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Old 26-04-2009, 20:14   #1
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Can Normal VHF Pick Up AIS ?

Hi Folks

The AIS frequencies are 161,975 MHz or 162,025 MHz VHF channels 87 or 88. (International)

Does this mean I can pick up AIS on my VHF and connect the Speaker Out to the computer sound card and then to a program like Shipspotter ShipPlotter

I'd try it but theres no AIS signals in this area at the moment.

Mark
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Old 26-04-2009, 23:14   #2
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Mark,

I've not tried it, but I believe the speaker or headphone audio out is filtered for voice frequencies so the AIS data is too distorted to be decoded. What people do is either use a radio with a "modem" output (unfiltered), or hack into the circuitry and take an output directly from the discriminator (FM detector circuit).
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Old 27-04-2009, 01:14   #3
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Thanks Paul.

Just hoping for a good, easy, cheap way
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Old 27-04-2009, 03:29   #4
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Mark,

AIS information is not audio frequency.

Class A AIS uses what is called SOTDMA (Self-Organizing Time Division Multiple Access) transmission protocol. In short, this means that an AIS will use two frequencies to alternate its trasmission cycle four slots ahead. AIS operates between 156 and 162 MHz but can vary in that range depending on the countries VTS.

Now, the modulation type for AIS is GMSK or FSK depending on what the AIS is transmitting.

An AIS will transmit two sentences basically.

$AIVDM - This sentence contains all the other ships static and voyage data that the host AIS is seeing.

$AIVDO - This is your own static and voyage data.

What is static data?? Static data is that data that describes your vessel and will include, but is not limited to, the following:
  • MMSI
  • Ship Name
  • Call Sign
  • IMO Number
  • Length
  • Beam
What is voyage data? Voyage data is data that is particular to the voyage you are currently on and may contain, but is not limited to,
  • Destination
  • Cargo
  • Souls on board
  • Time to Destination
AIS data is just that over the airwaves....data. Think of AIS as the same as DSC, teletype or fax with respect to whether you can audibly understand it or not.

NOW!! There are VHF radios out there that can take a NMEA feed from an AIS unit and display AIS data on thier screens. I'll let you guys figure out who those companies are
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Old 27-04-2009, 04:50   #5
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SOTDMA (Self-Organizing Time Division Multiple Access) transmission protocol.

I need an acronym like that like a hole in the head

Thanks for the good info

I shall wait and save my pennies. I do want one and when I grow up I want a transponder.
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Old 27-04-2009, 05:02   #6
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MarkJ,

No doubt you have already checked the prices here in Aus, they are around $800 - $100 for a receiver set, this also required an additional VHF antenna. This would then need to be connected so some compatable PC program (like SOB) or a compatable (newer) chart plotter.

I would have loved to have this system up and running on my last cruise but will wait until the equipment catches up a bit, I don't need it for now.

I know you are travelling north and could be heading towards Asia? If I was heading in that direction it may be worth the expense. Will follow you progress and see what the outcome is!!
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Old 27-04-2009, 07:19   #7
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Does this mean I can pick up AIS on my VHF and connect the Speaker Out to the computer sound card and then to a program like Shipspotter ShipPlotter
Iv'e done this in the way Paul described by taking the signal directly from the discriminator output on an old Icom M100. Not something for the average user to attempt.

Eric
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Old 29-04-2009, 07:22   #8
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@mark, have a look here Index of /files/sailing and download the icts2008_lowcostais.pdf
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Old 29-04-2009, 14:47   #9
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@mark, have a look here Index of /files/sailing and download the icts2008_lowcostais.pdf
Thanks muchly
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Old 29-04-2009, 15:10   #10
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Does this mean I can pick up AIS on my VHF and connect the Speaker Out to the computer sound card and then to a program like Shipspotter ShipPlotter
Like Fairbank56, I have used the discriminator output from a Yaesu FT2600 2m FM ham radio to drive Shipplotter which worked very well. The Yaesu had the raw discriminator output wired to a DB9 on the back of the radio which made the task much easier.

I have modified other VHF units to do the same thing but you need some fine soldering skills and should know your way around a circuit board. See this site for some examples: Discriminator Output
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Old 30-04-2009, 04:12   #11
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my next project
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Old 18-05-2009, 03:30   #12
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i have with success used my Discriminator Output AR-108/COM307 . had 31 vessels in the solent on the chart.
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Old 20-09-2010, 18:51   #13
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Iv'e done this in the way Paul described by taking the signal directly from the discriminator output on an old Icom M100. Not something for the average user to attempt.

Eric
I have a M100 HF and would like to know where to put the tap on the discriminator circuit for AIS data. how can find where to place the tap?

Dave
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Old 20-09-2010, 20:12   #14
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VHF Radio with Integrated AIS receiver

Now that there are VHF radios on the market that have an integrated AIS receiver built into them this gives a very cost effective way to go. See details of an example of such a unit in the link below.

http://www.navagear.com/2010/02/standard-horizons-new-vhf-radios-with-ais-integration/
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Old 21-09-2010, 16:48   #15
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I wish they'd had these 18 months ago when I purchased a new Uniden UM 525. I just can't bring myself to spend the money on a new radio so soon.

I have an old ICOM M100 VHF I'd like to use to receive the AIS data grams. But I need help finding the correct point in the circuit to tap off the signal before it's filtered.

Dave
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