Navman FISH 4500/4600 Installation And Operation Manual page 16

Frequency and cone width
The pulse generated by the FISH 4500/4600
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 50 kHz it is 45°,
whereas at 200 kHz it is 11°. The chart shows
how the cone width varies over depth for each
frequency used. Figures are approximate.
Depth 50 kHz
0
45°
50
41
100
83
150
127
200
166
250
208
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 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
16
200 kHz
11°
9
19
26
38
46
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
Sonar display of same area
NAVMAN FISH 4500/4600 Installation and Operation Manual
Cone width Cone width
at 50 kHz at 200 kHz
8
16
25
33
41
50
58
66
74
83
127
166
249
331
414
497
580
663
746
828
2
4
6
7
9
11
13
15
17
19
26
38
58
77
96
116
135
154
173
192