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Old 16-03-2014, 17:25   #16
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Re: AIS Class-B Transponder and GPS Receiver

Dave is right, there are no Class B SOTDMA 5W units on the market yet and although the specification exists, I am not aware of any manufacturer having released a product and gone through the approval process.

The AMEC product is slightly worrying. Having a Class B transponder with its own internal GPS receiver ensures that the product works in a completely self contained "stand alone" manner - just turn it on and it works.

Based on the number of DSC radios you see where the owner has not bothered setting them up or connecting them to a GPS, I am concerned that AMEC are promoting this external GPS connection option as a feature/benefit. Surely it will just increase the chances of the transponder not working as it is intended.
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Old 16-03-2014, 17:36   #17
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Re: AIS Class-B Transponder and GPS Receiver

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Originally Posted by Paul_DY View Post
Dave is right, there are no Class B SOTDMA 5W units on the market yet and although the specification exists, I am not aware of any manufacturer having released a product and gone through the approval process.

The AMEC product is slightly worrying. Having a Class B transponder with its own internal GPS receiver ensures that the product works in a completely self contained "stand alone" manner - just turn it on and it works.

Based on the number of DSC radios you see where the owner has not bothered setting them up or connecting them to a GPS, I am concerned that AMEC are promoting this external GPS connection option as a feature/benefit. Surely it will just increase the chances of the transponder not working as it is intended.

The AMEC product actually applied the letter of IEC 62287-1 . It comes with an internal gps as is required by the specification. It's then applies the section 6.3 degradation of sensors rules to allows gnss input from the NMEA interface. This is all according to the spec.

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Old 16-03-2014, 20:35   #18
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Re: AIS Class-B Transponder and GPS Receiver

Re the amec... I don't think they promote it.... its only in the manual and then it is highlighted in red... no mention of the feature in the manual for the newer Amec.
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Old 17-03-2014, 02:39   #19
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Re: AIS Class-B Transponder and GPS Receiver

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The AMEC product actually applied the letter of IEC 62287-1 . It comes with an internal gps as is required by the specification. It's then applies the section 6.3 degradation of sensors rules to allows gnss input from the NMEA interface. This is all according to the spec.

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Hi Dave, my concern is not whether the AMEC product meets the spec or not, but rather that allowing users to add their own separate GPS will reduce the overall reliability and integrity of the transponder.
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Old 17-03-2014, 08:27   #20
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Re: AIS Class-B Transponder and GPS Receiver

What a delight to have such informed discussion on my inquiry in less than twelve hours. Many thanks to all who commented.

If I may summarize:

--all the AIS Class-B transponders presently being made are of the carrier sense time division multiple access type (CSTDMA), as opposed to the self-organizing time division multiple access (SOTDMA) that is used in Class-A devices; and these Class-B transponders are all 2-Watt transmitters;

--there is some allowance for a sort of hybrid Class-B transponder with SOTDMA and 5-Watt transmitters, but there are actually none of these available on the market today;

--the regulations require an AIS Class-B transponder to have a dedicated GPS receiver, and with good reasons, including having a single integrated system that provides the entire functionality needed and to be able to certify the device or system as being compliant;

--but some models of AIS Class-B transponder allow for configuration of the device to use an input from another GPS receiver, thus ignoring their own internal GPS receiver.

Is that a fair summary?
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Old 17-03-2014, 09:14   #21
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Re: AIS Class-B Transponder and GPS Receiver

It is a good summary but I have some additional new info to add.

Apparently, there was a recent amendment to IEC 62287-1 A1 Ed.2 (EPL/80_12_0072) which tightened up this issue of using an external GPS with a Class B Transponder.

The external GPS position will only be used if it is <26m different to the internal GPS position. This means you can’t use external GPS without the internal also operating. The Class B also checks for the GBS sentence (RAIM) from the external GPS, which leisure grade equipment typically does not output.

As a result of this change, I don't think you will be seeing any more Class B transponders that will work with just an external GPS source.
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Old 17-03-2014, 09:55   #22
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Re: AIS Class-B Transponder and GPS Receiver

It also occurs to me that if one changes the source of position data for an AIS transponder to an external GPS receiver from the internal GPS receiver, the antenna of the external receiver could be in a different position on the vessel than the antenna of the internal receiver. This would result in the data being sent about the location of the sensor on the vessel in the AIS transmission being inaccurate.

I suppose since Class-B transponders are associated with smaller vessels, the error might not be significant.

This leads to a corollary question:

In the U.S.A, where the owner of a Class-B transponder is not supposed to be able to change the configuration once he receives the transponder, is that limited to just the MMSI? Can other data, such as the position of the sensor be changed by the user of a Class-B transponder in the USA? Or, is all the configuration data a once-only parameter?
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Old 17-03-2014, 18:38   #23
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Re: AIS Class-B Transponder and GPS Receiver

Quote:
Originally Posted by Paul_DY View Post
It is a good summary but I have some additional new info to add.

Apparently, there was a recent amendment to IEC 62287-1 A1 Ed.2 (EPL/80_12_0072) which tightened up this issue of using an external GPS with a Class B Transponder.

The external GPS position will only be used if it is <26m different to the internal GPS position. This means you canít use external GPS without the internal also operating. The Class B also checks for the GBS sentence (RAIM) from the external GPS, which leisure grade equipment typically does not output.

As a result of this change, I don't think you will be seeing any more Class B transponders that will work with just an external GPS source.

Indeed, there now seems to be a complete nonsense as laid out in section 6.3 f that document and then section 6.6.3 in relation to sensor tailback procedures. Essentially the external DGNSS data can only be used when the internal DGNSS is good enough !!!!!

http://www.dft.gov.uk/mca/bckgrd/iec...is_class_b.pdf


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Old 17-03-2014, 22:46   #24
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Re: AIS Class-B Transponder and GPS Receiver

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In the U.S.A, where the owner of a Class-B transponder is not supposed to be able to change the configuration once he receives the transponder, is that limited to just the MMSI? Can other data, such as the position of the sensor be changed by the user of a Class-B transponder in the USA? Or, is all the configuration data a once-only parameter?
The FCC requirement pertains to MMSI. The end user is not permitted to configure or change the MMSI. Other fields may be changed if the manufacturer allows it. However, it is a violation of the FCC rules for anyone to input inaccurate data.
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