AIS misinformation, and a worry
I hate to be a scold, but an otherwise fine new article about AIS in Cruising World contains this flawed paragraph:
Once an AIS signal is received by the antenna, it’s sent to a black box that translates the data into NMEA streams that can be sent at 4,800 or 38,400 baud. The lower baud rate works with electronics suites still using the NMEA 0183 communication protocol; the higher baud rate works with proprietary networks, such as RayMarine’s, and devices using the more capable NMEA 2000 communications protocol.
Every AIS transponder and receiver I know of outputs the same way—NMEA 0183 data messages at 38,400 baud. The 38.4k speed rate is called NMEA 0183–HS (high speed) and is included in the current standard. As far as I know there is no AIS using the NMEA 2000 standard or a proprietary communications protocol, though the new Furuno receiver does do Ethernet in addition to 0183–HS and the junky NASA unit apparently filters out some AIS messages before it sends them down the 0183 pike (though NASA claims it uses N2K, God knows why).
I’ve heard a very ugly rumor that the Class B delay at the FCC may be something serious and long term. Can anyone elaborate?
Interestingly, I saw a press release yesterday (from SRT?) saying that the “FCC Approval” that had been granted was a “mistake” and was being withdrawn, but that SRT would be applying for a waiver in the meantime. Sadly, I can’t lay my hands on it at the moment…
I don’t know of any AIS unit that works at 4800, and indeed, since the data comes through at 9600 on two channels, I can’t see how it could… all together now: “you canna change the laws of physics, cap’n”
It’s my understanding that you can purchase a Class B transponder in Europe. And you can sail/ship/motor a boat from Europe to the US.
Once you get to the US, are you supposed to disconnect the unit?
I had an Icom “Euro” model VHF in my boat for five years, was I violating the law because it wasn’t FCC approved?
It’s hard to see how the FCC can really stand in the way of this happening for very long.
The Furuno FA100 can be set to output at 4800 baud.
How this works capn.
Is only the vessels position and mmsi number are sent.
The rest of the recieved data is stored in the internal memory of the set this is than transmidded out the nmea 0183 port when a gap arrises.
I am appalled that CW would make this error. How is this imcompetance able to pass?
Well, it’s not necessarily “incompetence”. Writers make mistakes. Editors don’t always catch them. Perhaps this writer was reading up on the Furuno FA100 that Murray Marine mentioned, and concluded that AIS receivers could output at either rate. It’s not THAT unreasonable a conclusion, and it CAN be difficult to find all the detailed information about all the units on the market.
Lots of erroneous information has been published in magazines over the years. In the past, though, only a few experts would ever catch it. The publisher might print a correction in the next issue, and almost nobody would notice it.
What I find most interesting is that the internet has made possible instantaneous notification and correction of published factual errors, as occured in this case. So general readers are going to become a lot more aware of the frequency and severity of publishing errors. How long before “all the world’s a Wiki”?
Well said, Tim, and a good chance for me to add that I’ve made plenty of mistakes my own self. I wish magazines, my own included, had the time and resources to have technical articles checked by appropriate experts, but it very rarely happens. Now I try to make my mistakes here, where they’re quickly correctable (thanks to you mutts), before I commit them to print!
By the way, I just checked the install manual for the Furuno FA150, which replaced the FA100 a while back, and it too will send AIS data at either 38,400 or 4,800. It doesn’t explain why you’d choose the lower speed, but I suspect it’s a workaround to accommodate gear that can’t use High Speed NMEA.
About Class B FCC approval
On 11 April 2007, Software Radio Technology announced that the Company’s AIS Class B transceiver had received approval from the FCC.
SRT has been notified by the FCC that the approval certificate granted and provided to SRT was issued in error and a certificate should not have been issued at that time.
The FCC has advised SRT that the grant of the approval was an administrative error and various matters are still under consideration. The FCC has further advised SRT that there is an approval waiver process which can be applied for
in the short term which may enable the AIS Class B technology to be sold in the USA prior to full FCC approval being granted. SRT intends to pursue this route. SRT remains confident that full FCC approval will be granted in due course and understands that the matters now under consideration relate to the FCC’s rules governing the deployment of significant numbers of AIS Class B units.
Simon Tucker, SRT’s Managing Director, said: “The granting of the approval earlier this week was well ahead of our expectations and it is naturally disappointing that this was due to an error. We are taking the necessary steps to apply for the waiver from the FCC and anticipate gaining full FCC approval within our original timescales.”
Does anybody know any Class B that I can buy and use in the US right now?
Steve H. wrote in: “I have recently installed some new electronics on my boat (well some are actually are still in my house) including a Smart Radio SR161 AIS Receiver. Although I have not tested it (I bought an Actisense MUX and loaded the newest software updates for my C80), the documentation claims that it has a configuration setting allowing it to output at the slower 4800 baud rate. I am not sure if there is the potential for data loss at this slower rate but it sounds like the device could work with equipment that does not support high speed NMEA.”
So…ahem…4800 AIS may be more common than I realize, but I still don’t think it’s the norm, or very desirable.
Ben,
Find comfort that your comment about the flaw in Cruising World (which incidently your post is appearing clearly on the web home page of Sail Magazine !), is still very much correct and needs no retraction.
Dan
I meant to say … don’t feel bad, there are other problems of the paragraph from cruising world that are still poorly written or wrong … that your not entirely off base which if good … because on Sail Magazines web site, the panbo box was just large enough to clearly display:
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I hate to be a scold, but an otherwise fine new article about AIS in Cruising World contains this flawed paragraph:
Once an AIS signal is received by the antenna, it’s sent to a black box that translates the data into NMEA streams that can be sent at 4,800 or 38,400 baud. The lower baud rate works with electronics suites still using the NMEA 0183 communication protocol; the higher baud rate works with proprietary networks, such as RayMarine’s, and devices using the more capable NMEA 2000 communications protocol.
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Considering security, information on the AIS system is NOT a great idea.
Also, the crude display on Furuno FA150 AIS system is a shame on Furuno.
Furuno displays on the autopilot and AIS are leftovers from 1990 and bad.
the furuno fa 100 manual says the gps input should be from an old gp80, can i feed it from my gp32? does the airmar h2183 feed the right heading and ROT ?