magnitude is proportional to the deviation from the
The base frequency is much lower than the trans-
correct IF, and the polarity determines the direction of
mitted frequency and is multiplied and mixed at dif-
the error. The error voltage corrects the frequency of
ferent levels. Since the local oscillator signal is picked
the local oscillator common to both the receiver mixer
off at the appropriate level, it is locked to the trans-
and the AFC mixer Many of the newer radar systems
mitter frequency without an AFC system. This also
eliminate the requirement for the AFC system by
allows frequency diversity and agility with each trans-
fusing a special coherent frequency generator system.
mitted pulse, which an AFC circuit could not track.
Figure 2-11.Radar receiver general functions.