False Echoes; Multiple Echoes; Side-Lobe Echoes; Blind And Shadow Sectors - Furuno 1720 Owner's Manual

FALSE ECHOES
Ocpasionally false eeltoes appear on the screen at positions where there is no
target. tn some cases the effects can be reduced or eliminated. The
operator should familiarize himself wlth the appearance and effects of theae
false eohoes, so as not to confuse them with echoes from legitimste oontacts.
Multiple Echoes
Multiple echoes occur when a
short range, strong echo is
received from a ship, bridge,
or breakwater, A aecond, 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
Fig.32- Multiple reflection
echoes can be reduced and
often removed by decreasing
the gain or properly adjusting
the A/C SEA*
Side-Lobe Echoes
Fig-32 Multiple Echoes
Every time the scanner
rotates, some radiation escapes
on each side of the beam—
called "sidc-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 gides of Uie true echo at
the same range, as shown in
Fig.33. Side lobes show
usually only on short ranges
and from strong targets.
They can be reduced through
careful reduction of the - gain
or proper adjuatment of the
A/C SEA Control.
Bl^d and Shadow Sectors
Funnels, stacks, masts, or
derricks in thé path of
antenna may reduce the inten-
sity of the radar beam. If the
angle
subtended at the
scanner
is mgre than a few
degrees a blind sector may be
produced* Within the blind
sector small targets at olose
range may not be detected
while larger targets at muoh
greater ranges
may
be
detected* See Fig.34.
Fig.33 Side-Lobe Echoes
Fig.34 Blind and Shadow Sector
39