Furuno 1830 - Collision Avoidance; Assessing the Risk

FALSE HCIIOHS
OfjnasionftUy false eohoes nppear on Ihe screen at positions where there is no
target. !n some cases the effects can be reduced or eliminated. The
operator shoold familiari^e himself with the appearance and effects of these
false echoes, so as not to confuse Ihem with echoes from legilimate contacts«
Multiple Echoes
Multiple echoes ocour when a
short range, strong echo is
received from a ship, bridge,
or breakwater. A second, a
third or more echoes may be
observed on the display at
douhle, triple or other
lEjultiples of the actual ranye
of the target as shown in
Fig.40. Multiple reflection
echoes can be reduced and
often removed by decreasing
the gain or properly adiusting
the A/C SEA.
Side-Lobe Echoes
Every time the scanner
rotates, some radiation escapes
on each side of the beam--
called "side-lobes." If a
target exists where it can be
detected by the side lobes as
well as the main lobe, the side
cohoco may bc represented on
both sides of the true echo at
the same range, as shown in
Fig.41. Side lobes show
usually only on short ranges
and from strong targels.
They can be reduced through
careful reduction of the gain
or proper adjustment of the
A/C SEA Control.
Blind and Shadow Seetprs
Funnels, stacks, masts, or
derricks in tlte path uf
antenna may reduce the inten-
sity of the radar beam. If the
angle subtended at the
scanner is more than a few
degrees a blind sector may be
produced. VVithin the blind
sector small targets at close
range may not be detected
while Larger targets at mueh
groater ranges may bc
detected. See Fig.42.
Fig.4l Side-Lobe Echoes
Fig.42 Blind and Shadow Sector
43