JRC JMA-5912-6, Instruction Manual

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6.4
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:
[I] 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.
[II] 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 Figure 6.5)
Figure 6.5
[III] 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 Figure 6.6.
Figure 6.6
6-9