"krj" wrote
Jack,
What is the difference between "D" class and "E" class DSC/GMDSS
krj

The differences listed below appear almost non-existent, but I believe that
the "E" manufactured radios are intended to allow greater flexibility in
both distress and general messaging instructions sent via DSC. In other
words, the receiving radios "might" be allowed to be commanded to a specific
frequency after DSC message on Ch-70.

Jack

http://www.navcen.uscg.gov/marcomms/gmdss/dsc.htm
Classes of Digital Selective Calling

Class D:
Minimum DSC capability for VHF marine radios carried by recreational
boaters, commercial fishing vessels, and other non-SOLAS regulated vessels.
Class D required capabilities include:

Distress call
All-ships call
Individual station call
Use of distress, urgency, safety and routine priorities
Nature of distress
Distress coordinates
Time for last (distress) position update
Type of subsequent communications
Radio VHF channel
Display
Receive distress relay and distress acknowledgment calls
Alarm

Class E:
Minimum DSC capability for HF marine radios carried by recreational boaters,
commercial fishing vessels, and other non-SOLAS regulated vessels. Class E
required capabilities include:

Distress call
All-ships call
Individual station call
Use of distress, urgency, safety and routine priorities
Nature of distress
Distress coordinates
Time for last (distress) position update
Type of subsequent communications
Radio channel or frequency
Display
Receive distress relay and distress acknowledgment calls
Alarm