Receiver Sensitivity; Suppressing Sea Clutter - Furuno MODEL 1622 Operator's Manual

1.7 Receiver Sensitivity

The [GAIN] key adjusts the sensitivity of the
receiver. It works in precisely the same manner
as the volume control of a broadcast receiver,
amplifying the signals received.
You can adjust the sensitivity manually, or let the
unit do it automatically. In either case, the proper
setting is such that the background noise is just
visible on the screen. Adjust the sensitivity on the
highest range since the background noise is
clearer on that range.
If you set up for too little sensitivity, weak echoes
may be missed. On the other hand excessive
sensitivity yields too much background noise;
weak targets may be missed because of the poor
contrast between desired echoes and the
background noise on the display.
Automatic adjustment of sensitivity
1. Press the [GAIN] key once or twice to display
the screen shown in Figure 1-5.
AUTO GAIN MOD
LOW
1
Figure 1-5 Dialogue for automatic
adjustment of gain
2. Press or to set level desired: 1, Low; 2,
Normal; 3, High.
Manual adjustment of sensitivity
1. Transmit the radar on long range.
MAN GAIN MOD
LOW
Figure 1-6 Dialogue for manual
adjustment of gain
2. Press the [GAIN] key once or twice to display
the screen shown in Figure 1-6.
3. Press or to set level desired. 61 levels
are available.
4
HIGH
2 3
HIGH
32
Note: The dialogues for adjusting sensitivity are
automatically erased when there is no TrackDisk
operation for 10 seconds. To erase them quicker,
press the [GAIN] key after completing the setting.

1.8 Suppressing Sea Clutter

In rough weather, returns from the sea surface
are received over several miles around own ship
and mask nearby targets. This situation can be
improved by properly using the [STC] key.
If the setting is too low, targets will be hidden in
the clutter, while if it is set too high, both sea
clutter and targets will disappear from the display.
In most cases adjust the key until clutter has
disappeared to leeward, but a little is still visible
windward.
A common mistake is too over-adjust the [STC]
key so that the surface clutter is completely
removed. By setting up for maximum STC effect,
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
sensitivity has not been properly adjusted.
Always leave a little surface clutter visible on the
screen. If no clutter is observed (on very calm
waters), turn off the circuit.
Sea clutter at
screen center
Figure 1-7 Appearance of sea clutter
STC adjusted;
sea clutter suppressed