Navman 4433, 4432 Frequency and cone width, Shadows, Example of shadows, Depth 83 kHz 200 kHz

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	200 kHz
0	20°	14°
50	18	12
100	30	25
150	55	37
200	73	50
250	91	62

Water	Cone width	Cone width
Depth	at 83 kHz	at 200 kHz
10	4	2
20	7	5
30	11	7
40	15	10
50	18	12
60	22	15
70	25	17
80	29	20
90	33	22
100	36	25
150	55	37
200	73	50
300	109	75
400	146	100
500	182	125
600	218	149
700	255	174
800	291	199
900	328	224
1000	364	249

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

Sonar display of same area

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

FISH 4432/4433 Installation and Operation Manual NAVMAN 18