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Old 23-02-2020, 16:22   #121
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Re: New price point for AIS class B+

I was just checking out the B600 and it is $1000 when not on sale....lol.
I cant say for certain but I think the B+ is how it handles messages to/ from satellites and ground station safety messages. Not a lot of talk about the + part of B+ other than in relation to futureproofing the satellite side of things.
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Old 23-02-2020, 17:06   #122
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Re: New price point for AIS class B+

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I was just checking out the B600 and it is $1000 when not on sale....lol.
I cant say for certain but I think the B+ is how it handles messages to/ from satellites and ground station safety messages. Not a lot of talk about the + part of B+ other than in relation to futureproofing the satellite side of things.
The B+ refers to the method of transmission arbitration, SOTDMA and the transmission power at 5 watts. It applies to all transmissions. It is not something special for Sattellite or land station communications.
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Old 23-02-2020, 17:56   #123
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Re: New price point for AIS class B+

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The B+ refers to the method of transmission arbitration, SOTDMA and the transmission power at 5 watts. It applies to all transmissions. It is not something special for Sattellite or land station communications.

Fair enough Paul, so what is the difference between B and B+ if both have 5 watts and SOTDMA?
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Old 23-02-2020, 18:09   #124
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Re: New price point for AIS class B+

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Fair enough Paul, so what is the difference between B and B+ if both have 5 watts and SOTDMA?
They don't. A plain B is 2 watts and uses CSTDMA. That is the difference between the two types of units.
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Old 23-02-2020, 19:12   #125
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Re: New price point for AIS class B+

"B+" is simply a marketing term used by some vendors/manufacturers to help differentiate Class B CSTDMA 2W from Class B SOTDMA 5W. Understandably they're trying to point out the differences in a way that consumers might understand. Both the USCG and the IEC definition simply uses "B/CS" and "B/SO".

Quote:
The main differences between Class B "CS" (IEC 62287-1) and Class B "SO" units are that the Class B "SO"
• covers all 25 kHz channels listed in Recommendation ITU-R M.1084-5,
• only uses the internal GNSS – no position sensor input is allowed,
• requires use of VDL Message 17 for correction of the internal GNSS,
• requires a presentation interface,
• has additional reporting intervals, down to 5 s,
• has two power settings, with a high level of 5 W, and
• has the capability to transmit binary messages.
IEC 62287-2 which defines B/SO also includes message 27 which is intended for use by satellite detection of SOTDMA signals. Class B/CS units do not use message 27 (although maybe vendors have an option to introduce this?) but the standard message 18 CSTDMA messages have been received regularly by satellites. Message 27 is shorter, does not include a timestamp, the AIS model information, or bunch of other stuff in order to improve satellite reception.
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Old 23-02-2020, 20:52   #126
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Re: New price point for AIS class B+

Related question on this, how do you actually test/know which unit do you have (Class B/CS or Class B/SO)? Transmission range will be different but I don't know how one can reliably/comparatively test them.

I think they will both show up as Class B on AIS receivers, so is there any way to actually test the difference in practice?
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Old 23-02-2020, 21:03   #127
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Re: New price point for AIS class B+

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Originally Posted by Tenedos View Post
Related question on this, how do you actually test/know which unit do you have (Class B/CS or Class B/SO)? Transmission range will be different but I don't know how one can reliably/comparatively test them.

I think they will both show up as Class B on AIS receivers, so is there any way to actually test the difference in practice?
All depends on whether your AIS will show you the messages or has a built-in decoder. In the standard Class B (both types) position report the last 20 bits of the message contain information on the communications status. The first of those 20 bits is set to 1 for CS, 0 for SO. The following 19 bits are only used in SO and describe the time source, the number of remaining transmissions in the current time slot before a re-negotiation occurs, and a few other odds and ends related to SOTDMA.

So every Class B position report contains the information on whether the transmitting unit is CS or SO, whether or not the AIS you have will tell you the details of the messages....

I've never looked at this on our Vesper unit, but ours does show a decode of the bits that tell me if the message was picked up and sent by a repeater (I've looked for that specifically) that are also some of the odd pieces of information that most users don't look at.
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Old 23-02-2020, 21:07   #128
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Re: New price point for AIS class B+

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So every Class B position report contains the information on whether the transmitting unit is CS or SO, whether or not the AIS you have will tell you the details of the messages....
Thanks Dsanduril, this is interesting information. This won't tell you which unit you have though but will tell others (if they decode the signals) which type you have. Maybe MarineTraffic and AIS Hub could add features to distinguish between B/CS and B/SO, then we could know But I guess it will require all participating stations (including mine) to send that information and it probably is not included there. Actually I am pretty sure it is not included in mine.
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Old 23-02-2020, 21:16   #129
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Re: New price point for AIS class B+

If your unit is Class B it sends message 18. And the definition of message 18 says it must include the information, so your unit has to be sending it. Getting a chance to see it is more difficult. However, the whole of message 18 is sent to NMEA 0183 through AIVDM/AIVDO, so if you have a friend that can receive your AIS signal and send it to their plotter using NMEA 0183 you can decode the last 20 bits.
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Old 23-02-2020, 21:25   #130
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Re: New price point for AIS class B+

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If your unit is Class B it sends message 18. And the definition of message 18 says it must include the information, so your unit has to be sending it. Getting a chance to see it is more difficult. However, the whole of message 18 is sent to NMEA 0183 through AIVDM/AIVDO, so if you have a friend that can receive your AIS signal and send it to their plotter using NMEA 0183 you can decode the last 20 bits.
This bit is interesting. So if the unit has a USB interface or Wifi spits out raw NMEA messages, one should be able to see this by decoding message 18 and looking at last 20 bits. That is cool.
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Old 23-02-2020, 22:06   #131
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Re: New price point for AIS class B+

Well, if you really want to dig into it, the SO/CS flag is at bit 148 (starting from 0) and the following 19 bits are static for CS. So, the last 20 of a CS message will look like this:

Quote:
11100000000000000110
while for SO it will look like:

Quote:
0xxxxxxxxxxxxxxxxxxx
(note that's lowest bit on the left, which is the opposite of how I think of it as a programmer, but how it is presented in the materials I found at ITU and other places)
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Old 25-03-2020, 12:22   #132
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Re: New price point for AIS class B+

Soooooooo, Do you have it yet Flyingnut40? You said it was on its way a month ago. I'm curious to see what you get.
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Old 25-03-2020, 13:02   #133
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Re: New price point for AIS class B+

Sadly, it is not here yet. It was sent in a timely manner and but the tracking stopped once it cleared customs and the country. That happens a lot, Canada Post tracking does not play well with international post. I got an email from the seller, anxious to get feedback from me.
I am sure that Canada Post and Storage is the problem. I gave up on them for anything but domestic deliveries because deliveries from USA would be 6-8 weeks. I got a mailbox in Niagara Falls NY so I could get my USA purchases in a few days.
Looks like NOTHING has changed. And now with COVID-19 it seems worse. I have confirmed that Canada Post is still operating, despite my mailbox not receiving ANYTHING in the last three days.
Waiting patiently.
Will post here as soon as it arrives.
Alaska should be good tho….. stand on the coast and throw east!!

Dennis
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