Navman Fish 4432 Installation And Operation Manual page 16

Frequency and cone width
The pulse generated by the FISH 4432/4433
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
FISH 4432/4433 Installation and Operation Manual
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
Water
Depth
10
20
30
40
50
60
70
80
90
100
150
200
300
400
500
600
700
800
900
1000
NAVMAN
Cone width Cone width
at 83 kHz at 200 kHz
4
7 5
11 7
15 10
18 12
22 15
25 17
29 20
33 22
36 25
55 37
73 50
109 75
146 100
182 125
218 149
255 174
291 199
328 224
364 249
Sonar display of same area
2
18