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From: Dave Cooper (no email)
Date: Wed May 09 2007 - 20:54:24 EDT
Some time back I had reported on our concern with the range of AIS reception
that we were seeing with our SR161 unit from Milltech.
Suggestions had been made by everyone as to antenna, cables, location etc,
etc as to why the unit might have what I perceived as poor sensitivity. We
were getting 10-15 miles with an occasional 20 miles target.
On our trip up from Venezuela I could generally see ships before the AIS
would.
I purchased another unit from them with the understanding that they would
refund this purchase on return of the other unit.
So what do we see with the new unit??? 40 miles routinely and a few at 42-44
with one at 48 so far, thank you very much :-) This is what I had expected
from the get go but we sure had to jump thru hoops to get there. We're using
the same cables and the same antenna. However I have replaced the 3 db with
a 6 db which hasn't seemed to provide any additional range improvement.
>From what we learned very few folks really understand AIS and what its range
is. One guy is ecstatic if he sees 20 miles when in fact he should be seeing
40 miles. Others blame this or that for generating noise or other
interference.
My advice is to keep pushing till you get this kind of range as it what the
AIS Standards expect. Anything less is BS, IMHO.
Now that we have so many targets in range we get to see how badly they have
been set up. A good target example is a 30 meter boat with a 160 meter beam
with a draft of 3 ft bound for Durban while anchored in Road Harbor, BVI
with a speed of 6kts. DUH!!! Sure makes you wonder who sets these up and who
the QC entity is that signs off on the installation.
SO we have a very good awareness of ships now long before the radar sees
them but the data we get is always suspect as it isn't controlled in any
way. This is an area that surely needs to be tightened up before the next
level of AIS class B transponders hit the market.
Anyone for the Chaos Theory???
As always YMMV,
Dave & Nancy
Swan Song
Roughwater 58
Caribbean Cruise '07
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