Chapter1 MDP-621/641/640
General Information
Operation manual
CAUTION
When near large targets or land, your boat's mast may sometimes appear as a
circular-arc shaped false echo.
3
1
Real echo
False sidelobe
echoes
Main lobe
Side lobes
Antenna
Figure 1. 11 False echoes of radar (Caused by side lobe)
D. 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 onscreen 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. The RA51/52/53/54/55 radar has
two levels of interference rejection control to eliminate interference. Turn it on to reduce or eliminate
the interference.
3
1
HU
Radar inrterference
Figure 1. 12 Radar interference shown on the screen
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