Measuring The Range - Furuno FMD-811 Operator's Manual

How to adjust A/C RAIN
The vertical beamwidth of the scanner is de-
signed to see surface targets even when the
ship is rolling. However, by this design the
unit will also detect rain clutter (rain, snow,
hail, etc.) in the same manner as normal tar-
gets. Figure 1-6 shows the appearance of rain
clutter on the display.
When rain clutter masks echoes over a wide
range, raise the A/C RAIN slightly to dis-
tinguish targets from the clutter.
Appearance of
rain clutter
Figure 1-6 Effect of A/C RAIN
Turning on/off A/C AUTO
The A/C AUTO function automatically sup-
presses sea clutter as well as rain clutter.
Note however that with the A/C circuit on
weak targets may be suppressed.

1.9 Measuring the Range

You can measure the range to a target three
ways: by the range rings, by the cursor, and
by the VRM (Variable Range Marker).
By range rings
Press the [RINGS] key to display the range
rings. Count the number of rings between
the center of the display and the target.
Check the range ring interval (at the top left
corner) and judge the distance of the echo
from the inner edge of the nearest ring.
A/C RAIN adjusted;
rain clutter suppressed.
By cursor
Operate the cursor pad to place the cursor
intersection on the inside edge of the target
echo. The range to the target, as well as the
bearing, appears at the bottom of the dis-
play.
By VRM
1) Press the [VRM] key to display the VRM.
2) Press the cursor pad to place the VRM
on the inside edge of the target. (The cur-
sor appears and is linked with the VRM,
allowing you to measure both range and
bearing to the target.)
3) Check the VRM readout at the bottom
left-hand corner of the display to find the
range to the target.
Note: The VRM is automatically anchored
when no cursor pad key is operated within
about 10 seconds.
To erase the VRM, press and hold down
the [VRM] key for about three seconds.
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