usually external to the transmitter.
The master oscillator in an externally synchronized system may be a BLOCKING OSCILLATOR, a
SINE-WAVE OSCILLATOR, or an ASTABLE (FREE-RUNNING) MULTI-VIBRATOR. When a
blocking oscillator is used as a master oscillator, the timing trigger pulses are usually obtained directly
from the oscillator. When a sine-wave oscillator or an astable multivibrator is used as a master oscillator,
pulse-shaping circuits are required to form the necessary timing trigger pulses. In an externally
synchronized radar system, the pulse repetition rate (prr) of the timing trigger pulses from the master
oscillator determines the prr of the transmitter.
In a self-synchronized radar system, the prr of the timing trigger pulses is determined by the prr of
the modulator or transmitter.
Associated with every radar system is an indicator, such as a cathode-ray tube, and associated
circuitry. The indicator can present range, bearing, and elevation data in visual form so that a detected
object may be located. Trigger pulses from the synchronizer are frequently used to produce gate (or
enabling) pulses. When applied to the indicator, gate pulses perform the following functions:
1. Initiate and time the duration of the indicator sweep voltage
2. Intensify the cathode-ray tube electron beam during the sweep period so that the echo pulses may
be displayed
3. Gate a range marker generator so that range marker signals may be superimposed on the indicator
presentation
Figure 2-1 shows the time relationships of the various waveforms in a typical radar set. The timing
trigger pulses are applied to both the transmitter and the indicator. When a trigger pulse is applied to the
transmitter, a short burst of transmitter pulses (rf energy) is generated.
