Raymarine e7 User Reference page 138

The table below shows typical maximum radar ranges for various
radar antenna heights and target heights. Remember that although
the radar horizon is greater than the optical horizon, the radar
can only detect targets if a large enough target is above the radar
horizon.
Antenna height Target height
(meters) (meters)
3 3
3 10
5
3
5 10
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 or
missing 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.
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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
Maximum range
similar to range rings, or a series of echoes forming a broken arc.
(Nautical miles)
7.7
10.9
8.8
12
Item
1
2
3
4
5
6
1
4
2 2
3
6
5
6
Description
Main lobe
Side lobes
Antenna
Arc
True echo
Side echoes
e7 / e7D — User reference
D1638-5