AIS aerial vs AIS/VHF splitter

[RichardS]

Since AIS broadcasts from each ship are repeated every few seconds, this is not normally noticeable in your tracking software

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

Ah yes, presumably that'll be the Richard who said "You'll just pick up any missing data on the next transmission sequence and any errors will be corrected"? :encouragement:

Richard

 

[RichardS]

That's only because most people don't understand the reality.

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

Lol .. perhaps this is the "reality" we should be understanding:

Yep, my splitter in action just off the Venice with AIS rings set at 20 miles, again.

Richard

 

[Yealm]

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

I agree ! (without having proof either way)
I moved from pushpit to masthead splitter last year to get better range and it seems to have worked.

 

[Daydream believer]

No rush, i was passing Titchmarsh this evening and disconnected your batteries, didn't want them going flat

So if they are not there in the morning we all know who to blame

 

[PaulRainbow]

Ah yes, presumably that'll be the Richard who said "You'll just pick up any missing data on the next transmission sequence and any errors will be corrected"? :encouragement:

Richard

That will be the same Richard that still does not grasp the facts.

a) Missing data will not be picked up on the next transmission, you missed it, it's gone, never to be heard again.

b) There is no error checking, none, nada, zilch. Data is broadcast, you either get it or you don't, it doesn't get resent or corrected in any way.

Since AIS broadcasts from each ship are repeated every few seconds, this is not normally noticeable in your tracking software

This statement is not entirely correct. Note though that they use the words "not normally noticeable". There can and are times when it is noticable, whether we are looking at the screen at the time is another matter. Miss a couple of transmissions and all of a sudden a vessel jumps ahead of it's last reported position. N

Not all information is transmitted every few seconds.

Message 24 (MMSI, boat name, ship type, call sign, dimensions eyc) is transmitted every 6 minutes for both Class A and Class B. Miss that and you have a 12 minute gap in information received. Likely to cause a collision, of course not.

Message 18 from a class B AIS vessel (MMSI, time, SOG, COG, longitude, latitude, true heading) is sent every 3 minutes for vessels travelling at less than 2 knots, miss that and you don't get vital information for 6 minutes, he's barely moving, so maybe not mush of an issue ? At speeds in excess of 2 knots this message is sent every 30 seconds, not exactly every "few" seconds, is it ? Miss that and it's a full minute before you get an update from that 75 foot, 30 knot mobo, he's now 1/2 a mile away from where the plotter last reported him to be. Life threatening, only if you're not paying attention. Might be inconvenient.

No one is say you'll crash and die if you are using a splitter, that's clearly not going to happen. I'm just pointing out some facts. Someone might think it's better to have a separate antenna, removing the above and giving a spare antenna. Someone else might prefer to have a splitter. Either way, facts help with that decision.

 

[PaulRainbow]

So if they are not there in the morning we all know who to blame

It's been 18 months, i dare say he re-connected them a long time ago

 

[moomba]

True, it's totally irrelevant, but at least we now know moomba can google...

I think this was totally relevant to the converstion as this is VHF to VHF
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

In telecommunication, degradation is the loss of quality of an electronic signal, which may be categorized as either "graceful" or "catastrophic", and has the following meanings: The deterioration in quality, level, or standard of performance of a functional unit.

I LOVE GOOGLE :encouragement:

 

[pvb]

I think this was totally relevant to the converstion as this is VHF to VHF

What was irrelevant was your reference to satellite AIS, it has absolutely nothing to do with leisure boating. The ABSEA technology, which you mentioned in your deleted post, is also irrelevant, the technology hasn't been incorporated in Class B transceivers and won't be for many years, if at all.

Your quote about signal degradation with splitters being "not normally noticeable" isn't entirely true, as PaulRainbow has pointed out in post 85.

 

[moomba]

The argument was also abut the data on AIS been stored and not lost when transmitting n VHF
your small irelevant digs are washing over me :encouragement:
However, when most splitters are installed, the use of the VHF radio to make calls will block AIS transmit-and-receive functions for the duration of the call. So, when critical things are happening and AIS should not be disrupted, use your handheld VHF or a second installed VHF radio with a dedicated antenna if you have one. This could be critically important in a MOB situation when a personal AIS beacon antenna is barely out of the water and with significant wave action present. In most cases, given the time between transmissions for Class B systems, unless the VHF is used on the receiving vessel extensively, and each transmission (the time that the mic key is held down) is long, this will not have an appreciable effect on the AIS display shown on the receiving vessel's MFD.
US B0AT

 

[moomba]

What was irrelevant was your reference to satellite AIS, it has absolutely nothing to do with leisure boating. The ABSEA technology, which you mentioned in your deleted post, is also irrelevant, the technology hasn't been incorporated in Class B transceivers and won't be for many years, if at all.

Your quote about signal degradation with splitters being "not normally noticeable" isn't entirely true, as PaulRainbow has pointed out in post 85.

If posts were deleted it was for a reason that the info was not correct and Why it was deleted by myself within 2 mins for posting , although this will go to peoples inbox before it is deleted I am not sure why you brought it up , you seem to be trying to make a point towards myself that I can not yet fathom, are you really bored :encouragement:

 

[PaulRainbow]

However, when most splitters are installed, the use of the VHF radio to make calls will block AIS transmit-and-receive functions for the duration of the call. So, when critical things are happening and AIS should not be disrupted, use your handheld VHF or a second installed VHF radio with a dedicated antenna if you have one.
US B0AT

Who'd have thought it

 

[lw395]

The argument was also abut the data on AIS been stored and not lost when transmitting n VHF
your small irelevant digs are washing over me :encouragement:
However, when most splitters are installed, the use of the VHF radio to make calls will block AIS transmit-and-receive functions for the duration of the call. So, when critical things are happening and AIS should not be disrupted, use your handheld VHF or a second installed VHF radio with a dedicated antenna if you have one. This could be critically important in a MOB situation when a personal AIS beacon antenna is barely out of the water and with significant wave action present. In most cases, given the time between transmissions for Class B systems, unless the VHF is used on the receiving vessel extensively, and each transmission (the time that the mic key is held down) is long, this will not have an appreciable effect on the AIS display shown on the receiving vessel's MFD.
US B0AT

Using a second antenna, you may still struggle to get enough isolation to avoid the VHF RT blocking the AIS receiver.
The selectivity of a lot of cheap AIS receivers is not marvellous.
The isolation between two antennas in the same band on a small boat won't be huge.
Personally, I'm not particularly keen on splitters (unnecessary complication) or pushpit-mounted antennas (seen too many pushpit-mounted things get broken in harbour, too much obstruction etc).
I think it's quite common not to receive every AIS transmission at the best of times.
I don't think it matters that much, we're using it to avoid ships in the channel, not pick our way through the racing fleet at the windward mark.

 

[moomba]

Using a second antenna, you may still struggle to get enough isolation to avoid the VHF RT blocking the AIS receiver.
The selectivity of a lot of cheap AIS receivers is not marvellous.
The isolation between two antennas in the same band on a small boat won't be huge.
Personally, I'm not particularly keen on splitters (unnecessary complication) or pushpit-mounted antennas (seen too many pushpit-mounted things get broken in harbour, too much obstruction etc).
I think it's quite common not to receive every AIS transmission at the best of times.
I don't think it matters that much, we're using it to avoid ships in the channel, not pick our way through the racing fleet at the windward mark.

Absolutely , the recommendations for 2 antennas is 3 meters from the horizontal and if possible different heights and if on the same mast at least 1 meter above and below
why those with a mizzen are the bomb and the rest put their second antenna on the push-pit, if not using a splitter.
Also they say from the loss of height from mast to push-pit will take around 3 to 5 miles of your range but still giving you around 6-8 miles , also to remember that large ships will have their antennas high up so range could be longer.
There is defo pros and cons to splitters and an extra Antenna
Second antenna vs Splitter
pro
Antenna much cheaper
second antenna for emergencies
no AIS loss of data

Pro splitter
Gain of full scan from 10 to 15 miles down to 6 to 8 miles (roughly)
not Having to run second cable through boat (cost)
No need to get up mizzen , maim mast or pushpit to fit second anntena

If this helps some one then all the bettter if its chewing mud for most I also speak hippo

 

[RichardS]

Ah yes, presumably that'll be the Richard who said "You'll just pick up any missing data on the next transmission sequence and any errors will be corrected"?

That will be the same Richard that still does not grasp the facts.

You really are not understanding this are you Paul?

Let me give an example using an analogue transmission which seems to be your bag.

OK, so I call up another boat on my VHF. Setting aside the procedural stuff, I say "Hi there, Queen Elizabeth, this is Richard on motor vessel Ajay".

I then suddenly realise that I'm not on a motor yacht, doh! So I call again "Hi there, Queen Elizabeth, this is Richard again. I'm afraid I've made an error which I will correct by stating that we are on sailing vessel Ajay. Out"

So there you go, error correction by re-transmission using analogue technology. Now, imagine what one could do with a digital technology which automatically re-transmits the correct data every few seconds. :encouragement:

The moral of this story is .... don't drink before using the VHF.

Richard

 

[Pinnacle]

I have run out of popcorn. Should I get a refill?

 

[RichardS]

I have run out of popcorn. Should I get a refill?

I reckon that this one will run and run.

Richard

 

[dom]

You really are not understanding this are you Paul?

Let me give an example using an analogue transmission which seems to be your bag.

OK, so I call up another boat on my VHF. Setting aside the procedural stuff, I say "Hi there, Queen Elizabeth, this is Richard on motor vessel Ajay".

I then suddenly realise that I'm not on a motor yacht, doh! So I call again "Hi there, Queen Elizabeth, this is Richard again. I'm afraid I've made an error which I will correct by stating that we are on sailing vessel Ajay. Out"

So there you go, error correction by re-transmission using analogue technology. Now, imagine what one could do with a digital technology which automatically re-transmits the correct data every few seconds. :encouragement:

The moral of this story is .... don't drink before using the VHF.

Richard

Surely the moral is to use the Buckingham Palace landline

 

[rszemeti]

So there you go, error correction by re-transmission using analogue technology. Now, imagine what one could do with a digital technology which automatically re-transmits the correct data every few seconds. :encouragement:

Richard

Sorry, but that is not error correction ... the next transmission is of a different message ... a newer, fresher, more timely message, but not the one that got lost. Once you have the new data, you no longer have any interest in the old data, so for AIS it is the correct procedure, but please, do not mistake it for "error correction" because it isn't.

Put simply, it is the difference between UDP and TCP connections in TCP/IP networking ... TCP has an "ack" and can request transmission of a error ridden packet ... UDP simply sends the packets and hopes for the best.

 

[RichardS]

Sorry, but that is not error correction ... the next transmission is of a different message ... a newer, fresher, more timely message, but not the one that got lost. Once you have the new data, you no longer have any interest in the old data, so for AIS it is the correct procedure, but please, do not mistake it for "error correction" because it isn't.

Seriously?

On the other hand, if it looks like a duck and quacks like a duck ...... guess what?

Richard

 

[moomba]

Seriously?

On the other hand, if it looks like a duck and quacks like a duck ...... guess what?

Richard

This PDF link from Digital Yacht gives a very comprehensive answer to AIS as an electronics company based around the boating industry I would tend to trust what they are saying
I bring your attention to page 17 and 18 of this PDF

CCons OF Splitter
•4x the cost of dedicated antenna
•Misses targets while VHF transmits
Single Antenna is shared by the AIS and VHF
•Two intelligent switches inside the splitter sense when AIS or VHF is transmitting
•A Class B AIS transmission only lasts 26mS so the detection and switching is very fast
•VHF gets priority and whilst transmitting no AIS reception is possible


http://digitalyacht.co.uk/wp-content/uploads/2017/10/AIS-Training-V1_01.pdf

Google is a tool to look for information , and the ability to use google can be a task as a previous research student we are taught not to look at the first thing that pops up, but look through countless pages and cross reference until a line of inquiry has multiply hits
So yes I use google to my advantage. sometimes Im way of the mark , and if so quickly say so, some on these forums might learn that too