Furuno FR-1500 MARK-3, User Manual

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1.14 Adjusting the Sensitivity
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 just visible on the screen.
1.15 Suppressing Sea Clutter
Echoes from waves cover 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. When sea clutter masks the picture, suppress it by the A/C SEA control, rotate for manual
adjustment, push for automatic adjustment.
1.15.1 Manual adjustment by the A/C SEA control
The A/C SEA control reduces the amplification of echoes at short ranges (where clutter is the
greatest) and progressively increases amplification as the range increases, so amplification will be
normal at those ranges where there is no sea clutter.
The proper setting of the A/C SEA control should be such that the clutter is broken up into small
dots, and small targets become distinguishable.
If the control is set 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 control until clutter has
disappeared to leeward, but a little is still visible windward.
1. Confirm that the sensitivity is properly
adjusted, and then transmit on short range.
2. Adjust the A/C SEA control so small targets
are distinguishable but some clutter remains
on the display.
A/C SEA OFF A/C SEA adjusted
1.15.2 Automatic adjustment by the A/C AUTO control
The A/C AUTO control automatically suppresses sea clutter as well as rain clutter. Push the A/C
SEA control to turn on the automatic A/C circuit. A/C AUTO appears at the bottom left corner when
the A/C circuit is on.
CAUTION
The auto A/C function can erase weak target echoes. Adjust the control carefully
watching the display.