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Old 02-09-2010, 15:01   #1
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AIS Alert

Quote:
CAUTION TO AIS USERS
NAVIGATING THE JAMES RIVER, YORK RIVER, UPPER CHESAPEAKE BAY, DELAWARE BAY, NEW JERSEY
SHORE, AND, NEW YORK HARBOR AND APPROACHES
YOU MAY BE INADVERTENTLY OPERATING ON DIFFERENT AIS CHANNELS
http://www.panbo.com/USCG%20Alert%200710.pdf

Hopefully this is all worked out by now. However, in as much as I can tell, if this feature is used by the competent authority [sic] most/all class B or listen only AIS's will no longer see or be seen by class A stations that have switched frequencies... AIS is great but it's newish so there are bugs and failure modes that we users aren't yet familiar with. Maybe too soon to chuck out the old RADAR or paint the pilot house windows black... Just saying

Tom
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Old 03-09-2010, 07:06   #2
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I saw that notice last week so I changed my radio that I use in my shop for monitoring AIS to channel 22 and found 1 cargo ship anchored in the Chesapeake Bay off Annapolis that was switched to that channel. All others were on the normal AIS channels. I routinely pick up AIS targets out to 150 miles in the early mornings.

Eric
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Old 03-09-2010, 07:16   #3
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Tom, I have posted the full notice here a few days back,
Caution to Mid Atlantic AIS Users
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Old 03-09-2010, 12:22   #4
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Originally Posted by Waterwayguy View Post
Tom, I have posted the full notice here a few days back,
Caution to Mid Atlantic AIS Users
Thanks. Sorry for the double post. I didn't see your post and I just came across the notice...

My concern isn't so much with the remote command as with the fact that not all AIS units (particularly the types that non-commercial users use) respond to it. That could lead to some units being switched and others not. Anyway, there's no point in having two threads on this so lets use yours.

Cheers,

Tom
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Old 03-09-2010, 13:25   #5
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Tom: this affects class A and B AIS transceivers equally. It is not fuel for the A vs B debate.
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Old 03-09-2010, 16:02   #6
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Originally Posted by sandy daugherty View Post
Tom: this affects class A and B AIS transceivers equally. It is not fuel for the A vs B debate.
I guess I was misinformed. I thought the message was optional for "B" -- I certainly read that somewhere but it would have been second hand since I don't have the annexes. In any case, my SR161 will not act on it. So it will certainly be a potential issue for some receive only units.

I didn't know there was an ongoing A vs B debate here. I certainly didn't mean to add fuel to it. Sorry.

Tom

PS. As a moderator can you combine the two threads?

Cheers

T.
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Old 09-09-2010, 13:19   #7
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We can merge threads, but it gets messy.
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Old 10-09-2010, 08:47   #8
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[QUOTE]most/all class B or listen only AIS's will no longer see or be seen by class A stations that have switched frequencies... QUOTE]

no it has nothing to do with that , CLass A receivers cannot filter out B messages.
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Old 10-09-2010, 11:50   #9
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[QUOTE=goboatingnow;518944]
Quote:
most/all class B or listen only AIS's will no longer see or be seen by class A stations that have switched frequencies... QUOTE]

no it has nothing to do with that , CLass A receivers cannot filter out B messages.
Well, I'm told I was mistaken but my understanding was that B was not required to have the channel switching capability (in response to an outside command). I based that on an old and non-official document that I used to write an AIS decoder and some comments on a blog. At the time at least the official documents were not freely available. At any rate, my fear was not that A's would filter B's but that B's and A's would end up on different channels. I believe this is an issue for some listen only AIS radios but I am told that the B spec does require the ability to change channels so it should not be an issue with them.

Tom
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