Onwa Marine Electronics KR-1338C v.1 - Manual (Page 24)

The [GAIN] control 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. The proper setting is such that the background noise is just
visible on the screen. If you set up for too little sensitivity, weak echoes may
be missed. On the other hand excessive sensitivity yields too much background
noise; strong targets may be missed because of the poor contrast between desired
echoes and the background noise on the display. To adjust receiver sensitivity,
transmit on long range, and adjust the [GAIN] control so background noise is
2.9 Adjusting Receiver Sensitivity
just visible on the screen.
Echoes from waves can be troublesome, covering the central part of the display
with random signals known as "sea clutter." The higher the waves, and the higher
the scanner above the water, the further the clutter will extend. Sea clutter appears
on the display as many small echoes which might affect radar performance. (See
the Figure 2-3.) When sea clutter masks the picture, adjust the A/C SEA control to
The [A/C SEA] control reduces the amplification of echoes at short ranges (where
clutter is the greatest) and progressively increases amplification will be normal at
2.10 Adjusting the A/C SEA Control (reducing sea clutter)
How the A/C SEA control works
reduce the clutter.
those ranges where there is no sea clutter.
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