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[aprssig] Re: AIS and DSC - lots of questions

KC2MMi kc2mmi at verizon.net
Thu Apr 7 23:28:26 UTC 2005


Jim-
 I'm not sure how AIS and DSC are topical here, except in that there has
recently been some provision to allow for "intelligent" radios that will do
things like poll the different frequencies and seek each other out. This is
an area of experimentation that hams have generally ignored, but obviously
it could solve the need for clear channels on APRS as well.

<<Theoretically all vessels are
supposed to apply for a 10 digit ship's identification number. >>
 Not quite. Commercial vessels, yes. Recreational vessels, no. Recreational
vessels are not even required to carry a radio. And, if they apply for a VHF
license, the fee is now $200--the same as for commercial vessels. The FCC
has effectively told recreational sailors not to apply for radio licenses,
and not to use any services that might require them. I don't know if you can
obtain an MMSI without one, but many sailors have very tight budgets, not
luxury yachts or yachts at all, and we're not replacing perfectly good
radios with DSC rigs. "Ain't gonna happen" except with the serious
racing/offshore/luxury trades.

<<So if you have the MMSI of a friends' boat...no other will be alerted
by an alarm. >> Yes, but again, most boating here is near-shore. Do you know
what happens when you call the USCG on the marine VHF? Their first question
is "Do you have a cell phone on board?" and they ask you to call them on the
cell, to clear the working channel. Typical cell range is up to 3 miles
offshore with no special equipment or provisions.

<<The AIS or Automatic Identification System is quite different than the
DSC>>
Yes, AIS is used with vessel in port traffic control systems. In a large
harbor (NY, Boston, etc.) the USCG requires all *commercial* traffic to
participate in the traffic control system. They did this long before AIS,
but then it was all manual calls and radar plotting. This is because ships
can take a mile or two to stop, and if they are confined to channels, you've
got quite a problem unless you've got 100% traffic control in the harbors.





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