Raymarine Pathfinder - Manual (Page 84)

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Blind sectors or shadow effect
Obstructions such as funnels and masts near the radar antenna may
obstruct the radar beam and cause radar shadows or ‘blind sectors’. If the
obstruction is relatively narrow, there will be a reduction of the beam
intensity, though not necessarily a complete cut-off. However, for wider
obstructions there may be a total loss of signal in the shadow area. There
may also be multiple echoes which extend beyond the obstruction. Blind
sector effects can normally be minimized by careful selection of the scanner
site prior to installation.
Sea clutter
Radar returns from waves around the boat can clutter the center of the
radar picture, making it difficult to detect real targets. Such ‘sea clutter’
usually appears as multiple echoes on the display at short range scales.,
and the echoes are not repetitive or consistent in position. With high winds
and extreme conditions, echoes from sea clutter may cause dense back-
ground clutter in the shape of an almost solid disc.
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Multiple echoes
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Rain clutter
The radar can see echoes from rain or snow. ReTurns from storm areas and
rain squalls consist of countless small echoes that continuously change
size, intensity and position. These returns sometimes appear as large hazy
areas, depending on the intensity of the rainfall or snow in the storm area.
Interference
When two or more radar-equipped boats are operating within range of
each other, mutual radar interference can occur. This usually appears as a
spiral of small dots from the display center. This type of interference is most
noticeable at long ranges.
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