kitling89
Active Member
Our Class B+ AIT5000 outputs on NEMA at both baud rates as well as NEMA 2000
Single GPS antenna, multiple devices
- Thread starter solder monkey
- Start date
Graham_Wright
Well-Known Member
That is true of mine. It is fed by a simple antenna.
john_morris_uk
Well-Known Member
But to get back to the OP's question.
I'll quote from Digital Yacht. "Unfortunately, the regulations surrounding AIS do not permit feeding an AIS transponder with an alternative GPS source from, for instance, a NMEA output from a chart plotter. All Class B transponders must have their own internal GPS and they will validate its accuracy and reliability prior to sending a position report. This helps ensure the system works as well as possible and that false data can’t be sent." AIS TRANSPONDERS - Do I need another GPS antenna? - Digital Yacht News
And from Vesper Marine "Class B AIS transponders must have a dedicated GPS and can't share one with another unit. And they cannot use NMEA-0183 data from another GPS. This is a type approval certification requirement." 210478506-Do-I-have-to-use-a-dedicated-GPS-antenna-or-can-I-use-the-one-I-have-
I understand that this doesn't stop you feeding the AIS Data from the AIS transponder to other devices such as a VHF radio, but my understanding is that for navigation purposes, there needs to be another independent GPS.
I'll quote from Digital Yacht. "Unfortunately, the regulations surrounding AIS do not permit feeding an AIS transponder with an alternative GPS source from, for instance, a NMEA output from a chart plotter. All Class B transponders must have their own internal GPS and they will validate its accuracy and reliability prior to sending a position report. This helps ensure the system works as well as possible and that false data can’t be sent." AIS TRANSPONDERS - Do I need another GPS antenna? - Digital Yacht News
And from Vesper Marine "Class B AIS transponders must have a dedicated GPS and can't share one with another unit. And they cannot use NMEA-0183 data from another GPS. This is a type approval certification requirement." 210478506-Do-I-have-to-use-a-dedicated-GPS-antenna-or-can-I-use-the-one-I-have-
I understand that this doesn't stop you feeding the AIS Data from the AIS transponder to other devices such as a VHF radio, but my understanding is that for navigation purposes, there needs to be another independent GPS.
GHA
Well-Known Member
Who says so?
Though does seem prudent. Non problem for signalk as you can prioritise similar data from different sources.
laika
Well-Known Member
A rummage through my mail archives shows I got the "you shouldn't share the AIS's internal GPS because (unspecified) rules!" from the response to a query I made to Raymarine about enabling GPS output on the AIS500. The manual said you could do it but didn't say how. Raymarine told me the manual was wrong and it was against (unspecified) rules to do so. I later found out how to enable GPS output (see link in earlier post) and a fair amount of googling has failed to turn up any guidance from the imo, mca, itu or anyone else about not sharing data from a class b unit's internal GNSS receiver. I therefore conclude that a prohibition on such sharing is not, as I previously thought, silly: As far as I can tell, no such prohibition exists.
TernVI
Well-Known Member
Why would it be 'prudent' for the chart plotter and AIS transponder to have potentially different GPS information?
john_morris_uk
Well-Known Member
I've tried to get the full rules from the IMO to check, but they're behind a paywall. Obviously you can do as you like, but I've only quoted what I was told and remember reading when I could get a copy of the regulations. On a commercial vessel it's certainly true that you need two independent nav systems and my understanding is that for type approval of AIS transponders, they need to have an independent GPS too. However, like so many things, on your own boat you can choose to do what you like and no-ones likely to trouble you. I'm happy to comply with the regulations though.
john_morris_uk
Well-Known Member
The AIS (if it's set up properly) knows where it's independent GPS antenna is on your boat. It doesn't make a lot of difference on a small craft, but for collision avoidance on larger vessels it does.
TernVI
Well-Known Member
Which is irrelevant to the point under discussion.
TernVI
Well-Known Member
3.3Internal global navigation satellite system receiver for position reportingThe Class B “CS”AIS should have an internal GNSS receiver as source for position, COG, SOG.The internal GNSS receiver may be capable of being differentially corrected, e.g. by evaluation of Message 17.If the internal GNSS receiver is inoperative, the unit should not transmit Messages 18 and 24 unless interrogated by a base station14.
From ITU
ITU-R M.1371-5
Rec. ITU-R M.1371-31RECOMMENDATION ITU-R M.1371-3*, **Technical characteristics for an automatic identification system using time division multiple access in the VHF maritime mobile band
I expect the IMO may have changed some 'shoulds' into 'musts'? Or maybe it's still controlled by the ITU. I slept through some of that stuff.
I think the ITU define what AIS is, and the IMO make rules about who must have it, but I could be wrong about that.
From ITU
ITU-R M.1371-5
Rec. ITU-R M.1371-31RECOMMENDATION ITU-R M.1371-3*, **Technical characteristics for an automatic identification system using time division multiple access in the VHF maritime mobile band
I expect the IMO may have changed some 'shoulds' into 'musts'? Or maybe it's still controlled by the ITU. I slept through some of that stuff.
I think the ITU define what AIS is, and the IMO make rules about who must have it, but I could be wrong about that.
john_morris_uk
Well-Known Member
I was explaining why the IMO insist on a separate GPS receiver. It's so that the physical position of the GPS antenna on the mother ship can be programmed into the AIS to aid collision avoidance. Even on our just under twelve metre boat I had to program the position of the GPS antenna. (It started on the push pit starboard side and like a complete PITA I've changed the position to just aft of middle of the boat because the old antenna failed. I had to take the laptop down to the boat and plug it in and change the settings on the AIS transponder!). It might not make much difference on a 12 metre boat but on a 120 metre boat the AIS (allegedly) takes the size of the vessel into account when calculating risk of collision.
TernVI
Well-Known Member
How is putting in data for the antenna position on the boat in any way relevant to whether that antenna feeds 1, 2 or a hundred GNSS data users?
PaulRainbow
Well-Known Member
AIS has to have it's own GPS receiver, this is built into the AIS unit. There is no way for users to change that, it's built in, as per regulations, end of story. You cannot supply the AIS with GPS data from an external source. We have no control of this, it's how they are built, because they have to comply with the regulations when they are built.
There is nothing to prevent the AIS unit from sending GPS data out via NMEA 0183, N2K or USB along with it's AIS data. I have fitted many AIS transducers and used the NMEA output to provide GPS data to other devices, very often the VHF for DSC.
Don't confuse the regulation that says the AIS has to have an independent GPS receiver with its ability to pass on GPS data to other devices.
There is nothing to prevent the AIS unit from sending GPS data out via NMEA 0183, N2K or USB along with it's AIS data. I have fitted many AIS transducers and used the NMEA output to provide GPS data to other devices, very often the VHF for DSC.
Don't confuse the regulation that says the AIS has to have an independent GPS receiver with its ability to pass on GPS data to other devices.
Zing
Well-Known Member
It is possible to feed an AIS unit and multiple other devices with the signal from a shared antenna, going through a GPS antenna splitter, I have tested such a setup and it works fine. This is different from getting NMEA data from an external GPS unit. It is also different from a VHF/AIS transmitter splitter, which can only do one transmit signal at one time. It still uses its own built in GPS receiver, but not its own antenna. I am not sure if the regulations are worded as to prevent such an installation.
AngusMcDoon
Well-Known Member
That's for AIS transmitters, but not for AIS receive only units like the Nasa one or mine which is built in to my VHF. I have an external GPS supplying my AIS receiver as it does not have its own. The post asking about AIS said transducer, which is ambiguous as to whether it's a transmitter or receiver only.
PaulRainbow
Well-Known Member
Last edited:
rogerthebodger
Well-Known Member
A transducer is a device that converts variations in a physical quantity, such as pressure or brightness, into an electrical signal, or vice versa.
A transceiver is a device that can both transmit and receive communications, in particular a combined radio transmitter and receiver.
A paddle wheel transducer only send data to the instrument or a pressure a temperature.
A transmitter receives or transmits RADIO signals.
Thy are different devices and to call a transducer a transceiver is not correct.
AngusMcDoon
Well-Known Member
That may be what it has informally become known as regarding AIS (which is why I said it's ambiguous), but it's incorrect terminology. A transducer is a one way device.
TernVI
Well-Known Member
If we're going to get picky, I think the OP may have meant 'Transponder'. A class B AIS may be considered either a transmitter/receiver, transceiver or a transponder.
A transducer is generally defined as something which turns one form of (signal?) energy into another like a speaker or microphone. It may be bi-directional ,for example the piezo ceramic element in a depth sounder.
PaulRainbow
Well-Known Member
I meant to say transponder, obviously.
