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1–12
A common mistake is too over-adjust the A/C
SEA control so that the surface clutter is com-
pletely removed. By rotating the control fully
clockwise, you will see how dangerous this can
be; a dark zone will be created near the center of
the screen, causing a loss of close-in targets. This
dark zone is even more dangerous if the gain has
not been properly adjusted. Always leave a little
surface clutter visible on the screen. If no clutter
is observed (on very calm waters), set the control
at the fully counterclockwise position.
1.12 Suppressing Rain Clutter
In adverse weather conditions, clouds, rain or
snow produce a lot of spray-like spurious echoes
and impairs target detection over a long distance.
This situation can be improved by using a Func-
tion key that is so programmed. If the Function
key fails to effectively suppress rain clutter, use
the A/C RAIN control.
The A/C RAIN control adjusts the receiver sen-
sitivity 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.
Appearance of rain
clutter on the display
A/C RAIN control adjusted;
rain clutter suppressed
Figure 1-10 Effect of A/C RAIN control
1.13 The Heading and North
Markers
The heading marker indicates the ship's heading
in all presentation modes. It appears at zero de-
grees on the bearing scale in the Head-up mode,
in any direction depending on the ship orienta-
tion in North-up and True Motion modes. The
north marker appears as a short dashed line. In
the Head-up mode, the north marker moves
around the bearing scale in accordance with the
compass signal.
To temporarily extinguish the heading marker to
look at targets existing dead ahead of own ship,
press the HM OFF (PUSH) control. The heading
marker reappears when the key is released.
1.14 Measuring the Range
There are three ways to measure the range to a
target: by the range rings, by the cursor and by
the VRM (Variable Range Marker).
Measuring range by the range rings
Use the range rings to obtain a rough estimate of
the range to a target. They are concentric circles
around own ship, or the sweep origin. The num-
ber of rings is automatically determined by the
selected range scale and their interval is displayed
at the upper-left position of the screen. Press the
RINGS (PUSH) control to show the range rings
if they are not displayed. Successive presses of
the RINGS (PUSH) control gradually increase
the brightness of the rings in four steps and a fifth
press erases the rings.
Measuring range by the cursor
Rotate the trackball to place the cursor on the in-
side edge of the target. The range to the cursor
appears at the bottom of the display.