Basic Radar Theory; Sidelobe Echoes; Indirect Echoes - Icom MR-1210RII Instruction Manual

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BASIC RADAR THEORY

Radar uses a form of electromagnetic radiation that can be reflected off a large vessel, bridge, or other metal ob-
jects that are in proximity. Because of this property, unwanted reflections off some objects may cause false echoes
to appear on the screen where in fact no actual targets exist. Operators should be familiar with the effect of this
phenomena. In some cases, echoes can be reduced.

■ Sidelobe echoes

Radiation can escape on each side of the beam inside
the sidelobes. If a target reflects this radiation, it will be
displayed on the screen as an echo.

■ Indirect echoes

Indirect echoes may be returned from either a passing
vessel, or returned from a reflecting surface, such as a
mast on your own vessel.
Scanner
Mast or
similar obstruction
Target
Bridge
39
Main beam
Sidelobes
Target
Your ship
An echo is reflected at this point.
Sidelobe echoes usually occur at short ranges and
as a result of large (strongly reflective) targets. They
can be reduced with proper adjustment of the [SEA]/
[ ] control.
See page 18 for details of the [SEA]/[
False
echoes
An indirect echo from a reflective surface will appear
on a different bearing from the direct (true) echo, but
the distance will be approximately the same for both.
True echo
Indirect echo
] control.
True
echo
True echo
False echo