Color Scanning Sonar Operator's Manual Model CSH-7

4-4
Rejecting Sonar Interference and Noise
While observing the sonar picture, you may encounter occasional
or intermittent noise and interference. These are mostly caused
by on-board electronic equipment, engine or propeller noise, or
electrical noise from other sonars being operated nearby.
Identifying noise source
To eliminate noise effectively, you should first identify the noise
source as follows:
1. Turn off the TX switch and operate all on-board equipment
one by one while observing the picture.
2. Run the boat at various speeds to check if the noise is speed
dependent.
If neither of the above two steps has effect on the picture, adjust
the IR (Interference Rejector) and NOISE LIM (Noise Limiter)
on the Scan menu as follows.
Rejecting noise with IR on the scan menu
This control is similar to the interference rejector on echo sound-
ers and radars. It is effective for rejecting random noise and sea
surface reflections in rough sea conditions. Set it so that noise is
just eliminated. Do not use an unnecessarily high setting since it
may also reject small wanted echoes.
Rejecting noise with NOISE LIM on the scan menu
Weak, unwanted reflections, colored light blue or green, are dis-
played when water is contaminated or plankton layers exist or
due to ship's noise. These echoes gradually become bluish as the
NOISE LIM setting is raised. Usually, setting “3” or “4” is suit-
able.