NorthStar EXPLORER 443D Installation And Operation Manual page 18

Frequency and cone width
The pulse generated by the Explorer 443d/443df
transducer travels down through the water,
spreading outwards to form a rough cone shape.
However, the cone width is dependent upon the
frequency of the pulse; at 83 kHz it is 20°, whereas
at 200 kHz it is 14°. The chart shows how the cone
width varies over depth for each frequency used.
Figures are approximate.
Depth 83 kHz
0
20°
50
18
100
30
150
55
200
73
250
91
The differences in the cone width affect what is displayed. See section 4-2 Single and Dual Frequency fishfinding.
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 83 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
18
200 kHz
14°
12
25
37
50
62
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 443d/443df Installation and Operation Manual
Water Cone width
Depth at 83 kHz
10 4
20 7
30 11
40 15
50 18
60 22
70 25
80 29
90 33
100 36
150 55
200 73
300 109
400 146
500 182
600 218
700 255
800 291
900 328
1000 364
Sonar display of same area
Cone width
at 200 kHz
2
5
7
10
12
15
17
20
22
25
37
50
75
100
125
149
174
199
224
249