Reference Manual Part 2

G-Series Reference Manual 132
• Side lobes
• Indirect echoes
• Multiple echoes
• Blind sectors
• Sea, rain or snow clutter
• Interference
Through observation, practice, and experience, you can generally
detect these conditions very quickly and use the radar controls to
minimize them.
Side lobes
Side lobe patterns are produced by small amounts of energy from
the transmitted pulses that are radiated outside the narrow main
beam.
The effects of side lobes are most noticeable with targets at short
range (normally below 3 nm) and with large objects. Side lobe ech-
oes form either arcs on the radar screen similar to range rings, or a
series of echoes forming a broken arc.
Indirect echoes
There are several types of indirect echoes, or ‘ghost’ images.
These sometimes have the appearance of true echoes, but in gen-
eral they are intermittent and poorly defined.
Multiple echoes
Multiple echoes are uncommon but can occur if there is a large
object with a wide vertical surface at a comparatively short range.
The transmitted signal bounces between the object and your own
vessel, producing multiple echoes. The false echoes are displayed
beyond the range of the true target echo, but on the same bearing.
Blind sectors
Obstructions such as funnels and masts near the radar antenna
can obstruct the radar beam and cause radar shadows or ‘blind
sectors’.
True echo Side echoes
Main lobe
Antenna
Arc
Side
lobe
Side
lobe
D1638-4
False echo
Passing
ship
True echo
D1641-4
True echo
False echo
Mast
or funnel
D1642-3
True echo
Multiple echoes