False Echoes; Multiple Echoes; Side-Lobe Echoes - Furuno FR-7062 Operator's Manual

4. FALSE 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 her-
self 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 echoes
may be observed on the display at double, triple
or other multiples of the actual range of the tar-
get as shown in Figure 4-1. Multiple reflection
echoes can be reduced and often removed by
decreasing the sensitivity or properly adjusting
the A/C SEA.
Own ship
Figure 4-1 Multiple echoes
True
echo
Multiple
echo

4.2 Side-lobe Echoes

Every time the antenna 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-lobe echoes may be repre-
sented 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 tar-
gets. They can be reduced through careful re-
duction of the sensitivity or proper adjustment
of the A/C SEA.
Main-lobe
Side-lobe
Spurious
target
Antenna
Figure 4-2 Side-lobe echoes
True echo
4-1