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Old 05-07-2012, 21:08   #1
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AIS using VHF/DSC with a PC

As a result of looking into RTL SDR DVB-T dongle and software for AIS, I found some interesting information about using a VHF/DSC radio to receive AIS on a PC.

Automatic Identification System - Wikipedia, the free encyclopedia
AIS transponders use
two different frequencies, VHF maritime channels 87B (161.975 MHz) and 88B (162.025 MHz), and use 9.6 kbit/s Gaussian minimum shift keying (GMSK) modulation over 25 or 12.5 kHz channels using the High-level Data Link Control (HDLC) packet protocol

HOW TO RECIEVE AIS
Ais Receiving Station
Communications/Scanner Receiver
You can also use a Communications Receiver or Scanner. This outputs audio and requires an audio decoding program running on a PC. This is really only a practical proposition if you already have a suitable receiver or wish to use the receiver for other purposes. Not all scanners or receivers are suitable as they need to be able to receive the right frequency and importantly need a wide enough bandwidth. For more information on suitable receivers and possibly modifying an existing receiver see

AIS (Automatic Identification System)
To receive AIS, there are several options:
Option 1: PC with soundcard
You'll need
A receiver with a discriminator output or 9600 bps packet radio output
An audio cable between your receiver and PC
A PC with soundcard, runningthe appropriate software:
- Shipplotter, a complete solution. Or
- AISMon, which converts the raw AIS signal into
NMEA, together with with navigation software like
SeaClear, OpenCPN or WinGPS. This requires
somewhat more computer knowledge to configure.

AIS reception with a PC
Be advised that your receiver should not be scanning when you want to receive AIS, since it would miss AIS transmissions (hence ships) while scanning other frequencies.

If you use a marine VHF, it should be on channel 87 or 88 constantly. Since it can't be used for normal traffic while monitoring AIS, it is advisable to use a (cheap) scanner or a second marine VHF for AIS. Further to that, not all marine VHF equipment is suited to receive AIS.

AIS reception with a marine VHF radiotelephone
AIS (Automatic Identification System)
New channel allocation
There is one snag however. AIS is transmitted on two frequencies: 161.975 and 162.025 MHz. In older marine equipment, as well as equipment with a USA channel allocation, this corresponds with duplex channels 87 and 88.

How do I know if I can use my VHF radiotelephone to receive AIS? There are several ways to find out:
Look in the manual. It usually contains a table of channels and corresponding frequencies If the receive frequency of channels 87 and 88 are 161.975 and 162.025 MHz, you can receive AIS. In some cases, the user can switch between two channel allocations.
Take a second VHF transceiver and tune both sets to channel 87 or 88. Transmit with the second marine VHF set. If you can receive the transmission on the first one, it has channel 87 or 88 programmed as a simplex channel. The receiving radiotelephone can't be used for AIS.

aismon : AIS_Monitor
AISMon, which converts the raw AIS signal into
NMEA, together with with navigation software like
SeaClear, OpenCPN or WinGPS. This requires
somewhat more computer knowledge to configure.
Description
This group is a discussion forum for AISMon, a high-performance freeware AIS demodulator/decoder which outputs AIS data in NMEA format. Input may be from any installed sound card (radio discriminator output required) or 44.1/48K .wav file. Output may be used to drive charting applications such as SeaClear or ShipPlotter.

-----------
Perhaps someone has tried this and will share how successful it was.
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Old 05-07-2012, 21:19   #2
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Re: AIS using VHF/DSC with a PC

Incidentally, you only need to pick up one of the channels 87 or 88 because AIS transmission occurs on both channels to provide backup, eventually you will receive all of the transmissions on one of the channels.

So how do we output a VHF/DSC set on channel 87 or 88 (set in recieve only mode) TO a PC? Say a USB port? Can we somehow use the Nema out wire and Nema Ground wire on the VHF/DSC?

How do we instruct the VHF/DSC to send channel 87 out on the Nema out wire?

This software would run on the PC between Opencpn, I guess.

AISMon, which converts the raw AIS signal into
NMEA, together with with navigation software like
SeaClear, OpenCPN or WinGPS.
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Old 05-07-2012, 21:42   #3
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Re: AIS using VHF/DSC with a PC

AisMon interfacing with NavMon Pc and OpenCpn
Yahoo! Groups
-----------

There is an open-source alternative called Com0Com, which does the same as VSPE in a much better way (IMHO).

If i remember right, it's on Sourceforge, but Google will probably find it too.

Excerpt from www.eterlogic.com:
"Virtual Serial Ports Emulator is a FREEWARE program on 32 bit platform and can be used absolutely free for any purpose."
I have been playing around with VSPE for quite a while, and I really love it. I haven't bothered to google for another equivalent.
It interconnects all of my stuff through physical and virtual COM ports, splitters, TCP client-server etc.

aismon@yahoogroups.com, "ttrengereid" wrote:
I suggest that you use VSPE from etherlogic.com to create virtual com ports. within VSPE, create a "connector" device, (example COM5)
You should now be able to connect AISMon to COM5 as well as your chartplotter software.

For further enhancements, you could additionally create a VSPE COM5-to-COM6 splitter. Connect AISmon to COM5, and connect chartplotter software, multiple if you want, to COM6.

I use the same technique also for GPS, where I distribute the GPS signals through a connector/splitter pair to OpenCPN, PolarCOM and whatever. I also connect a VSPE TCP server to the same splitter for transportation over a IP network.
Trygve

In aismon@yahoogroups.com, "joaquin180556" wrote:
If my "Ais Mon screen Settigns" show :
Square Checked, "Serial Output.........Port COM 3". Baud Rate 34800.
How must I configure Aismon, NavMonPc and OpenCpn, to see the SHIPS??? TVM
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Old 05-07-2012, 22:04   #4
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Re: AIS using VHF/DSC with a PC

this DOES work. I picked up a hand-held scanner at a yard sale for 5$, found the discriminator output thanks to Discriminator Output and the above directions and so can see traffic on Opcn....so it seems it could work using the RTL SDR DVB-T output to AISMON instead of (my) clumsy soldering in a scanner...
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Old 06-08-2012, 19:57   #5
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Re: AIS using VHF/DSC with a PC

There are multiple threads on same issue now
Fast cheap AIS using $20 rtl-sdr DVB-T SDR Dongles !
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Old 23-11-2012, 21:48   #6
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Re: AIS using VHF/DSC with a PC

Can opencpn act as a message creating and sending front end for a nmea connected DSC vhf radio.

I know Opencpn recieving AIS data is able to display DSC message "position report.s" etc.

But is it possible to to click on a vessell in opencpn and by right clicking send a message to that vessels mmsi via DSC ie "We are going to collide"

Do certain radios have more DSC capability than others or do I only have to worry about it conforming to the latest DSC 2011 "D" (from memory) standard.

I am thinking of getting a Uniden UM380 DSC radio. It has NMEA IN and out.

I would love to hear how others are using / interfacing their dsc radios .

George
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Old 24-11-2012, 01:43   #7
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Re: AIS using VHF/DSC with a PC

There is supposed to be a "hidden" feature i OpenCPN making it possible to make a direct call to a MMSI number if a DSC capable VHF is connected.
Way back in this post http://http://www.cruisersforum.com/...tml#post471158 Dave wrote......

Quote:
Here is a "feature request" from me...

If you have DSC capable VHF radio, connected to opencpn by some means, then right click on AIS target should have context menu option to place direct bridge-to-bridge DSC call to this target.

I don't have such a radio, but they are becoming cheap and common in US waters.
I don't think that any user ever came back to Dave. The "feature" is not documented, because it was never tested in real life.
I don't know if this ability is still in the code, or if it needs to be restored.
Dave's post was made just before the release of OpenCPN 2.0.1.

It would be great if users with access to a DSC could do some testing.

Thomas
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Old 24-11-2012, 03:13   #8
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Re: AIS using VHF/DSC with a PC

Thomas that is exactly the kind of thinking I am talking bout.

A cheap dsc radio given computer intelligence by interfacing opencpn has enormous potential.

Does anyone know the best or the easiest dsc radio to interface to opencpn?

A opencpn radio front end would be great. I might start searching the net and report back.

George
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Old 24-11-2012, 08:10   #9
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Re: AIS using VHF/DSC with a PC

Quote:
Originally Posted by HappySeagull View Post
this DOES work. I picked up a hand-held scanner at a yard sale for 5$, found the discriminator output thanks to Discriminator Output and the above directions and so can see traffic on Opcn....so it seems it could work using the RTL SDR DVB-T output to AISMON instead of (my) clumsy soldering in a scanner...
Details...details.....this is really interesting. Checked my handheld Uniden MHS 350 and 88 and 87 are set to the correct freq to receive. Next step is to figure out how to get the signal out of the unit...

Manual: http://www.uniden.com/content/ebiz/u...s/MHS350om.pdf

Once i get the signal out, should be able to deal with it on linux.

/ch
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Old 24-11-2012, 08:24   #10
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Re: AIS using VHF/DSC with a PC

I was thinking that taking the serial out to a serial-bluetooth might work, but not sure if a driver would be involved.
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Old 24-11-2012, 12:23   #11
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Re: AIS using VHF/DSC with a PC

Quote:
Originally Posted by sailias View Post
Details...details.....this is really interesting. Checked my handheld Uniden MHS 350 and 88 and 87 are set to the correct freq to receive. Next step is to figure out how to get the signal out of the unit...

Manual: http://www.uniden.com/content/ebiz/u...s/MHS350om.pdf

Once i get the signal out, should be able to deal with it on linux.

/ch
Your scanner looks like it'll have the frequency, alright, even though I didn't see it listed at the site. When you open your scanner up, and look, if the chip index http://www.discriminator.nl/ic/index.htm fails.... I was able to discover the discriminator pin connection on an unlisted IC by googling a likely prospect.(note to self :report my radio+IC there!)

In one instance, I had some good luck in that I was able to find a directly-connected test pin that was easier to solder to, so visually trace these unconnected-looking pins if they are near the target IC .

I had no real luck just listening to an earphone output (with (AISMon) but it's so easy , I'd always try it! but the machine's audio stage and squelch were the nuisance . I think you'd need an AIS station really close to hear it this way!

As a general tip to anybody shopping for old scanners in particular, try to find one with a better memory. Some older scanners forget your frequency choices when the power switch is merely off .Many more will forget when the batteries/12v supply is removed, but these are not so bad. VHF Transceivers will not have this problem at all.
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