Raymarine C140w - Manual (Page 102)

Antenna height
(meters) Target height
(meters) Maximum range
(Nautical miles)
5 10 12
Radar image quality
A number of factors can affect the quality of a radar image, including
echoes, sea clutter, and other interference.
Not all radar echoes are produced by valid targets. Spurious echoes
may be caused by:
• 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 ranges (normally below 3 nm), and in particular with larger
objects. Side lobe echoes form either arcs on the radar screen
similar to range rings, or a series of echoes forming a broken arc.
True echo Side echoes
Main lobe
Antenna
Arc
Side
lobe Side
lobe
D1638-4
Indirect Echoes
There are several types of indirect echoes or ghost images. These
sometimes have the appearance of true echoes, but in general they
are intermittent and poorly defined.
False echo
Passing
ship
True echo
D1641-4
True echo
False echo
Mast
or funnel
102 C-Series Widescreen user reference