Installation Instructions

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case, some objects produce a complete shadow and some produce a partial shadow. In
an extreme case, the shadow of an object may extend to a position far away and can-
not be displayed on the screen at all. Since these shadows can be discovered when in-
stalling an antenna, the problem can be avoided by changing the place of antenna in-
stallation to minimize the shadow. Targets in shadow zones are difficult to display on
the screen.
False echoes
A false echo of an actually nonexistent object may sometimes appear on the
screen when sailing. The following explains the cause of each of such phenomena.
A. Ghost echoes
It sometimes happens that one large object near the ship appears at two different
bearings. One is the actual echo and other is a ghost echo generated as the wave is re-
reflected from the ship's own smokestack or mast. The former appears at the correct
distance and bearing on the screen and the latter appears behind the smokestack or
mast. This type of false echo is also generated by re-reflection of waves from bridges
and quay walls other than the ship itself.
B. Multiple echoes
If there is a large vertical reflecting plane near the ship as in the case when your
ship passes alongside a large ship, the wave is repeatedly reflected back and forth
between your ship and the other object. For this reason, two to four images appear on
the screen at equal intervals in the same bearing. A false echo that is generated by
such multiple reflections is called multiple echoes. In this case, an image appearing at
the nearest position is the real echo. Multiple echoes disappear as the ship moves
away from the reflecting object or its bearing changes. Therefore, it is not difficult to
determine the correct image.
Target
Direct reflection
path
Secondary
reflection path
Mast etc.
Real echo
Ghost echo
Direction of ghost echo
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HU
Fig.2-5 False echoes of radar (Ghost echoes)