Blocking; Check The Noise Yourself - Simrad SX90 - REFERENCE MANUAL REV D Reference Manual

307670/D
the bottom, you will still be able to identify the school of fish. In
situation (B) you will be able to identify the upper school of fish,
but the lower school will be hidden in the shadow of the rock.
Be aware of that other vessels close to you will also generate
reverberation due to the water disturbance caused by the wake,
the propellers and the cooling water spill.

Blocking

The movement of your vessel through the water will often
— especially in higher sea states — cause air bubbles to be
generated, and these bubbles will move along the hull. This is
called blocking. In order to prevent this noise from disturbing
your sonar operations, it is important to lower the sonar
transducer as far down below the hull as possible.

Check the noise yourself!

If you are bothered with acoustic or electric noise, you can easily
run a few simple tests to identify the cause of the problem.
Check the noise
1 Click the tab to open the menu.
Setup
2 Click the button to open the
Test
3 Click the
Test config
parameter dialog.
4 Click the button in the parameter dialog to close it.
Close
The level your read in the button is the current noise in the
direction of the cursor. The noise is provided in dB, and the
number should be as negative as possible. For example, a reading
of –50 dB means that you have less noise than if you read –40 dB.
In order to reduce the noise, try to adjust the propeller pitch and
the number of revolutions.
Check electrical noise
1 Switch off all electric equipment that can cause electrical
noise.
2 Switch the equipment on again one at the time, and check
the sonar every time.
With luck, you will spot which of your electrical systems that
create the noise. To deal with the problem, consult your dealer
and/or a certified ships electrician.
System test
button, and select
Noise and VR
Basic theory
menu.
in the
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