Snowpetrel, et al,
While I have no interest in tracking, nor posting
my track / position....but, also have no worries that "Big Brother" has been doing this for a while now...
But, I would like to comment on the AIS antenna
being used on your folk's boat...
A 400mm long antenna
(about 15" - 16") seems like a rather odd choice for AIS on a pleasure boat, where you're using a Class B AIS (at 2 watts output), and you would want as good antenna as you could effectively mount to maximize your lower-powered (2-watt) Class B AIS...
Shakespeare's 5216 is their 15" VHF
antenna, and in the real world will have about 2db - 3db less
gain that the standard 3' (1m) SS Whip...
And, if they're using a loaded "big duck" antenna (a 16" long "rubber duckie"), figure on another
1db - 2db loss...
Originally Posted by Snowpetrel
So far it seems to have worked to a limited extent on my folks boat, with updates every few hours while offshore
, less when in enclosed waters.
I wonder if tilting the antenna horizontal would improve reception
Their antenna is a short 400mm stubby one
which probably has less gain than a longer one so maybe this helps?
Class B AIS is 2 watts, not one watt...
But, with the above antenna, it's at best effectively 1 watt....and probably less...
Originally Posted by Snowpetrel
I am pretty impressed (and slightly concerned) with the detail so far. Seems like it is reasonably viable even with a weak 1w class B. It probably helps a lot that the southern hemisphere is pretty quite boat wise. Seems like the system has limited capacity and in heavy traffic the weak class B signal struggles to get priority. I did hear some rumors of a new S-ais protcol that excludes class B. But also some new class B tech that will boost s-ais reception
. Interesting field.
I have been researching antenna types. It might be that the high gain antennas dont work so well for S-Ais due to them concentrating the signal around the horizon. Maybe a short low gain antenna might work better.
For what its worth my folks have (I think) a 1/4 wave ground dependant antenna without the ground plate. At the moment it is very inefficient giving only 5 miles of reliable range. It will be interesting to see what happens when they install the ground plane. Antenna theory is a deep rabithole! Anybody who actually knows what its all about care to comment?
I suspect that there is a "ground" on that antenna...whether the mounting itself, mast
, railings, etc....or even the coaxial shield....the antenna probably has a ground/counterpoise (although this antenna is certainly not a very effective one!)
And, while a "lower-gain" antenna usually has a wider antenna pattern (less directivity), antennas that are lower gain because of their shortened/loaded design and/or their inefficiencies, do NOT have a wider pattern, but rather the same pattern of their full-size counterparts, just with lower gain...
Also, note that while a Quadrafiler helix antenna would be best for horizon-to-horizon satellite
tracks, the main purpose of AIS is for terrestrial use, not satellite
But, I suspect that these S-AIS transponders are designed with Quadrafiler antennas in mind???
I do hope you don't mind the comments....as they are already out there, and their AIS is working, so there's nothing to do now....just thought you all might want some further info...