Furuno 1761 MARK-3 - Manual (Page 21)

2-10
Note 2: A target echo does not always mean
a landmass, reef, ships or surface objects but
can imply returns from sea surface or pre-
cipitation. As the level of these returns varies
with environment, the operator should (prop-
erly) adjust the A/C SEA, A/C RAIN, FTC and
GAIN to be sure target echoes within the
guard zone are not overlooked by the alarm
system.
Guard zone
to set * G (IN)
(2) Drag cursor to
top left corner of
zone and press
[GUARD].
Asterisk blinking
Drag cursor
here.
(1) Mentally create
the guard zone to set.
G (IN)
(3) Drag cursor to
bottom right corner
of zone and press
[GUARD]. (4) Guard zone
completed.
G (IN)
Guard
zone
Drag cursor
here.
A
B C
D
A
C
Figure 2-11 Setting Guard Zone
Auto In/Out Alarm
When the guard zone is set completely, the
radar starts searching for targets inside the
guard zone for 8 to 12 seconds. The indica-
tion “GUARD” appears during this period.
Case 1: When there are targets inside the
zone, the alarm zone is automatically set to
“Auto Out Alarm” mode and the indication
“GUARD” is replaced by “G (OUT)”. The au-
dible alarm sounds only on targets which go
out of the zone or disappear. See Figure 2-
13 (1).
Note: The audible alarm does not sound for
the target originally existing the zone.
Case 2: When no targets exist inside the
zone, the alarm zone is automatically set to
“Auto In Alarm” mode and the indication
“GUARD” is replaced by “G (IN)”. The au-
dible alarm sounds only on targets which go
into the zone. See Figure 2-13 (2).
Dashed line:
no alarm
IN ALARM OUT ALARM
Guard
zone
Figure 2-12 Auto In/Out Alarm
2.25 Watchman
The watchman function turns on the radar
and transmits its for about 30 seconds at a
predetermined interval to check for targets
in a guard zone. This feature is useful when
you do not need the radar’s function continu-
ously but want to be alerted to radar targets
in an area.
When the watchman feature is on, an inter-
nal timer turns on the radar every 5, 10 or 20
minutes and the radar transmits for 30 sec-
onds to check for the existence of radar tar-
gets in a guard zone.
St-by
5, 10 or
20 min
Tx
1 min
Tx
1 min
St-by
5, 10 or
20 min
Watchman
starts.
Figure 2-13How watchman works