User's Manual

Chapter 3
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TRUE AND FALSE ECHOES ON DISPLAY
3.4
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FALSE ECHOES
3-5
3
INSTRUCTION MANUAL
3.4 FALSE ECHOES
The radar observer may be embarrassed with some echoes that do not exist actually.
These false echoes appear by the following causes that are well known:
3.4.1 SHADOW
When the radar scanner is installed near a funnel or mast, the echo of a target that exists
in the direction of the funnel or mast cannot appear on the radar display because the
radar beam is reflected on the funnel or mast. Whether there are some false echoes due to
shadows can be checked monitoring the sea clutter returns, in which there may be a part
of weak or no returns. Such shadows appear always in the same directions, which the
operator should have in mind in radar operation.
3.4.2 SIDE LOBE EFFECT
A broken-line circular arc may appear at the same range as the main lobe of the radar
beam on the radar display. This type of false echo can easily be discriminated when a
target echo appears isolated.(See Fig. 3.4-1.)
Fig. 3.4-1
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3.4.3 FALSE ECHO BY SECONDARY REFLECTION
When a target exists near own ship, two echoes from the single target may appear on the
radar display.
One of those echoes is the direct echo return from the target and the other is the
secondary reflection return from a mast or funnel that stands in the same direction as
shown in Fig. 3.4-2.