NAVMAN
8120/8084
Installation and Operation Manual
47
10-5 Sonar A-Scope window
The window shows the sonar history on the
left and the A-Scope window on the right.
The A-Scope shows:
A, B, C,
The strengths of echoes being
received now from different depths - the
longer the horizontal line the stronger the
signal:
A
Unwanted noise echoes.
B
Echoes from fish and the bottom
C
The strongest echo, usually from the
bottom
D
A vertical line showing the threshold,
the weakest echo to display on the sonar
history
E
A vertical line showing the gain setting;
echoes above this strength will display as
the maximum signal strength
Use the A-Scope while adjusting the gain and
threshold settings manually (see section 9-6).
Setting gain and threshold
It is convenient to use the A-scope window
when adjusting gain and threshold manually.
Follow this procedure to adjust gain and
threshold for normal circumstances:
1 Switch to a sonar window (see section 9). If
necessary, press or to adjust range so
that the bottom is displayed.
2 If necessary, select the sonar frequency to
adjust the settings for. Press
MENU
, select
Frequency
and select
200 kHz
or
50
kHz
.
A
B
C
D
E
3 Press
MENU
, select Sonar splits then select
Split A-scope.
4 Press
ENTER
to display the Gain window. To
adjust gain or threshold for a frequency,
press or to select the setting to
adjust, then press or to change the
setting.
5 Set threshold to zero.
6 Adjust Gain so the peak of the strong
signal from the bottom just touches the
gain line.
7 Adjust threshold so that it is just to the
right of the noise.
8 Press
ESC
to close the gain window.
9 If required, repeat these steps to
adjust gain and threshold for the other
frequency.
Note:
Setting the gain higher will display
more detail from weak echoes, like fish, but
will loose detail from the strong echo from
the bottom.
Fish recognition
The echo strengths shown on the A-scope
can be useful in recognizing the type of fish.
Different species of fish have different sizes
and shapes of swim bladders. The air in the
swim bladder reflects the ultrasonic pulse, so
the strength of the echo varies between fish
species according to the size and shape of the
swim bladder.
When catching fish from a school, note the
species and the strength of the echo that
it returns on the A-scope. Then, when that
particular echo is seen again, it is likely to be
the same fish species.
Bottom type
The shape of the echo strengths in the
A-Scope can help you to recognise the type
of bottom.
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