JRC JMA-7710-6, Instruction Manual

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[II] Influence of Side Lobe
An ark with an broken line may appear in the same distance as the video by the scanner beam main
lobe. Such false echo is relatively easier to be detected when the target is isolated (see Fig. 6.4).
Fig. 6.4
[III] False Echo by Secondary Reflection
When a target exists near the own ship, two echoes, true echo and indirect echo of the same target
may appear. The true echo is caused by direct reflection from the target, and the indirect echo is
caused by secondary reflection from mast or funnel as shown in Fig. 6.5. The indirect echo appears
in the direction of the mast or funnel.
Direct radio wave path
Radar scanner
Funnel
Radio wave path
affected by secondary
reflection
True echo
Indirect echo caused by secondary
reflection from funnel
Fig. 6.5
[IV] Indirect Echo by Multiple Reflection
When there is a building or a large ship having a large vertical surface as shown in Fig. 6.6, evenly
spaced echoes caused by multiple reflection may be displayed. In this case, nearest echo is the true
echo of the target.
Fig. 6.6
6.4