NorthStar EXPLORER 657 Installation And Operation Manual page 33

A Single fish
B Large school of fish
C Small school of fish
D Bottom
Bottom types
Mud, weed and sandy bottoms tend to weaken
and scatter the sonar pulse, resulting in a weak
echo. Hard, rocky or coral bottoms reflect the
pulse, resulting in a strong echo.
Frequency and cone width
The sonar pulse
generated by the 657
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.
A
B
C
D
A Kelp / Weed
B
C
Water Cone width
Depth at 50 kHz
25
50
100
150
200
300
400
600
800
1000
Northstar Explorer 657 Installation and Operation Manual
Soft bottoms such as mud, weed and sand
show as narrow bands
Hard bottoms such as rock or coral show as
wide bands
20
40
80
45° cone
130
170
250
330
500
660
830
A
B
C
Cone width
at 200 kHz
5
10
20
11°
30 cone
40
60
80
120
150
190
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