NorthStar Explorer 660 Installation And Operation Manual page 33

Frequency and cone width
The sonar pulse
generated by the Explorer
660 transducer travels
down through the water,
spreading outwards in
a cone shape. The cone
width is dependent
upon the frequency of
the pulse; at 50 kHz it
is approximately 45°,
and at 200 kHz it is
approximately 11°.
The differences in the
cone width affect what is
displayed. See section 8-3.
Shadows
Shadows are created around areas where the ultrasonic beam cannot 'see'. These areas include hollows
on the bottom or beside rocks and ledges, where the strong echoes returned off the rocks obscure the
weak echoes of the fish and may also create a double bottom trace. See following for an example of the
sonar display in such an environment. A double bottom trace is shown on the display.
When looking for fish with the wide angled 50 kHz frequency, be aware of increased shadows. Use the
high frequency 200 kHz in areas that have rocks and ledges because this frequency reduces the shadow
effect considerably.
Example of shadows
Water
Depth
25
50
100
150
200
300
400
600
800
1000
fish is visible on the display
fish is hidden by the strong echoes off the
bottom and is not shown on the display
fish is visible on the display
Northstar Explorer 660 Installation and Operation Manual
Cone width
at 50 kHz
20
40
80
45° cone
130
170
250
330
500
660
830
Sonar display of same area
Cone width
at 200 kHz
5
10
20
11°
30
cone
40
60
80
120
150
190
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