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Simrad SN90 Reference Manual
Tip
The most practical way to use the AGC (Automatic Gain Control) is to first switch it off.
Adjust the echo presentation using the normal gain functionality until you have the
best possible result, then activate the AGC.
The AGC works best with even background (homogenous noise conditions) and
pronounced targets. With uniform environmental conditions you may benefit from strong
compensation. However, if you are looking at scattered fish, reduce the automatic gain
control, and try to add normal gain instead.
If you work close to other vessels, the noise from their propellers may be misinterpreted
as echoes. This will also reduce the visibility of other echoes. The same applies if the
bottom conditions place your vessel with decreasing depth on one side of the vessel and
your targets on the other side. Reduce the automatic gain control.
If you have a large school located close to your vessel (typically closer than 150 meters)
the school gives you a strong echo. The AGC may misinterpret the school echo for noise.
Reduce or disable the automatic gain control.
The filters in the SN90 system are implemented in "series". The gain compensations
are made before the AGC. For this reason, your current gain setting will always have
an effect on the automatic gain control.
Procedure
1
Click in any view to make it active.
The active view is identified with a thicker border.
2
Open the
Active
3
Select
(Automatic Gain Control).
AGC
4
Select a value from the options provided.
The choice you make is by default only applied to the currently selected (active)
view.
Select the middle of the button to open a small menu with the available options.
Select the left side of the button to select a "lower"' menu choice. Select the right
side of the button to select a "higher"' menu choice.
Related topics
Operating procedures, page 82
Improving the recognition of fish and schools using receiver filters, page 118
AGC (Automatic Gain Control) function, page 479
120
menu.
381294/E
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