When I was planning to buy a handheld with DSC I came across this article with I copied to my notes program. i don't remember exactly where I found it on line but it looks like it came from Boat US.
"Courtesy of BoatUS:
To Test Your DSC System
To run a test call the nationwide Coast Guard MMSI number, 003669999. Enter this number into your radio’s calling memory and select the “Test Call” option from the radio’s list of individual DSC calls, you can then press the “call” or “enter” key. Your radio will silently hail the Coast Guard with a digital signal on channel 70. If everything is working properly, your radio will almost immediately receive the Coast Guard’s acknowledgement of your call, providing assurance that both your radio and the Rescue 21 system are operating properly. You must be boating in an area served by Rescue 21 to use this test. Alternatively you may also use the DSC function to privately hail another boater’s MMSI number so that they can verify what MMSI came up on their ID. The DSC functions do not work at all until an MMSI number is entered into your VHF radio. If connected to a GPS, the signal will also provide your exact coordinates. TowBoatUS Captains with DSC radios will do a radio check with you if requested.
Using the DSC System
IF YOU HEAR A DSC DISTRESS CALL. Shut the radio alarm off by pressing
any button on your radio. Write down the MMSI and position information showing
on your radio display screen. Wait 3-5 minutes for an authority to answer the call.
If no other station replies attempt to verbally relay the MMSI and position
information to USCG. Contact the station in distress if no one else does and go to
their rescue, if you are able to do so.
IF YOU ACCIDENTALLY MAKE A DSC DISTRESS CALL. Shut the call off.
Get on the VHF Distress, Safety and Calling Frequency (VHF Ch-16) or SSB
Safety and Hailing Frequency (4125 kHz, USB) and make an all stations
announcement to cancel the DSC Distress Call. "
It is my understanding that the DSC Alarm will continue until an authority (USCG) or another boater acknowledges the DCS call. Then my radio will switch to Ch 16 for voice communication for additional information.
Based on the above it is probably not a good idea to acknowledge a DSC Call unless it continues without the USCG acknowledging it. Press any key to silent the alarm.
It sounds like if you acknowledge the alarm you are taking the responsibility of communicating with the vessel in distress and either will respond to assist and/or will relay with the proper authority.
On our boat the Admiral knows to Push To Talk on a hand held but that is about it. If she managed to get the USCG I can hear it going like this:
Admiral "Help, my husband fell in the water"
USCG " What is your location?"
Admiral "We are in the Barnegat Bay"
USCG " Can you give us a more precise location please?"
Admiral "Well, I can see the lighthouse"
USCG " Can you give us a description of your boat"
Admiral "We are in a white sailboat with white sails"
So I bought a handheld with DSC and GPS so all she really needs to know now is to press and hold the red button until the alarm sounds. When someone responds and talks to you, just PTT. The radio will be on the correct channel and they should have the GPS coordinates.
I agree with Scott, the radio chatter is not that bad on the BB. Some is stupid, some is annoying but not enough that I turn of the radio. A lot of radio check requests are referred to channel 27 for the automated check, which I do sometimes.
Waiting for an emergency before we turn the radio on, then having to wait until it gets the GPS coordinates, defeats the ease of use it provides in an emergency.
