Furuno FA-2805, Operator'S Manual

Page: 30 / 169

1-15
has not been properly adjusted. Always
leave a little surface clutter visible on the
screen. If no surface clutter is observed
(on a very calm water), set the control at
the fully counterclockwise position.
1.14 Suppressing Precipitation
Clutter
In adverse weather conditions, clouds,
rain or snow produce a lot of spray-like
spurious echoes and impairs target de-
tection over a long distance. This situa-
tion can be improved by using a function
key provided that it is so programmed. If
the function key fails to offer a favorable
suppression of the rain clutter, adjust the
A/C RAIN control on the front control
panel.
OFF ON
EBL
BRILL A/C RAIN GAIN A/C SEA
FUNC4 FUNC1 FUNC2 FUNC3
A/C
AUTO
A/C RAIN
control
The A/C RAIN control adjusts the receiver
sensitivity as the A/C SEA control does
but rather in a longer time period (longer
range). Clockwise rotation of this control
increases the anti-clutter effect.
A/C RAIN control
OFF A/C RAIN control
adjusted
1.15 Interference Rejector
Mutual radar interference may occur in the
vicinity of another shipborne radar oper-
ating in the same frequency band (9 GHz
for X-band, 3 GHz for S-band). It is seen
on the screen as a number of bright spikes
either in irregular patterns or in the form
of usually curved spoke-like dotted lines
extending from the center to the edge of
the picture. This type of interference can
be reduced by activating the interference
rejector circuit.
The interference rejector is a kind of sig-
nal correlation circuit. It compares the re-
ceived signals over successive
transmissions and suppresses randomly
occurring signals. There are three levels
of interference rejection depending on the
number of transmissions that are corre-
lated. These are indicated by the legends
IR1, IR2 and IR3 at the upper-left posi-
tion of the screen.
Mutual radar interference
Press the INT REJECT key to activate the
interference rejector circuit. Successive
presses of the key increase the effect of
interference rejection, up to level 3. A
fourth press deactivates the interference
rejector. Switch off the interference rejec-
tor when no interference exists; otherwise
weak targets may be lost.
HL
OFF
ECHO
TRAILS
MODE
ORIGIN
MARK
VECTOR
TRUE/
REL
VECTOR
TIME
GUARD
ALARM
EBL
OFFSET
OFF
CENTER
X2
ZOOM
BKGR
COLOR
INDEX
LINES
CU, TM
RESET
INT
REJECT
RINGS
Inside mode panel