AIS aerial vs AIS/VHF splitter

RichardS said:
AIS includes digital error correction....
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You had this argument in a thread a couple of years ago, the final post of which said...

Barnac1e said:
Just as I postulated earlier in my quoted text, the message is discarded. That means, no error correction on individual AIS messages. It is patently obvious there cannot be with no extra support data within the packet or any mechanism in any other communications layer to do so if there is no FEC support as allocated for but not ultimately implemented - probably due to overhead in high traffic scenarios.
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http://www.ybw.com/forums/showthread.php?457184-Masthead-VHF-antennas
 
PaulRainbow said:
Wrong. You cannot digitally correct for data loss that was missed because the splitter was allowing use of the VHF. That transmission will have been missed, end of.
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Wrong. You'll just pick up any missing data on the next transmission sequence and any errors will be corrected, and even that's assuming that the data is not buffered sufficiently to enable it to be processed without any errors. Please find me a single documented case where using an active AIS splitter has caused any data reception problems with AIS .... ever. :encouragement:

Richard
 
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Well, no ... he's right in his own way, in that the data picked up in the next transmission is NOT the data you missed .. the one that was missed is gone forever and won't be repeated.

However, even with separate aerials instead of a splitter, you would STILL miss the data, as the front end of the AIS receiver will be swamped by the main transmitter, which is "in band", effectively blocking any AIS reception.
 
Fitting my AIS in March ready for the season ahead and was going down the second antenna route for 2 reasons for me

price point , a splitter is considerable more money that an VHF antenna , and the little labour required to run a cable from either my mizzen mast or push pit is minimal.

this also gives me a second VHF antenna if the main goes down, although granted its range is significantly reduced due to height , but hopefully still able to communicate
my 2 pence worth
 
rszemeti said:
Well, no ... he's right in his own way, in that the data picked up in the next transmission is NOT the data you missed .. the one that was missed is gone forever and won't be repeated.
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Well, no... he's right full stop, no "in his own way", how rude !

The incoming data is missed, end of story.

However, even with separate aerials instead of a splitter, you would STILL miss the data, as the front end of the AIS receiver will be swamped by the main transmitter, which is "in band", effectively blocking any AIS reception.
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Maybe, maybe not. Would depend on antenna siting, strength of VHS signal, strength of AIS signal etc
 
RichardS said:
Wrong. You'll just pick up any missing data on the next transmission sequence and any errors will be corrected, and even that's assuming that the data is not buffered sufficiently to enable it to be processed without any errors. Please find me a single documented case where using an active AIS splitter has caused any data reception problems with AIS .... ever. :encouragement:
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You don't pick missing data up on the next transmission, it's gone, there is no time warp for missed transmissions.

There is no error corrections, how can there be, there was no error, you missed the transmission. There is no error correction.

There is no buffering, there is nothing to buffer, you didn't receive the tramsmission.

I don't need to waste my evening looking for proof of something that i know to be true, just to prove myself you you Richard, but feel free to do so yourself. Common sense tells you (or at least it should do) that the AIS receiver will miss transmissions from time to time, as the splitter can only handle VHF or AIS data, not both together and it's designed to give priority to VHF traffic.

Your theory of which data will gets missed is incorrect. You miss whatever was supposed to have been received and processed during use of the VHF, there is no way to say how far away that target is or to give any percentages.
 
PaulRainbow said:
I don't need to waste my evening looking for proof of something that i know to be true, just to prove myself you you Richard, but feel free to do so yourself. Common sense tells you (or at least it should do) that the AIS receiver will miss transmissions from time to time, as the splitter can only handle VHF or AIS data, not both together and it's designed to give priority to VHF traffic.

Your theory of which data will gets missed is incorrect. You miss whatever was supposed to have been received and processed during use of the VHF, there is no way to say how far away that target is or to give any percentages.
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In the entire history of AIS, albeit that is relatively small number of years, I can guarantee there has never been a single case of an active splitter causing any loss of signal which has been noticeable to any human being and which has therefore made any difference to a collision avoidance decision.

However, every human being on the planet, if given the opportunity, would notice the lack of reception of a pushpit mounted antenna compared to mast head antenna through an active splitter.

I appreciate that you really, really don't like it Paul .... but that's just the way it is, I'm afraid. :encouragement:

Richard
 
RichardS said:
In the entire history of AIS, albeit that is relatively small number of years, I can guarantee there has never been a single case of an active splitter causing any loss of signal which has been noticeable to any human being and which has therefore made any difference to a collision avoidance decision.

However, every human being on the planet, if given the opportunity, would notice the lack of reception of a pushpit mounted antenna compared to mast head antenna through an active splitter.

I appreciate that you really, really don't like it Paul .... but that's just the way it is, I'm afraid. :encouragement:

Richard
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You are mistaken Richard, i really, really don't care one way or the other. I have the system that i prefer, for me and my boat. What others choose to fit is up to them, i fit whicher my customers opt for, makes absolutely no difference to me whatsoever.

I've already said, both systems work, if you bothered to read it. Both have pros and cons, depends if you'd rather see pointless targets a zillion miles away, or have a backup VHF, amongst other things. I have both :encouragement: But, i can still objectively look at othe solutions :)
 
RichardS said:
However, every human being on the planet, if given the opportunity, would notice the lack of reception of a pushpit mounted antenna compared to mast head antenna through an active splitter.
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What? A few miles less range? When most plotters can only display a limited number of the closest targets? Dream on....
 
PaulRainbow said:
You are mistaken Richard, i really, really don't care one way or the other. I have the system that i prefer, for me and my boat. What others choose to fit is up to them, i fit whicher my customers opt for, makes absolutely no difference to me whatsoever.

I've already said, both systems work, if you bothered to read it. Both have pros and cons, depends if you'd rather see pointless targets a zillion miles away, or have a backup VHF, amongst other things. I have both :encouragement: But, i can still objectively look at othe solutions :)
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But why keep going on about "lost data" through a splitter when, even if it happens (and I don't actually think it does to a meaningful degree), it doesn't make the slightest bit of difference to the effectiveness of the system.

You might as well say that using a splitter is to be discouraged because a masthead antenna is more likely to be hit by a flying seagull than a pushpit antenna and that would certainly cause a loss of data. The truth is that in the real world the "flying seagull" catastrophe is the more likely data-loss scenario. :)

Richard
 
Post 9 was interesting, but didn't have me rolling in the aisles.

I have a half-wave on the masthead and on the pushpit, but having the option of switching them about and multiplexing both onto either appeals. You can never have too many options.

I did begin drawing up a simple PIN Diode splitter, with a Rx preamp when in RX mode (to mop up any switching losses, and make up for the usual crap cable used in yacht installations), and with transmit paths going the other way, giving priority to the VHF transceiver over the AIS in transmit operation. When the VHF was transmitting, I planned to route the AIS to a small dummy load.

I got most of the way through it, but got distracted modelling various PIN diode driver circuits ... and from there, it never re-surfaced. I may finish it off if it rains over New Year. Or I may get drunk ... decisions, decisions.
 
Not taking sides :D
but I d like a good mystery and go and try and find some knowledge all I could find was for class A that use satellites for their locations , but am aware that Class B can sometimes pigback these satellites if needed

In high-density shipping areas where thousands of ships may be transmitting AIS messages, it is a challenge for S-AIS systems to efficiently collect, process, and download all of the messages. The result of this is that many messages are lost due to data collisions. Research indicates that typical S-AIS receivers are able to receive less than 50% of messages in medium to high-density areas.The S-AIS provider then has to clean (or “de-collide”) the data in order to extract useful information from it. This data processing exercise adds a delay (known as “latency”) to the delivery of the message.
https://www.polestarglobal.com/medi...ould_undermine_your_organisationsplusgbmp.pdf

Note that AIS transmissions may get scrambled and/or lost when received by satellites (Sat AIS). This can happen because satellites have a wide reception footprint which includes multiple groups of AIS-equipped vessels that transmit different data packets using the same slots - this situation is know as "packet collision"
https://help.marinetraffic.com/hc/e...-attributed-to-correct-vessels-in-busy-areas-

Since you have two receiving devices on one antenna, you may also experience some small amount of signal degradation with some splitters. While broadcasting on the VHF radio, you will likely see some interruption of incoming AIS signals. Since AIS broadcasts from each ship are repeated every few seconds, this is not normally noticeable in your tracking software
Digital Yatch
 
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pvb said:
True, it's totally irrelevant, but at least we now know moomba can google...
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We also know
Since you have two receiving devices on one antenna, you may also experience some small amount of signal degradation with some splitters. While broadcasting on the VHF radio, you will likely see some interruption of incoming AIS signals. Since AIS broadcasts from each ship are repeated every few seconds, this is not normally noticeable in your tracking software
Digital Yacht
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Which is what i said all along. No doubt the sane amonst us would have been able to work that out for ourselves, so that just leaves Richard :)
 
RichardS said:
But why keep going on about "lost data"
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I mentioned it, along with mentioning that it's not likely to cause any significant issues, although things might get "interesting" if you're on the radio for an extended time, in which case, those of us who accept messages get lost will be fore armed and not be fooled into thinking that everything is bulletproof and our 5 zillion nautical mile AIS range is warding all vessels off of our gelcoat.

It's only been a protracted discusion because you won't accept reality Richard :)

Anyway, have a nice New Year celebration:very_drunk::very_drunk: Richard
 
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