TRACKFISH 6500
Installation and Operation Manual
43
NAVMAN
Setting gain and threshold
It is convenient to use the A-scope display
when adjusting gain and threshold manually.
Follow this procedure to adjust gain and
threshold for normal circumstances:
1 Switch to a sonar display (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
, select
Frequency
and select
200 kHz
or
50
kHz
.
3 Press
, select Sonar splits then select
Split A-scope.
4 Press
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
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 recognising 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.
