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Page 34 Radar Installation Manual
Real echo
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Multiple
echoes
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Figure A.1.2a - Multiple Echoes
False echoes caused by side lobe
An antenna’s side lobe emissions are low power, and will not register distant targets.
However, if there is a strong reflecting target near your boat, it sometimes may appear as
a circular-arc false echo on the screen.
WARNING
When near large targets or land, your boat's mast may sometimes appear as circular-arc shaped
false echo.
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Antenna
Main beam
Side lobes
Real echo
False sidelobe
echoes
Figure A.1.2b - False Echoes caused by side lobe
Distant False echoes caused by duct phenomenon
The duct phenomenon sometimes occurs when meteorological conditions create a
temperature inversion between layers of air. When this happens, radar waves propagate
erratically and can reach a location considerably farther away from your boat than the
radar’s maximum distance range. What appears on screen is a false echo that looks to be
nearer than the actual target. Since the true echo from the distant target is outside the
measurement capabilities of the radar, its apparent distance will change when you change
ranges, and you can conclude that it’s a false echo.
Radar interference
If another boat’s radar is operating on the same frequency as yours, it can create
interference on your display. The interference usually appears as spiral or radial patterns.
This radar has an interference rejection control to eliminate interference. Turn it on to reduce