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AIS Receiver Range Record?

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Paul

Jan 1, 1970
0
I just received a SR162 dual-channel AIS receiver, which I will be using on
my sailboat -- the old single-channel SR161 will end up at home. I've been
testing at my house it these last couple of days, and have been amazed at
the range I have been getting. I've seen many ships 100 to 200 nautical
miles from my position, and last night saw one at 492 miles, and another at
673 miles" (this one was "Ikarugu", a freighter heading to Long Beach, CA)

Of course, I also moved my whip antenna from the deck railing to the roof,
which has to help a tiny bit. I am at about 1000ft elevation, 4 miles from
the coast, and 40 miles north of the Golden Gate Bridge. Still, this is so
far beyond line-of-sight that it has to be tropospheric ducting.
Occasionally, VHF signals make the trip from Hawaii to California (about
2000 miles), and an interesting by-product of widescale AIS deployment is
that there are now all these AIS "beacons" spread out all over the oceans,
running continuously.

AIS DXing - who holds the record?

-Paul
 
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Larry

Jan 1, 1970
0
[email protected] wrote in @h48g2000cwc.googlegroups.com:
Paul, this is very impressive. Is there a chance noaa is repeating
traffic from a bouy in your area?

-Mark

NO bouy has, or ever will have, an AIS system in it. There MAY be an AIS
repeater in his area, but it will be on a real tower, not a bouy. To mark
the bouy's position, a shore station may send the bouy's information, which
AIS is designed to do but, of course as usual, America is 20 years behind
Europe in implementing everything, any more.

To make a bouy show up on your AIS, all the shore station does is transmit
its data. The position of the actual transmitter has no bearing,
whatsoever, on where anything shows up, like a radar return does. It's
just DATA...even bad data as someone reported a ship traveling overland the
other day...miles from its position.

Caveat Emptor
 
P

Paul

Jan 1, 1970
0
Paul, this is very impressive. Is there a chance noaa is repeating
traffic from a bouy in your area?

-Mark

Mark,

The "AIS repeater" thought did occur to me, and I haven't researched it, but
I am not aware of any AIS repeaters in the area. The DX signals do seem to
be most prevalent when the local "marine layer" (fog) comes in in the
evening, and I am assuming that the ducting, if that is what's really going
on, is occuring when there is stratification in the lower atmosphere. Also,
my best DX was from the "Ikaragu", at lat 30.57N lon 132.56W, which is about
630 NM out from the nearest coastline. I would be very surprised if there
were repeaters within LOS of that point, and if so how would they send the
signal back to the mainland? They could use satellite, but that seems
unlikely. Further speculation on my part would be silly...

Does anyone know if there are any AIS repeaters currently operational? This
technology is so cool, but I have to remind myself occasionally that it
isn't infallible -- see my recent posting about AIS position errors.

-Paul
 
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Paul

Jan 1, 1970
0
Sorry, here is the direct link to the PDF -
http://www.uscg.mil/d13/units/vts/AISSRSFinal.pdf
NO bouy has, or ever will have, an AIS system in it. There MAY be an AIS
repeater in his area, but it will be on a real tower, not a bouy. To
mark
the bouy's position, a shore station may send the bouy's information,
which
AIS is designed to do but, of course as usual, America is 20 years behind
Europe in implementing everything, any more.
[...]

Larry, Mark, it sounds like you're both right. The buoy repeater described
in the link is surprisingly like what I had conjectured in my previous
posting -- it is more of a remote receiver (transceiver?) than a true
repeater. I haven't been able to find details of *any* type of repeater
deployment in the San Francisco area, but I assume that there may be some in
operation, used to fill in radio dead-spots.

Still, as far as explaining the reception I was getting (from a ship 673 NM
distant), I can't see any reason for wanting to repeat that signal in the
S.F. Bay area. S.F. VTS may be interested in what a distant remote receiver
buoy is hearing, but they would get that data through their land network,
and would be unlikely to re-transmit it over the air. Tropospheric Ducting
is my theory, and I'm sticking to it!

-Paul
 
H

Holger

Jan 1, 1970
0
During recent good propagation conditions I have decoded targets a goo
350 nm away - with a receiver in Norway right across the North Sea t
the Scottish coast and along the coast of Belgium. Equally impressiv
where stations received across 200nm of land -right across Sweden....

The use of repeaters sounds interesting, anyone knows some details?

Holge
 
P

Paul

Jan 1, 1970
0
Queeg said:
Paul - I am assuming that the SR162 and SR161 have the same range, and
that either would have made the same long distance discovery. Is this
right? Or does the dual channel have a better chance of seeing
something far away?

Do you notice much difference in the speed of target information
acquisition between the two? Is the SR162 noticeably faster? My SR161
picks up targets and shows their speed quickly, but can take 5 or 10
minutes to fill in the name, size, destination, etc.

Gary,

I haven't compared the specs, but I am assuming that the sensitivity is
similar between the two units. I haven't done enough comparison to say for
sure, but the dual-channel unit ought to acquire the info more rapidly --
and that does seem to be the case from my brief experience. I will move my
older single-channel unit to my house (just for fun, and as part of my
development platform).

I want the dual-channel unit on the boat, because my antenna will be mounted
on the stern rail (not as good as on the mast), and I want to acquire the
signals ASAP. I, too, have seen the fast initial acquisition of the dynamic
data, which gets sent often, and the slow (or not at all) acquisition of the
static data, which is sent less frequently. The dynamic data is all you
really need for collision avoidance, but it is nice to get the ship name
(contained in the static data).

I will report back once I get more experience with the system. So far, the
SR162 seems very nice, although the price delta from the single-channel unit
is a bit steeper that I would like.

-Paul
 
P

Paul

Jan 1, 1970
0
Holger said:
During recent good propagation conditions I have decoded targets a good
350 nm away - with a receiver in Norway right across the North Sea to
the Scottish coast and along the coast of Belgium. Equally impressive
where stations received across 200nm of land -right across Sweden....

The use of repeaters sounds interesting, anyone knows some details?

I finally decided to go to the source (regarding AIS repeaters in the San
Francisco area), so I sent email to the Training Director at the S.F. Vessel
Traffic Service. He tells me that there are currently no AIS repeaters in
the Bay area, nor are there any virtual aids to navigation at this time. I
asked nicely, and he offered to give me a tour of the VTS facility! I will
report back on any AIS info I learn from the visit.

Here is a link he sent me about AIS as used here:
http://www.uscg.mil/d11/vtssf/Training/ais_main.htm There isn't much new,
but one of the documents listed contains the dock codes for the various
facilities around here. Now, if I see a destination like "US OAK 58", I
know where it is.

-Paul
 
P

Paul

Jan 1, 1970
0
A follow-up to my original posting:

I have been using my Pocket PC program to capture and process the AIS data
being received by the SR162 receiver, and just wrote a quick program to
diaplay the tracks on Google Earth. Here is a link to my boat's blog, where
I have put some GE screen images, as well as the GE track-file:
http://www.sailvalis.com/wordpress_1/?p=129

By the way, I did visit the San Francisco VTS facility, and learned that
there are no AIS repeaters in the Bay area. This propagation is due to
tropo ducting for sure.

-Paul
 

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