VHF with DSC - Mayday

[fairbank56]

Well, it was illegal to import, sell, manufacture or install these radio's as of March of last year but that has now been extended until Jan 1st, 2013 due to the outcry of vendors trying to unload their stock. This is ridiculous in my opinion. The FCC and CG want us all to have modern class D radio's but they have changed the cutoff date to allow vendors to get rid of their stock by selling them to unsuspecting boaters. What a joke!

Eric

[delmarrey]

Originally Posted by Wotname

FWIW, Oz has no official shore based infrastructure that supports DSC - we are the poor cousins here!

Here's some info about OZ>>> http://www.amsa.gov.au/publications/...hfdsc_fact.pdf

[goboatingnow]

Im afarid Orrissails post is very misleading

Lets review some terminology

Pushing the red button ( all radios should have a 5 secs delay as mandated by COMSAR)
this called a "undesignated distress alert". Its so as you do not have the option of indicating the nature of the distress

Next up , is a "designated distress alert ", this is activated from the menus, involves picked an distress designation ( flooding etc) and the distress alert is activated from the menu.

All this is followed up by a voice Mayday procedure.

As correctly point out the US only ( nobody else allowed them) SC101 radios, can't follow the proper procedure. But lets stay with Class D

ANybody with a DSC class A radio can acknowledge a DSC distress alert. But normally its the coastguard and everyone must wait to allow them to do so.


Next up is a "Urgency call", this is the DSC equivalent to Pan Pan. Its activated from the menu, its normally sent to the MMSI of the closest CG radio station. Its followed up by a Voice Pan Pan, the Urgency call does not have a auto repeat function


After that we have normal DSC calls , either to specific, or group MMSIs

dave

[osirissail]

Originally Posted by fairbank56

Wrong. After you send a DSC distress call, your radio will automatically switch to channel 16 but will continue to send the distress call on channel 70 (in the background) until it is acknowledged. . .
Only the CG can acknowledge a DSC distress alert via DSC. Class D radio's cannot do this. If a boater continues to hear an unacknowledged distress call, they can contact the boater in distress via channel 16.
. . .
Eric

Double wrong and also right -depending upon the make and model of your DSC radio. I stated that the OP needs to read the manual that came with his radio as different radios do different things with DSC Distress Calls.

My Icom 502 specifically states that if you "manually" re-channel the radio before receiving an acknowledgement, the DSC Distress repeat will be cancelled. Same with my Standard Horizon.

And both of my radios will respond with an acknowledgement to a DSC Distress call - and I have done that down island where there is no USCG anywhere around.

Even different models of a manufacturers radio will respond differently. For instance there is no way to "turn off" the automatic channel switching on my two radios. Newer model radios may do something else.

These radios are available and in use world-wide, not just where the USA Coast Guard is located. So, bottom line, read your radio's manual to learn how your radio works with DSC. It is a wonderful feature, IMHO, and I wish more people would utilize it especially the DSC Call function to your "buddy boats."

[osirissail]

Originally Posted by goboatingnow

Im afarid Orrissails post is very misleading

Lets review some terminology

Pushing the red button ( all radios should have a 5 secs delay as mandated by COMSAR)
this called a "undesignated distress alert". Its so as you do not have the option of indicating the nature of the distress. . .

dave

Welcome to the "misleading" group - be careful when you use the word "all" - because it ain't necessarily so. My Standard Horizon initiates the DSC Distress after holding the red button down for "3 seconds."

Different radios do different things with DSC Distress . . .

[fairbank56]

Originally Posted by osirissail

I stated that the OP needs to read the manual that came with his radio as different radios do different things with DSC Distress Calls.

The OP clearly stated that "Recently purchased a VHF with DSC and AIS" indicating that he has a modern class D radio.

My Icom 502 specifically states that if you "manually" re-channel the radio before receiving an acknowledgement, the DSC Distress repeat will be cancelled. Same with my Standard Horizon.

This only applies to older SC-101 radio's, and the manual does not "specifically state" that. I have both the M502 and M502A manual. The 502 says push 16*9 to cancel the call repeat mode and the 502A says push any key except distress to cancel the call repeat mode. The SC-101 standard was a pitiful attempt in the U.S. to "cheaply" introduce users to DSC. The idea to ban it has been in the works for years. Unfortunately, the gov't works very slowly.

And both of my radios will respond with an acknowledgement to a DSC Distress call - and I have done that down island where there is no USCG anywhere around.

I have an M502 in my shop and have just done a controlled bench test for this. The 502 cannot acknowledge a distress call. Neither SC-101 nor class D was ever intended to do this. You can only acknowledge an individual call.

Even different models of a manufacturers radio will respond differently. For instance there is no way to "turn off" the automatic channel switching on my two radios. Newer model radios may do something else.

Another SC-101 flaw.

These radios are available and in use world-wide, not just where the USA Coast Guard is located. So, bottom line, read your radio's manual to learn how your radio works with DSC. It is a wonderful feature, IMHO, and I wish more people would utilize it especially the DSC Call function to your "buddy boats."

Agree, and I understand now that you were referencing radio's with the SC-101 standard and were unaware of the differences between that and a true class D DSC radio. The OP has a class D radio.

Eric

[btrayfors]

I N C R E D I B L E ! ! !

Here is proof positive that VHF DSC has thus far been badly conceived and implemented. If anything, HF DSC is even worse (witness the 39 pages of DSC instructions in the Icom 802 manual).

In this thread we've seen that even experienced sailors and radio buffs have very different understandings of how some basic DSC functions are supposed to work.

DSC implementations vary by radio model, further muddying the waters.

And, in the U.S., the issuance of MMSI numbers by Boat U.S. and other private entities which aren't recognized by the international community (since they are not entered into the ITU database, as are FCC-issued MMSI numbers) has stirred the murky pot even further.

Perhaps this is why a very experienced professional radio tech -- who has been a strong advocate of DSC use -- chose VHF voice comms (and NOT DSC) when his boat was in serious difficulty off the Pacific Coast.

In a situation where many (most?) boaters have problems sorting out the use of their 1-2-BOTH battery switch, how in the world did the DSC designers envision that this complex system would be widely and correctly used?

Bill