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18
Suppressing Seabed and Sea Surface Reflections in
Shallow Fishing Grounds
In shallow fishing grounds with hard or rocky bottom, seabed reflec-
tions often interfere with wanted fish echoes and they can not be
eliminated sufficiently with the aforementioned TVG and AGC con-
trols, especially when the TILT is set to a larger angle in order to
track fish schools approaching within 400 m. In such cases try to
reduce the output power by setting the OUTPUT in the scan menu
without turning down the gain. The picture becomes clearer when
output power is reduced rather than when the gain is decreased as
illustrated below.
No Good
Good
Fish echo
TVG & AGC adjusted
with OUTPUT
maintained high
OUTPUT decreased
with gain maintained
constant.
Fish echo
Fish echo
weakened
Rejecting Sonar Interference and Noise
While observing the sonar picture, you may encounter occasional or
intermittent noise and interference as shown below. 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.
* Turn off the TX switch on the control box and operate all on board
equipment one by one while observing the picture.
* Run the boat at various speeds to check if the noise is speed de-
pendent.
If neither of the above two steps has effect on the picture, adjust the
IR (Interference Rejector) and NOISE LIM (noise limiter) controls
as follows.