What does AIS sound like ?!

[whipper_snapper]

This may seem a strange question, but, does anyone know what the modulation system used for AIS is and if I will hear it if I listen to the appropriate frequency in FM or some other mode ?

I don't suppose any radio ham with the capability to listen in and is in range of shipping could try listening and let me know what, if anything they hear.

The reason for asking this is that we have a NASA AIS engine connected to a PC and chart plotter which is capable of receiving AIS and which we believe is set up correctly. We have however, never seen a single target.

There are 2 possible explanations:

1. No one is transmitting AIS
2. Something is wrong with our setup.


1. Is in fact perfectly possible given piracy fears in the waters we sail in. I know of no way of generating a test signal. The only test I can think of which is independent of the 'VHF antenna-AIS-computer-charting software system is simply to listen for noises on a separate receiver; I have a Yaesu FT-857 which can listen on AIS frequencies and in any mode. Also which of the two is mostly likely to be transmitted ? Is the older generation NASA AIS engine capable of hearing both channels?


Thanks

 

[tillergirl]

Kenya is in the Piracy risk area and the advice to ships is to switch off their AIS. If you go to the public world AIS sites, you will see no AIS data displayed in that area (Mind you that might also be because there are no linked receiving stations). Certainly I was told in Mauritius that no ships use AIS in their area as they are on the edge of the piracy zone which doubles their work in their EEZ. You could say its pointless you having an AIS receiver in that area, at least for the estimated period that piracy is expected to last which I think is ages, years and years. Whether ships trun on their AIS on closing Kenya ports, I don't know but I doubt it.

 

[whipper_snapper]

Yep, that is what we always assumed. However, the advice is:

In the Somali Basin or further afield where there are far fewer warships an AIS transponder should be switched off unless the yacht is either aware of military forces in their vicinity, or is under attack.

So we would very much like to know if our system is working, so that we could see a ship in trouble and in fact the 'snapshot of shipping movement' does show several vessels transmitting positions in Kenyan and Tanzanian waters.

 

[rivonia]

We have AIS send and receive. It has two switches that are as follows; I= turn on 2= receive AIS siganal but do not send out your own. Number two is ideal for areas of Piracy/terrorists.

If you are not getting signals, try to find someone in your area who also has AIS and see if you can read each other.

Good luck

Peter

 

[LadyInBed]

what the modulation system used for AIS

AIS is composed of small bursts of data sent over normal marine VHF but using GMSK modulation instead of FM

and if I will hear it if I listen to the appropriate frequency in FM or some other mode ?

No.

 

[Bilgediver]

Yep, that is what we always assumed. However, the advice is:




So we would very much like to know if our system is working, so that we could see a ship in trouble and in fact the 'snapshot of shipping movement' does show several vessels transmitting positions in Kenyan and Tanzanian waters.

If you get a scanner radio and tune to the ais frequencies you will hear short bursts of noise at irregular intervals .

See Here for frequencies

http://www.euronav.co.uk/Downloads/manuals/AI3000 manual revV.pdf

The output from the AIS engine is nmea so makes a different noise it can be read using hyperterminal in windows.

The AIS frequencies can be listened to using a VHF scanner or ham walkie talky with wide band receive.

 

[Tranona]

Go onto the following link
www.willrite.co.uk/AIS/downloads/commtool.exe

That is the website of John Harris who wrote the software for NASA and the download is a tool to test your receiver is capable of receiving.

I had the same problem when I first set mine up, even though I am only 3 miles from Poole Harbour because the number of ships transmitting is very low and I thought I would see masses. Works fine in practice except my charting software only shows basic information.

Hope this helps

 

[alant]

Check online?

Yep, that is what we always assumed. However, the advice is:




So we would very much like to know if our system is working, so that we could see a ship in trouble and in fact the 'snapshot of shipping movement' does show several vessels transmitting positions in Kenyan and Tanzanian waters.

http://www.marinetraffic.com/ais/

Why not check possible targets in your area, on this site & also see if 'you' are showing up.
Then check the 'target' on your own AIS to see if working ok.

 

[slisand]

do you checked the baudrate? plotter an AIS needs the same.
i had that problem.

andreas (GER)