False Echoes; Side-Lobe Echoes.3-6 - Furuno 1751 Operator's Manual

3. APPLICATION
False Echoes
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. TTie operator should familiarize himself with
the appearance and effects of these false echoes, so as not to confuse them with echoes from
legitimate contacts.
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 target as shown in Figure 3-4. Multiple
reflection echoes can be reduced and ofren removed by decreasing the gain or properly
adjusting the A/C SEA.
Figure 3-4 Multiple Echoes
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 echoes may be represented on both sides of the true echo at the same range,
as shown in Figure 3-5. Side-lobes show usually only at 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.
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