Seiwa SWRx series - Manual (Page 50)

52 User Manual
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Antenna
Main beam
Side lobes
Real echo
False sidelobe
echoes
Fig. A.2.3.3 - False Echoes caused by side lobe
A.2.3.4 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.
A.2.3.5 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 interfer-
ence. Turn it on to reduce or eliminate the interference.
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Radar interference
Fig. A.2.3.5 - Radar interference