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Old 01-07-2016, 11:01   #61
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Re: Satelite AIS.

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Originally Posted by hoppy View Post
I don't care about S-AIS for SAR for myself. I have a GPS EPIRB, PLB and I have included my YellowBrick tracking site and my current satphone number when I registered my EPIRB with AMSA


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If your boat were to go off with a very loud bang one day S-AIS records may be all they have.

With simple yotreps position reporting via HF I have found it quite 'flakey' ... quite often gaps of several days when i go on the net for a looksee when I know I was sending them daily.

Re accessing the data.... my AIS has been switched off for a fortnight but I can still access this from marine traffic..
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Old 01-07-2016, 11:43   #62
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Re: Satelite AIS.

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Originally Posted by El Pinguino View Post
If your boat were to go off with a very loud bang one day S-AIS records may be all they have.

With simple yotreps position reporting via HF I have found it quite 'flakey' ... quite often gaps of several days when i go on the net for a looksee when I know I was sending them daily.

Re accessing the data.... my AIS has been switched off for a fortnight but I can still access this from marine traffic..
No problem with my YellowBrick, so far
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Old 01-07-2016, 15:31   #63
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Re: Satelite AIS.

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...
Quote:
Originally Posted by Snowpetrel View Post
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 by satelites

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...
Quote:
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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 tracking...
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...


Fair winds..

John
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Old 01-07-2016, 17:11   #64
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Re: Satelite AIS.

Thanks John for your excellant input. I have no idea why they used that particular antenna. It specifically says it needs a base plate to work properly. Probably designed to go on a car roof or something.

Maybe you are right and there is enough mass below it, with the sea water and the hull and adding the base plate wont help much, in which case a new antenna might be in order, because its range for AIS is not really good enough at the moment.

They could use a splitter, on the masthead one, but I like the simplicity and redundancy offered by having two separate antennas.

It would be very interesting to see how much a sat optimised antenna, like the quad helix would degrade terrestrial performance? Or if laying a whip horizontal would help?

Anyway thanks for the comments.

Cheers

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Old 03-07-2016, 02:19   #65
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Re: Satelite AIS.

It's still working nicely, with a few odd weird lags.

Yesterday they wandered over to another bay and Marine traffic showed the move nicely even though it wouldn't give me boat details I knew it was them. Satelite tracking worked fine.

Somehow they must have got a brief signal through to a land station today, Enough to notify me they were moving via email, and show full details for a while. Got a good sat fix, and another now.

Its quite fun tracking them, though at some stage the novelty will wear off, or they will get sick of it and turn the thing to receive only!
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Old 03-07-2016, 03:35   #66
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Re: Satelite AIS.

As I stated before, the AIS web site tracking sites do not necessarily show live situations. I know from where our boat is moored, that it can sometimes be "lost" for hours at a time when I know that the station that records it (the marine rescue group that I belong to) gets the signal but Marine Traffic does not show it, even though they access this data.
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Old 03-07-2016, 06:50   #67
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Re: Satelite AIS.

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Originally Posted by clownfishsydney View Post
As I stated before, the AIS web site tracking sites do not necessarily show live situations. I know from where our boat is moored, that it can sometimes be "lost" for hours at a time when I know that the station that records it (the marine rescue group that I belong to) gets the signal but Marine Traffic does not show it, even though they access this data.
I realise the info is not live, this is interesting info, I guess it takes a huge amount of processing power to track the numbers of vessels they do, but so far it seems to be reasonably current. At least usually not much more than say 4 hours or so on average via satellite with occasional longer breaks, and the rough age of the position is given (though there does seem to be the odd discrepancy in this info). Since I am getting the satellite info for free, I am pretty impressed so far.

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Old 03-07-2016, 08:04   #68
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Re: Satelite AIS.

Would you still be impressed if you were to start paying? 😜


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Old 03-07-2016, 08:20   #69
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Re: Satelite AIS.

Well, Yes, I would still be impressed. But I wont be paying.. even if it were to be only $100 a year because I don't have the 'need ' for all that info.

Also, I don't feel the 'need' to tell the world where I am every 5 minutes. I don't use Facebook either.. I'm old fashioned... I send emails to people to let them know where and what... and not group emails either.. personalised ones.. how quaint is that
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Old 03-07-2016, 08:41   #70
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Re: Satelite AIS.

Quote:
Originally Posted by Snowpetrel View Post
Thanks John for your excellant input. I have no idea why they used that particular antenna. It specifically says it needs a base plate to work properly. Probably designed to go on a car roof or something.

Maybe you are right and there is enough mass below it, with the sea water and the hull and adding the base plate wont help much, in which case a new antenna might be in order, because its range for AIS is not really good enough at the moment.

They could use a splitter, on the masthead one, but I like the simplicity and redundancy offered by having two separate antennas.

It would be very interesting to see how much a sat optimised antenna, like the quad helix would degrade terrestrial performance? Or if laying a whip horizontal would help?

Anyway thanks for the comments.

Cheers

Ben
I would venture that 99% of the ships that are being reliably received by the sats have bog standard vertical AIS ants...

Why don't your parents just buy an ordinary VHF ant. Mine is a basic GME masthead mount job that is secured to the taffrail.... works good.
I can't find that model listed any more ( EDIT.. found it ! https://www.whitworths.com.au/main_i...003&search123= )but this one is cheaper anyway.. GME AIS Antenna
I'm sure you could just custom build a securing arrangement... mine involves the alloy stand off ( for masthead fitting) that came with it plus a plastic clamp thingo from Enzed hydraulics.
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Old 03-07-2016, 09:51   #71
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Re: Satelite AIS.

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Originally Posted by El Pinguino View Post
I would venture that 99% of the ships that are being reliably received by the sats have bog standard vertical AIS ants...
I would venture that 99% of them have class A equipment and high db ants.

How does this add to the picture?

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Old 03-07-2016, 10:10   #72
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Re: Satelite AIS.

http://www.navcen.uscg.gov/pdf/AIS_C...n_By_Class.pdf

We are talking 12.5 W vs. 2 W TX.

Also very likely lower db antenna unless the boat is a motor yacht/trawler.

These sure do not affect how well the sats can pick up the signal?

I would guess otherwise, if I were to judge from the info I posted above.

IMHO (my working, not fixed, view): you want to be seen and so you want the strongest signal out. Similar to VHF, SSB and sexual attraction.

Open to discussion. I am nearly lay when it comes to radio.

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Old 03-07-2016, 14:37   #73
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Re: Satelite AIS.

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I would venture that 99% of them have class A equipment and high db ants.

How does this add to the picture?

b.
A high db antenna as you put it ( it should be "dB" small d for deci and big B for Bell) will not help satellite reception, in fact most likely the opposite.

Very basically all 1/4 wavelength vertical antennas used as AIS antennas will have a radiation pattern resembling a donut. The higher the gain of the antenna the flatter the donut. More signal going out horizontally and less upwards. A lower gain antenna will in general radiate vertically better than a higher gain one and therefore potentially reach the sats better.

This is the same reason we use a simple 1/4 wavelength whip antenna on sailing yachts that roll around a lot and higher gain antennas on motor yachts which are more stable and where the high gain can be used. If a high gain antenna is used on a sailing vessel when the vessel is healed, say whilst sailing, the donut will be inclined with the power going towards the sea on one side and into the sky on the other; hence the usual advice to fit low gain antennas to sailing vessels.

The AIS satellites are in fairly low earth orbits (I'd have to do some research to see exactly what height they orbit at) which means that the path loss of the signal from the ship to the satellite is not great. I chatted to the Soviet MIR space station with just a few Watts of power from a hand-held 2M band VHF once. I receive weather satellite signals on the VHF band all the time. Reaching space (or vice versa) with low powered VHF isn't a problem.
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Old 03-07-2016, 15:36   #74
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Re: Satelite AIS.

On the move... This is fun!

Wish I had known about it earlier when we crossed the tasman.

Saying that I think its only working so well because there are hardly any other boats about where they are. It seems the satellites get swamped pretty easy due to the massive footprint they have.

Makes me laugh that I seem to always get fortress anchor adds. Google must know I am an anchorholic, but it obviously know I already have 3 of them!
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Old 03-07-2016, 16:06   #75
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Re: Satelite AIS.

What Chris said at 73

And also...
these new AIS-Sarts only transmit at 1W and the antennas are that short I reckon they would be near omni-directional
http://www.kannadmarine.com/download...SART_specs.pdf
http://www.kannadmarine.com/images/s...t%20manual.pdf

Someone should buy one and bust it open to see what the ant looks like.. not me.. I've already risked all with my trial subscription to MarineTraffic.

Meanwhile.. my latest bit of info from Marine traffic.... you can see the tracks of 5 super trawlers here ... quite a few are Vanuatu registered ... the one pictured is German and 140 metres LOA. Vessel details for: ROS171 (Fishing Vessel) - IMO 9182801, MMSI 218066000, Call Sign DEAN2 Registered in Germany | AIS Marine Traffic

They will be hoovering up the mackerel that is converted into fishmeal for the salmoneras ... 4kg of mackerel to produce 1 kg of salmon... plus the salmon are full of antibiotics... and the salmonellas are taking up all the good anchorages.....!!! OK..rant over... back on track.

Ben, they reckon the AIS sats can handle everything that comes their way.. dunno how.
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