Instruction Manual

RA51/52/53/54/55 INSTRUCTION MANUAL – 05 5

Fig.2-7 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 ap-

parent 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 re-

duce or eliminate the interference.

Fig.2-8 Radar interference

Antenna

Main beam

Side lobes

Real echo

False sidelobe

echoes

Radar inrterference