Furuno MODEL CSH-73 Operator's Manual page 25

Interference from
other sonar
Figure 3-4 Forms of interference
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
one of the following:
Interference rejector (data setting window: SIGNAL,
SIGNAL PROCESS)
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.
Changing Tx cycle (data setting window: TVG•TX,
CYCLE)
When other sonars operate nearby at the same transmission in-
terval as that of own ship's sonar, an interference ring caused by
other sonars is displayed. To erase the interference ring from the
screen, reduce the CYCLE on the data setting window.
Cruising (propeller)
noise of own ship
Cruising noise
from other boat
3-5