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Old 28-12-2012, 18:08   #1
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AIS Made Easy, Sort Of

I wrote this for people who want to use an existing radio as an AIS receiver. In other words people who like to do things the hard way. The easy way is to buy a dedicated AIS receiver and plug it in. The hard way, my way, involves finding a suitable radio or modifying an unsuitable one, getting three additional software programs, two of which are not used as their developers intended, then getting it all to work together. It is not overly complicated but rather involved. I am using 64 bit Windows Home Premium.

I am going to start by assuming you have a suitable radio. I avoided the whole problem by using my Icom 706 which has a data port for digital data. If you want to persue radio modifications try here: lDiscriminator Output

The first step is decoding the raw AIS signal, via your computer's sound card, into a NMEA data stream that OpenCPN can understand. For this you need AISMon. Go to groups.yahoo.com/group/aismon/ look under "Files" and download "AISMon_2.2.0.exe" and "LA_LB_Snippet.wav". The wav file will be used for testing. Note that you will have to register in order to access this site. Install the software.
Now we have a NMEA date stream. Unfortunately AISMon and Opencpn will not talk to each other directly. We need some Virtual Com ports. This part took half a day of internetting and fiddling around. The favorite software, VSPE, that people used in the past will not work with 64 bit Windows 7 unless you get the paid version. In one of the forums someone mentioned NavMon which is a program for displaying GPS and AIS data but also has the ability to create virtual ports. This is the way I went. Go to www.navmonpc.com and under "Downloads" get "Version 1.13 Setup". Get the four user guides as well as this program does much more than creating virtual ports. Alas the virtual port feature does not work with 64 bit Windows either but there is a patch. Go to GpsGate Client - Products - GpsGate.com and download "Free GpsGate Client For Windows". GPS Gate Client is intended for sending data from one GPS to several programs but it integrates itself into NavMon. Install GPS Gate Client first then NavNon. NavMon will ask if you want to install Franson Serial Tools. Say no, this is what the patch fixed. If, perchance, you have already installed NavMon on your computer you have to uninstall it and the Franson drivers before doing the new install. See NavMonPc User's Guide Supplement 1.13 for more information. Incidently NavMon has an active users group at NavMonPc : NavMonPc Gen 2.
Now for some configuring. Close everything down then open NavMon. Go to "File/Connections/Virtual Port A,B,C". Virtual ports are on the left. We need two ports. Set "Virtual Serial Port A" to an unused Com port number (I used 7). Click "Connect" and tick the "Autostart" box. Do the same for Port B using a different Com Port number (I used 8). Open OpenCpn. Under "Tools/AIS" in the "AIS Data Port" drop down menu select one of your Virtual Port numbers (I picked 8). Open AISMon. Tick the Serial Output box, set the Com Port to your other Virtual Port ( 7 ) and set Baudrate to 38400.

Now to see if it works. In AISMon click "Replay File" and navigate your way to where you stored the LA_LB_Snippet.wav file. AISMon should show the following under Demodulator Counts, Syncs: 103, Valid: 99 96%, Errors: 4 4% if it is decoding properly.
Open up NavMon. Click "AIS" on the Tool bar. Click on the little "AIS List" box. If the Virtual port configurations are still visible click "Done". Now go back to AISMon, replay the wav file and click "Start Monitoring". The NavMon AIS Status box should go green and say 39 targets. Also you will get a listing of all the 39 targets.
Open up OpenCpn and head to Los Angeles (33deg42min N, 118deg15min W). You will see a bunch of yellow triangles (Ships!). Everything works.
Because the data input is not continuous after a few minutes the programs consider the data out-of-date and it will disappear. Go back to AISMon and replay the wav file.

Note that no changes are necessary to any of your GPS input settings.

After a fresh boot open NavMon first to get the virtual ports started, then AISMon and OpenCpn. GPSGate does not need to be started. However it starts itself when the computer boots. I thought this was rather presumptuous of it and disabled it's autorun function.

After connecting an antenna to the 706, tracking down a corroded audio connector and adjusting the volume settings everything worked. May you be so fortunate.

Regards

Lew
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Old 29-12-2012, 09:46   #2
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Interesting. Thanks.
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Old 29-12-2012, 10:29   #3
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Re: AIS Made Easy, Sort Of

Most impressive!

If you are the geek type that does not mind making life complex then that sounds like an interesting way of going about it. For us mere mortals with IQ's below 160, a plain Jane AIS receiver sounds like the way of going about it.
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Old 29-12-2012, 16:48   #4
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You lost me at Discriminator output.......
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Old 30-12-2012, 16:35   #5
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Re: AIS Made Easy, Sort Of

The words "discriminator output" form a link.
Follow that, and you'll be enlightened.

Roughly, it is the pure receiver output of your (VHF-) radio, before filtering out frequencies that the human ear is not supposed to register, and before the squelch cicuit.

The link explains this and how to get to it for a lot of radios.

Not everyone has all the money in the world to spend for gimmicks like an AIS receiver.
The chance to have some spare radio laying around is quite good, so you'll be able to save some money this way.

But do remember that this will get you only 1 channel per radio and you cannot use that radio for other purposes.
This doesn't have to ba a problem, as moving AIS targets are sending their data about every 10 seconds, and the channels they use for that are alernating (i'm not sure if this is also true for class B AIS'es).
A good AIS receiver, receives both channels.
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Old 30-12-2012, 16:40   #6
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Re: AIS Made Easy, Sort Of

That is about as simple as Chinese arithmetic.
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Old 17-06-2014, 01:42   #7
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Re: AIS Made Easy, Sort Of

Lew,

>"But do remember that this will get you only 1 channel per radio and you cannot use that radio for other purposes."

I'm not familiar with using the discriminator so does this mean if you make the modifications to a VHF radio it cannot be used on other VHF frequencies?

Thanks for the clarification in advance.

Terry
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Old 17-06-2014, 02:40   #8
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Re: AIS Made Easy, Sort Of

Can this decode AIS channel A and B at the same time like the rtlsdr decoders can? What is the advantage of this compared to using an rtlsdr usb dongle? Won't it use a lot more power?
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Old 17-06-2014, 03:59   #9
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Re: AIS Made Easy, Sort Of

Quote:
Originally Posted by boat_alexandra View Post
Can this decode AIS channel A and B at the same time like the rtlsdr decoders can? What is the advantage of this compared to using an rtlsdr usb dongle? Won't it use a lot more power?
The low cost approach described here uses an existing, modified vhf radio and only software to display AIS targets on a navigation program such as OpenCPN.

No other investment such as the rtlsdr dongle is required.

It only receives AIS data on one channel. But after 9 years using a single channel dedicated AIS receiver I don't consider that a big drawback.

Terry
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Old 17-06-2014, 04:16   #10
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Re: AIS Made Easy, Sort Of

Quote:
Originally Posted by yachtvalhalla View Post
The low cost approach described here uses an existing, modified vhf radio and only software to display AIS targets on a navigation program such as OpenCPN.

No other investment such as the rtlsdr dongle is required.

It only receives AIS data on one channel. But after 9 years using a single channel dedicated AIS receiver I don't consider that a big drawback.

Terry
To clarify: It saves you the cost of an $8 rtlsdr dongle, but you lose the ability to pick up AIS channel A and B at the same time, and you have the additional power consumption of whatever the vhf radio uses when receiving. You also lose the use of the microphone jack (which my chrome book shares with speaker output so I can't listen to music) and it is not possible to receive weather faxes at the same time either, but you won't need a usb port.
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Old 27-08-2014, 01:12   #11
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Re: AIS Made Easy, Sort Of

Today I successfully routed AIS signal laden sound from a Discriminator tap applied to my aged Uniden VHF marine radio to the sound card on my Windows 7/64bit Notebook and read by AISMon interpreted as valid AIS data (as verified in the log file). I am an IT professional with 25 years experience yet the process you describe of creating a virtual com port that OpenCPN can receive this data from has eluded me despite your careful instructions thank you for the effort to write them.

Is anyone in the OpenCPN development community working on a native method for adding this functionality as an authorised addon to OpenCPN to avoid all the painful stuff with 3rd party software packages? There has to be an easier more elegant way...

Cheers

Peter Mc
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