DSC date question

[markcouz]

I have an old Garmin GPS 12xl which sends GPS info to my Icom 412 and 802 radios, which would be used if I ever need to press the Big Red Button.

The GPS 12xl is the only GPS I have on board which the radios will accept, the others being higher baud rate which the radios will not accept.

The issue I have is that while the GPS provides perfect time and location info, the date provided is about 20 years ago as a result of the fairly well known EOW Rollover Error.

I have done quite a bit of research and it appears that while Garmin did publish a fix for the previous Rollover Error 20 years ago, they will not be releasing a fix for the 2019 Rollover Error related to these old units.

My question for those with knowledge of the DSC system is what effect will this incorrect date have on my transmission? Is date even transmitted as I assume time and location would be more than enough info for emergency services to take action?

[continuouswave]

For help in understanding the a contents of a DSC message, see my article at

continuousWave: Whaler: Reference: Data Interface in Digital Selective Calling Class-D Radios

A DSC message of type DISTRESS ALERT includes in the message the time in UTC.

Non-distress DSC messages also usually include the time in UTC.

I don't see any indication that the date is sent. From my understanding, messages received by a DSC radio are presumed to be sent at the moment they are received, so the date would be assumed to be that day's date. The only exception to this might be a DSC DISTRESS ALERT RELAY message, which might be a re-transmission of the original message.

Re your set up of various GPS or GNSS receivers: you generally can change the baud rate of an NMEA-0183 interface on a radio to be either the standard 9600-bps or the optional NMEA-0183HS 34,800-bps. This may allow the use of a different GNSS receiver for input to the radio for position and time.

[markcouz]

Thanks for your reply, which confirms my thought that the incorrect date will not have any adverse effect on a DSC transmission in an emergency (I will read your linked document for additional insight).

Regarding the radios, they accept NMEA 0183 V2.1 at 4800 baud and that's it, no adjustment available.

I am able to adjust the old Garmin unit to provide that output and the radios accept it - I have tried more modern GPS set to 4800 and it is rejected by the radios (although I can see the sentences in OpenCPN no problem), probably version incompatibility or whatever but after several attempts over several days I am now ready to just keep using the old Garmin!