CR40
42
/50 MKII Radar operation
Chapter 7
86
7.1.8 Side lobes
Echoes on the radar screen are not always the direct returns to the radar
antenna. There are many types of false echoes that can appear on the
display if certain conditions occur. The sections that follow, briefly
describe the echo patterns that may be produced by these false echoes
and their likely cause. It should be noted that the radar operator,
through observation, practice, and experience usually can detect these
conditions very quickly.
A very small part of the RF (Radio Frequency) energy from each trans-
mitted pulse is radiated outside the radar’s narrow beam, producing
side lobe patterns. Side lobes normally have no effect from distant or
small surface objects, but the echo from a large object at short range
may produce an arc pattern on the radar screen similar to a range ring,
or appear as a series of echoes forming a broken arc. Side lobe echoes
normally occur at a range below 3 miles and usually can be reduced by
adjustment of the SEA clutter control.
7.1.9 Radar interference
Whenever two or more radar equipped vessels are operating within
reception range of each other, mutual interference is likely when the
radars are operating near the same frequencies. This interference
usually appears on the screen as a series of small dots. The interference
seems to move from the PPI center (radar screen), sometimes in a
straight line, but more often in a long, sweeping curve. This type of
interference is more noticeable on longer range scales. This does not,
as a rule, impair the effectiveness of the radar as a navigational aid.
Since the interference can be completely eliminated by turning IR
“ON” in the function menu. The IR feature is normally left “on”.
7.1.10 False echoes
Occasionally, echoes may appear on the screen at positions where there
is no actual target. This type of target is called a False Echo.
Sometimes they are known as Ghost Images, Indirect Echoes or
Multiple Echoes depending on how they are generated.
Ghost images usually have the appearance of true echoes, but, in gene-
ral, they are intermittent and poorly defined. A true ghost image retains
