Furuno FR-2805 Series - Manual (Page 29)

1-14
1.12 Adjusting the Sensitivity
The GAIN control is used to adjust the
sensitivity of the receiver, and thus the
intensity of echoes as they appear on the
screen. It should be adjusted so that
speckled background noise is just visible
on the screen.
To become acquainted with the way the
GAIN control works, try rotating it between
fully counterclockwise and clockwise po-
sitions while observing the radar picture.
You will notice that clockwise rotation in-
creases the echo intensity level. A low
gain setting results in the loss of weak
echoes and a reduced detection range. If
you turn the GAIN control too far clock-
wise for an excessive gain setting, desired
echoes will be masked in the strong back-
ground noise.
OFF ON
EBL BRILL A/C RAIN GAIN A/C SEA
FUNC4 FUNC1 FUNC2 FUNC3
A/C
AUTO
GAIN control
1.13 Suppressing Sea Clutter
In rough weather conditions returns from
the sea surface are received over sev-
eral miles around own ship and mask
close targets. This situation can be im-
proved by properly adjusting the A/C SEA
(Anti-Clutter Sea) control.
OFF ON
EBL BRILL A/C RAIN GAIN A/C SEA
FUNC4 FUNC1 FUNC2 FUNC3
A/C
AUTO
A/C AUTO key A/C SEA control
A/C SEA control
off A/C SEA control
adjusted
Automatic anti-clutter control
The easiest way to suppress the surface
clutter is to use the automatic control.
Press the A/C AUTO key next to the EBL
rotary control at the left corner on the con-
trol panel. Use of a function key is also a
good method for reducing sea clutter. For
this purpose, presetting is required. Con-
sult a FURUNO representative.
CAUTION CAUTION
The auto A/C function can erase weak
targets.
Manual anti-clutter control
From the fully counterclockwise position,
slowly turn the A/C SEA control clockwise.
For optimum target detection, you should
leave speckles of the surface return
slightly visible.
The anti-clutter sea control is often re-
ferred to as STC (Sensitivity Time Con-
trol) which decreases the amplification of
the receiver immediately after a radar
pulse is transmitted, and progressively
increases the sensitivity as the range in-
creases.
A common mistake is to over-adjust the
A/C SEA control so that the surface clut-
ter is completely removed. By rotating
the control fully clockwise, you will see
how dangerous this can be; a dark zone
is created near the center of the screen
and close-in targets can be lost. This dark
zone is even more dangerous if the gain