Furuno 1942 MARK-2 - Manual (Page 29)

4-1
4. FALSE ECHOES
4.2 Side-lobe Echoes
Every time the scanner rotates, some radia-
tion 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-lobe echoes may be
represented on both sides of the true echo
at the same range, as shown in Figure 4-2.
Side-lobes show usually only at short ranges
and from strong targets. They can be reduced
through careful reduction of the sensitivity or
proper adjustment of the A/C SEA.
True echo
Sprious
target
Main-lobe
Side-lobe
Antenna
Figure 4-2 Side-lobe echoes
Occasionally false echoes appear on the
screen at positions where there is no target.
In some cases the effects can be reduced or
eliminated. The operator should familiarize
himself or herself with the appearance and
effects of these false echoes, so as not to
confuse them with echoes from legitimate
contacts.
4.1 Multiple Echoes
Multiple echoes occur when a short range,
strong echo is received from a ship, bridge,
or breakwater. A second, a third or more ech-
oes may be observed on the display at
double, triple or other multiples of the actual
range of the target as shown in Figure 4-1.
Multiple reflection echoes can be reduced
and often removed by decreasing the sensi-
tivity or properly adjusting the A/C SEA.
Own ship
True
echo
Multiple
echo
Figure 4-1 Multiple echoes