Context
The AGC (Automatic Gain Control) function runs an automatic analysis of the echo strength. Based on this analysis the ST90 system maintains a proper dynamic range based on all the current echo values. This is done by automatically reducing the gain if you have reverberation and noise, or increasing the gain if the acoustical
conditions permit it.
TipThe 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 ST90 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.