Emc Conformance - Raymarine DSM250 Owner's Handbook Manual

Chapter 2: Installation 2-15
If the transducer cable is accidentally removed while the
DSM250 is powered on, remove power from the sounder module,
replace the transducer cable, and then return power to the
module. As a safety feature, the DSM250 only recognizes that the
transducer is connected at power-up.

EMC Conformance

Always check the installation before going to sea to make sure
that it is not affected by radio transmissions, engine starting, etc.
Figure 2-9: Properly Mounted Sounder Module