Справочник Пользователя для Furuno 1834C-BB

2. RADAR OPERATION 

Occasionally echo signals appear on the screen at positions where there is no target or 
disappear even if there are targets. False target situations may be recognized, however, if 
you understand why they are displayed. Typical false echoes are shown below. 
 
Multiple echoes 

Multiple echoes occur when a transmitted 
pulse returns from a solid object like a 
large ship, bridge, or breakwater. A 
second, a third or more echoes may be 
observed on the display at double, triple or 
other multiples of the actual range of the 
target as shown below. Multiple reflection 
echoes can be reduced and often 
removed by decreasing the gain 
(sensitivity) or properly adjusting the A/C 
SEA control. 
 
Sidelobe echoes 

Every time the radar pulse is transmitted, 
some radiation escapes on each side of 
the beam. This stray RF is called a 
“sidelobe.” If a target exists where it can 
be detected by the sidelobes as well as 
the main lobe, the side echoes may be 
represented on both sides of the true echo 
at the same range. Sidelobes show 
usually only on short ranges and from 
strong targets. They can be reduced 
through careful reduction of the gain or 
proper adjustment of the A/C SEA control. 
 
Virtual image

 

A relatively large target close to your ship 
may show at two positions on the screen. 
One of them is the true echo directly 
reflected by the target and the other is a 
false echo which is caused by the mirror 
effect of a large object on or close to your 
ship as shown in the figure below. If your 
ship comes close to a large metal bridge, 
for example, such a false echo may 
temporarily be seen on the screen. 
Virtual image 

Own ship

Target

True
echo

Multiple 
echo

Target B
(True)

Target B
(Spurious)

Target A

True

echo

False
echo

Own
ship

Target ship

Mirror image
of target ship

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