NorthStar Navigation Explorer 660 - Manual (Page 41)

Northstar Explorer 660 Installation and Operation Manual 41
9-5 Sonar A-Scope display
The display shows the sonar history on the
left and the A-Scope display on the right. The
A-Scope shows:
• the strengths of echoes from different depths
- the longer the horizontal line the stronger
the signal
9-4 Sonar 50/200 display
The display shows the 50 kHz sonar history on
the left and the 200 kHz sonar history on the
right. Gain can be set independently for each
frequency (see section 8-5). Range applies to
both frequencies (see section 8-6).
200 kHz sonar
history 50 kHz sonar
history
• a vertical line showing the gain threshold, the
weakest echo to display on the sonar history
• 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 8-5).
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.
Threshold line
Gain line
Unwanted
noise signal
Peak of
bottom
signal
A-scope display Sonar history