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I am just about to make my inland waterways’ marine VHF radio license in Germany. In Germany, all inland marine VHF radios must be equipped with an ATIS transmitter, which basically sends the stations’ call sign digitally by frequency shift keying when releasing the PTT, on the same channel as the voice transmission.

Unlike DSC used in international shipping, the ATIS codes are not decoded on the receiving units and can neither be used by other ships to identify the sender, nor there is a way to call a ship or land station, if its ATIS number would be known. I have no idea if anybody can or does decode these digital transmissions, and with which benefit. To my eyes, the system only has drawbacks, mainly you need additional circuits inside your maritime radio, and the “noise” it causes, or even more circuits, called “ATIS killer”, to suppress that noise on the receiving side. (I searched for, but I didn’t either find a smart phone app that uses its microphone to decode the ATIS signal, if the onboard units can’t. There is such for weather fax, that was why I started digging for it.)

I was searching for the reasons why ATIS was introduced for inland waterways’ marine VHF, but I was not able to find anything informative. What were the reasons why those countries introduced the ATIS system for inland waterways’ marine VHF radio? What problem should it solve, and did it actually solve it?

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    $\begingroup$ Wild guess: Was introduced when it was considered unlikely that all vessels would have continuous electrical power, so that a AIS-style continuous transmitter was impossible. However, assuming every ship has at least a battery of which it runs the voice radio, and since these frequencies were allocated, anyway, this was a "cheap" way of having people broadcast their ID in crowded areas. Thus, my assumption would be that port authorities have decoders for it and possibly are even able to triangulate transmitters. If the protocol is really as easy as the wikipedia article suggests, it … $\endgroup$
    – Marcus Müller
    Commented Dec 20, 2017 at 8:42
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    $\begingroup$ … should be rather quick to build a decoder yourself (using, e.g., GNU Radio). If the VHF calling frequency is covered by one of the popular RTL-SDRs, let me know. We can make it so that you can make an RF recording, and share it, and then we can work together on implementing a decoder. (decoding slow FSK like that is kind of easy to do. And itu.int/rec/R-REC-M.493-14-201509-I/en is an open standard.) $\endgroup$
    – Marcus Müller
    Commented Dec 20, 2017 at 8:46
  • $\begingroup$ @Marcus I'm also interested in the project and was thinking of doing something similar in GNU Radio for a while now. I can provide some ATIS recordings next week, if Paramaeleon doesn't record some in the meantime. $\endgroup$
    – AndrejaKo
    Commented Dec 21, 2017 at 12:34
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    $\begingroup$ @AndrejaKo that, of course, would be awesome. $\endgroup$
    – Marcus Müller
    Commented Dec 21, 2017 at 14:04
  • $\begingroup$ I am not able to provide recodings, sorry. I am not living close enaugh to any shiphable inland waterways to receive any. $\endgroup$
    – Matthias Ronge
    Commented Jan 8, 2018 at 13:39

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ATIS simply provides automatic identification of the vessel transmission. This is helpful in eliminating the requirement for the typically non professional ship radio operator to manually identify. It also effectively shortens transmission time allowing better utilization of crowded channels while ensuring easy identification of the ship and transmitter. This is particularly helpful with authenticating distress, interfering, or unlawful calls.

ATIS is a subset of DSC (Digital Select Calling) with a format specifier of 121. Thus any standard DSC decoder on the receive channel can read the ship identification information. ATIS data is only sent on the transmitting channel (unlike full DSC on channel 70) and only upon key release with an ~285 ms data burst. Because the data sent is only an index to the ship identification, the 'Belgisch Instituut voor Postdiensten en Telecommunicatie' database must be accessed to resolve the actual vessel name.

The data packet is sent with 1200 baud FSK using 1.3 kHz and 2.1 kHz tones. Because the tones are in the normal audio passband and because the data transmission is quite short, fully blocking of the data audio is difficult without applying a digital delay to the audio channel. If you wish to homebrew a decoder instead of simply blocking the packet, the DSC message format is well documented.

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