Basic Radar Theory; Side-Lobe Echoes; Indirect Echoes - Icom MR-1200RII Instruction Manual

7

BASIC RADAR THEORY

Radar uses a form of electromagnetic radiation which, like light, can be reflected. Because of this property, some
objects may cause false echoes on the screen where in fact no targets actually exist.
These echoes may appear if a large vessel, bridge, or other metal object is in proximity. Operators should be famil-
iar with the effect of this phenomena. In some cases, echoes can be reduced.

■ Side-lobe echoes

Radiation can escape on each side of the beam inside
the lobes. 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
ship, or returned from a reflecting surface, such as a
mast on your own ship.
Scanner
Mast or
similar obstruction
Target
Bridge
25
Main beam
Side lobes
Target
Your ship
An echo is reflected at this point.
Side-lobe 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 9 for 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